Page 954 - Clinical Small Animal Internal Medicine

892 Section 9 Infectious Disease

were detected in the US. Over 90% were wild animals, Humans have spread rabies variants in the US by mov-
VetBooks.ir with raccoons, bats, and skunks constituting over 80% of ing infected animals. Before the late 1970s, the raccoon
variant had been limited to the southeastern area of the
the total. Rabid foxes add another 5%. The island of
Puerto Rico has consistently reported about 30–40 rabid
people shipping raccoons from south to north for hunt-
mongooses each year. US. It was translocated to the mid‐Atlantic states by
Rabid cats (4% of rabid animals) have outnumbered ing purposes. The canine variant of rabies, which was
rabid dogs (1%) for many years, most likely because of considered officially eliminated from the US in 2007,
better vaccination coverage in dogs. In North America, could be reimported at any time from countries where
rabies cases are more frequent in spring and summer. canine rabies is still enzootic. Rabid dogs have been
The number of rabid animals reported typically reflects imported into the US many times but fortunately were
only those confirmed by laboratory testing; it is thought quickly detected, isolated, and euthanized. If imported
that the number of undiagnosed rabies cases in wild ani- rabid dogs were released into populations of unvacci-
mals is far higher. nated dogs, such as into a city with a significant stray
There are multiple rabies virus substrains (aka vari- dog population, canine rabies could become reestab-
ants), that are uniquely adapted to their reservoir hosts. lished in the US.
Rabies variants tend to be found in identifiable geographic Mice, rats, and rabbits can be experimentally infected
locations. This phenomenon is very useful for investigat- with rabies, but rabies is very rare in them in nature.
ing the source of individual rabies cases. As an example, if Rabies has been detected in larger rodents in the US,
a stray dog in the US was found to be rabid, analysis of the such as woodchucks, groundhogs, and beavers, usually
variant could reveal the source of the infection. Finding a in areas where the raccoon variant is enzootic. It has also
North American bat, skunk, or raccoon variant in the dog been rarely seen in rabbits attacked by raccoons.
would reveal that it caught the virus from indigenous Opossums are partially resistant to experimental
wildlife. Finding a Thai dog variant would suggest the dog rabies infection. So far, no marsupial has been found to
had recently been imported from Thailand, or had been be a rabies reservoir. Nonetheless, opossums can
bitten by a rabid dog from Thailand. become infected. In California (where skunk and bat
In the Americas, insectivorous bat rabies variants are rabies variants are enzootic), 11 rabid opossums were
widely distributed. Vampire bat variants are found in detected between 1983 and 2012 (data from Dr Curtis
certain areas in South America, Central America, and Fritz, California Department of Public Health). The
southern Mexico. The canine rabies virus variant has omnivorous nature of opossums would make it natural
been eradicated from the US but is still present in parts for them to investigate a dying, rabid animal, and to
of Central and South America. So far, no feline variant potentially be bitten.
has been reported. The pathogenicity and virulence of Practitioners should have full understanding of the
the variant, the behavior of the reservoir species (natural rabies variants that are common in their area. However,
behavior and behavior when rabid), and the degree of since rabies may be imported, a thorough travel history for
overlap in habitat between the reservoir species and all patients should also be taken, with special focus on the
other mammals all affect the risk of rabies transmission previous six months. The Centers for Disease Control and
to pets and people. Prevention (CDC) maintains an online list of nations that
The risk of rabies exposure for domestic animals is present a higher risk for importation of rabies in animals.
higher in areas where variants associated with terrestrial
animals (i.e., not just insectivorous bat variants) are prev-
alent. The risk is highest where the canine variant is
enzootic (example: India), and much lower in areas where Signalment
only insectivorous bat rabies variants are found (example:
southern California). Many islands in the world, such as Any breed of dog or cat may present with rabies. Rabies
Hawaii, are considered completely rabies free. is highly unlikely in animals less than 4 weeks of age.
The raccoon variant is found throughout the eastern
quarter of the US and in parts of eastern Canada.
Multiple variants of skunk rabies are found in large areas History
in the center of North America, California, and parts of
Mexico. Fox variants have been found in Alaska, Arizona, Taking a thorough history is vital for clinical diagnosis.
New Mexico, and Texas in the US, and in Ontario, The risk of rabies depends on the geographic area where
Canada. One variant found periodically in southern the pet lives or has spent time, especially in the previous
Texas and northern Mexico appears to be adapted to six months. Knowledge of the clinical course of illness
both dogs and coyotes. before presentation is also essential for diagnosis.