Database Reference
In-Depth Information
1: TOTAL ADULT MOSQ
2: TOTAL BIRD POPULATION
1:
20000
2:
1500
2
2
1:
10000
1
2:
750
1
1
2
2
1
1:
0
2:
0
0.00
273.75
547.50
821.25
1095.00
Days
Fig. 12.10
12.4.2 Avian Demography and Disease Persistence
As we saw in our simple SIR model in section 12.3.1, a disease like WNV might
easily sweep through a population rapidly and be extinguished without the addition
of new susceptible individuals (Figures 12.7 and 12.8). Juvenile birds have been
speculated to be key players in persistence of WNV in wild bird populations both
due to their immunological naivety to the disease and due to an increased suscep-
tibility to mosquito bites until they develop a full adult plumage
11
. If we run our
expanded WNV model with the avian demographic rates (BIRD BIRTH RATE and
BIRD DEATH RATE) set to zero, not surprisingly, we see a sharp rise in seropreva-
lence in the first year of exposure, with extinction of the disease due to lack of
susceptible hosts in the second season (Figure 12.11). Alternatively, with seasonal
avian population growth, we see seasonal reductions in seroprevalence due to the
influx of new susceptible juveniles, followed by increasing eroprevalence as that
season's outbreak progresses (Figure 12.12).
A sensitivity analysis of BIRD BIRTH RATE (with values ranging from 0.005 to
0.05 offspring per individual per day) demonstrates the effect of avian reproductive
output on disease transmission. At the high end of the reproductive range (number
6 in Figures 12.13 and 12.14), seroprevalence in the host remains low while the
infection prevalence in mosquitoes reaches high levels. At a low reproductive rate,
seroprevalence in the avian hosts increases quickly resulting in low disease preva-
lence in the mosquito vector (Figures 12.13 and 12.14).
11
Scott, T.W. and J.D. Edman 1991. Effects of avian host age and arbovirus infection on mos-
quito attraction and blood-feeding success. In:
Bird-Parasite Interactions: Ecology, Evolution, and
Behavior.
Loye, J.E., and M. Zuk, eds. New York: Oxford University Press. 179-204.
