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300 Cards in this Set

  • Front
  • Back
Fungi
- decomposers of organic matter
- aerobic or facultatively anaerobic
- chemoheterotroph
Facultative Anaerobe
- Grows best under conditions of oxygen, but can switch to fermentation in the absence of oxygen
Fungi used for food
- mushrooms
Fungi used for fermentation
Yeast- production of alcohol and bread
- production of drugs (penicillin)
Saccharomyces cerevisiae
- yeast used in beer making (produces ethanol) and to raise dough (produces carbon dioxide)
- Budding yeast
How many species of fungi known?
How many are pathogenic?
- More than 10,000 species known
- Only about 100 are pathogenic
Mycology
the study of fungi
Chemoheterotroph
an organism that uses organic molecules as a source of carbon and energy
Hyphae (singular hypha)
long filaments that make up the body of a mold
Mycelium
Filamentous mass of hyphae
(concerning molds)
- mold becomes visible to the unaided eye
Yeast
- Nonfilamentous
- unicellular
- Reproduce by budding or by fission
- Most are facultatively anaerobic
Budding yeast
- divides unevenly to produce a small cell (bud) from a parent cell

(Saccharomyces cerevistiae)
How are fungi identified?
By the spores they produce
Pneumocystic jiroveci
- illness it causes
- who is it a problem for?
- what does it do?
- does it always cause a problem?
- cause of pneumonia in immunosuppressed patients
- problem for AIDs patients
- Cysts tend to obstruct air chambers
- Opportunistic pathogen- frequent resident of healthy human lungs where it causes no problem
Opportunistic Pathogen
A microorganism that does not ordinarily cause a disease but can become pathogenic under certain circumstances
Histoplasma capsulatus
- where and when founded?
- Illness?
- where does it infect?
- how does it grow?
- When is the initial infection?
- how does it travel inside the body?
- prevalence?
- how is it transmitted?
- What animals is it associated with?
- Causative fungus discovered at Vandy in 1932
- Causes the tuberculosis-like disease histoplasmosis
- Example of systematic mycosis
- Yeast-like growth in tissue
- Mold-like growth in soil
- Pathogen in the lungs can spread to other parts of the body
- Yeast-like form can travel inside macrophages
- prevalent in TN and states around it
- Spores in air infect lung, associated with bird and bat droppings
Histoplasmosis
- Resembles tuberculosis
- Infects the lungs
- May spread in the blood and lymph causing lesions in all organs in the body
Systematic mycoses
Fungal infection in deep tissue
- Usually caused by fungi that live in the soil
- transmitted by inhaling the spores
- Starts in the lungs but then spreads to other body tissues
- Histoplasmosis
Macrophages
A phagocytic cell; a mature monocyte
Phagocyte
A cell capable of engulfing and digesting particles that are harmful to the body
Coccidiodes immitis
- illness caused?
- how does it grow?
- Symptoms?
- Causes tuberculosis-like illness (coccidiomycosis or Valley fever or San Joaquin fever)
- yeast-like form in tissue, mold-like form in soil
- Causes chest pain, fever, weight loss
Coccidiomycosis
- caused by?
- how spread?
- Symptoms?
- Where prevalent?
- Caused by coccidiodes immitis
- spread through inhalation of spores
- symptoms include chest pain, fever, weight loss
- Prevalent in US southwest only
Phytophthora infestans
- led to?
- infects what?
-caused loss of Ireland's potato crop in the mid 1800
- resulted in widespread famine and deaths
- Still infects potatoes, soybeans, and cocoa
Cryphonectria parasitica
- Effects what?
- killed American chestnuts
Ceratocystis ulmi
- What host does it effect?
- Carried by what?
- How does it effect the host?
- Dutch elm disease, destroyed most American elms
- Carried by bark beetles
- Blocks fluid transport in the plant
Lichen
- What is it?
- Explain the relationship
- how many species?
- where can they be found?
- combination of a green alga and a fungus
- Exist in a symbiotic relationship
- Both organisms benefit, neither can survive without the other
- Alga produces food by photosynthesis and secretes some food for the fungus
- Fungus provides protections from desiccation and attachment for the alga
- 13,500 species
- Colonize diverse and unique habitats
Algae
- what are they?
- how do they get nutrients?
- how do they reproduce?
- why important?
- Simple eukaryotes
- Simple plants- no roots, stem, leaves
- Photoautotrophic
- Mostly unicellular
- Some can be filamentous (chains) or have a multicellular body (thallus)
- Absorb nutrients from water
- Reproduce asexually by fragmentation or by cell division
- Some species reproduce sexually
- Important fixing carbon from CO2 into organic compounds and producing oxygen
- 80% of atmospheric oxygen is produced by algae
Photoautotroph
An organism that uses light as its energy source and carbon dioxide as its carbon source
Thallus
- multicellular body (Algae)
(seaweeds)
- Consist of parts that anchor, stem-like part, and leaflike blades
Asexual reproduction (fragmentation)
- Occurs in multicellular algae with thalli and filamentous forms
- Each piece is capable of forming a new thallus or filament
Asexual reproduction (Cell division)
- Occurs in unicellular alga
- The nucleus divides and the cell splits into two complete cells
Diatoms
- Algae that produces neurotoxins
- Humans are poisoned if they eat shellfish that have been feeding on certain diatoms
Dinoflagellates
- Algae that produces neurotoxins
- Genus Alexandrum (causes red tides)
- Humans are poisoned if they eat shellfish that have been feeding on certain dinoflagellates
Alexandrum
- genus of the dinoflagellates that cause red tides
Protozoa
- unicellular
- Eukaryotes
- Chemoheterotrophs
- 20,000 species
- Only a few are pathogenic
Trichomonas vaginalis
- Phylum?
- Causes? Symptoms?
- How do you get it?
- protazoan pathogen
- Lack mitochondria, so in phylum Archeozoa
- causes vaginal infection, discharge
- Sexually transmitted
Giardia lamblia
- phylum?
- where does it inhabit?
- How does it affect the host?
- Symptoms?
- How is it transmitted?
- Resistant?
- protozoan pathogen
- Phylum Archeozoa (lacks mitochondria)
- Inhabits human intestine
- Causes prolonged diarrhea
- Infection can interfere with food absorption (may cause weight loss)
- 7% of healthy population are carriers (shed cysts in feces)
- Outbreaks from water contaminated by human or animal feces (beavers and other wild mammals)
- Cysts are relatively resistant to chlorine
Entamoeba histolytica
- phylum?
- Causes?
- how transmitted?
- protozoan pathogen
- Phylum Rhizopoda
- Causes amoebic dysentery
- Cysts excreted in feces can then infect new hosts
- In the intestine, cyst walls are digested, trophozoites forms are released
- Trophozoites multiply in intestinal epithelial (outer layer) cells
- Dysentery (severe diarrhea) and abscesses may result
Trophoziote
- feeding and growing stage
- the vegetative form of a protezoan
Malaria
- caused by? (3 species)
- Affects how many people?
- how many deaths?
- who does it affect?
- immunity?
- presence in the US?
- Intermediate host?
- Definitive host?
- What makes it lethal?
