Rabies In Your Cat Or Dog

Ron Hines DVM PhD 5/4/06

Rabies is one of the oldest recognized diseases of man and animals. The organism is a bullet-shaped RNA virus ,of the genus Lyssavirus in the Rhabdoviridae family. Rabies has a mystique that rests upon its finality and the striking psychological disturbances the disease produces. This makes it the most feared of all viral diseases. The stereotypic mad dog is actually not the commonest form of the disease.

Fifty years ago, people in the United States usually contracted rabies from their pet dogs and dogs were the largest reservoir of the disease. With the advent of effective rabies vaccines and public compliance with vaccination laws, the epidemiology of the disease has changed. Now more than 90% of the reported cases of rabies occur in wildlife – chiefly carnivores and bats. These animals constitute its new reservoir.

All warm-blooded animals can contract rabies. In 2001, the latest figures that I have, 49 states, the District of Columbia and Puerto Rico reported 7,437 cases of rabies in animals and no cases in humans. Historically, one or two cases occur in people in the United States every year. Hawaii is the only state that has never reported a case.

Ninety three percent of the rabies cases in the United States were in wildlife in 2001.. Raccoons are the most common animals affected by rabies (37.2%), followed by skunks (30.7%) bats (17.2%) and foxes (5.9%). Domestic animals account for only 6.8% of reported rabies cases in the United States. Cats, dogs, cattle, horses, sheep and goats comprise most of the domestic animal cases. Rabies is twice as common in cats as in dogs, The largest number of domestic animal rabies was reported in the state of Pennsylvania followed by New York.

Rabies virus attacks the brain causing acute encephalitis (inflammation), which destroys brain cells and ultimately causes death. The early signs of rabies in animals and man are not specific. They consist of fever, and general malaise. In humans headache is often the first sign of the disease. As rabies progresses, neurological signs begin which include confusion, aimless motion, agitation, blindness, paralysis, salivation, difficulty swallowing and seizures. Death usually occurs within two weeks.

Although only a few human deaths occur in the United States each year, in southern Asia, many thousands of people die from the disease. Australia, England and Antarctica are the only large geographical areas entirely free of the disease. In Europe, the primary carrier of rabies is the fox. In Africa it is the jackal and in Asia dogs and mongoose. In South America dogs and vampire bats spread the disease. In the Midwestern United States, skunks are the prime carriers of rabies. Along the Eastern Seaboard, raccoons are the prime carriers. Throughout the US some cases in dogs and humans are derived from contact with foxes and bats. The Center For Disease Control in Atlanta has not recorded a single case of human rabies derived from the bite of a squirrels or other rodent.

Risk Factors For Human Rabies
People most likely to handle or be exposed to injured and sick wildlife are most at risk for contracting rabies. An effective vaccine is marketed to immunize these high-risk individuals.
Dogs that come into contact with wildlife are also at a higher risk for the disease. Vaccines to protect these people and dogs are highly effective.

Rabies Transmission
Rabies is only transmitted through bites of infected animals. The only exceptions are people or animals that frequent caves with large populations of bats. In these bat caves the virus becomes airborne in dust and secretions. It can then be inhaled by passing humans and animals. The rabies virus is present in large numbers in the saliva of infected animals. However, not every animal or person bitten by a rabid animal develops the disease. Less than two in ten untreated people bitten by rabid animals develop rabies.

Symptoms Of Rabies
The rabies virus leaves the site of the bite and travels slowly through nerves taking 3-8 weeks to reach the brain. An exceptional case might take twelve month to make this journey. Most animals then go through one or more classical stages before they die from the disease. Skunks are an exception. They can become life long healthy carriers of the rabies virus.

The Prodromal Phase
Following infection, the virus enters an eclipse during which its effects on the body are negligible. At the site of the bite the rabies virus enters directly into the peripheral nerves or replicates in tissue at the bite site, entering the nerves later.

In dogs, this phase of the disease typically lasts for two or three days. During the next period the animal becomes nervous and anxious. It may withdraw from contact and run a fever. Personality changes become common. Friendly dogs may become fearful or aggressive and normally fearful or aggressive dogs may become friendly. The site of their bite evidently itches or stings them, because they frequently lick and worry the area. Cats go through this phase more rapidly than dogs.

The Furious Phase
Once the virus has entered the peripheral nerves it is transported via sensory and motor nerve fibers to the brain. The virus also spread from the brain to other highly innervated (supplied) sites including the salivary glands. This is the time the virus is present in the animals saliva.

