Living in suburban Chester County, PA, our doctors at the Animal Clinic at Thorndale often see (and smell) the results of pets tangling with wildlife. One of our biggest concerns is the potential exposure of a pet to a rabid animal, especially if that pet is not current with its rabies vaccination.
Rabies is a viral disease that may infect any warm-blooded animal. Regardless of the initial site of virus introduction into the animal, the virus eventually invades the central nervous system. With rare exception, it is a fatal disease. Pennsylvania State Law requires that ALL dogs be vaccinated against rabies. If all dogs were properly vaccinated, rabies in dogs would be effectively eliminated from concern. Unfortunately, this vaccination blanket is not the reality.
Contributing Factors
For domestic pets, such as cats and dogs, the greatest risk factor for contracting rabies comes from failing to receive proper rabies immunization and then coming in contact with a rabid animal. Hunting and predatory dogs are at higher risk.
Prevalence
Rabies is found on a worldwide basis. Even though all warm-blooded animals can become infected, some species are more susceptible than others. Skunks, raccoons, and bats are considered most susceptible, with cats, dogs, horses, and humans intermediate in susceptibility. Opossums and birds are relatively more resistant to the virus compared to other species. It is important to note that while wildlife represents the major reservoir of rabies in nature, cats and dogs are the principal source for rabies transmission to humans.
Causes/Transmission
The usual source of rabies infection is the bite of an animal infected with the virus. The virus is found in high concentrations within saliva. Once inoculated into the victim, the virus travels up nerve endings to the central nervous system. There have been a few rare cases of humans contracting rabies by inhaling aerosolized virus in bat caves.
Clinical Signs
Rabies is classically divided into three distinct stages: prodromal, furious, and paralytic. The prodromal stage lasts 2-3 days and is characterized by major behavior changes. Normally friendly domestic animals, such as dogs and cats, become aggressive. In contrast, wildlife will lose fear the normal fear of humans. Also, wild animals that are normally seen only at night (nocturnal species) may be seen during the day. During the furious stage, dogs will typically become very vicious and make lunge at any moving object. They may have muscle tremors and incoordination. During the final stage, the paralytic stage, paralysis sets in and death follows. Most dogs die from rabies within 2-7 days after they begin to show signs of the disease.
Diagnosis
Rabies can be suspected based on clinical signs, but it can only be confirmed by microscopic examination of brain tissue. For this reason, animals suspected of having rabies are usually autopsied with a sample of brain tissue submitted to a pathologist. Although this can be upsetting for owners, remember that there is no room for error with rabies. If a human has been exposed and does not receive treatment, death is inevitable.
Whenever an animal without proper rabies vaccination bites a human, the animal is usually required to be confined and observed by a veterinarian for at least a 10 day period. Humans bitten by stray or wild animals should contact their human health care providers immediately.
If your dog has been bitten by an unknown assailant, it is presumed exposed to rabies until proven otherwise. Dogs currently vaccinated against rabies are given a booster and should be observed closely for 6 months. If there is not a current rabies vaccination history, the recommendation is euthanasia of the dog to minimize human risk of exposure. Some public health departments may allow a strict 6 month quarantine of the dog at a veterinary hospital. If the dog shows any potential signs of rabies during the quarantine it would need to be humanely destroyed and the brain tested for rabies.
Therapy
Treatment is not recommended for animals with rabies because of the potential risk for human exposure to the virus. There have been a limited number of cases of humans surviving rabies once signs develop. It is essential that any potential exposure to rabies in humans be treated immediately, before signs develop, for a successful outcome. The old “injections in the stomach” human treatments no longer exist and effective immediate post exposure treatment consists of a series of intramuscular injections. Contact your human health care provider IMMEDIATELTY if you have any concerns about a rabies exposure, even if you are pre-vaccinated.
Prognosis
Rabies is always fatal in warm-blooded animals that develop signs of the disease. Immediate post exposure treatment in humans is almost always effective in preventing the disease.
Transmission to Humans
Rabies can be transmitted to a human through the bite of an infected animal or inoculation of rabies-infected saliva into an open wound. Whenever a human is bitten by an animal, a physician should always be promptly contacted. In some areas, physicians are required to contact local animal control officials so that the vaccination status of the animal can be verified and an appropriate quarantine initiated.
If your dog has bitten a human, even if it is current on its rabies vaccinations, you will likely be required to present the dog to your veterinarian 10 days after the bite occurred so that your dog can be examined a certified as free of signs of rabies.
Prevention
Because rabies-immunized pets represent an important buffer between humans and the rabies reservoir found in wildlife, the importance of regular rabies boosters for pets cannot be overemphasized. The State of Pennsylvania requires all dogs over 12 weeks of age to have a current rabies vaccination.
The first rabies vaccine is given at 12 weeks of age, followed by regular boosters. After the initial vaccination, a booster is required one year later, regardless of the type of vaccine used. Thereafter, boosters need to be given every one or three years, depending on the particular licensing of the vaccine being used by your veterinarian. These vaccines are considered safe and effective.