- caused by protozoan pathogens
- caused by Plasmodium vivax, Plasmodium ovale, and Plasmodium falciparum
- affects 300 million people worldwide
- Causes 2-4 million deaths
- young children and visitors from outside of endemic areas are most affected
- adults have limited immunity in endemic areas
- Present in the US until effective mosquito control
- Complex life cycle (Fig 12.18)
- Humans are intermediate hosts
- Anopheles mosquitoes are the definitive hosts
- Parasites can be lethal if they interfere with circulation to the brain
Intermediate host
the organism that harbors the asexual stage of the parasite
(malaria- humans)
Plasmodium falciparum
- causes malaria
- most dangerous species
Definitive host
- the organism that harbors the adult (sexually mature) form of the parasite
(malaria- mosquito)
Diagnosis and treatment of malaria
- diagnosed by examination of parasites in a blood smear
- treated with quinine and chloroquine
- But resistant strains are spreading rapidly
- Vaccine to sporozoites is being developed (may need vaccine to other stages as well for effective control
Sporozoite
- infective stage of the malaria causing pathogen, Plasmodium
Toxoplasma gondii
- Agent of?
- Carried by?
- How transmitted?
- protozoan pathogen
- agent of toxoplasmosis
- Intermediate stage tachyzoites replicated in domestic cats
- Oocysts are passed into feces
- humans may ingest the oocysts, trophozoites emerge and infect human tissues
Toxoplasmosis
- Affects what parts of the body?
- Prevalence?
- How transmitted?
- Immune defense?
- Dormancy?
- Effects on pregnant women?
- Effects on immunosupressed people
- Disease of the blood and lymphatic vessels
- Fairly common infection
- Usually not recognizable because the immune system controls the infection
- humans may ingest the oocysts from cats, trophozoites emerge and infect human tissues
- Immune response develops and controls the spread
- Parasites form dormant cysts and the infection is inactive unless the immune system is suppressed
- May cause damage to fetus (severe retardation) in pregnant women
- May cause vision damage, neurological impairment in immunosuppressed state
Tachyzoite
rapidly growing trophozoite (vegetative) form of a protozoan
Oocysts
- contain sporozoites that invade host cells and form tachyzoites
Cryptosporidium parvum
- Symptoms?
- Where does it live?
-Transmitted by?
- Death?
- protozoan pathogen
- Causes diarrhea in immunocompromised hosts
- lives in intestinal cells
- transmitted in feces of cows, dogs, cats
- can be life-threatening because of dehydration from diarrhea
Trypanosoma brucei gambiense and
Trypanosoma brucei rhodesiense
- Illness?
- Transmitted by what arthropod?
- Affects how many people?
- Where does it affect people?
- What part of the body does it affect?
- What does it do?
- Where is initial infection and where does it move?
- Death?
- Current drugs?
- Vaccine?
- Protozoan pathogens
- causes African sleeping sickness (also called African trypanosomiasis
- Transmitted by the Tsetse fly
- Affects 1 million people in Central and East Africa
- disorder of the nervous system
- decreased mental and physical activity
- Trypanosomes are initially in the blood and then move to cerebrospinal fluid
- leads to death when untreated
- Currently there are only moderately effective drugs
- Vaccine being developed
Trypanosoma cruzi
- illness?
- Carried by what arthropod?
- Where does it grow in the arthropod?
- How is it transmitted from arthropod to human?
- How does it infect?
- What part of the body does it affect?
- Protozoan pathogen
- Causes American Tryponosomiasis (Chagas disease)
- caused by the "kissing bug" (reduviid bug)
- grows in the gut of the bug
- Bug bites and defecates
- Trypanosome enters new host cells and replicates causing severe damage
- Causes severe disease of the cardiovascular system in some people
Chagas disease
- other name?
- Affects what part of the body?
- Prevalence in North American?
- American Tryponosomiasis
- causes severe disease of the cardiovascular system in some people
- present in Texas, Mexico, 1 case in Murfreesboro, TN
Reduviid bug
- Illness?
- Pathogen?
- Where does pathogen grow in the bug?
- How is the pathogen transmitted?
- the kissing bug
- causes American Tryponosomiasis by transmitting Trypanosoma cruzi
- Trypanosomes grow in the gut of the bug
- Bug bites and defecates and pathogen enters new host
Helminth
Parasitic roundworm or flatworm
Plathelminthes
- two kinds
- Phylum of flatworms
- Contains Trematodes (flukes) and Cestodes (tapeworms)
Nematoda
- Phylum of roundworms
Parasitic helminths
- Organ systems?
- Some lack what?
- Some have reduced what? why?
- complex organism with digestive, circulatory, nervous, excretory, and reproductive systems
- Some lack digestive system (absorb food from host)
- Some have reduced nervous system because they do not need to search for food or respond to the environment
- Means of locomotion may be reduced
- Reproduction may be complex
Trematodes
- shape of body?
- important part of body? what does it do?
- 2 examples
- parasitic flatworm
- Fluke
- flat leaf-shaped bodies
- Oral sucker (holds organism in place and sucks nutrients from host)
- Ex. lung fluke and liver fluke in humans
Paragonimus westermani
- Intermediate hosts?
- parasitic flatworm
- Human lung fluke
- Complex life cycle (Fig 12.26) - two intermediate hosts (snail and crayfish)
- humans are the definitive host
Schistosoma mansoni
(and other Shistosomes)
- Causes?
- Intermediate host?
- Illness? why?
- Parasitic flatworm
- Causes intestinal inflammation
- Causes damage to other organs when eggs lodge there
- life cycle (Fig 23.27)
- Snail is intermediate host
- Causes swimmer's itch because of immune reaction to cercariae (an intermediate stage of schistosome parasite in waterfowl)
Cercariae
intermediate stage of a schistosome parasite of waterfowl
Cestodes
- where does it live?
- important body parts?
- Digestion?
- parasitic flatworm
- tapeworm
- intestinal parasite
- head (scolex) has sucker for attachment
- No digestive track (absorbs already digested nutrients from host
- Segments are called proglottids (each contains male and female reproductive organs)
Scolex
- Important function?
- produces?
- the head of a tapeworm
- has suckers for attachment
- produce proglottids
Proglottids
- segments of a tapeworm's body
- continually produced by the head (scolex)
- each segment contains both male and female reproductive organs
Taenia saginata
Taenia solium
- Definitive host?
- How transmitted?
- beef tapeworm ( T. sagniata)
- pork tapework (T. solium)
- Humans are definitive hosts
- Shed eggs and proglottids in feces
- Animals (cattle) consume eggs and proglottids when grazing
- Hatched cysts become larva, migrate to muscle and encyst as cysticeri
- Humans eat undercooked meat and tapeworm attached to gut wall
Contamination cycle of tapeworms
- Cow eats grass contaminated by eggs. The eggs hatch and larvae move to the cow's muscle and encyst in muscle as cysticeri
- Meat consumed by human leads to new infection if not cooked well
- Human is the definitive host
- Tapeworm grows in human digestive track
- Eggs and proglottids are passed in feces
- Cow eats contaminated grass
Cysticeri
encysted tapeworm larvae
Nematodes
- Digestive system?
- 2 examples
- parasitic roundworms
- Complete digestive system
- Ex. pinworms, hookworms
Enterobius vermicularis
- where do they live?
- how transmitted?
- parasitic roundworm/ nematode
- pinworm
- adults live in the intestines
- eggs escape at night
- humans exposed to contaminated bedding accidently ingest eggs
Necator americanus
- Infectious stage?
- WHere does it live?
- How transmitted?
- How carried in body? to where?
- When was it a problem and why is it not anymore?
- Parasitic roundworm/ nematode
- hookworm
- Larval stage is infectious
- lives in small intestine of humans
- eggs excreted in feces, hatch to larvae in soil
- picked up on soles of feet
- carried by blood to lungs
- coughed up and swallowed
- used to be a problem in the rural south; now most people wear shoes and we have better sanitation and sewage disposal
Trichinella sprialis
- How transmitted?
