Rabies in South Dakota cattle
Rabies is a fatal viral disease that is enzootic (i.e. established in animal populations) in South Dakota.
Over the past 10 years, this disease has been reported in animals from all but seven of South Dakota’s 66 counties. Rabies has the potential to affect any mammal— including humans. In our part of the country, the skunk is the reservoir for rabies, and is by far the most common wild animal species diagnosed with rabies.
But what would you guess is the most common domestic animal species diagnosed with rabies over the past 10 years in South Dakota? It’s not dogs, and it’s not cats— that honor would fall on the bovine. Sixty-eight cattle were diagnosed with rabies from 2002-2011, compared with 38 dogs and 37 cats. So far in 2012, there already (as of 4/25/12) have been three South Dakota bovine cases diagnosed through the South Dakota State University (SDSU) Animal Disease Research and Diagnostic Laboratory.
Cattle contract rabies in the same manner that other domestic animals in South Dakota contract it: through bites or scratches by rabid skunks. Cattle on pasture are particularly exposed to skunks; however, dairy animals also have been exposed when rabid skunks enter their enclosures. After the virus first enters the body of the susceptible animal, it divides and replicates at the site of entry, eventually invading nerve endings. Once this starts, the virus makes its way up to the spinal cord and brain. When the rabies virus enters the brain, that’s when clinical signs ensue.
This process—the virus moving from the point of entry to the brain—takes a variable amount of time. It depends greatly on how much virus first entered the body, and where it entered the body. An exposure through a bite on the nose will result in clinical signs appearing more quickly than a similar bite on the leg, for example. In general, this takes two weeks, but incubation periods of several months have also been reported.
The signs of rabies in cattle are often vague and can be confused with signs caused by other conditions. In general, cattle show signs more consistent with the “paralytic” or “dumb” form of rabies: acting weak and uncoordinated, eventually becoming unable to rise, and comatose before dying. Behavioral changes such as abnormal persistent bellowing, and persistent signs of estrus are also commonly reported in cattle with rabies. Rabies is a fatal disease. Affected animals do not live more than five to seven days past the time when the first clinical signs are noted.
Animals can transmit rabies after the virus has entered the brain and descended down to the salivary glands, where it is shed from the body in large amounts through the saliva. Therefore, when people work with cattle suspected to have rabies, particular care should be taken to avoid contact with the animal’s saliva. Since the virus is rapidly inactivated once it leaves the body, exposures to live animals are normally the only significant ways that the virus can be transmitted.
Diagnosis of rabies can only be made by examining the tissues of the brain, so euthanasia of rabies suspects needs to be done in a manner that does not destroy brain tissue. Veterinarians can submit samples, or the whole head or carcass to the SDSU ADRDL (Animal Disease Research Diagnostic Laboratory) for rabies testing.
When the subject of rabies vaccinations is brought up, people first think of dogs and cats. But there are rabies vaccines approved, available, and effective for cattle and horses as well. While it is not likely practical to vaccinate whole herds of dairy or beef cattle for rabies, vaccination should be considered for animals that will have more contact with the public such as cattle going to shows, exhibit, or petting zoos.
Your local veterinarian is an excellent source of answers regarding cattle rabies, its signs, diagnosis, and prevention. In addition, SDSU Extension publication “Rabies in South Dakota: Animal and Human Aspects,” provides an overview of rabies in South Dakota. — Dr. Russ Daly, South Dakota State University