Ph 162A Lec 6: Host Parasite Relationship

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Infections disease account for ____ % of the acute illnesses in the U.S

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70%

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infectious disease

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The basis for all infectious diseases is this host-parasite relationship.

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parasite

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an organism dependent on another organism for its existence (called a host)

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Disease

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an injury or abnormal finding in a living organism which results in recognizable effects.

notes: you may have growth and multiplication in or on the host, but it does not necessarily mean disease

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morbidity

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illness

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disease are broken down by ___ and ____

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a. signs
**are objective evidence of disease--recognizable by a third party

b. symtoms
**subjective evidence of disease--something that is stated by the patient which cannot be verified by anybody else

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mortality

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death

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infectious disease

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one that results from an infection with an organism

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non-infectious disease

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disease that do not result from infection e.g heart disease, high blood pressure, diabetes etc.

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What kinds of organisms cause infectious disease?

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bacteria, protozoa, and viruses. Every organism that we have covered so far, with the exception of algae.

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PSP (paralytic shellfish poisoning) with algae. Is that an infectious disease?

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no, because to be an infectious disease, the organism must grow in the host. Instead, PSP would be an example of intoxication.

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epidemiology

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the study of the distribution and causes of disease in a population

**apply to both infectious and non-infectious diseases

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where do these microorganisms come from?

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reservoir

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reservoir

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**It can be a host or place where the parasitic organism normally lives and multiplies.

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a reservoir is a source of the disease agent

**there are 3 reservoirs. What are they?

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1. Soil
2. animals
3. humans

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organisms that live in the soil

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saprophytes

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saprophytes

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free living microorganisms, i.e not usually parasitic, or dependent on another organism for its existence

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saprophytes are also called ___ or soil-loving

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geophilic

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opportunistic infection

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this is when the organisms do not normally have a host, but infection can still happen w/ certain types of organism

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non-human animals reservoir

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these organisms are always parasitic and we consider them to be zoophilic, or animal loving

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sometimes we get in the way of these diseases, we would be called ______, but not the primary host. Diseases such as these are called _____

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a. casual hots
b. zoonoses

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[humans as reservoir]

Organisms with reservoirs as humans are always parasitic and are termed _______

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anthropophilic = person-loving

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how do organism get in and out of the host?

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**Through portal of entry = place where a parasite enters a host (e.g mouth, nose, skin) and
** portal of exit = place where a parasite leaves the host (e.g feces, urine, saliva, mucus, tears, blood, or pus)

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[Transmission from reservoir to host: how do we acquire these infections disease organism?]

Mode of transmission

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The mode of transmission is the mechanism by which an organism can make its way to the host

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vector

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an arthropod which carries the organism from reservoir to the host e.g flies, mosquitos

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biological vector

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one in which a different phase of the microorganism multiplies. A part of the life cycle takes place w/in the biological vector.

e.g mosquito responsible for malaria, the mosquito is part of the life cycle of the Plasmodium organism that infects humans

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mechanical vectors

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one that transfers the microorganism passively w/no multiplication of the microoganism occuring e.g things like flies, where the organism is transferred passively

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fomites (singula r= fomes or fomite)

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inanimate objects (surface that you touch, bart, classroom) that carry the organism from reservoir to host

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[what are the 4 modes of transmission?]

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1. respiratory route or droplet infection
2. fecal-oral route
3. blood-borne route
4. contact route

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respiratory route

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**the reservoir is a human or animal.
**The portal of exist is the respiratory tract of an infected individual.
---The droplets contain the microorganism and are projected by coughing, sneezing, and maybe even just breathing.
** the portal of entry of the new host will be the respiratory tract. The deposition of droplets onto fomites is also possible. Someone can pick that up in their hands and transfer them to their mouth or eyes. So you can also have this secondary transfer via fomites

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fecal-oral route

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**human or animal as reservoir.
**portal of exist is the GI tract of the infected individual. **Feces contain the organism. **The portal of entry is going to usually be the mouth of the other individual.
**The vectors are going to be something like a fly. It could be fomites as well.
**e.g You could have a case where you have poor sanitation and food or water is contaminated. Something as simple as not washing your hands can transfer these organisms to raw foods or liquids.

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blood-borne route

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**reservoir is humans or animals.
**The portal of exit is a wound of the infected person.
**The portal of entry is the wound of the uninfected peson **can be transmitted by vetors or formites

ex: share needles needle,
**The blood-borne route of transmission is caused by an exchange of blood.
**organism can also be passed by anything that can transmit blood from one person to another.