- causes trichinosis
- comes from eating undercooked pork
- larvae hatch from cysts in the meat
- adults mature in the gut and reproduce to send larvae out to encyst in other tissues
Borrelia Burgdorferi
- arthropod vector
- illness
- carried by deer ticks (Ixodes scapularis)
- causes lyme disease
Plasmodium spp.
- arthropod vector
- illness
- carried by anopheles (mosquitos) (arthropod)
- causes malaria
Trypanosoma brucei gambiense
Trypanosoma brucei rhodesiense
- arthropod vector
- illness
- carried by the Tsetse fly (Glossina sp.)
- Causes African sleeping sickness (African trypanosomiasis)
Trypanosoma cruzi
- arthropod vector
- illness
- carried by the kissing bug (Tritoma sp.)
- Causes American trypanosomiasis
Rickettsia prowazekii
- arthropod vector
- illness
- carried by louse (lice) (Pediculus humanus)
- Causes typhus
Rickettsia rickettsii
- arthropod vector
- illness
- carried by ticks (Dermacentor andersoni)
- Causes Rocky Mountain Spotted Fever
Yersinia pestis
- arthropod vector
- illness
- Carried by rat fleas (Xenopsylla cheopis)
- Causes Bubonic plague
Virus
- Contains?
- Function of protein coat?
- How classified?
- How does it multiply?
-Small infectious particles containing protein and nucleic acid
- Protein coat protects the virus from the environment and is necessary for transmission from one host cell to another
- Classified by differences in their protein coats
- Obligate intracellular parasites (requires living host cells in order to multiply)
Obligatory intracellular parasites
require living host cells in order to multiply
Virion
one complete, fully developed, infectious viral particle
Why study viruses?
- 2 reasons
- viruses are major causes of human disease
- the study of viruses has instructed scientists about how cells function
History of virology
- Who first visualized viruses?
- What what the 1st visualized virus?
- When was it 1st visualized?
- How was it 1st visualized?
- After the discovery of bacteria, it became known in the late 1800s and early 1900s that some plant diseases were caused by agents that were smaller than most bacteria
- These agents would pass through a filter
- In 1935, Wendell Stanley isolated and purified tobacco mosaic virus (1st virus visualized by electron microscopy)
Characteristics of viruses
- size?
- replication?
- Making viral proteins and nucleic acids?
- Smaller than bacteria (20-100 nm in size)
- Require living cells in order to replicate
- Use host cell "machinery" to make viral proteins and nucleic acids
Nucleic Acid Genome
- composed of?
- Size?
- (one complete copy of the genetic information in a cell)
- composed of either RNA or DNA
- Size varies from 3,000 to 250,000 nucleotides
Viral coat
- may be non-enveloped coat or may be covered by a lipid-containing envelope
Genome
one complete copy of the genetic information in a cell
Host Range
- Definition
- Broad vs. narrow
- Spectrum of host cells that a virus can infect
- Broad host range: virus that can infect many different hosts
- Narrow host range: viruses that can only one cell type in one species
- Viruses bind to specific host cell receptors
Host Cell Receptors
- Specific receptor sites on the surface of a cell in which viruses bond
Nucleic Acid of a Virus
- genetic material makeup?
- Stranded?
- Shape of core?
- can be single stranded or double stranded
- Made of either DNA or RNA
- Shape may be linear, circular, or segmented
Capsid
Protein coat around the nucleic acid core
(Viruses)
Capsomeres
Individual protein units composing a capsid
(Viruses)
Envelope
Composed of lipids, proteins, and carbohydrates that surround the capsid
- only some viruses have this additional envelope
Viral shapes
- how seen?
- 3 shapes, explanation, and example
- seen by electron microscopy and X-ray crystallography
- Helical: nucleic acid cores wrapped in a helical protein capsid (Ex. Rabies virus)
- Polyhedral: multi-sided or icosahedral (Ex. adenovirus)
- Enveloped helical: roughly spherical with underlying helical shape (Ex. influenza virus)
Taxonomy of viruses
- who is responsible for naming?
- What are the three criteria names are based on?
- responsibility of International Committee on Taxonomy of Viruses
- Bases in nucleic acid type, replication strategy, and morphology
- Viruses are given descriptive common names (Human Immunodeficiency Virus: HIV)
Growing Viruses in the Laboratory
- Can be grown on what?
- What is needed for the study of human viruses?
- Expense?
- Eggs: why useful?
- Viruses can be grown in animal hosts; for the study of human viruses, this only works if there is a good animal model for the disease (more expensive to keep and use animals that to grow viruses in tissue culture)
- Viruses can be grown of embryonated eggs
- Early embryos have limited immune defenses, so the virus can replicate un-checked
- Different parts of the egg are useful for cultivating different viruses
- Egg method still used for the production of viruses for vaccine development
- Viruses can be grown in cultured cell lines; for primary cell cultures, cells can be isolated by dissociation of tissue
- Most viruses are grown on immortal cell lines
Cell cultures
- consists of ?
- why used?
(viruses)
- growth medium for many viruses
- consist of cells grown in culture media in the laboratory
- more convenient to work with than whole animals or embryonated eggs
Immortal cell lines
- transformed (cancerous) cells that can be maintained through an indefinite number of generations
- Frequently grow as a monolayer on the culture plate
(viruses)
Ernest Goodpasture
- Where from?
- What did he do?
- Why important?
- Vanderbilt scientist in the department of Pathology
- Pioneered the method of growing viruses in embryonated eggs
- 1931, centrally important contribution to the new science of Virology
Bacteriophages
- definition
- what does it do to the host cell?
- Another name?
- viruses that infect bacteria
- Viruses that replicate in bacterial host cells
- When virus infects and replicates, it kills the host cell
(also called phages)
Plaque Method
- the death of host cells provides a way to enumerate the bacteriophages

- Bacteriophages are mixed with bacteria
- Bacteria with attached phages are mixed with melted agar
- The melted agar is poured in a very thin layer over solidified nutrient agar
- When the viruses replicate, they kill the host cell and are released into the adjacent agar
- They infect adjacent bacteria and kill them too
- The result is a transparent spot in a cloudy lawn of growing bacteria
- Each spot is a plaque and corresponds to one bacteriophage
- Number of plaques is recorded in plaque-forming units (PFU)
Plaques
The clearings when using the plaque method
Plaque-forming units
- Measures the concentration of viral suspensions
- Number of plaques
- PFU
Cytopathic effect (CPE)
- describes what?
- can be used for what?
- Describes the incidence when cells are infected with viruses and they die or change morphology
- Can be used to enumerate viruses
(culture of animal viruses)
Viral replication
- where learned?
- 2 Cycles
- Principles of virus replication were learned from the study of bacteriophages
- Lytic Cycle
- Lysogenic Cycle
Lytic Cycle
- what does it do?
- Illustrated by?
- Ends with?
- 5 Steps?
- One method of viral multiplication
- illustrated by the T-Even Bacteriophages
- Ends with the lysis and death of the host cell

- Attachment
- Penetration
- Biosynthesis
- Maturation
- Release
T-Even Bacteriophages
- numbers
- Example of what cycle?
- Use what common host?
- Characteristics of virions?
- Characteric of structure?
- T2, T4, T6
- their multiplication has been studied extensively
- E. coli
- Example of the lytic cycle
- Virions are large, complex, and nonenveloped
- Characteristic head-and-tail structure
Attachment
- when does it occur?
- what attaches to what?
- How attached?
