Px3108 08 Infection

Front 1

When microbes cause disease, the nature and extent of disease depend on:

• V________ (p______________) of the organism
• R_________ of _____
  

Back 1

When microbes cause disease, the nature and extent of disease depend on:

• Virulence (pathogenicity) of the organism
• Response of host

Front 2

What must happen in order for infection to occur?

Back 2

For infection to occur, local defences have to be undermined, and/or the organisms have to develop strategies to overcome barriers

Front 3

What is the innate immune response, and what are some examples of it?

Back 3

Innate immune response refers to the first line of defence, which does not adapt to repeated attacks, e.g. physical barriers, phagocytic cells, complement and inflammatory response

Front 4

What is the adaptive immune response?

Back 4

Adaptive immune response refers to responses mediated by T and B cells, stimulated by each exposure to an antigen, and these response will improve which each successive contact

Front 5

What are the various classes of human pathogens?

Back 5

1. Prions (27kD protein)
2. Virus
3. Chlamydiae
4. Rickettsiae
5. Mycoplasmas
6. Bacteria
7. Fungi
8. Protozoa
9. Helminths (10 m tapeworm)

Front 6

What is the structure of bacteria?

• Cell wall made up of?
• Shape?

Back 6

Bacteria are prokaryotic cells with cell walls made up peptidoglycans (mixture of sugars and amino acids). Depending on whether the cell walls retain cyrstal violet stain, they are classified Gram negative or Gram positive. The main shapes are spherical (cocci) and rod-shaped (bacilli)

Front 7

How does Gram staining differentiate between Gram positive and Gram negative bacteria?

Back 7

Gram positive bacteria are stained purple.

Gram negative bacteria are stained red.

Front 8

How does Gram staining work?

Back 8

Crystal violet is used to stain a fixed plate. Iodine is then applied to fix the stain. The excess dye is then washed off with ethanol. The plate is then counterstained with a counterstain such as safranin.

Front 9

What is the principle behind Gram staining?

Back 9

Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan (50–90% of cell envelope), and as a result are stained purple by crystal violet, whereas gram-negative bacteria have a thinner layer (10% of cell envelope), so do not retain the purple stain and are counter-stained pink by the safranin.

Front 10

Viruses c____________ the host cell's b___________ and r__________ a__________ for their own p____________. They cannot be seen by light microscope, but often form characteristic ____________ ________ in infected cells.

Back 10

Viruses commandeer the host cell's biosynthetic and replicative apparatus for their own proliferation. They cannot be seen by light microscope, but often form characteristic inclusion bodies in infected cells.

Front 11

Fungi have t_____ cell walls, and can grow as r________ y_____ cells or s______ f___________ h______ (______).

In immunocompetent people, they usually only cause superficial infections involving the skin, hair and nails (dermatophytes, e.g. ringworm).

Back 11

Fungi have thick cell walls, and can grow as rounded yeast cells or slender filamentous hyphae (mould).

In immunocompetent people, they usually only cause superficial infections involving the skin, hair and nails (dermatophytes, e.g. ringworm).

Front 12

How do fungi cause disease? (3 ways)

Back 12

Fungi cause disease by

1. Tissue necrosis
2. Hemorrhage
3. Vascular occlusion

Front 13

Protozoa are s______ c______ e__________ that can survive within the human body (____________ and _____________).

Back 13

Protozoa are single celled eukaryotes that can survive within the human body (intracellular and extracellular).

Front 14

How are protozoa infections transmitted? What are some examples of each category?

Back 14

Modes of transmission of protozoa:

1. Close sexual contact, e.g. Trichomonas vaginalis
2. Encysted forms through faeco-oral transmission, e.g. Giardia lamblia, Entamoeba histolytica
3. Blood-sucking insect vectors, e.g. Plasmodium

Front 15

Helminths (p________ _______) are highly d______________ m____________ o___________. They often have c________ life cycles.