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contact route

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**reservoir human or animal or soil.
**portal of exit is the lesion (wound or injury) or the sore that is contaminated: a contaminated secretion.
**The portal of entry is another open wound or sore.

ex:
**a shared towel. You might wipe a wound or sore with a towel--transmitted whatever is contaminating onto the towel

**If the disease is transmitted from the soil, there is no port of exit because the soil is not a living thing; it is just a reservoir.

----exmples include a skinned knee onto the soil

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what is communicability

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the ability of the infected organism to pass from one host to another

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communicable diseases

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infectious disease that can be transmitted from one human or animal to another human being or animal (contagious)

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non-communicable diseases

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infectious disease that is not usually transmitted from one human or animal to another

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[Disease Patterns]

endemic

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a disease constaly present in an area but involving relatively few persons at any given time

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sporadic

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a disease that occurs occasionally and involves only a few individuals

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epidemic

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a disease involving a large number of persons for a limited period of time

**For example, one person with Legionnaire’s disease is fine. If someone else in the same building has it, however, you have an epidemic

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pandemic

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describes a series of epidemics that involve a large part of the world

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emerging infectious disease

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a disease of infectious origin whose incidence in humans has increased w/in the past two decades (20yrs) and threatens to increase in the near future

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types of emerging infectious disease:

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a. new disease caused by a newly identified microoganism or newly identified strain of a known microorganism
ex: Legionnaire's disease
e.g disease caused by opportunistic organisms in immunosuppressed patients
b. previously recognized disease that are recently discovered to be infectious. Old disease, new organisms.
ex: petic ulcers

c. reemerging infectious disease which is a disease that was once prevalent, decreased in incidence, and is now increasing in incidence again

ex: Mycobacterium, the organism responsible for TB

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[infection vs. infectious disease]

transiency

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presence of a mircroorganism in or on a human or animal w/o multiplication; not a true host-parasite relationship

**organism is there by coincidence and does not lead to real host-parasite relationship

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colonization

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an infection that does not cause disease (no host changes).
**usually the case w/ the endogenous organisms that live w/in us

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endogenous/indigenous organisms are called

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normal fllora

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normal fflora

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organisms that live on humans w/o causing disease; many of these organisms are necessary for good health
*live on or in humans w/o causing disease

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covert infection (subclinical)

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This means that your body started an infection and responded to it, but you do not recognize the problem.

**You may have experienced a slight sniffle without developing a full-blown disease.

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Overt infection (clinical)

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infection that causes conspicuous injury to the host
*have symtoms

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incubation period

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time b/w exposure to a microorganism and the appearance of signs and symptoms of the disease

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[Host-Parasite Relationship]

pathogen

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an organism capable of causing disease

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non-pathogen

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an organism which cannot cause disease

**does not have the mechanism to live w/in a human or animal

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opportunist

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Organisms can cause disease on occasion when provided a compromised host. This means that the host has something about them that would allow the organism to infect and cause disease.

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There are several host factors that play a role in determining infection: (10 factors)

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1. Genetic composition
2. Age
3. Hormonal balance
4. Nutritional status
5.Integrity of an organ system
6. Integrity of the host's immune system
8. Host's immune status w/ regard to the particular parasitic microorganism
9 Presence of anti-microbial agents w/in the host- generally as prevention of prophylaxsis
10. Endogenous organisms already present on the host

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1. Genetic composition: name two

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1. species specificity
**only certain organisms wll infect certain host

2. certain genetic trait= disease susceptibility
**racial factors
e.g certain populations that carry genes for sickle-cell anemia and this confers resistence to malaria
**infectious diseases w/ the human immune system-- which it is controlled by a group of genes called the histocompatibility group
**genetic disease that make them susceptible to infectious diseases

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what is histocompatibility group?

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this put certain markers on our cells
**infectious disease agents that will target these makers on our cells

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Age: which group are mostly likeley to be host factor?

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*young children esp. premature babies
*old age

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3 Hormonal balance:

Female hormones affect microorganisms iin the ____

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vaginal tract

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Increased levels of ______, the normal stroidal hormones produced by the adrenal gland, can suppress the immune system

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glucocorticoids

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It has also been noted that such steroidal hormones can be elevated during time of ____

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stress

**more susceptible to disease

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4. Nurtitional status:

plays important role in ____

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fighting off infection

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5. integrity of an organ system:

why is this important?