- Occurs after a chance collision between phage particles and bacteria
- Attachment site on virus attaches to a complementary receptor site on the bacterial cell
- Chemical reaction and weak bonds are formed
Penetration
- Lytic cycle: Step 2
- Lysogenic Cycle: Step 2
- After attachment, T-even bacteriophage injects its DNA into the bacterium
Biosyntheses
- Lytic Cycle: Step 3
- Host protein synthesis is stopped by the virus
- Phage uses host cell's nucleotides and several enzymes to synthesize copies of phage DNA
- No complete phages; only separate component
Maturation
- Lytic Cycle: Step 4
- Bacteriophage DNA and capsids are assembled into complete virions
Release
- Lytic Cycle: Step 5
- Release of virions from the host cell
- Host cell membrane breaks apart to release virions and host cell dies
Lysogenic Cycle
- Illustrated by?
- What happens to host cell?
- Steps
- Illustrated by Bacteriophage lambda
- Host cell remains alive

- Attachment
- Penetration
- DNA of virus forms a circle
- Virus can enter the lytic cycle or recombine with the bacterial host DNA
- Inserted DNA replicates along with the bacterial chromosome
- Phage is inactive; host cell is called a lysonogenic cell
- DNA is cut back out of the bacterial chromosome and it completes the lytic cycle
Prophage
- the inserted phase DNA in a host cell during Lysogenic Cycle
Lysogeny
- phage is inactive
- Host cell may acquire new properties (Ex. ability to produce a toxin)
- When the prophage exits the bacterial chromosome, it can carry and package adjacent bacterial genes (specialized transduction)
Lysogenic cell
host cell when the phage is inactive (in lysogeny)
Specialized transduction
- one result of lysogeny
the process of transferring a piece of cell DNA adjacent to a prophage to another cell
How does replication of animal viruses differ from phage replication?
In the replication of animal viruses:
- Penetration: instead of injection of the nucleic acid, the whole virus enters by endocytosis or pinocytosis
- Uncoating of the host is carried out by host cell enzymes
- DNA viruses replicate the DNA in the nucleus
-Capsid proteins are synthesized in the cytoplasm
- New viral proteins then more into the nucleus to assemble the complete virion
- Virions are then transported along the endoplasmic reticulum for membrane fusion and release
(Ex. Papova virus)
Pinocytosis
(replication of animal viruses)
- active cellular process by which nutrients and other molecules are brought into a cell
Fusion
(replication of animal viruses)
- Method of entry of virus into eukaryotic cells
-Viral envelope fuses with the plasma membrane and release the capsid into the cell's cytoplasm
Uncoating
(replication of animal viruses)
- the seperation of the viral nucleic acid from its protein coat once the virion is enclosed within the vesicle
Herpes simplex virus
- Symptoms?
- Numbers?
- DNA virus
- Herpesvirus
- Causes cold sores and genital lesions
- HHV-1 and HHV-2
Varicella zoster virus
- Illnesses?
- Number?
- DNA cirus
- Herpesvirus
- HHV-3
- Causes chicken pox and shingles
Lympocryptovirus
- Illnesses?
- HHV #?
- DNA virus
- Herpesvirus
- Causes infectious mononucleosis and Burkitt's Lymphoma
- HHV-4
Papovaviridae
- Symptoms?
- DNA virus
- causes warts and tumors
Human papillomavirus
- Associated with?
- Vaccine?
- DNA virus
- Papovaviridae
- Associated with cervical cancer
- New vaccine that prevents cervical caner
Poxviruses
- Symptoms?
- Human diseases?
- Middle ages in Europe?
- Vaccination? Found by who?
- DNA virus
- causes skin pustules
- Human diseases are smallpox and cow pox
- In middle ages in Europe, 80% of the population was affected by smallpox; 30% death rate
- Edward Jenner used cow pox to vaccinate against smallpox
Hepadnavirus
- Illness?
- DNA virus
- named because they caused hepatitis and contain DNA
- Causes hepatitis B (other kinds of hepatitis are caused by RNA viruses)
- Synthesized DNA by copying RNA using viral reverse transcriptase
Picoranviruses
- RNA Virus
- Positive-sense genome
- Ex. Poliovirus
- Small viruses with RNA genome
- From viral RNA, proteins are synthesized that inhibit transcription and translation of host proteins
- One of them is RNA-dependent RNA polymerase
Reverse transcriptase
- uses viral RNA as a template to produce complementary double-stranded DNA
Positive-sense genome
- Viral RNA that can act as mRNA
Oncogenic Viruses
Oncoviruses
- Definition
- How?
- Examples of viruses and what they lead to
- viruses that cause cancer
- Can integrate their genetic material into the host cell DNA and replicate along with the host cell chromosomes
- Papilloma viruses: cause warts and cervical carcinoma
- HTLV-1: causes leukemia
- Epstein-Barr Virus: herpesvirus; causes Burkitt's lymphoma and nasopharyngeal cacinoma
Latent Virus Infections
- examples
- Herpes simplex virus (HHV-1 and HHV-2): nearly everyone who is infected recovers from the virus, but the virus hides in the nerve cells that enervate the skin; a fever or sunburn may reactivate the infection and cause a fever blister
- Varicella virus: causes chicken pox; after recovery, can come out of latent state as shingles
Persistent Virus Infections
- Example
- Potential affect
- Some viruses persist very slowly replicating populations long after the initial infection has been cleared
- Ex. Measles virus
- In rare cases, persistent viruses cause a rare brain infection called subacute sclerosing panencephalitis (SSPE)
Subacute Sclerosing Panencephalitis (SSPE)
- rare brain infection caused by persistent viruses
Prions
- Definition
- Example diseases
- How spread?
- Infectious proteins that catalyze a change in the conformation of normal protein molecules and cause disease
- Ex. Mad Cow Disease, Creutzfeld-Jacob Syndrome, Kuru
- Spread by eating products contaminated with brains of affected individuals
Virus: HIV
- Disease
- Family
- Disease: AIDS
- Family: Retroviridae
Virus: Influenza virus
- Disease
- Family
- Disease: Influenza (flu)
- Family: Orthomyxoviridae
Virus: Measles virus
- Disease
- Family
- Disease: Measles (Rubeola)
- Family: Paramyxoviridae
Virus: Human Herpes Virus 1 and 2
- Disease
- Family
- Disease: Fever blisters, genital herpes
- Family: Herpesviridae
Virus: Mumps virus
- Disease
- Family
- Disease: Mumps
- Family:Paramyxoviridae
Virus: Human papilloma virus (HPV)
- Disease
- Family
- Disease: genital warts, cervical cancer
- Family: Papoviridae
Virus: Epstein-Barr Virus (HHV-4)
- Disease
- Family
- Disease: Infectious mononucleosis
- Family: Herpesviridae
Virus: Variola virus
- Disease
- Family
- Disease: Smallpox
- Family: Poxviridae
Virus: Varicella-zoster (HHV-3)
- Disease
- Family
- Disease: Chickenpox (Varicella)
- Family: Herpesviridae
Virus: Hepatitis C virus (HCV)
- Disease
- Family
- Disease: Hepatitis C
- Family: Flaviviridae
Virus: Hepatitis B virus (HBV)
- Disease
- Family
- Disease: Hepatitis B
- Family: Hepadnavirus
Virus: Poliovirus
- Disease
- Family
- Disease: Polio
- Family: Picornaviridae
Epidemiology
the science that studies when, where, and how diseases are transmitted
Diseases
- definition
- when might a disease result?
- an abnormal state of health in which all or part of the body is not adjusted or capable of performing its normal functions
- a disease may result when the immune defenses of the host are not effective in controlling the growth of a pathogen
Why study epidemiology?