Back 15

Helminths (parasitic worms) are highly differentiated multicellular organisms. They often have complex life cycles.

Front 16

What are the three classes of helminths?

Back 16

The three classes of helminths are:

1. Roundworms (nematodes)
2. Flatworms (Cestodes)
3. Flukes (Trematodes)

Front 17

How do helminths cause disease?

Back 17

Helminths cause disease

1. By sheer numbers in the gut (e.g. iron-deficiency anemia or poor growth in children)
2. Because of host inflammatory response

Front 18

What are the common factors in parasitic infections?

Back 18

The common factors in parasitic infections are

• Immunosuppression; results in systemic spread of infection
• Eosinophils play an important role in defence; increased numbers are seen in blood and tissue during infection
• Tissue damage by necrosis, or by inducing hypersensitivity responses

Front 19

What are the various host barriers?

Back 19

• Skin
  
• GI tract
  
• Respiratory tract
  
• Urogenital tract
  

Front 20

How does the skin function as a host barrier?

Back 20

The skin is a protective keratin layer. Its normal pH and fatty acids inhibit microbial growth, and it is constantly shed and renewed. Most micro-organisms penetrate through breaks in the skin.

Front 21

How does the GI tract function as a host barrier?

Back 21

Gastric acid, viscous mucus secretions, pancreatic enzymes and bile, antimicrobial peptides, IgA antibodies and normal gut flora are all part of the GI host defence.

Front 22

What are the methods used by microbes to penetrate through the GI barrier, and what are examples of each method?

Back 22

• Resistance to digestive enzymes (e.g. cysts of protozoa)
  
• Release of powerful toxins (e.g. Cholera)
• Able to bind to the epithelium (e.g. Giardia)

Front 23

How does the respiratory tract function as a host barrier?

Back 23

Large microbes are trapped in the nose and upper respiratory tract by mucus. They are then transported by ciliary action of the respiratory epithelium to the back of the throat, where they are swallowed. Smaller organisms which are inhaled are phagocytosed by alveolar macrophages.

Front 24

What are the methods used by microbes to penetrate through the respiratory tract, and what are examples of each method?

Back 24

Virulent pathogens evade defences by

• Adhering to respiratory epithelium (e.g. influenza)
• Surviving phagocytosis (e.g. tuberculosis)

Front 25

How does the urogenital tract function as a host barrier?

Back 25

The urinary tract is usually sterile as it contains filtered fluid, and is flushed many times a day. The vagina is protected by low pH produced with the help of commensal lactobacilli

Front 26

What factors are likely to lead to infection via the urogenital route?

Back 26

Obstruction and stasis in the urogenital tract increase the risk of infection.

Pathogens can adhere to the epithelium (e.g. E. coli)

Front 27

What are the various ways in which infections can be transmitted from one person to another?

(Total: 7)

Back 27

• Environmental (some microbes can survive for extended periods in dust/food/water)
  
• Inhalation
• Ingestion
• Sexual transmission
• Vertical (from mother to baby)
• Insect/animal bites
• Injection (blood, blood products, cuts, needles)

Front 28

How does the infection spread after getting inside its host?

(Total: 6 ways)

Back 28

• Organisms may be motile or able to secrete lytic enzymes
• Local proliferation
• Lymphatic
• Haematogenous (within plasma and within cells)
• Tissue fluids
• Nerves

Front 29

How do microorganisms evade the immune system?

(Total: 6 ways)

Back 29

• Remain inaccessible to host immune system (e.g. stay inlumen of gut or form cysts)
• Viral latency within host cells
• Vary surface antigens
• Resist destruction by extracellular or intracellular agentswhich are part of innate defence system
• Viruses may prevent infected cells from presenting antigen
• Viruses may directly infect immune cells (e.g. HIV)
  

Front 30

What are the general mechanisms through which microorganisms cause disease?

Back 30

1. Directly cause cell death or dysfunction
2. Local or systemic release of bacterial products (e.g. toxins)
3. May induce immune responses that cause tissue damage

Front 31

How do bacteria in particular cause disease?

