RABIES and HORSES

Did you know that this is a disease that is very common in mammals, but that many people do not realize horses can get it, too ?  You vaccinate your dogs and cats for it – but do you vaccinate your horses against rabies?  Only your Vet can vaccinate for this disease !  Read on to learn more about Rabies.

RABIES – GENERAL INFORMATION

The rabies virus (genus Lyssavirus--the word lyss is Greek for "madness" or "rage") is a member of the rhabdovirus family. The virus can cause disease in any mammal, but horses and humans are two species with above-average susceptibility to the disease.  Worldwide, over 48,000 HUMANS die of rabies infection each year.  Once the neurological signs of rabies are detected, the disease is 100% fatal. (One person in 2004 was saved by inducing a coma and providing treatment).  In animals, there is no known cure.

Bites and licks are the big risk because the virus is found in infected animals' salivary glands and is transmitted through their saliva--usually through a bite or a scratch, but potentially also through contact with the victim's mucous membranes or an existing wound.  You can't get rabies through unbroken-skin contact with a rabid animal. There must be saliva-to-wound contact (most likely a bite) or saliva-to-mucous membrane contact.  Blood and urine do not contain the rabies virus.

Rabies is a disease of the central nervous system. When a horse or other mammal is bitten by a rabid animal, the virus enters the victim's body through the bite wound. It proceeds to replicate in the local area of the bite, thereby invading the local nerves. There might be some localized redness or itchiness around the bite wound but in many cases, no symptoms exist.

During the incubation period, the rabies virus migrates (replicating by the billions as it goes) to the central nervous system and eventually to the horse's brain, by working its way up the local nerve pathway. The length of the incubation period varies widely, depending on the location of the bite. It could take as long as six months for the virus to reach the brain — with no clinical signs of illness. But if the bite were close to his brain--say, on his nose--the incubation period could be as short as two weeks.

As the virus multiplies, it consumes the brain matter, and the resulting symptoms vary depending on what parts of the brain the virus invades. This is the swift and final stage of the disease; death is at most three to five days away.

Acute rabies causes encephalitis or meningitis whose symptoms can include a high fever, temporary or permanent blindness, behavior change, depression, excessive salivation, difficulty swallowing (caused by paralysis of the facial muscles and the salivary glands, where the virus is concentrated), heart arrhythmia, abnormal aggressive or excitable behavior, colic, depression, and seizures.  The horse might exhibit photophobia or hydrophobia from the maddening combination of excessive thirst and an inability to drink caused by paralyzed face and throat muscles.

A rabid horse which displays aggressive behavior is said to be afflicted with the "furious" form of the disease. One which shows extreme depression and lethargy is said to suffer from the "dumb" or "stuporous" form. In horses, the latter form is more common, or may be followed by the “furious” form.  If the horse is not humanely destroyed soon after it begins showing symptoms, he'll eventually lapse into a coma as the disease ravages his brain, and death soon will follow.

Several pharmaceutical manufacturers offer rabies vaccines, and four are licensed for use in horses.  Foals as young as three months of age can (and should) be vaccinated against rabies, with regular follow-up annual boosters. Rabies vaccine is effective only when administered prior to exposure, and in most states must be administered under supervision of a licensed veterinarian to be legally recognized.

Horses with neurological injuries suspected of having rabies (self-mutilation, etc.: see picture below) must be carefully handled to prevent exposure of attending personnel (veterinarian, staff, owner, etc.).  Horses displaying signs compatible with rabies infection (fever, lack of appetite, lameness, colic, facial nerve paralysis, weakness, restlessness, progressing to lack of coordination, self-mutilation, aggressiveness, vocalization, drooling and paralysis) should be examined by a veterinarian immediately. 

When the vet discovers a possible rabies case, they must contact the State Veterinarian’s office, County Animal Control and the County Health Department immediately for notification of possible rabies.

Suspect Rabies Case - General Handling Precautions

The animal should be isolated by direction into a safe enclosure such as a round pen or stall that is difficult to kick out of.  

Avoid contact with the horse directly – if the horse must be touched for the euthanasia procedure, all personnel should be double gloved and take precautions to prevent saliva and mucosal surface / secretion contact.  It is preferable that personnel have pre-exposure rabies vaccination titers.

Clothing for personnel should be full coveralls with long sleeves, boots and double gloves. Only saliva contains the virus - clothing that touches these fluids of the animal should be sanitized with bleach and all facilities cleaned thoroughly.  Blood or urine do not contain the rabies virus.

Photographs and/or video documentation of the horse’s behavior prior to euthanasia should be taken and submitted to the state veterinarian for assistance with diagnosis and history.

Quarantine of Other Animals on Property

Other mammals (dogs, cats, horses, etc) with or without proof of rabies vaccination should be isolated on the property and quarantined in accordance with the State Rabies Control Officer (State Health Department) in consultation with the State Veterinarian's Office.

Euthanasia

Have the vet draw a blood sample prior to euthanasia to be retained pending rabies diagnosis and to facilitate differential diagnosis of other neurological diseases. Field euthanasia with a firearm/captive bolt is not indicated, because it will destroy the brain and make laboratory diagnosis difficult.

Submitting Sample for Diagnosis

The entire animal should be transported ASAP to the State Veterinary Diagnostic Lab for identification and diagnosis of the case. In the event that rabies is diagnosed by examination of brain tissue, the local health department will investigate and consult with individuals who may have been exposed to the rabid animal and help determine if human post-exposure rabies treatment is necessary.

Diagnosing Rabies In Horses

Two positive horses seen by one veterinarian in the Upstate of SC in the last 5 years were alert and
responsive to their environment. 

Behavioral characteristics were the most common sign exhibited – aggression toward self and other animals and people, progressing to self-mutilation and excess salivation.  Both cases were initially diagnosed as colic – due to excessive rolling, pawing, sweating and looking at sides.

Rabies cannot be diagnosed through blood, saliva, or urine tests or by any other means in a living animal. The only way to obtain a definitive diagnosis is by examining the victim's brain tissue after death.  A special stain (direct fluorescent antibody test or dFa) can identify Negri bodies (clusters of the rabies virus) in affected brain matter. Blood and urine do not contain the rabies virus.

Contact with brain, lymph nodes and nervous tissue, which may contain significant virus levels, should be avoided.  Virus may be shed in saliva a few days before clinical symptoms occur (exact time unknown for horses).

For more information about rabies in animals and humans, contact the

Centers for Disease Control and Prevention,
Rabies Section,
MS G-33,
1600 Clifton Rd. NE,
Atlanta, GA 30333;
or
visit the CDC on the World Wide Web.

The Web site contains a number of free, downloadable articles as well as statistics and links to related sites.

Rabid Horse: Self-Mutilation