- 3 reasons
- the ability to define where a disease occurs suggests the cause
- the ability to identify when a disease occurs suggests how many people may be affected at a given time
- allows for the development of a strategy for control
Pathology
- scientific study of diseases
Etiology
- Study of the cause of a disease
Pathogenesis
the manner in which a disease develops
Infection
Colonization or invasion by a microorganism only
- may or may not lead to a diseased state
Normal Microbiota
- the microorganisms that establish permanent residence in the body but do not produce disease under normal circumstances
- Present in the gut, respiratory track, skin, genitourinary track
Mutualism
- Definition
- Examples
- Examples of microbial antagonism
- a type of symbiotic relationship that benefits both organisms
- Ex. E. Coli bacteria in the colon produce vitamin K, some B vitamins. They gain nourishment from their host
(Microbial Antagonism)
- Microorganisms in the human vagina maintain a low pH (3.5-4.5) that inhibits growth of yeast (Candida albicans) that may be harmful
- Normal microbiota of the large intestine prevent growth of Clostridium difficile bactera that are also present; when this normal population of microorganisms is reduced by antibiotics, Clostridium difficile causes diarrhea or inflammation on the colon
Opportunistic Pathogen
- Definition
- Example
- may be normal resident organisms that can cause disease if they gain access to a different part of the body or
- if immune defenses are weakened, they can become pathogenic
- Pneumocystis jiroveci is not a pathogen in healthy individuals, but can be pathogenic when immune defenses are unable to control it (AIDS)
Pathogens that are benign in one part of the body, but cause disease elsewhere
- E. Coli: not a pathogen in the gut, may be a pathogen in urinary bladder or lungs
- Neisseria meningitidis: may live quietly in respiratory tract, can cause meningitis if it gains access to central nervous system
- Streptococcus pneumoniae: normal resident of the nose and throat, but becomes pathogenic and causes pneumonia when it enters the lungs of a susceptible host
Koch's Postulate
- what is it?
- What are the 4 steps?
- Why does it not work sometimes?
- How you establish the cause of a disease
1. Same pathogen must be present in every case of the disease
2. Pathogen must be isolated from the diseased host and grown in pure culture
3. Pathogen from the pure culture must cause disease when it is inoculated into healthy, susceptible laboratory animal
4. Pathogen must be isolated from the inoculated animal and must be shown to be the original organism

Not all organisms can fulfill Koch's Postulate:
- some organisms can't be grown in pure artificial medium
- Viruses must be grown on cells- possibility of contaminating virus from the cells
- Some human pathogens don't cause the same disease in an animal host
- It is unethical to inject live pathogens into humans
Symptoms
Changes in the body that suggest infection or disease (pain, discomfort)
- cannot be observed directly
Signs
- Changes in physical appearance (rash, swelling, fever, paralysis)
- these changes can be observed
Syndrome
a group of symptoms and signs which are always associated with a disease
Communicable disease
any disease that spreads from one host to another
Contagious disease
disease that is easily spread from one host to another
Noncommunicable disease
- not spread
- Ex. diseases that have a genetic origin (Sickle Cell Anemia)
Incidence of disease
- number of people who develop disease during a specific time period
- indicates spread on disease
- AIDS in 2004 = 40,000
Prevalence of disease
- number of people who have a disease at one time
- includes both old and new cases
- AIDS in 2004: ~1 million
Sporadic disease
- occasional occurrence of a disease
- Ex. Typhoid fever
Endemic Disease
- always present
- Ex. common cold
Pandemic Disease
- Epidemic disease that occurs worldwide
Acute disease
develops rapidly
Chronic disease
develops slowly, persists
Latent disease
- agent of disease is inactive, but the disease recurs
- Ex. Genital herpes, shingles from herpes-zoster virus
Herd immunity
- when many immune people are present in a population, so the population will be protected rapid spread of a disease
- Nonimmune people will be protected because of the unlikelihood of coming into contact with an infected person
- Vaccination leads to herd immunity
Classification of Infection and Disease
According to extent of host involvement
Local infection
-infection confined to small area
- Ex. Local abscess
Systemic Infection
- Infection throughout the body
- Ex. Measles
Septicemia
-blood poisoning
- pathogens multiply in the blood
Bacteremia
bacteria in the blood
Viremia
viruses in the blood
Toxemia
presence of toxins in the blood
Primary infection
acute initial infections
- AIDs is primary infection
- Influenza is primary infection
Secondary infection
- caused by an opportunistic invader when the defenses are weakened by primary infection
- Pneumonia is secondary infection
- Streptococcal pneumonia is the secondary infection
Predisposing factors of disease
- name 6
- Factors that make one more susceptible to disease
1) Chemotherapy
2) Young child, old age
3) Poor nutrition
4) Environment (smog)
5) Emotional disturbances
6) Bad habits (smoking, alcoholism)
Incubation Period
- definition
-depends on? (4 things)
- time between first infection and appearance of disease
- Depends on: specific agent of disease, number of infecting organisms, resistance of host, virulence of pathogen
Prodromal period
- period of early mild symptoms
Period of illness
- period of acute symptoms and signs such as fever, chills, pain, sore throat, lymph node enlargement, gastrointestinal upset
Period of decline
- signs and symptoms of disease diminish
- vulnerable to secondary infection
Period of convalescence
-regain strength, return of body to normal state
- may be a time when affected person can be a carrier of disease
- Ex. of diseases transmitted by carriers, but not ill themselves: Typhoid fever, Cholera
Reservoir of Infection
- a living organism or nonliving material that provides a pathogen with adequate conditions for survival and multiplication prior to transmission
Human reservoirs
- people who harbor pathogens
- may be showing symptoms and signs of disease
- May show no signs of illness (carriers)
Animal reservoirs
- animals who harbor microorganisms that can transmit disease to humans
Zoonoses
- diseases that occur primarily in animals but can affect humans as well
- Ex. Rabies, anthrax, hantavirus
Nonliving reservoirs
- nonliving materials that sustain organisms until they infect humans
- Soil harbors Clostridium tetani, the organism that causes tetanus
- Soil harbors Clostridium botulinum, the organism that causes botulism
Contact transmission
spread of an agent of disease by direct contact, indirect contact, or droplet transmission
Direct contact transmission
- person to person
- physical contact
- no intermediate objects involved
- Sex, kissing, touching
Indirect contact transmission
- transmitted by non-living material (formite)
Formite
Any nonliving object involved in the spread of an infection
- Ex. bedding, towels, thermometers, syringes
Droplet transmission
- transmission by mucous droplets that travel short distances (less than 1 meter)
- droplets are discharged by sneezing, coughing, laughing, and talking
- One sneeze = 20,000 droplets
Vehicle transmission
transmission of disease agents by a medium, such as water, food, air
Water borne vehicle transmission
-water containing untreated sewage
Food borne vehicle transmission
- foods incompletely cooked or poorly refrigerated
Air borne vehicle transmission
- droplet nuclei may dry, travel as dust more than 1 meter
- Tuberculosis organisms are resistant to drying
- Can remain in room dust
Transmission by vectors
- passive vs. active
- flies on animal wastes, carry it to humans (passive)
- Insects bites (active) when insect carries pathogen
- Malaria carried by mosquitoes
- African sleeping sickness carried by Tsetse fly
Agent: Mycobacterium tuberculosis
- Disease
- Portal of entry
Disease- tuberculosis
Portal of entry- respiratory route
Agent: Bordetella pertussis
- Disease
- Portal of entry
Disease- Whooping cough
Portal of entry- respiratory route
Agent: Steptococcus pneumoniae
- Disease
- Portal of entry
Disease- Pneumonia
Portal of entry- respiratory route
Agent: Streptococcus pyogenes
- Disease
- Portal of entry
Disease- Scarlet fever
Portal of entry- respiratory route
Agent: Salmonella enterica
- Disease
- Portal of entry
Disease- Salmonellosis
Portal of entry- Feces
Agent: Vibrio cholerae
- Disease
- Portal of entry
Disease- Cholera
Portal of entry- Feces
Agent: Salmonella typhi
- Disease
- Portal of entry
Disease- Typhoid fever
Portal of entry- Feces
Agent: Shigella
- Disease
- Portal of entry
Disease- Shigellosis
Portal of entry- Feces
Agent: Treponema pallidum
- Disease
- Portal of entry
Disease- Syphilis
Portal of entry- Urogenital tract
Agent: Neisseria gonorrhoeae
- Disease
- Portal of entry
Disease- Gonorrhea
Portal of entry- Urogenital tract
Agent:
- Disease
- Portal of entry
Disease- Cold Sores
Portal of entry- Skin
Nosocomial infection
- does not show any evidence of being present or incubating at the time of admission to a hospital
- acquired as a result of a hospital stay
- hospital environment contains pathogens
- patients often have weakened immune defenses
- many possible sources of transmission
- care-givers
- contact transmission from nonsterile materials, bedding, catheters
- Airborne transmission from other patients
Microorganisms involved in most nosocomial infections
- Staphylococcus aureus, other staphylococci, and other enerococci: 34%
- E. Coli, Pseudomonas aeruginosa, Enterobacter spp., and Klebsiella pneumoniae: 32%
- Clostridium difficile: 17%
- Fungi, mostly Candida albicans (yeast): 10%
- Other gram-negative bacteria: 7%
Control of Nosocomial Infections
- Aseptic (germ free) techniques
- Frequent and thorough hand washing
- Isolation rooms, for example if TB is suspected
- Disinfection of respirators, catheters, etc.