After passing through the prodromal phase dogs and cats pass through a stage characterized by irritability to stimuli of sight and sound.
This stage can last one to seven days. These animals become restless, aggressive and viscous. I have seen dogs in this phase chew the metal bars of their cage until they injured themselves severely. Dogs and cats in this stage of the disease may roam and wander great distances in an aimless fashion. Eventually these animals become ataxic (wobbly) and may develop seizures and die.

The Dumb Phase
This is sometimes called the paralytic phase. Some animals develop this stage after a prodromal or furious period. This is the stage in which the nerves of the head and throat become paralyzed. Animals in this state drool and walk about with their mouth agape. They are unable to swallow. Owners often think their pets in this condition have some object lodged in their throat. During a period of about a week these animals become more and more paralyzed and finally die. Many more dogs pass directly into this stage from the prodromal stage, never developing the furious stage of rabies. Cows in this phase often bellow and extend their necks as if their throat was obstructed. It is common for farmers to attempt to remove a suspected apple or corncob from these animals’ throat and in so doing they become exposed to rabies.

Rabies Diagnosis
The traditional method of rabies diagnosis requires submitting the suspect animal’s brain to a laboratory for microscopic examination. The pathology of rabies infection includes cellular changes that denote encephalitis (brain inflammation) and myelitis (spinal cord inflammation). Blood vessels within the brain become surrounded with white blood cells (perivascular cuffing). Often, reddish globular inclusion bodies form within the nerve cells (Pyramidal and Purkinje cells) of two portions of the brain, the cerebellum and hippocampus. These inclusions are called Negri bodies. They are diagnostic for rabies.

Treatment
There is no treatment for rabies. Once the disease is in progress death is inevitable. There are a few accounts of survival in the literature but they are exceedingly rare and unproven. If an unvaccinated dog or cat is bitten by a known rabid animal it is recommended that the pet be destroyed immediately. If the owner are unwilling to do this the animal should be vaccinated for rabies and placed in strict isolation for 6 month. It should be vaccinated again against rabies one month before release. If the pet is current on its rabies vaccination it should be revaccinated immediately and closely observed for 45 days.

Prevention
It is always a good procedure to vigorously scrub and disinfect animal bites. However, the only certain way to prevent infection is prior vaccination or vaccination subsequent to being bitten. Laws throughout the United States and most other countries require periodic rabies vaccination of dogs and cats. Both modified (weakened)live virus and killed virus vaccines are available. Some brands are approved for use in ferrets, horses, cattle and sheep as well as dogs and cats. These vaccines are quite effective and almost never fail. The problem is that less than half the dogs and only one in ten cats receive their rabies vaccinations in the United States. Vaccine manufacturers suggest that cats and dogs receive their first rabies inoculation at twelve weeks of age and then again when they are one year old. From then on some vaccines require yearly booster vaccinations while others protect for three years.

Excellent vaccines exists for people at high risk of animal bites.

Oral rabies vaccination of wildlife with Raboral V-RG® has been used in the United States since 1990. Currently, there are 15 states distributing this oral vaccine for raccoons. Texas distributes vaccine baits for gray fox and coyote. There have been nearly 48 million doses of Raboral V-RG® distributed in the U.S. and Canada, and 63 million doses have been dispersed worldwide. This vaccine is a recombinant vaccine made from a living pox virus that carries the rabies antigen in the form of rabies glycoprotein. The vaccine cannot cause rabies because it contains only the non-infective surface proteins of the virus, not the viral nuclear material.

Human Bites
Whenever an animal bites a human it should be quarantined for a 10-14 day observation period. Alternatively it can be humanely destroyed and its brain sent to a laboratory equipped to do rabies diagnostic tests. State law determines the conditions of quarantine. Conditions may differ for vaccinated and non-vaccinated animals. If the biting animal can not be located for quarantine or if it should prove to have been rabid, a series of five inoculations of human immune globulin should be given. Individuals at high risk of bites should receive a three shot series of human diploid cell line vaccine to prevent rabies.

Subsequent to an animal bite, the type of post-exposure treatment depends on whether the person had been previously vaccinated against rabies. Unvaccinated people should receive five 1-ml doses of human rabies vaccine plus one dose of human rabies immune globulin. If the individual was previously vaccinated for rabies they should receive two 1-ml doses of rabies vaccine and no immune globulin.

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