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Unit 6
infectious agents
89
Pathology
Undergraduate 3
12/09/2014

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Term
What is an infection
Definition
colonization of tissue by an organism
(pathogen has invaded & multiplied)
Term
What is the difference between infectivity & pathogenicity?
Definition
infectivity = ability to colonize
pathogenicity = ability to cause disease
Term
What are low-grade pathogens?
Definition
opportunistic, only cause disease in immuno-compromised hosts
Term
True or False

Viruses are obligate intercellular organisms
Definition
true
Term
What are facultative organisms?
Definition
can growth both inside & outside of cells
Term
How does an organism gain entry to the body?
Definition
-natural passages (skin, resp tract, intestinal tract, urogenital tract)
-trauma
-direct inoculation
Term
True or False

The heart, bones, brain & muscle can only be infected via the blood
Definition
true
Term
What are the principal methods of spread of infection? (4)
Definition
-physical contact
-airborne infection
-food borne infection
-insect borne infection
Term
What are the possible outcomes of infection? (3)
Definition
-invader dies (nonspecific/specific immune defense)
-invader survives, but no clinical signs of disease
-invader survives, multiplies, clinical disease
Term
What aspects of the pathogen affect the outcome of infection?
Definition
virulence & dose of exposure
Term
What aspects of the host/environment affect the outcome of infection?
Definition
-status of nonspecific defense systems of the host (skin etc.)
-immune status of the host
Term
What is a subclinical infection?
Definition
pathogen elicits an immune response but no clinical signs are evident
Term
How would you diagnose parasitemia?
Definition
blood smears to ID the parasite
Term
How would you diagnose viremia or bacteremia?
Definition
blood cultures
Term
What is transient bacteremia?
Definition
small levels of bacteria are in the bloodstream being removed by the body
Term
What is toxemia?
Definition
bacterial toxins in the blood
Term
What is septicemia?
Definition
disease due to large levels of bacteria/toxins in the blood
Term
What are the characteristics of clinical septicemia?
Definition
drop in blood pressure
high fever
Term
What organisms are obligate intracellular parasites?
Definition
viruses
prions
rickettsia
chlamydia
Term
Why do certain viruses only affect certain cell types?
Definition
they have preference for specific parenchymal cells (which express different receptors)
Term
What are the types of injury caused by viruses?
Definition
1. Virally-mediated cell necrosis
-cell injury & alteration of apoptosis pathways

2. Inflammatory & immune-mediated cell death

3. Virally-induced cell transformation & proliferation = neoplasia
Term
How might viruses cause cell injury?
Definition
-viral replication inducing cell lysis
-inhibition of host DNA/RNA/protein synthesis
-damage to cell membranes
Term
What are cytopathic viruses?
Definition
viruses that cause cell death
Term
What are inclusion bodies? What causes them? Where do they occur? Why are they useful?
Definition
-assembled viral particles or parts of viral nucleic acid synthesis

-viral replication in viruses & rickettsial infections

-in cytoplasm or nucleus

-can be used to ID specific viral infections e.g. rabies
Term
Are viral hepatitis infections persistent or cytopathic?
Definition
persistent/chronic
Term
What virus causes cirrhosis?
Definition
Hepatitis C
Term
How is HCV transmitted?
Definition
blood innoculation
Term
What is organotropism?
Definition
which kind of cells a virus can bind to
Term
HCV infection can lead to...
Definition
Acute hepatitis
Chronic hepatitis (cirrhosis)
Resolution
Term
What is cirrhosis?
Definition
loss of lobular architecture of the liver
necrosis -> scarring -> nodular regeneration
Term
How are viruses & apoptosis related?
Definition
some cells may undergo apoptosis to control viral infection

viruses can encode genes which impair apoptosis to promote persistent infection
Term
A viral infection will show an ______ in lymphocytes and _____ in neutrophils
Definition
increase
decrease/no change
Term
How are viruses & immune-mediated cell death related? (2 concepts)
Definition
-viral infection causes proteins to be expressed on cell surface
-CD8 lymphocytes recognize, induce cell-mediated immune response & lysis