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because abnormal structure or function of a particular organ system may predispose you to certain infections

e.g anatomical abnormalities in the kidneys or the ureters can increase urinary tract infections

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6. Barrier of natural secretions

Our skin has a variety of _____ that are batericidal (kills bacteria) to many species

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fatty acids

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Our nasal sections, saliva, tears, and most of our mucosal membranes contain the enzyme

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lysozyme

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lysozyme

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Lysozyme can cause the *lysis of gram positive organisms.
*degrade gram negatives, but *it does a great job on gram positives.

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there are also bactericidal substances in our ____ that naturally kill organisms in a non-specific way

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blood

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7. Host immune status:

immunodeficient

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cells of the immune system are impaired

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immunosuppressed

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immune system is artificially suppressed by the application of certain drugs

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nosocomial infection

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infectious diseases starting during a person's stay in the hospital (cuaght disease there)

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the presence of antimicrobial agents ins some cases prevents

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prophylaxis = prevention of disease

e.g People get loaded with antibiotics, upsetting their normal flora. They get a secondary infection

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10. Endogenous organisms already present on the host

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**Probiotics we are now adding them to food. Some replace organisms that may have beneficial effects but have been damaged by antibiotic use.

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2 interactions among parasitic organism

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**Interference- (microbial antagonism)
**Synergism- 2 organism work together to cause disease

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interference- (microbial antagonism)

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microbial antagonism: What you have is microbes growing at the expense of other microbes. This is primarily how our endogenous organisms protect us from disease. Some of these organisms may excrete an antibiotic substance of their own. Whereas their neighboring endogenous organisms are used to this secretion, newly introduced organisms cannot deal with the antibiotics.

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synergism

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*two microorganisms working together to cause disease.
e.g influenza and pneumonia, influenza being caused by a virus and pneumonia a bacterium. Influenza usually sets you up for bacterial infection

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two aspects of the parasitic organism which affect the balance

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**Exposure does

**Attributes of the microorganism

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Virulence

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is the potency of this pathogenicity, the capacity to cause disease. Do you need a million or something cells? With Shigella, ten cells and you have shigellosis.

**the extent of pathogenicity

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pathogenicity

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ability of a species of organism to cause disease

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pathogenesis

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the disease process; the mechanism by which a micro-organism causes an infectious disease

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strain type

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a genetic variant w/in a species

**only strain types can cause disease

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specific attributes of the parasite that determine virulence: ]

invasiveness

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this is the ability of organism to proliferate and spread w/in the host

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If the disease spreads by direct extension what does this mean?

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it means that is is invading into healthy tissue directly adjacent to the site of primary infection

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metastasis

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spead of an infection, via blood or lymph, to distant sites not ajacent to the site of primary infection

**the spread to a distant secondary infection

e.g microorganism can move to diff sites and metastasize to that llocation

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septicemia

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(blood poisoning)
**presence of microoganisms or thier toxins in the blood

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viremia

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presence of viruses in the blood

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bacteremia

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bacterial presence in the blood

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fungemia

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fungal presence in the blood

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parasitemia

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refers to protozoans in the bloodstream.

e.g Malaria

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[strategies of invasiveness]

anti-phagocytic strategies:

What kind of strategies would an anti-phagocytic do if it would to be engulf by a host white blood cell (by phagocytosis)?

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1. produce toxins to kill the phagocytes
2. inhibit the phagocytosis (phagocytes= are the blood cells capable of phagocytosis)
3. thick capsule layer for protection (notes: the one w/o the capsule are more virulent

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[strategies of invasiveness]

Production of extracellular subtances: what does it produce? and what does it do?

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**produce extracelluar substances that can break down the host tissues
**by damaging the host tissues, they can grow into it

**protozoans, bacteria, fungi

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There are some bacteria that can survive once they enter a white blood cell... how do they do that?

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Once the white blood cell brings the bacterium in, it typically will surround the vacuole that contains the bacterium with a different group of organelles (lysosomes) that will dump enzymes and destroy the bacterium. Some bacteria can inhibit that from happening, and they begin to grow within the white blood cell itself. In one instance, they produce a chemical that recruits ribosomes from the cell to coat this vacuole. When the lysosome that contains lysozyme comes over, it no longer recognizes the vacuole as containing a foreign substance.

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invasive strategies: intracellular growth

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viruses that can only grow w/in a host cell.
**they are protected w/in the host

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microganisms that destroy _____ by producing certain ____ and destroying tissues. They can do this by _____ or ____ through tissues.

