Rabies in Cattle

Filed Under: Cows, Diseases

Does your cow appear to be choking? Think twice before extending your arm down the animal’s throat bare handed to look for a foreign body. One of the most common ways for ranchers, farmers, and veterinarians to be exposed to rabies is through exposure to a supposedly choked cow.

Rabies is an acute viral encephalomyelitis that may affect any warm blooded animal. Once clinical signs appear, the disease is always fatal. Rabies virus is found throughout the world with some notable exceptions. Rabies-free areas tend to be island nations that have strict quarantine regulations, thereby ensuring that the virus will not be introduced into their country.

Transmission is usually by the introduction of virus-laden saliva into the tissues of a cow by the bite of a rabid animal. In cattle, the incubation period (the time from bite to the time clinical signs are seen) is usually about three weeks, but may be anywhere from two weeks to several months in length and often depends on the area where the animal was bitten and the amount of virus present in the bite. The virus will multiply at the bite site for a considerable length of time before moving on. The virus then travels up the peripheral nerves to the spinal cord and proceeds to the brain. Once the virus reaches the brain, it will then travel up the peripheral nerves and proceed to the salivary glands.

Clinical signs of rabies may vary. The most reliable clinical signs are a sudden change in behavior, unexplained clinical signs that are related to the central nervous system, or progressive paralysis in the affected patient.

Two forms of rabies are possible with totally different clinical signs. In the furious form of rabies in cattle, normally docile animals may attack humans and other animals. Milk production ceases abruptly in dairy cattle. The cow may appear hypersensitive and will follow sounds and movements intensely. The affected cattle may exhibit abnormal bellowing which may continue intermittently, or voiceless attempts to bellow described as yawning.

In the paralytic form, the first sign of trouble may be paralysis of the throat. Drooling of saliva, grinding of the teeth, extension of the head, and bloat may occur. The cow may appear to be choked. An owner or an attending veterinarian may become exposed to rabies themselves by searching for an offending foreign body in a choked animal bare handed. Animals affected in this way rarely attempt to bite. Weakness in the hindquarters may occur and is always accompanied by decreased sensation to the affected area. Paralysis of the anus and penis in the bull may be seen. Eventually the animal will go down and be unable to get up as paralysis becomes complete.

No treatment should be attempted after clinical signs are evident. The animal should be euthanized and laboratory confirmation should be made on the brain tissue.

Prevention of rabies may be achieved by vaccination in areas where infections are common. Farm dogs and cats should be vaccinated since exposure of rabies to cattle is usually through the bite of a carnivore. There are several rabies vaccines licensed for cattle including “Rabguard-TC”, produced by Pfizer Animal Health. Calves should be given a vaccination at three months of age or older, followed by annual revaccination in endemic areas.

References:

Kahn, Cynthia. Editor. The Merck Veterinary Manual. 9th Edition. 2005. Pp. 1067-1071.

Blood, D.C., J.A. Henderson and O.M. Radostits. Veterinary Medicine. 1970. Lea and Fibiger. Philadelphia. Pp. 682-685.

Smith, Bradford. Large Animal Internal Medicine. Second Edition. 1996. Mosby. Pp. 1024-1028.

Topics: cattle, rabies

Symptoms: hypersensitivity, paralysis, weakness, yawning

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