Database Reference
In-Depth Information
TRANSMISSION
EFFICACY
B TO M
MAT URAT ION
RAT E
TOTAL
ADULT
MOSQ
TRANSITION
RAT E
+
BITE
RAT E
TOTAL
ADULT
MOSQ
+
MOSQ
LARVA
MOSQ
INFECT
MOSQ
EXPOS
MOSQ
SUSCEP
MOSQ %
INFECTED
INCUBATION
MOSQ
DEVELOPING
MOSQ
BIRT HING
MOSQ
INFECTING
+
OVIPOSITION
RAT E
MI DYING
LARVAL DYING
ME DYING
MS DYING
MOSQ
DEAT H
RAT E
MOSQ
DEAT H
RAT E
LARVAL
DEAT H
RAT E
BIRD
INFECT
MOSQ
DEAT H
RAT E
Fig. 12.6
winters in northern areas of the United States
9
. Using estimates of the proportion of
overwintering mosquitoes infected with WNV to initiate the transmission cycle, the
small PERCENT MOSQUITOES INFECTED in the overwintering mosquito pop-
ulation (which were used to initiate the transmission cycle) begins to rise in early
summer when the mosquitoes emerge to begin breeding and biting hosts. This rise
is accompanied by a rise in the PERCENT INFECTED BIRDS, or disease preva-
lence in the host population (Figure 12.7). Since very few studies of WNV have the
resources to test birds directly for viremia, we can also evaluate the simulated out-
break in terms of SEROPREVALENCE, or the proportion of individuals that test
positive for disease exposure by the presence of antibodies to the disease in their
bloodstream. This value includes not only currently infected individuals, but also
recovered individuals who can no longer transmit the disease but have been exposed
at some time in the past.
12.3.2 Questions and Tasks
It has been proposed that vertical trans-ovarial transmission—the passage of WNV
from female mosquitoes to larva through the ovary—may contribute to overwinter-
ing and early season amplification of WNV
10
.
1. How would you include vertical transmission into the model structure?
2. How might the addition of trans-ovarial transmission affect disease transmission?
9
Bugbee, L. and L. Forte. 2004. The discovery of West Nile Virus in overwintering Culex pipiens
(Diptera: Culicidae) mosquitoes in Lehigh County, Pennsylvania. Journal of the American Mos-
quito Control Association. 20(3): 326-327.
10
Baqar, S., C.G. Hayes, J.R. Murphy, and D.M. Watts. 1993. Vertical transmission of West
Nile virus by Culex and Aedes species mosquitoes. American Journal of Tropical Medicine and
Hygiene. 48: 757-762.
