1. Parasitism and Disease
Lyme Disease Cycle in the UK

2. Evolution of Host-Parasite Interactions

3. 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

4. Fungal parasites alter insect behavior
Giant ant w/o and with fungus

5. Moose and White-tailed Deer

6. Deer – Moose brain worm interaction

9. Avian malaria occurs in areas below white line on Island of Hawaii – highest incidence between yellow and white lines

10. Hawaiian Crow – Extinct in Wild

11. I’iwi Honeycreeper – highly susceptible to avian malaria

12. Akiapolaau Honeycreeper – restricted to high elevation today

13. Amakihi Honeycreeper – shows evidence of evolving resistance

14. Lord Robert May Sir Roy Anderson

15. Spread of HIV in Russia

16. Terms used in box model equations
x - # of susceptible uninfected hosts
y - # of infectious hosts (infected individuals)
H = x + y - total number of hosts
a - per capita host birth rate - assumed to be = for x and y
b - natural (non-disease) host mortality rate
r = a - b (intrinsic rate of increase of host)
alpha  - disease induced mortality rate (pathenogenicity)
beta  - transmission coefficient
gamma  - rate of host recovery from infection

17. 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

18. 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

19. Global HIV data

25. Incidence of HIV in Africa

29. You’re never too old to need protection