Parisitism Flashcards
parasite
consumes tissues or body fluid of the host
Harm, but don’t immediately kill, the organisms they eat
endoparasite
lives inside its host
ectoparasite
lives on outside of host
Pathogens
microparasites that cause diseases
They do not directly consume the host tissue
parasitoids
insects whose larvae feed on a single host and almost always kill it
examples of diseases caused by parasites
influenza, tuberculosis, cholera, AIDS
what does malaria success depend on
surviving in two hosts, developing into 3 different life forms, and being transmitted correctly
example of single host parasite
tapeworm
how can some parasites complete their life cycles
alter behaviour of host
how can parasites improve transmission
change host mating system eg Wolbachia cause females to becoming parthenogenetic (unfertilized ovum develops directly into new individual)
are parasites sufficient to explain the occurrence of cycles in host population sizes
cycle amplitude decreased with increasing application of anti-nematode drugs (anti-infection of nematodes)
Suggests nematode parasites shape (grouse) pop densities
how else can parasites effect communities
affecting outcome of species interactions, can alter outcome of competition
virulence
harm done by a parasite to its host following an infection
why does virulence vary dramatically among pathogens ie some are lethal, some produce no symptoms
virulence changes and evolves in response to a number of variables
many observations are consistent with conventional wisdom hypothesis, others aren’t
conventional wisdom hypothesis
given enough time a state of peaceful coexistence becomes established between host and parasite
observation examples consistent with conventional hypothesis
lyme disease, ebola and SARS result from human infection with symbionts of other species that have recently jumped into humans
observation examples not consistent with conventional wisdom
virulent pathogens eg gonorrhoea where humans are the unique or dominant hosts and vector
In malaria and tuberculosis, there is evidence of a long association with humans
Trade off hypothesis
natural selection should favour strategy that maximises pathogen individual fitness
predicts trade off between rate of transmission and duration of infection
Assumes virulence is result of pathogen pop growth
Virulent strain of parasite may incr in frequency if, in the process of killing hosts, it sufficiently incr chances of being transmitted
Virulence should be result of optimal compromise between length of infection and growth to maximise transmission
different ways for transmission to be accomplished
horizontal, sexual transmission
which mode of transmission favours higher virulence
horizontal
