29 September 2022

3 minute read

By attacking the nervous system, brain and spinal cord, Rabies can cause brain deterioration and death. It is preventable through the use of vaccinations, an option available since Louis Pasteur introduced a vaccine in 1883.

All mammals are thought to be susceptible to the rabies virus, a fatal viral zoonosis caused by the Lyssavirus causing acute inflammation to the brain (Encephalitis). It is considered to be all but 100 per cent fatal.

Although not an issue in Western Europe, the virus is a 'high risk' problem in parts of South America, Africa, Russia and much of Asia. Much of the world is affected by bat rabies but concern intensifies when the virus is in fox, raccoon and skunk populations.

Cause

A bite from an infected wild animal, such as a fox or raccoon, is a common method of infection in cattle. In Europe, rabies in dogs is a growing concern,in Africa the threats come from Jackals and in Northern Europe, Wolves are a prime vector of the virus.

Saliva is the main method of transmission of the virus being shed through infected cattle and spreading through the body via the bloodstream. It travels to the spinal cord where it can incubate for months on end, although 3-12 weeks is common. From the spine the virus moves into the brain, at which point clinical signs of rabies often appear in cattle.

It is possible for the virus to enter the body through orifices and lacerations to the skin. This however, is uncommon. Open wounds, mucous membranes, eyes and the mouth are possible entrance points for the virus. Under normal conditions the virus is not spread through the air, though this method of transmission is possible.

Often presented in a single animal rather than the full herd, rabies can be spread due to the curious nature of cows who will inspect raccoons, dogs, foxes etc. that are exhibiting strange behaviour.

Transmission from unpasteurised cow's milk to humans is currently being scrutinised although properly cooked meat and pasteurised milk from infected animals poses no danger to humans.

Clinical Signs

In the absence of anti-viral rabies drugs, progress to death is rapid once clinical signs appear. Milk production and feed intake may drop gradually before rapidly falling and cows may look very alert, staring at objects.

Aggressive, excitable or exaggerated movements can be signs of rabies. Sexual activity can be increased, including mounting behaviour. Bulls can have persistent erections or a prolapsed penis.

Other Signs Include

• Inapettence (lack of appetite)
• Dyspahgia (difficulties swallowing)
• Altered vocalisation
• Seizures
• Incoordination of hindquarters - unsteady gait

Prevention

Education and vaccination of wild animal populations can control rabies transmission. By limiting the number of wild animals carrying the virus and the chance that those animals will come in contact with pasture and farmland, the likelihood of rabies transmission is reduced.

Cautious handling of cattle with undetermined illnesses is recommended, especially if neurological signs have been observed. Examining a cow's mouth should be done with gloves to avoid exposure of the veterinarian's or stockman's hand to saliva.

The Centre for Disease Control and Prevention recommends the following to limit rabies spread;

• Characterize Virus Characterize the virus at the national reference laboratory
• Identify and Control Source Identify and control the source of the virus introduction
• Enhance Surveillance Enhance laboratory-based surveillance in wild and domestic animals
• Increase Vaccination Increase animal rabies vaccination rates
• Restrict Animals Restrict the movement of animals
• Vector Population Evaluate the need for vector population reduction
• Coordinate Response Coordinate a multiagency response
• Provide Outreach Provide public and professional outreach and education

Tests and Vaccination

There are no tests available for rabies in live animals. Determination normally requires a post-mortem inspection of the brain.

Several companies currently produce rabies vaccines. These vaccines do not use live viruses but are killed vaccines.