Database Reference
In-Depth Information
Chapter 12
Indirect Susceptible-Infected-Resistant Models
of Arboviral Encephalitis Transmission
∗
12.1 Modeling West Nile Virus Dynamics Emily Wheeler
and Traci Barkley
West Nile virus (WNV) is an arthropod borne, or arboviral, disease historically en-
demic to Africa. In Africa, the disease circulates between populations of wild birds
and mosquitoes, but only occasionally results in significant disease outbreaks in
wildlife
1
. After emerging in North America in 1999, however, WNV spread rapidly
through avian communities, causing unexpected mortality in many bird species and
encephalitis epidemics in secondary hosts, such as horses and humans. WNV is
one of a number of related flaviviral encephalitides, including eastern equine en-
cephalitis, Japanese encephalitis, and La Cross encephalitis. These diseases are all
transmitted among hosts by mosquitoes and can result in symptoms ranging from
mild malaise to severe neurological disease and death
2
.
Dynamic modeling of emerging diseases like WNV benefits understanding of
the diverse interactions of EXTRINSIC drivers, such as weather, seasonal demo-
graphics or habitat types, on INTRINSIC host and vector interactions that deter-
mine the severity, location, and timing of disease amplification and transmission
(Figure 12.1). While complicated by these extrinsic drivers, the intrinsic compo-
nents of an arboviral encephalitis system like WNV can be reasonably described by
extension of a classical epidemiological model, the common Susceptible-Infectious-
Resistant (SIR) model. With a few simple changes, this model can be extended to
accommodate indirect disease transmission among two or more interacting popu-
lations of hosts and vectors. After building this base indirect SIR model, extrinsic
drivers can be added to show how the outbreak might change with this increased
complexity.
∗
This model was developed by Emily Wheeler and Tracy Barkley.
1
Jupp, P. 2001. The ecology of West Nile virus in South Africa and the occurrence of outbreaks in
humans. West Nile Virus: Detection, Surveillance, and Control Annals of the New York Academy
of Science. 951: 143-152.
2
Center for Disease Control and Prevention. West Nile Virus [cited 2007 September 9]. Available
from http://www.cdc.gov/ncidod/dvbid/westnile/index.htm.
