Lecture 4: Pathogenesis Flashcards
Definition of disease
Alteration in normal cell, tissue, organ, organ system or organismal activity
Likelihood and severity of parasitic disease depends on (3)
Status of host defenses (genetics, age, etc)
Number of parasites present
Parasite pathogenicity
*interactions with each other
pathogenicity: definition
Ability of infectious agent to damage a host = produce disease
Virulence: definition
Relative capacity of infectious agent to cause damage in host
Parasite pathogenicity: 2 components
Pathogenicity
Virulence
Interaction of pathogenicity and parasite numbers
As virulence increases = fewer parasites needed to cause detectable symptoms in infected host
Interaction between host defenses and parasite numbers/pathogenicity
As host defenses weaken = fewer parasites needed to cause disease/mild pathogenic parasites can cause severe disease
Pathology can result from (5)
Damage to/loss of host cells, tissues, organs
Alteration of host cellular growth patterns
Interference with host nutrition
Toxins released by parasite
Host immune response to infection/infestation = collateral damage to host
Examples of mixed infections with GI parasites (2)
GI protozoan parasites: Coccidia and Giardia
GI nematodes
Ostertagia ostertagi: how developing larvae damage host cells
L4 nematode
Develop in gastric glands
Damage mucosa of abomasum
Hookworms and ticks: how feeding damages host tissues
Feed on blood and cause tissue damage
Hookworms —> blood leaks from damaged tissues
Eimeria: How reproduction damages host cells
With multiplication of intracellular Protozoa = host cell rupture
Cause destruction of enterocytes
Tapeworms: How compression of structures damage host tissues
Tissue cysts (larval stages) of various tapeworms compresses nerves, spinal cord, brain
Flukes: how distension of structures damages host tissues
Adult liver flukes distend and damage bile ducts
Alteration of host cellular growth patterns: 4 types
Cellular hypertrophy
Hyperplasia
Metaplasia
Neoplasia
How parasites interfere with host nutrition (2)
Divert nutrients to parasite
Malabsorption of nutrients
How does Giardia cause malabsorption of nutrients (2)
Damage to microvilli and apaoptosis of enterocytes
Blocks interaction between brush border enzymes and their substrates
Hemozoin: definition, 2 organisms that ingest and produce hemozoin
Crystallized dimers of heme
Plasmodium produce and ingest
macrophages/phagocytes ingest
Why plasmodium use hemozoin
Get rid of toxic effects of free heme (free heme lyses membranes and inhibits enzymes)
How hemozoin affects macrophages
Can’t be digested by endomembrane system of phagocytes
Builds up in cells and impedes phagocytosis
Parasite induced immunopathology definition
Damage that occurs as a result of an inappropriate immune response to infection/infestation
Example of parasite induced immunopathology: flea allergy dermatitis
Hypersensitivity to allergens in flea saliva
Parasite induced behavioral pathology: definition, example with Tania multiceps tapeworm
Behavioral changes that facilitate transmission of parasites
Larval stage in sheep brain —> gid = ataxia, circling —> easy prey for canids
*sheep = intermediate host, canids = definitive host
example of how behavioral changes are side effects of infection: Oestrus ovis
sheep nasal botfly
larvae infect nasal sinuses of sheep/ruminants –> larvae sometimes migrate into brain and cause “false gid” –> sheep are easy prey but larval botflies die
virulence factors definition
traits that confer pathogenicity
3 examples of virulence factors from parasitic protozoa: species, how it works
hemozoin - plasmodium
proteases - leishmania, tissue invasion/survival in macrophages/immune modulation
kinases - toxoplasma gondii, disrupt host cell signaling
what does immune modulation mean
dampen immune responses so parasite can persist
what are metazoan parasites
worms, arthropods
3 GENERAL examples of virulence factors from metazoan parasites (worms, arthropods)
proteases
anticoagulants of blood feeding helminths and ectoparasites
excretory/secretory products of helminths
examples of host factors that affect likelihood and extent of parasitic disease (5)
age = young and old at risk
sex/reproductive condition = males carry more parasites
nutritional state = malnourishment (decreased resistance)
immunological competency = immunodeficient
genotype
explain how immunological competency affects likelihood and extent of parasitic disease
prior exposure –> partial immunity –> reduced number, migration, development and reproduction of parasites
premunition definition and function
partial immunity due to chronic, low level infection
protect host against superinfection and more severe pathology
factors affecting pathogenic potential of parasite (6): PMSFIT
predilection site
migratory pathway
sites of parasite development
feeding habits
immunopathology
transmission of other infectious agents
ostertagia ostertagi: PMFIT
Predilection = abomasum
migration = local within abomasum
site of development = gastric glands of abomasum
feeding = adults feed on abomasal contents
immunopathology = inflammation by larvae and adults
no transmission by other agents
how ostertagia ostergati develops in abomasum (and damage)
larval growth erodes parietal and chief cells = increases pH, decreases pepsin = impaired protein digestion, bacterial overgrowth, diarrhea
how ostertagia ostertagi causes inflammation
more loss of parietal and chief cells
mucous neck hyperplasia
metaplasia: parietal and chief cells replaced by mucous neck cells
increased vascular permeability = epithelium leaky = loss of serum proteins/diarrhea