Back 31

Bacteria

• Produce toxins that lead to cell and tissue damage
• May directly cause an acute inflammatory reaction (abscess)
• May cause a host response (type III/IV) due to surface antigens

Front 32

How do viruses in particular cause disease?

Back 32

Viruses

• Directly damage host cells by entering them and replicating at the host's expense
• Often interfere with normal cellular functions, which may transform infected cells into neoplastic cells
• May cause cell death directly or via host immune response

Front 33

How are bacterial infections diagnosed?

Back 33

• Microscopy and culture
  
• May require use of special stains that identify organisms based on their cell wall or cell coat characteristics
• Use of specific antibody probes
• Measuring serum antibody titres (indirect way)

Front 34

How are viral infections diagnosed?

Back 34

• Detection of surface antigens
• Detection of host antibodies
• Molecular diagnostics, e.g. PCR, based on nucleic acid characteristics

Front 35

What are the various inflammatory responses to infection?

Back 35

1. Suppurative (purulent) inflammation - pyogenic bacteria and some fungi form abscesses
2. Granulomatous inflammation, e.g. TB, some fungi
3. Cytopathic reactions - viruses
4. Tissue necrosis
5. Chronic inflammation and scarring - any chronic inflammation

Front 36

What are some causes of immunosuppression?

Back 36

• Congenital
• Impaired bone marrow function
• HIV infection
• Any break in host barriers, e.g. pt with severe burns

Front 37

What factors predispose hospital patients to getting infections?

Back 37

• Antibiotic resistance
• Immunosuppression
• Surgery
• Instrumentation

Front 38

What are some examples of viruses, and the mechanisms through which they cause disease?

Back 38

• Influenza: cell necrosis; direct cytopathic effect or host immune response
• HPV: cell proliferation
• Herpes zoster: latent infection; virus integrates into host genome and is reactivated later
• HBV: persistent infection; slow replication of virus, evading immune response. May be asymptomatic

Front 39

What is the structure of influenza?

Back 39

Influenza virus consist of single-stranded RNA bound by nucleoprotein (A/B/C determines its type). The spherical surface of the virus is a lipid bilayer containing viral haemagglutinin and neuraminidase, which determines the subtype of the virus.

Front 40

What type of influenza virus is the major cause of epidemics and pandemics?

Back 40

Type A influenza virus

Example: Avian influenza is caused by certain type A strains of the virus

Front 41

What is SARS, and what is the microorganism causes it? How is the infection transmitted?

Back 41

Severe acute respiratory syndrome (SARS) is caused by coronavirus (SARS-CoV). This coronavirus is able to cause severe pneumonia. Transmission is by close personal contact

Front 42

What is MERS, and what is the microorganism causes it? What are the manifestations of infection?

Back 42

Middle East Respiratory Syndrome (MERS) is caused by the MERS-coronavirus (MERS-CoV). It causes severe pneumonia and renal failure

Front 43

What is an example of a viral infection increasing the risk of cancer? How does it increase the risk of cancer?

Back 43

Human papilloma virus (HPV) is an oncogenic DNA virus. Viral infection affects normal growth-regulating proteins, resulting in transformed cells, which are capable of autonomous growth and are susceptible to acquisition of future mutations

Front 44

What is an example of a chronic latent viral infection? How does it cause disease?

Back 44

Herpes zoster or varicellar zoster virus (VZV) is the virus that causes chickenpox during its primary infection. The virus then establishes latent infection in the neurons of the dorsal root ganglia. Reactivation in adults manifests as painful vesicular skin eruption in skin supplied by that nerve, a disease known as shingles

Front 45

What is an example of a virus that can have different outcomes? What are the various outcomes it leads to?

Back 45

Hepatitis B virus (HBV) causes damage to virus-infected cells by CD8+ cytotoxic T cells. If the immune system is not properly calibrated to clear virus, it may cause widespread liver damage.