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organs
toxins
blockage
physical migration

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Once inside the host, some of these organisms can change their appearance called by ___

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altering the cell surface or virus surface

**they can appear to be host tissues, and therefore, the body's immune system will not respond

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[strategy for invasiveness] flagella cause ____, and this is how the organism moves around.

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mobility

**b/c it moves making it harder for the host cells to catch

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bacteria also have ___, these hair like filaments can enhance attachment onto a host cell.

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pili

**help them stay in one location and to grow

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genetic integration this is....

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the incorporation of the genome of the microbe into a host cell w/ permanent alteration.

**this is what happens when you have viruses that can cuase tumors or cancer

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toxigenicity of the cell

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this is the ability of a cell to produce a potent toxin or poisonous substance w/in the cell

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there are two types of toxin:

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endotoxins and exotoxins

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many of the most potent toxins are produced by, typically when infected by a _____

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bacteria

lysogenic bacteriophage

notes: some may not produce toxins, but they can get a piece of DNA introduced to them that does produce toxins

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What is an endotoxin? name all the characteristic and damages it does to the host?

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1. endotoxin is physically residing on the bacteria itself; it is only released when the cell dies of lysis
**it is typically polysaccharides and lipids
**typically part of the cell membrane or cell wall of a gram negative organism= resistant to heat
**poor antigens = something that stimulates immune response
**no strong tissue tropism = do not target any tissues and organs
**its going to result in a systemic effect on the host b/c
the toxins is part of the physical make up of the organism

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exotoxin

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**something produced by living cell
**it is a product of cell metabolism
**excreted by the organism to the environment
**tends to be protein in nature
**mostly gram positive organisms (some negative)
**extraodinarily potent.
**heat labile (can be destroy by heat)
**make great antigens (so we can produce vaccines to have a protective immune system agaisnt toxins
**tend to have a specific tissue tropism, so they will target something very specific w/in the host
**lysogenic conversion= an exotoxin will be coded for in an extra piece of DNA that can be introduced by a phage and be passed by lysogenic conversion.

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what is lysogenic conversion

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conversion of an avirulent strain of bacteria to a virulent strain by infection of the bacteria by a phage containg a gene for toxin

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The microorganism also have the ability to elicit a hypersensitivity response. what is hypersensitivity response?

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an exaggerated (too much) and detrimental immune responseof the host to a prasite or allergen, which causes tissue destruction

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immediate hypersensitivity

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a detrimental (causing damage or harm) humoral immune response (production of antibodies) that occurs as an allergic response to the excretions of helminths and arthropods and products released by bacteria and fungi

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delayed hypersensitivity

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where you have initial exposure, and everything seems to be normal as far as immune response is concerned, but u get a large immune response that is detrimental to the organism

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The pathogenicity can be determined by ...

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invasiveness
toxigenicity
hypersensitivity
or any combination of those

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[Evolution of the host-parasite relationship]
There are sebveral ways that the organism can adapt in order to survive: (name 5)

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1. survive longer b/w hosts
2. use a vector for transmission so there are two host species to survive in
3. develop a long latency period so spread by asymptomatic carriers is possible
4. incr. in virulence
5. decrease in virulence so it can reside longer w/in

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[Host adaptations to increase resistance to the parasite]

Many of the host adaptations are related to the practice of _____

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agriculture

**domesticate animals
--overtime, organisms that were infecting animals have begun to adapt to humans and vice versa

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Examples: the influenza virus can come from _____ and ____.

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avian (birds) and pigs

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Example: the measle virus originated from ____

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bovine (ox, cow, or buffalo) virus or possibly even a dog

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Ex: Mycobacterium tuberculosis arose from _____

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Mycobacterium bovis-- which can be found in cows

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ex: the smallpox virus probably comes from ____

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cowpox

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ex: the diphtheria bacillus was probably from a ____

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cow bacterium

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The degree of host resistance evolved and became apparent during the Age of ______

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Exploration

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Drastic epidemics occurred when humans from ________ population carried microorganisms to never-exposed _____ populations.

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1. agricultural populations
2. hunter/ gatherer populations

e.g (1850s) 95% East African villages that had never develop agriculture die of TB due to trading exposure to Europeans.
**Native American were cut 95% due to smallpox from european
--Germ warfare

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Is it possible for hunter-gatherer populations to infect the agricultural populations w/ their germs? give an example

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yes

**HIV might have evolved by the simian form of the virus
--group of hunters had been exposed to these monkeys and used them for food, they had developed constant contact and more resistance. Also, the Ebola virus wiped out visitors.