Parasitism and Disease Lyme Disease Cycle in the UK
Evolution of Host-Parasite Interactions
European rabbits as pests in Australia
Introduced pests in Australia – red fox, rabbit, cat, pig, & goat
Parasite effect on host population Parasite can cause direct mortality but then can only persist in a large host population Usually parasite lowers host reproduction, growth or survival - often this effect is indirect by way of 1) lowers host stamina - more subject to predation, competition 2) increases conspicuousness - predation risk increases 3) disorient host via neurological damage 4) alters host response to environmental stimuli
Fungal parasites alter insect behavior Giant ant w/o and with fungus
Moose and White-tailed Deer
Deer – Moose brain worm interaction
Avian malaria occurs in areas below white line on Island of Hawaii – highest incidence between yellow and white lines
Hawaiian Crow – Extinct in Wild
I’iwi Honeycreeper – highly susceptible to avian malaria
Akiapolaau Honeycreeper – restricted to high elevation today
Amakihi Honeycreeper – shows evidence of evolving resistance
Sir Robert MayRoy Anderson
Spread of HIV in Russia
Dynamics of parasite populations Most important parameter is basic reproductive rate of the parasite, symbolized Rp Rp will: 1) increase with increasing density of susceptible hosts - N 2) increase with increasing transmission rate beta β 3) increase with increasing fraction of infected hosts that survive long enough to be infectious to other hosts - symbolized by f 4) increase with increasing average time that host remains infectious - symbolized by L
Dynamics of parasite populations We can also examine the reproductive rate of infection (Ri) = average number of secondary cases of infection generated by one primary case in a population where almost everyone is susceptible to infection Ri > 1 each infection has more than one "offspring" - chain reaction of epidemic Ri < 1 infection cannot sustain itself
Incidence of HIV in Africa
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