Rabies in the Dog and the Cat

Rabies in the Dog and the Cat

Did you know that rabies is responsible for the death of one person world-wide every 10 minutes?  Children are affected with rabies more than any 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 vaccination 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 parts 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 following exposure to bats.  Most domestic animals are infected from 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 prevents possible transmission to humans.

The incubation period for the development of clinical rabies is variable and may be days or months and depends on the amount of virus inoculated by a bite and the extent of the nerve innervation (number of nerves) to the original site of injury.  The virus travels up the peripheral nerves to the brain and spinal cord were clinical signs of disease become apparent and the virus becomes capable of being further transmission 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 behavior changes.  Paresthesia (increased skin sensitivity) at the site of the original bite wound may be present.

Rabies is typically characterized by a change in temperament although any animal exhibiting neurologic 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).  Pets that are normally docile may become aggressive.  They may become incoordinated progressing to seizures and death.

In the dumb or paralytic form, the pet will exhibit dysphagia (problems eating or swallowing), have excessive salivation.  Dogs and cats will often drop the lower jaw.  The animal will become comatose and eventually die from 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 insure rabies virus was not inoculated following a bite in a dog or cat only.  The quarantine period does not insure that an animal could not be harboring the rabies virus as the incubation period for the development of clinical rabies is variable, but 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 period may not be applicable to other species of animals as the period from the 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, 49 states in the U.S. and Puerto Rico reported 6, 940 cases of rabies in various animal species and 3 cases in humans to the Centers 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, 92% of the cases were in wildlife while 8% of the cases were in domestic animals.   The major animal groups were represented by the following percentages:  37.7% in raccoons, 24.4% bats, 21.5% in skunks, 6.2% foxes, 4.6% cats, 1.2% cattle, 1.1% dogs.  All animal categories showed increases over 2005 except cattle.

The number of domestic animals reported rabid in 2006 represented a 10.7% increase 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 paresthesia (increased sensation such as a crawling or burning sensations).  No single course of treatment for rabies in humans has been efficacious after clinical signs of rabies develop.

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.

Rabies 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 you eliminate canine rabies in developing countries, the number of human deaths from rabies goes down dramatically.

An effective vaccination program in Africa has also led 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 manufactures 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 manufacturer’s 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.  6^th Edition.  2000. P. 650 and 829

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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.  9^th Edition. 2005.  Pp. 1067-1071.

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

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