-IFN is produced by CD4+ in the Th3 response
-IFN interferes with viral translation
Term
What causes significant cellular loss in HBV?
Definition
DC8+ T-cell mediated cytolysis of large numbers of cells
Term
What does cytokine interferon (IFN) do? (3)
Definition
activates macrophages
enhance NK cell activity
antiviral effects
Term
How do viruses cause neoplasia?
Definition
-infection causes some cells to be transformed
-transformed = immortal, grow indpendently of regulating signals (CANCER)
Term
What is the damaging effect of Epstein-Barr Virus (EBV)?
Definition
causes neoplasia
Term
What are latent viral infections?
Definition
viral genes are present in host cell but not expressed, may be reactivated later in life
Term
How might a latent viral infection become reactivated? (3)
Definition
1. Fever/trauma etc causes fluid filled-vesicles to appear (inter & intra cellular edema)

2. Cells balloon & form intranuclear acidophilic viral inclusions

3. Adjacent cells fuse to form multinucleated prokaryons
Term
What is stomatitis?
Definition
inflammation of the oral mucosa
Term
What is a major complication associated with viral infections
Definition
secondary bacterial infections
Term
How do filoviruses affect the body?
Definition
-highly cytopathic
-cause fever, muscle pains, anorexia, rashes, abdominal pain, hemorrhage
Term
What are the facultative intracellular organisms?
Definition
mycobacteria
fungi
Term
The cellular response to viruses, Rickettsia & Chlamydias is typically....
Definition
mononuclear
(lymphocytes, plasma cells, macrophages)
Term
What causes psittacosis?
Definition
chlamydia
Term
What causes trachoma?
Definition
chlamydia
Term
What causes typhus?
Definition
rickettsia
Term
HOw are rickettia transmitted?
Definition
require arthropod vectors e.g. fleas ticks mites
Term
What differentiates a prion from a virus?
Definition
prions do not have nucleic acid (RNA or DNA)
Term
What are infectious prion proteins? What do they do? How are they transmitted?
Definition
-abnormal forms of normal proteins that induce changes in conformation of host proteins
-cause accumulation of proteins in tissues (esp brain)
-contagious, familial or sporadic
Term
What do abnormal prion proteins (PrPsc) cause?
Definition
spongiform encephalopathies (vacuolar degeneration in the brain)

-accumulation = dysfunction of brain tissue = neuronal loss
Term
Prion infection is characterized by...
Definition
progressive loss of function
Term
True or False

Prions induce an inflammatory reponse
Definition
false
Term
What are opportunistic bacteria?
Definition
bacteria which are beneficial in normal circumstances, but will flourish if host is immunosuppressed or they go to a part of the body where they aren't supposed to be
Term
How can bacterial infections be treated?
Definition
Bacteriostatic agents - inhibit growth/multiplication

Bactericidal agents: kill bacteria
Term
How do bacteria cause cell/tissue injury? (3)
Definition
1. Adhering to host cells
2. Releasing toxins
3. Producing local vasculitis
Term
What are bacterial adhesins? Give an example
Definition
surface molecules that bind to host cells

-cocci
Term
How do gram positive & gram negative cocci bind?
Definition
Gram positive:
-fibrillae bind to fibronectin on host surface
-M proteins prevent phagocytosis

Gram negative
-fimbriae (pili) allow gene exchange & mediate adhesion
Term
What do bacterial endotoxins do?
Definition
-generalized peripheral vasodilation -> shock

-endothelial injury & activate coag cascade -> acute resp distress & DIC

-cytokine release -> acute phase response
Term
What do locally-acting bacterial exotoxins do? (3) give examples
Definition
Locally-acting: enzymes which break down compounds & facilitate tissue invasion

Staphylococcus aureus
Clostridium perfringes
Term
What do remotely-acting bacterial exotoxins do? Give some examples
Definition
-induce formation of antibodies
-secreted by bacteria, carried by bloodstream elsewhere in body

Staphylococcus aureus - Toxic Shock Syndrome
Clostridium tetani - tetanus
Clostridium botlinum - botulism
Term
What is necrotizing fasciitis?
Definition
-rapid necrosis of subcutaneous issues extending into deep fascia
-secondary gangrene
-causal bacteria secrete exotxin
-often starts due to some minor trauma/surgical pound
Term
What does the exotoxin of clostridium tetani do?
Definition
-travels from wound to spinal cord, causes violent muscle spasms
Term
What does the clostridium botulinim exotoxin do?
Definition
-blocks release of neurotransmitters leading to flaccid paralysis
Term
What do enterotoxins do? Give some examples
Definition
exotoxins which affect intestinal mucosal cells (enterocytes)

