Rabies in Dogs and Cats

Filed Under: Dogs, Cats, Diseases

Did you know that rabies is responsible for the death of one person worldwide every 10 minutes? Children are affected by rabies more than every other age group with approximately 100 children, primarily in Asia and Africa, dying each and every day. In the United States, where there are strict requirements for rabies vaccinations in domestic animals, we still diagnose, on average, from one to three cases of rabies in humans each year.

Most viruses tend to be species or group-specific. One of the largest exceptions to this rule is the rabies virus. Any mammal may become infected with rabies. The rabies virus is a lyssavirus, which is a member of the Rhabdovirus family. There are many variants of the lyssavirus, which are typically found in a particular reservoir species within a specific geographic region. In the United States the most common reservoirs of rabies in the wild are raccoons, skunks, bats, foxes, and coyotes. The most commonly affected domestic animals are cats, dogs, and cattle. The variant of the rabies virus is often named for the particular reservoir harboring that viral variation in a particular area such as skunk rabies, which is the common variant seen in the south central United States, as compared to the fox variant more commonly seen in the southwestern part of the United States.

Rabies transmission occurs through exposure to an infected animal usually through a bite wound, although conjunctival transmission has been shown to occur after following exposure to bats. Most domestic animals are infected by wildlife. Most human exposure to rabies is through contact with domestic animals. Pets should be vaccinated for rabies by a veterinarian to prevent them from acquiring the disease from wildlife, and thereby prevent possible transmission to humans.

The incubation period for the development of clinical rabies is variable and may be days or months depending on the amount of virus inoculated by a bite and on the extent of nerve innervation (number of nerves) to the original site of injury. The virus travels up the periphial nerves to the brain and spinal cord where clinical signs of disease become apparent and the virus becomes capable of being further transmitted through virus multiplication in the salivary glands.

There may be a prodromal phase of 2 to 3 days that will be characterized by nervousness, anxiety, or other behavioral changes. Paresthesia (increased skin sensitivity) at the site of the original bite wound may be present.

Rabies is typically characterized by a change in temperature, although any animal exhibiting neurological or behavioral abnormalities should be suspect, especially when they have an uncertain vaccination history. Typically two forms of the virus exist, a dumb or paralytic form and a furious form.

In the more commonly-known furious form the animal will appear irritable and restless. They may exhibit pica (chewing on abnormal objects), photophobia (intolerance to light), and hyperesthesia (increased skin sensitivity). Pats that are normally docile may become aggressive. They may become uncoordinated, progressing to seizures and death.

In the dumb or paralytic form, the pet will exhibit dysphagia (problems eating or swallowing), and will have excessive salivation. Dogs and cats will often drop the lower jaw. The animal will become comatose and will eventually die of respiratory paralysis.

Death occurs within 6 days after the onset of clinical signs of rabies encephalitis. The 10-day rabies quarantine period is used to ensure that the rabies virus was not inoculated following the bite in a dog or cat only. The quarantine period does not ensure that an animal is not harboring the rabies virus, as the incubation period for the development of clinical rabies is variable; it shows that exposure from a certain bite did not result in transmission of the virus. Should a dog or cat bite a person a second time it would be subjected to a second quarantine period. The 10-day rabies quarantine may not be applicable to other species of animal as the period of onset of clinical signs and viral transmission may be unknown in that particular species.

No treatment is recommended for animals being diagnosed with rabies. The pet should be euthanized and brain tissue should be collected and submitted to a diagnostic laboratory for analysis. Definitive diagnosis is obtained by demonstration of the virus by direct florescent antibody testing (FA).

In 2006, 40 states in the U.S. and Puerto Rico reported 6940 cases of rabies in various animal species and 3 cases in humans to the Center for Disease Control in the United States. The number of reported cases of rabies represented an 8.2% increase from 2005. Of those cases reported in animals. The major animal groups were represented by the following percentages: 37.7% in raccoons, 24.4% in bats, 21.5% in skunks, 6.2% in foxes, 4.6% in cats, 1.2% in cattle, and 1.1% in dogs. All animal categories showed an increase since 2005 except cattle.

The number of domestic animals reported rabid in 2006 represented a 10.7% increase in from the total reported in 2005. Pennsylvania reported the largest number of rabid domestic animals with 72 cases.

Of the human cases reported in 2006, two were obtained from exposure to bats. The third case was in a patient who had recently emigrated from the Philippines, and that case was associated with a dog bite received before coming to the United States. All three cases of rabies in humans reported in 2006 resulted in fatalities.

Rabies should be considered on a differential diagnosis in humans when you have an unexplained, acute, rapidly progressive encephalitis, dysphagia (difficulty eating and swallowing), hydrophobia (fear of water), paresis (weakness or incomplete paralysis), or parasthesia (increased sensation such as crawling or burning sensations). No single course of treatment for rabies in humans has been efficacious once clinical signs of rabies have developed.

The number of reported cases of rabies represents only a fraction of the total cases that occur each year. Many rabid animals are never observed and therefore go undetected and untested.

According to the World Organization for Animal Health, or OIE, rabies kills 50,000 to 60,000 people each year around the globe, primarily in Africa and Asia, and it is a completely preventable disease. Unfortunately, 60% to 70% of rabies cases in humans are in children from 5 to 15 years of age. When canine rabies is eliminated in developing countries, the number of human deaths from rabies decreases dramatically.

An effective vaccination program in Africa has also lead to the resurgence of the African wild dog population which was nearly wiped out in 1990 from around the Serengeti National Park area.

Rabies vaccinations are available from various drug manufacturers for a wide variety of species, including small animal species such as dogs, cats, and ferrets to larger animals such as horses and cattle. Most are given on a yearly to three-year basis dependent on the type of vaccine used and on manufacturers’ recommendations.

References:

Blanton, Jessie, MPH and Cathleen A. Hanlon. VMD, PhD and Charles Rupprecht, VMD, PhD. “Rabies Surveillance in the United States During 2006". JAVMA, Vol 231, No 4, August 15, 2007. Pp 540-556.

Ettinger, Stephen. Edward Feldman. Textbook of Veterinary Internal Medicine. 6th Edition. 2000. P. 650 and 829.

Heflin, Marissa. “Companies Step Up for Rabies Day Observance.” Veterinary Practice News. September 2008. Vol. 20. No. 8. Pp. 1-8.

Http://www.cdc.gov/rabies/qanda/general.html

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

Rezendes, Allison. “Rabies Prevention a Worldwide Effort”. JAVMA Vol 231. No. 4/News. August 15, 2007. Pp. 513-514.

Topics: necessary vaccinations, rabies, terminal diseases, vaccines

Symptoms: anxiety, behavior changes, hyperesthesia, nervousness, photophobia, seizures

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