- Infection control officer or committee at each hospital
Cholera epidemic in London
- Early example of epidemiology
- 1848-1849
- John snow, British physician, analyzed death records
- interviewed victims families
- Mapped outbreak and showed most deaths were in people who drank from a public water pump
- Pump handle removed, cholera declined
Childbirth fever in Vienna
- Early example of epidemiology
- 1846-1848
- First maternity clinic, 13-18% of women who gave birth died due to sepsis of uterus that spread
- Wealthy women stayed home, nurse came in, fewer deaths
- Poor women gave birth at home, then went to hospital afterward
Ignaz Semmelweiss realized that women in First MAternity Clinic were attended by medical students who also conducted autopsies
- Ordered hand washing
- Death rate dropped 2%
Case reporting
- epidemiology depends on it
- health care workers required to report specific diseases to local, state, and national health officials
- Notifiable diseases: AIDS, Measles, Tetanus, Typhoid fever, Gonorrhea
- case reporting helps establish a chain of transmission
- with chain of transmission info in hand, epidemiologists develop a control strategy
Emerging Infectious Diseases
- new diseases or old diseases showing increased incidences
- Lyme Disease caused by Borrelia burgdorferi (1975)
- Hemorrhagic Diarrhea caused by E. Coli (1982)
- Diptheria caused by Corynebacterium diptheriae (1994)
- Hantavirus pulmonary syndrome caused by Hantavirus (1993)
- Mad Cow Disease caused by Bovine spongiform encephalitis agent (1996)
- Ebola hemorrhagic fever caused by the ebola virus (2002)
- Severe Acute Respiratory Syndrome (SARS) caused by SARS-associated coronavirus (2003)
Center for Disease Control and Prevention (CDC)
- Branch of US Public Health Service located in Atl., GA
- Publishes an online journal called Emerging Infectious Diseases
- Publishes Morbidity and Mortality Weekly Report
- Tracks notifiable diseases
Pathogenesis
-the manner in which disease develops
- to cause disease, microbes generally need to overcome host defenses
Virulence
degree of pathogenicity
How do microbes cause disease?
- successful microbes have co-evolved with their host cells
- they are adapted to exploit host weaknesses
- it is not the aim of the microbe to cause disease, it is the goal to survive and reproduce
Disease results when the pathogen:
- gains access to the host
- adheres to host tissue
- evades host defenses
- damages host tissue
Agent: Herpes Simplex Virus
- Disease
- Portal of entry
Disease- Genital herpes
Portals of entry- urogenital track
Access and Pathogenicity depend on number of invading organisms
LD50= lethal dose 50= dose necessary to cause death of 50% of infected hosts

ID50= infectious dose 50= dose required to produce a demonstrable infection in 50% of exposed hosts

- LD50 and ID50 may change with differences in state of the host (immunity, physical conditions, etc.)
Adherence to Host Tissues
- pathogen has adhesins or ligands (surface molecules on the pathogen that bind specifically to complementary surface receptors on the cells of certain hosts)
Adhesins
- surface molecules on the pathogen that bind specifically to complementary surface receptors on the cells of certain hosts
- may be on cell wall or on flagella, pili, fimbriae
- Usually glycoproteins or lipoproteins
Capsules
- contribute to the ability of bacteria to invade a host
- sticky sugar coating outside of cell wall
- made of polysaccharides, peptides
- Highly organized and firmly attached to cell wall
- Inhibits phagocytosis by macrophages unless specific antibodies are attached
- capsule make the organism slippery
- Streptococcus pneumoniae causes pneumonia only if the strain has a capsule
-other encapsulated pathogens: Klebsiella pneumoniae, Haemophilus influenza (meningitis in kids and pneumonia), Bacillis anthracis (Anthrax), Yersinia pestis (bubonic plague), Neisseria meningitidis (Meningitis and Septic Shock)
Cell Wall components that contribute to virulence
- M protein of Streptococcus pyogenes (strep throat, scarlet fever, childbirth fever, meningitis, pneumonia)
- aids in attachment to epithelial cells
- resists phagocytosis
- Immunity depends on antibodies to M protein

- Waxy lipids in cell wall of Mycobacterium tuberculosis ( tuberculosis)
- resists phagocytosis
- Organism can persist inside macrophage
Phagocytosis
the ingestion of solids by eukaryotic cells
Virulence contributed by Microbial Enzymes
- Leucocidins are membrane active toxins that kill phagocytic leukocytes
- they can degrade lysosomal compartment of phagocytic cells (neutrophils, macrophages)
- produced mostly by staphylococci and streptococci
- Hemolysins: cause disruption of cell membranes of red blood cells and white blood cells
- Streptolysins are the hemolsins produced by streptococci
- Hemolysins are produced by staphylococci, streptococci, and Clostridium perfringens (gas gangrene)
- Coagulases: builds blood clots (clot may protect the bacteria from phagocytosis)
- Bacterial Kinasis: dissolves clots
- alloes infection to spread
- Hyaluronidase
- secreted by streptococci, dissolves hyaluronic acid necessary for connective tissue
-helps organism to spread
- Collagenase: breaks down collagen- connective tissue
-allows organism to spread
How do bacteria gain access to host cells?
- attachment by bacterial adhesins to cell receptors
- Salmonella enterica (Sallmonellosis) and E. coli interacting with host cell membrane release invasins that interact with the actin in the cytoskeleton to disrupt it
- Results in membrane ruffling
- Microbe sinks into the ruffle and is taken up
- Shigella (shingellosis, bacillary dysentary) uses actin to propel itself through the cell cytoplasm from one cell to the next
- evades immune defenses
Invasins
surface protein produced by microbes that rearranges nearby actin filaments of the cytoskeleton
How do bacterial pathogens damage host cells?