-attach to gut mucosal cell receptors, cause structural or functional diarrhea

Vibrio cholerae
Toxigenic escherichia coli
Term
What is food poisoning? What are the two categories? Give an example of each
Definition
acute gastroenteritis due to bacterial toxins

Infection type
-bacteria multiple in contaminated food, produce toxins in the bowel
e.g. Salmonella enteritidis

Toxin Type
-bacteria produce toxins in the food
e.g. Satphylococcal food poisoning
Term
What will cause more rapid clinical signs, infection type of toxin type food poisoning?
Definition
toxin type
Term
What is bacterial local vasculitis?
Definition
-highly virulent bacteria cause thrombosis of small blood vessels leading to ischemic necrosis in the area
-toxins can also cause vascular injury
Term
What are the characteristics of the body's response to bacterial infection?
Definition
Acute inflammation
-lots of neutrophils present

Suppurative inflammation
-liquefactive necrosis, pus, abcesses
Term
When would suppurative inflammation in response to bacterial infection be especially likely to occur?
Definition
where drainage & resolution of acute inflam is inhibited by anatomical factors
Term
What is hardware disease?
Definition
metal trapped in reticulum punctures wall, will eventually penetrate pericardial sac
-severe fibrinopululent inflammation results (fibrin & pus)
-affects heard & lung function
Term
What are Koch's postulates? Why do we use them?
Definition
Used to determine causal bacteria of a disease

1. causal organism can be found in the disease lesions & isolated in culture
2. secondary introduction of the isolated organisms causes lesions in experimental animals
3. the organism can be recovered from the experimental animal
Term
What is require for fungi to grow?
Definition
warmth, high humidity, oxygen
Term
What is the association between antibiotics & fungi?
Definition
antibiotic overuse destroys 'good' bacteria which limit fungal growth
Term
How do fungi cause tissue injury?
Definition
-induce DTH hypersensitivity responses to fungal antigens
-may see granulomatous lesions in the tissue
-some directly invade small vessels causing thrombosis & necrosis of nearby tissue
Term
What are systemic fungal diseases? Give some examples
Definition
-diseases which affect deeper tissues

e.g. histoplasmosis, coccidioidomycosis
Term
What are superficial fungal diseases? Give some examples
Definition
-diseases which affect superficial tissue

Dermatomycoses (ringworm/athletes foot)
Candidiasis
Term
What is candidiasis?
Definition
disease caused by opportunistic candida bacteria

-vaginitis, espophagitis, chronic & subcutaneou candidiasis etc
Term
What is a definitive host?
Definition
the host of the adult (mature, reproducing) form of a parasite
Term
What is an intermediate host?
Definition
host of immature form(s) of a parasite
Term
What are the characteristics of inflammatory reactions to parasitic infectoin?
Definition
-eosinophils
-granulomatous inflammation
Term
How are protozoa transmitted?
Definition
via insect vectors or by ingestion
Term
What is malaria?
Definition
protozoal infection of the parasite Plasmodium
Term
How do protozoa cause disease?
Definition
1. Sporozoites enter blood stream, undergo asexual repro
2. Sporozoites multiple forming lots of merozoites
3. Merozoites are released, infect RBCs
4. Merozoites form trophozoites (asexual repro) or produce gametes which will infect a mosquito
Term
What are the clinical features of malaria and what causes them? (4)
Definition
-spikes of chills/fever as mew merozoites are released every 48hrs
-hemolytic anemia (parasites destroy RBCs)
-RBCs release brown pigment (dark liver, lymph nodes, bone marrow)
-phagocytic defense leads to hyperplasia of mononuclear phagocytes leading to an enlarged spleen
Term
True or False

Helminths are opportunistic organisms
Definition
false
Term
What are the types of helminths? Do they require intermediate hosts? Give examples of each
Definition
Nematodes (Roundworms)
-no intermediate host
-pinworms, hookworms, roundworms

Cestodes (tapeworms)
-intermediate hosts eg. beef, pork, fish
-rarely cause disease in human hosts

Trematodes (flukes)
-require int host e.g. snails
-schistosomiasis (infect bladder, cause hematuria)
Term
Why are arthropods a concern?
Definition
they act as vectors of disease (viral & bacterial)

e.g. lice, fleas etc.
Term
How do arthropods act as vectors?
Definition
Mechanically
-picks up infecting agent, deposits it on foods or passes on by contamination of biting mouth parts

Biologically
-arthropod is essential in completing the life cycle of the infecting agent
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