RABIES - Medicine for Mountaineering and Other Wilderness Activities - page 485

Figure 32-2. Rabies in bats, 1998 (989 cases total)
Essentially all mammals are susceptible to rabies and capable of transmitting the infec-
tion, but transmission by rodents has not been documented. The United States and Canada
are unique in that rabies epizootics (rabies epidemics in animals) are recognized in a num-
ber of wild animals: raccoons, skunks, foxes, and bats. Bat rabies is endemic in all areas of
the continental United States, both urban and rural, including Alaska.
An epizootic in raccoons that began in the late 1970s has spread to involve the entire
U.S. East Coast ( Fig. 32-3 ). Only one human rabies infection has resulted from this epizo-
otic, although extensive vaccination programs have been required after humans contacted
animals infected with the raccoon virus.
A coyote and gray fox epizootic in southern Texas originated from unvaccinated dogs
crossing the Rio Grande from Mexico. It spread to dogs in Texas, resulting in two human
rabies deaths in 1991 and 1994 and over 2000 humans having to be vaccinated. This epi-
zootichasbeencontrolledwithbaitscontaininganoralrabiesvaccine,mostofwhichwere
dropped from aircraft, the largest program of this type every accomplished.
TRANSMISSION OF RABIES
Ininfectedanimals,therabiesvirustravelsthroughnervesfromthecentralnervoussystem
tothesalivaryglandsandispresentinthesaliva.Transmissionoftheinfectionoccurswhen
a bite wound, a preexisting wound, or a weeping skin rash is contaminated with the saliva
of a rabid animal. The infection can also be transmitted by scratches because animals lick
their paws and their claws are contaminated with saliva containing the rabies virus. The
virus cannot penetrate intact skin but can pass through intact mucous membranes such as
the lining of the mouth, nose, or eyelids. Licking alone can transmit the infection if saliva
contacts these surfaces.
Theaverageincubationperiodbetweenthetimeofthebiteandtheappearanceofaclin-
ically evident infection is thirty-five days. (Approximately 1 percent of human rabies in-
fections appear following an incubation period of a year or more.) The virus travels along
nerves at 15 to 100 mm a day to reach the brain. Bites on the extremities allow more
time for treatment than bites about the face, which are particularly dangerous and must be
treated urgently.