In Texas, most cases of rabies are spread by skunks, but occasionally by coyotes, foxes or bats. Alexander has also seen cattle come from Mexico that developed vampire bat rabies.

“Incubation time in large animals can be weeks or months, depending on the bite location. The virus works its way along the nerves to the brain. If a horse or cow is curious about a skunk and gets bitten on the nose, this would result in a shorter incubation time than if bitten on the hind leg,” he explains.

Most pets are vaccinated for rabies, to protect both the animals and their owners. The American Association of Equine Practitioners now recommends all horses be vaccinated for rabies, listing it as a “core” vaccine in every vaccination program.

Cattle, however, are rarely vaccinated. But, in regions where rabies cases occur, valuable animals should be vaccinated, along with any cattle handled by people. Alexander recommends vaccination for 4-H, FFA and other show animals.

Alexander points out that in a herd of cattle, generally only one animal becomes infected. It’s rare to have multiple cases.

“The worst situation I know of was a herd of registered Shorthorns west of San Angelo during a surge of fox rabies a few years ago. One rancher lost seven head. A fox or bobcat probably went berserk and bit numerous animals in that herd,” he says. Or, since cattle will sometimes attack a predator to protect calves, the cows might have grouped around it attempting to chase it off.

Rabies variants

Rabies has many genetically different strains, each of which is adapted to a particular species of animal. This adaptation makes that species a reservoir for that variant, as the host species isn’t killed as quickly as a species into which that variant spills over.

“This enables the variant to survive and propagate in nature,” says James Alexander, regional zoonosis control veterinarian, Texas Department of State Health Services. “There are several rabies variants in skunks, including the North Central Skunk, South Central Skunk, and Spotted Skunk, and even more variants in bats.”

The variants were named for the species (and sometimes the region) in which first detected. Many distinct rabies virus variants have been identified in different bat species – there are as many as 40 bat species that may each have their own rabies variant.

Rabies variants in the U.S. include raccoon, skunk, fox and mongoose (Puerto Rico). “Fox variants include the Texas Gray Fox, Arizona Fox, Arctic Fox, Red Fox, etc., while different canine variants are the predominant form of rabies in other countries,” Alexander says.

A new rabies virus variant associated with Mexican free-tail bats was identified in the U.S. in 2008 after the death of a Mexican immigrant who was exposed to bats prior to her arrival in the U.S.