Spatial Pestilence Dynamics - Dynamic Modeling of Diseases and Pests - page 253

rabies is an epidemiological disease. This concept is important for the development
of a spatial model that describes the spread of the disease over a landscape and for
the evaluation of possible control measures.

15.2.4 The Rabies Virus

Canine rabies transmitted to humans has been reduced in the United States, although
it is still a factor in over 75,000 human cases worldwide and is still considered
a human health issue 15 . The disease, like many communicable diseases, appears to
occur in cyclical waves. Its spread can best be understood through comprehensive
study of the behavior of its mammalian hosts and the pathogenesis of the virus 16 .
Typical host populations are heterogeneous in nature and field studies are difficult.
There appears to be a hierarchy of susceptibility to rabies, with foxes, wolves, and
coyotes being the most susceptible 17 . The fox adds to this complexity with shy
and elusive behavior 18 . Although foxes do not typically interact with humans as
frequently as other medium-sized mammals, they do come in contact with feral
felines and canines. This contact increases the risk of stray cats and dogs contracting
the rabies virus, and that risk places humans and domestic pets at risk.
The primary mode of rabies transmission is through the bite of an infected an-
imal. To a lesser extent, scratching and licking can also transmit the disease. The
virus replicates at the site of entry and once it reaches a sufficient titer the virus
travels via the neural pathways to the brain 19 . The virus titer is defined as the small-
est amount of virus per unit volume capable of producing infection 20 . The virus then
travels from the central nervous system via peripheral nerves to the salivary glands,
where it continues to multiply. Shedding of the virus in the saliva may occur before
the appearance of clinical signs 21 . The incubation period, the time from inoculation
to the appearance of clinical signs, can vary depending on the site of entry and its
proximity to the central nervous system as well as the amount of virus entering the

15 Fenner, F.J., E. Paul, J. Gibbs, F.A. Murphy, R. Rott, M.J. Studdert, and D.O. White, 1993.
Veterinary Virology, Academic Press, New York, NY, 2nd ed.
Rupprecht, C.E., J.S. Smith, M. Fekadu, and J.E. Childs., Emerging Infectious Diseases 1.
1995. 107-114.
16 Kaplan, C. , G.S. Turner, and D.A. Warrell. 1986. Rabies: The Facts, Oxford University Press,
Oxford, England, ed. 2.
17 MacDonald, D.W. 1980. Rabies and Wildlife: A Biologist's Perspective, Oxford Univ. Press,
Oxford, UK.
Fields, B.N., D.M. Knipe, R.M. Chanock, M.S. Hirsch, J.L. Melnick, T.P. Monath, and
B. Roizman. 1990. Virology, Raven Press, New York, NY, 2nd ed.
18 MacDonald. 1980.
19 Scherba, G. April 1998. Presentation to Ecological Modeling Group, Associate Professor of
Veterinary Virology, University of Illinois.
20 Fields et al. 1990; Scherba 1998; G.P. West, 1973. Rabies in Man and Animals, Arco Publishing
Co,NewYork,NY.
21

West 1973.