- direct damage at site of invasion
- Microbes multiply, use host resources
- Production of toxins
Direct damage
- cells may fill up with bacteria or viruses and rupture
- bacteria excrete enzymes that damage host cell
Use of host resources
- Bacteria need iron
- Iron is not readily available (usually tied up in hemoglobin or other iron-binding proteins)
- some bacteria detect low iron environment, secrete toxin, kill cell and take iron
- other bacteria produce proteins called siderophores
- Siderophores bind more tightly to the iron and steal it from host proteins and bring it to the bacteria
Toxin production
- toxins are cell poisons
- Toxins are either endotoxins or exotoxins
- toxins are the primary factor contributing to pathogencity
Exotoxins
- produced by bacteria and released from the cell
- include cytotoxins, neurotoxins, and enterotoxins
- exotoxins are proteins
- Highly specific inhinitors of host metabolism
- Made primarily by gram positive bacteria
- Most toxins are carried on plasmids or contributed by infection with a bacteriophage
- toxoids are exotoxins inactivated by heat or chemicals
- they no longer cause disease, but they can induce immune response
- Diphtheria toxiods and tetanus toxoids are part of the vaccine for these agents
Cytotoxins
- exotoxin
- attack many kinds of cells
- bacterial toxins that directly kill host cells or alter funtion
- Erythrogenic toxin of Streptococcus pyogenes (strep throat, scarlet fever, childbirth fever, meningitis, pneumonia) causes scarlet fever rash
Neurotoxins
- Exotoxins
- Attack nerve cells
- Botulinum toxin
- Tetanus toxin
Enterotoxins
- Exotoxins
- attack lining of gastrointestinal tract
- cholera toxin
- Staphylococcal enterotoxin
A-B Toxin
- Protein consisting on "A" active domain and "B" binding domain
- Diphtheria toxin, Corynebacterium diphtheriae produces diphtheria toxin if it possesses a lysogenic phage carrying the tox gene
-Two-domain structure ("B" binding, "A" active)
- inhibits protein synthesis especially in nerve, heart, and kidney cells. Does so by inhibiting a step required for movement of ribosomes along the mRNA
- Cholera toxin (enterotoxin)
-"A" subunit activates an enzyme called adenylate cyclase
- This results in an unregulated overproduction of cyclic AMP
- By a mechanism that is not understood, this results in loss of fluids across epithelial cells and watery diarrhea
- Muscle contractions are also disturbed leading to diarrhea and vomiting
Staphylococcal Enterotoxin
- Staphylococcus aureus (skin infections, food poisoning, toxic shock syndrome) produces a product that induces an intense immune response (superantigen)
- it has the same disruptive effect on the cells of the digestive tract as cholera toxin
- Some strains produce toxic shock
- Diarrhea, fever, vomiting are followed by vascular complication and low blood pressure (shock)
- Associated with nasal surgery and absorbent packing, highly absorbent vaginal tampons, or with complications after giving birth
Superantigen
- antigens that produce a very intense immune response
- Bind to receptors on T lymphocytes and trigger activation, proliferation, and release of "cytokins"
- Results in fever, nausea, vomiting, diarrhea, shock, and death
Cytokine
a small protein released from human cells that regulates the immune response; directly or indirectly may induce fever, pain, or T-cell proliferation
Membrane-Disrupting toxins
- results in disruption to the integrity of the plasma membrane of host cells
- One example is Staphylococcus aureus (skin infections, toxic shock syndrome, food poisoning) exotoxins
-it forms protein channels in cell membranes
- Another example is Clostridium perfringens (gas gangrene, diarrhea) exotoxins
- interacts and disturbs phospholipids in membrane
Neurotoxins
- interfere with nerve impulse transmission
- Ex. Botulinum toxin (Clostridium Botulinum) binds to nerve cell
- Acts on proteins in the synaptic vesicles
- Inhibits release of the neurotransmitter acetylcholine
- Ex. Tetanus toxin (Clostridium tetani) binds to nerves that relax muscles and inhibits transmission, relaxation is prevented
- Toxin binds membrane and is internalized
- Inside the cell, toxin flows with the axon
- Degrades proteins involved in release of inhibitory neurotransmitters
- the unbalance prevents muscles from relaxing
Endotoxins
- Lipopolysaccharides (LPS) are part of the cell wall of most gram negative bacteria
- The lipid portion, lipid A, is the endotoxin
-It is released when the cell dies
- Antibiotic treatment can release LPS
- Symptoms worsen, then improve
- Induce chills, fever, weakness, aches
- In the worst cases, endotoxins result in massive vascular complications that result in shock
- Blood clotting decreases vascular supply to tissue
- This phenomenon is called disseminated intravascular coagulation (DIC)
Septic Shock
- Shock is a life-threatening loss of blood pressure
- Shock caused by gram negative bacteria is called septic shock
- Shock is mediated in part by IL-1 and another cytokine called tumor necrosis factor (TNF)
- Capillary (small blood vesseks) permeability is disturbed, lose fluid, blood pressure drops
- Ex. of endotoxin-producing bacteria
- Neisseria meningitis (Meningitis, Septic shock)
- Salmonella typhi (Typhoid fever)
Interleukin-1 (IL-1)
- cytokine
- local cellular hormone
- its release causes a fever response
Tumor necrosis factor (TNF)
-polypeptide secreted by phagocytes
- binds to tissues in the body and alters their metabolism
Pathogenicity of viruses
- depends on access to host
- depends on evading host immune defenses
- due to damage to host cell
- virus has attachment site specific for cell surface molecule (receptor)
Evasion of host immune response
- pathogens can enter cells, replicate inside cell (hiding out strategy)
- Pathogens can cause cells to turn off molecules involved in presentation of virus to immune system
How do viruses kill cells?