1. Acute hepatitis with recovery
2. Chronic hepatitis with recovery
3. Progressive chronic hepatitis leading to cirrhosis or development of cancer
4. Fulminant hepatitis with massive liver necrosis
5. Asymptomatic carrier state

Front 46

What is the life cycle of the HIV?

Back 46

HIV requires CD4+ molecule to enter cell. Upon entering, its viral DNA integrates into the host genome. The virus mainly resides in the lymph nodes and spleen. It also infects macrophages and monocytes. The virus constantly varies the antigens on expressed proteins to evaded the immune system. Host proliferation eventually leads to cell death.

When CD4+ counts become very low, there is a breakdown of host defenses and clinical disease ensues

Front 47

What is Pneumocystis jirovecii?

Back 47

Pneumocystis jirovecci is a fungus that causes opportunistic infections. Pneuomnia due to this is the frequent presenting illness of AIDS, and is known as PCP. This is usually the result of a re-activation of previous infection

Front 48

What are the various opportunistic infections seen in ADIS patients?

Back 48

• Pneumocystics jirovecii pneumonia
• Recurrent mnucosal Candida infection
• Disseminated cytomegalovirus infection
• Severe Herpes ulceration
• Mycobacterial infection (TB or others)
  

Front 49

What are some neoplasms that HIV infected patients have a high risk of developing?

Back 49

• Kaposi sarcoma (HHV-8)
• Non-Hodgkin lymphoma
• Carcinoma of cervix

Front 50

What is an example of a bacteria that causes pyogenic bacterial infections?

Back 50

Staphylococcus aureus induces large amounts of localized suppuration, i.e. pus, which consists of neutrophils, necrotic cells and edema fluid. S. aureus is a Gram+ bacterium that is found on the skin. Some strains are antibiotic resistant (known as MRSA). Some strains produce potent toxins which may food poisoning. Localized infection of the skin by toxin-producing bateria may cause bullous impetigo; septicemia may cause blistering at many sites

Front 51

What are the diseases that Streptococcus pneumoniae causes?

Back 51

Strep pneumoniae is a Gram+ bacterium that colonizes the respiratory tract. It is a common cause of community-acquired pneumonia, and affects especially pts with congenital or acquired Ig defects, and those with decreased or absent splenic function. It can also cause acute otitis media and mengitis. Its virulence is due to its invasiveness and thick capsule

Front 52

What are the effects of released cytokines in Gram- septicemia?

Back 52

• Systemic vasodilation (hypotension)

• Diminished myocardial contractility

• Diffuse alveolar capillary damage

• Activation of coagulation system, leading to disseminated intravascular coagulation

May lead to septic shock and multiorgan failure

Front 53

What is the microorganism causing meningococcal disease? How is it spread?

Back 53

Menigococcal disease is caused by Gram- coccus Neisseria meningitidis. It is spread by droplets. It causes meningitis and Gram- septicemia; pts will have a characteristic rash.

Front 54

What are the symptoms of Clostridium difficile infection?

Back 54

Cytotoxin-producing strains of Clostridium difficile may overgrow after systemic antibiotic use, resulting in psuedomembranous colitis and severe diarrhea

Front 55

What is malaria, and how does it develop?

Back 55

Malaria is caused by a protozoa (several types of Plasmodium), and leads to paroxysmal fevers and anemia.

In humans, the parasite mainly resides in the liver and in RBC. Fever coincides with rupture of RBC and release of parasites. Anemia is caused by RBC destruction.

Plasmodium falciparum may cause cerebral malaria - high levels of parasites causes the infected RBC to become sticky and occlude capillaries in the brain

Front 56

What is amoebiasis, and how does it develop?

Back 56

Amoebiasis is caused by protozoan Entamoeba histolytica. The cysts are ingested, and 'hatch' into amoebae. They cause damage to the mucosa of the colon, resulting in abdominal pain and diarrhea. May spread to the liver, causing amoebic abscesses