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. Parasites can change host species distribution

6. Moose and White-tailed Deer

7. Deer – Moose brain worm interaction

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

11. Hawaiian Crow – Extinct in Wild

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

13. Akiapolaau Honeycreeper – restricted to high elevation today

14. Amakihi Honeycreeper – shows evidence of evolving resistance

15. Rabies in Europe

16. Rabies

17. Model of Rabies Transmission

18. Lord Robert May Sir Roy Anderson

19. Spread of HIV in Russia

20. 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

21. 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

22. 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

23. Global HIV data

29. Incidence of HIV in Africa

33. You’re never too old to need protection