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