- cell fills up with viruses, dies
- Viral protein modify host membrane, cell dies
- Viral product inhibits synthesis of host DNA, RNA, proteins; cell dies
- Viral products destroy lysosomes, enzyme contents kill cell
Cytopathic Effects (CPE) of Viruses
- Definition: the visible effects of viral infection of a cell
- When cells are infected with viruses, they may die or change morphology (Cytopathic effect)
- Can be used to enumerate viruses just like the plaque assay
- Herpes simplex interferes with host cell synthesis of DNA
- Mitosis comes to a halt
- Cells fail to replicate and repair, eventually die
- Examples:
1. Some viruses (measles, respiratory syncytial virus) cause cells to fuse and form large multinucleated cells (synctium, pl. syncytia)
2. Replicating components of viruses may be detected as "inclusion bodies"
3. Viral infections induce changes in the host cell surface. The host's immune system attacks
4. Viral infections may result in chromosomal breakage and translocation, may lead to transformation to a tumor cell with loss of growth control
PAthogenic effects of fungi
- may produce capsule resistant to phagocytosis
- Cryptococcus neoformans can cause meningitis. I has a capsule resistant to phagocytosis
- Candida albicans secretes a protease that may aid in colonization of the skin
- Fusarium mold produces toxins called tricothecenes
- Can cause headaches, chills, nausea, vomiting, visual disturbances
- Aflatoxin from fungus growing on peanuts causes malaise and loss of appetite, damage to liver
- Aflatoxin is also a carcinogen causing tumors in the liver and other organs
- Toxin (alkaloid) from fungus living on food grains can cause hallucinations, poor blood circulation, and gangrene. Was called Ergot poisoning. Common in the middle ages. Modern milling usually removes the poisonous part
- Amanita mushrooms produce a neurotoxin
Pathogenic effects of Protozoa
- Malaria grows in red blood cells and causes them to rupture
- May cause anemia (too few red blood cells and poor oxygen transport to tissues
- Malaria induces "knobs" on red blood cells, bind to blood vessels, block circulation
Pathogenic Effects of Helminths
- Use host tissues for their own purposes
- waste products of parasites can cause illness
- Ex. Wuchereria bancrofti ( agent of elephantiasis) lives in lymphatic circulation, blocks it, fluid accumulates, causes swelling of legs and other body parts
Innate Defenses
- first line of defense
- Rapid, need no previous exposure
- Somewhat non-specific
- Skin, mucous membranes and their secretions, normal microbiota
Skin
- innate defense (1st line of defense)
- epithelial cells are closely packed and layered to form a barrier
- top layer is dead, contains keratin (protective protein)
- Some fungi can digest keratin and invade
Mucous Membranes
- Innate defense (1st line of defense)
- Line gastrointestinal, genitourinary, and respiratory tracts
- Epithelial layer secretes fluid (mucus)
- Some pathogens thrive there, penetrate [Ex. Treponema pallidum (syphillis)]
- Mucus traps microbes in sticky material
Lacrimal (tears) apparatus
- Manufactures and drains away tears
- washes, cleanses the eye continuously
- flushes out irritants
- tears contain lysozyme, lyses gram positive bacteria
Saliva
- cleanses mouth
- dilutes microorganisms
- contains lysozymes
lysozyme
an enzyme capable of hydrolyzing bacterial cell walls
Respiratory or Ciliary escalator
- goblet cells produce mucus, trap orgaisms
-ciliated cells in low respiratory tract
- propel. sweep out material with mucus
Red blood cells
- most abundant type of blood cell
- also called erythocytes
Leukocytes
- white blood cells
Neutrophils
- white blood cells
- most abundant in the blood in the early part of an infection by bacteria
- as infection progresses, more macrophages mature and they dominate the response
- They scavenge and eat dead and dying bacteria (phagocytosis)
Mechanisms of Phagocytosis
- Chemotaxis
- Adherence
- Ingestion
- DIgestion
Chemotaxis
- Phagocytes are chemically attracted to microbes
- Among the chemotactic chemicals that attract phagocytes are bacterial products, damaged tissue cells, complement factors
Adherence
- Attachment of phagocyte to bacterial cell membrane or foreign material
- Adherence is inhibited by: capsules, M proteins of Streprococcus pyogenes (strep throat, scarlet fever, childbirth fever, meningitis, pneumonia) , waxy coat of Mycobacteria
- Adherence is greatly improved if the bacteria are coated with antibodies or complement in a process called opsonization
Opsonization
- coating process that coats microorganisms with certain serum proteins that promote attachment of the microorganisms to the phagocyte
Ingestion
- plasma membranes surrounds bacteria
- Extensions of plasma membrane are called pseudopods
- The fluid-filled pocket formed becomes a sac called a phagosome
Digestion
- Phagosomes fuse with lysosomes containing proteolytic enzymes. The new sac is called a phagolysosome
- Enzymes kill most bacteria within 10-30 min (lysomes, lipases, proteases, ribonuclease, deoyribonuclease)
- pH of phagolysosome is about 4.0
- Lysomes also contain reactive oxygen products that are toxic to bacteria
- Indigestible material becomes a residual body and is excreted from the cell
Mechanisms of evasion of Phagocytosis
Coxiella burnetii (Q-fever) replicates in the low pH environment of phagolysosomes
- Bacterial toxins may kill phagocytes (Ex. Staphylococci)
- Shigella flexneri and Listeria monocytogenes (Listeriosis) lyse phagolysosomes by enzymatic action of bacterial enzymes
- escape into cytoplasm and use cell resources
- Mycobacterium tuberculosis (tuberculosis) and Chlamydia inhibit fusion of phagosome and lysosome and inhibit the acidification of the lysosomes
- Microbes then multiply, kill cell
Fever
- temperature is increased by increasing metabolism and involuntary muscle contractions (shivering)
-causes the sensation we call "chills"
- Blood vessels constrict, skin seems cold
- Fever is defensive because it speeds up metabolism and immune mechanisms work better
- It may also inhibit growth of some microbes
Interferons
- a class of antiviral proteins produced by cells after viral infection
- Their principle function is to interfere with viral multiplication
Alpha interferons and Beta interferons
- Produced by virus-infected host cells in small quantities
- they diffuse to neighboring cells and induce synthesis of antiviral proteins (AVPs)
- AVPs interfere with various steps of viral replication
Adaptive Immunity
- highly specific
- Require some time to develop
- Cellular and Antibody-mediated immunity due to lymphocytes
- adapts to a microbial invader or foreign substance
Immunity
- a specific defensive response to foreign organisms or other foreign substances
Antigen
- a substance that evokes an immune response
Immune response
- production of specific antibodies or effector lymphocytes
Acquired Immunity
- Immunity that develops during an individual's lifetime
Humoral Immunity
- due to the presence of antibodies in body fluids
- Antibodies are produced by B lymphocytes (B cells)
- Defense against bacteria, bacterial toxins, free virus
Cell-Mediated Immunity
- Due to the presence of T lymphocytes and phagocytic cells
- T cells are of several types
- Helper T cells help B cells make antibodies
- Cytotoxic T cells directly kill virus-infected host cells
- Regulatory or suppressor T cells regulate other immune cells
- T cells regulate the activity of macrophages
- Primarily responsible for immunity to fungi, protozoa, helminths, intracellular viruses
- Responsible for rejection of transplanted tissues
Antigens
- antigens are usually proteins or polysaccharides
- BActerial antigens are: capsules, cell walls, flagella, fimbriae, toxins
- Specific regions of the molecules that are recognized by antibodies are antigenic determinants or epitopes
- Each antigen fits with a specific antibody like a lock and key
Epitopes and Antigenic determinants
- the specific regions on antigens that antibodies recognize and interact with
Antibodies
- Proteins with two identical heavy chains and two identical light chains, held together by disulfide bonds
- The amino acid sequence of the variable regions determine the binding sire that will combine with antigen
- Members of a class of proteins called immunoglobulins
- Opposite end of the variable regions is the constant region
- Protease treatment releases the Fc (fragment, crystalline) and the Fab (fragment antigen binding) fragments
- Structure of bivalent antibody (2 binding sites)
Immunoglobulin G (IgG)
- monomer
- Primary serum antibody, 80% of serum antibodies
- Immune antibody
- Opsonization and neutralization
- Activates complement
- Crosses placenta
Immunoglobulin M (IgM)
- pentamer
- 5-10% of serum antibodies
- 1st antibody expressed by B cells
- Secreted by B cells during primary immune response after 1st antigen exposure
- Activates complement, aggutinates bacteria, promotesphagocytosis
Immunoglobulin A (IgA)
- present in mucosal secretions
- 10-15% of serum antibodies
- Present in milk to protect newborns by immune exclusion
- Activates complement by the alternative pathway
- Dimer
B cells
- develop in adult bone marrow or fetal liver
- Mature B cells move through the blood to lymph nodes or spleen
- If they meet an antigenic determinant to which they have a unique receptor, they will be activated, divide into a clonally expanded population, and mature into antibody factories called plasma cells
Clonal Selection
- Each B cell produced in the bone marrow is unique
- Each B cell produces identical copies of one immunoglobulin and displays it on the surface of the cell
- B cells circulate continuously
- If they meet an antigen that can bind to the unique receptor, they will divide and form a clone of B cells
- Thus, the antigen selects and expands the responsive B cell
- The variety of B cells allows us to respond to about 100 million different antigens
- Diversity of the Ig receptors is determined by rearrangements of the genetic determinants
Why doesn't the immune system make antibodies to self-molecules?
- Immunological self-tolerance develops by early clonal deletion of any B or T cells that can react with self-molecules