Rabies and the Domestic Ferret

What is Rabies?
Rabies is a viral disease in the rhabdovidae family. The virus is bullet-shaped and relies on a liquid medium for transmission from one infected animal to another. All warm blooded mammals (including humans) can contract rabies. An infected animal must be secreting the virus in its saliva to transmit it through a bite.

After exposure, three outcomes are possible: no response, asymptomatic infection, or disease. Different species may have a different susceptibility to the rabies virus.

When an infected animal secretes the virus through its saliva and bites another receptive animal, it deposits the particles in the wound. Particles not deposited in the wound and exposed to air will die. Those particles deposited in the wound begin a reproduction process. The virus spreads throughout the body by using the fluid transport of the nerves. The virus eventually reaches the brain (which can take days to years depending on the species), causing the infected animal to exhibit outward signs as either the "furious" stage, which causes extreme pain and aggression and provokes the animal to bite, or "dumb" stage, which causes the animal to become lethargic, withdrawn and depressed.

It has been well documented in The Natural History of Rabies that not all humans develop rabies even after severe exposures to rabid animals. Factors that may influence the results of untreated exposures include the species of animal responsible for exposure, rabies virus variants, and genetic and other host differences.

Shedding Period
Shedding period is the time an infected animal can pass the virus to another (most commonly through biting). There must be an exposure and transmission before the virus can be shed. Clinical studies have shown cats can secrete the rabies virus in their saliva from one day before to three days after onset of clinical signs and virus has been recovered from saliva up to eight days after signs of clinical disease appear. Dogs can shed the rabies virus 1-14 days before symptoms occur and dog and cat incubation periods can be longer than a year.

What is Exposure?
There are two types of exposure - bite and non-bite. Exposure requires that there be infective virus and penetration of the virus into wounds or mucous membranes. Non-bite exposures include scratches, licks, inhalation of aerosols and other events that lead to contamination of an open wound or mucous membrane. Non-bite exposures were considered the probable or definite source of infection in only 5 of the 275 cases of human rabies reported in the U.S. between 1946 and 1987, none appeared to have been caused by licks of rabid animals. Experimental evidence supports the epidemiologic finding that licks on mucous membranes are rarely responsible for the disease.

Post Exposure Treatment
Postexposure treatment for humans bitten by a suspected rabid animal consist of initial cleansing of the wound with soap and water followed by vaccinations of 1 dose of HRIG (rabies immune globulins that provide rapid, passive immune protection for a short time - half-life of approximately 21 days) and 5 doses of HDCV (rabies vaccines that induce an active immune response that requires approximately 7-10 days to develop) over a 28-day period. For adults the vaccine should be administered IM (intramuscular) in the deltoid (shoulder) area. For children the anterolateral aspect of the thigh is also acceptable. Once symptoms occur in humans, rabies is normally fatal (2 complete and 1 partial recoveries have been documented). In clinical studies, dogs, pigs and other animals have made a 100% recovery.

Animal Rabies Testing
The procedure for testing an animal for rabies is to kill, decapitate, and examine the brain. Diagnosis is confirmed by specific Fluorescent Antibody staining of brain tissue or by virus isolation in mouse or cell culture systems.

Ferrets and Rabies
Ferrets are in the Subfamily Mustelinae which includes weasels, polecats, martens, fishers, minks, ermines, wolverines and Family Mustelidae which includes their distant relatives badgers, otters, and skunks.

Data shows that Mustelinae are less susceptible to the rabies virus. From 1974-1984 there were 5 cases in weasels, 1 case in mink, and 4 cases in ferrets compared to >25,000 cases in skunks and >6,000 cases in domestics.

The only rabies virus strains that ferrets have been found to be naturally infected with are the skunk and raccoon strains in the US and the fox strain in Europe. A study conducted in 1995 at CDC Headquarters on the skunk strain determined that ferrets do not shed this virus in their saliva, incubation periods ranged from 2 weeks to >3 months, and disease duration is approximately 4 days. A 1996 CDC study determined ferrets do secrete the raccoon strain 2-3 days before showing symptoms with death occurring by day 8. Research conducted in 1982 at the French National Center for the Study of Rabies by Blancou and Artois determined that domestic ferrets are remarkably immune to the European fox derived street rabies strain. The virus was not shed in the ferrets' saliva. The susceptibility of the ferret to the rabies virus isolated from the fox appears to be approximately 50,000 times less than that of the fox species, and more than 300 times less than that of the hare. Furthermore, research determined that ferrets are not susceptible to rabies virus through ingestion. Although it is possible for a ferret to contract rabies, as it is for any warm blooded mammal, the chance is extremely remote. In addition, there is a USDA approved- licensed rigorously tested and proven effective rabies vaccine for use in ferrets (Imrab3). There has never been a transmission of rabies from a ferret to a human. There have been less than 30 cases of rabies in ferrets ever recorded in the United States compared to thousands of cases in dogs, cats, and agricultural animals.

There are an estimated 50 million dogs and 10 million pet ferrets in the United States.

In the United States in 1992 alone, there were 732 cases of rabies in domestic animals which included 182 dogs (1 case in every 274,725 dogs), 290 cats, 257 agricultural animals, 1 llama, and only 2 domestic ferrets (1 case in every 5,000,000 ferrets).

Applying scientific data that is currently available, humans are more likely to contract rabies through organ transplant, inhalation, blood transfusion, ingestion, or from a dog, cat, other companion animal, or livestock bite than from a ferret bite.

 

Rabies Surveillance Reports
Dog, Cat, Ferret, Cases of Rabies in the United States, 1989-1994

 

Year

 

Dogs

 

Cats

 

Ferrets

 

1989

 

160

 

212

 

0

 

1990

 

148

 

176

 

0

 

1991

 

155

 

189

 

0

 

1992

 

182

 

290

 

2

 

1993

 

130

 

291

 

1

 

1994

 

153

 

267

 

1

 

Total

 

928

 

1425

 

4



Bite Control Recommendations
The CDC endorses the Compendium of Animal Rabies Control, 2001, which includes ferrets in the exact same recommendations as dogs and cats -

Part III, Section A.3. "DOMESTIC ANIMALS: Local governments should initiate and maintain effective programs to ensure vaccination of all dogs, cats, and ferrets" and Section B.6., "A healthy dog, cat, or ferret that bites a person should be confined and observed for 10 days; . . ." and "Management of animals other than dogs, cats, and ferrets depends on the species, the circumstances of the bite, the epidemiology of rabies in the area, and the biting animal's history, current health status, and potential for exposure to rabies.

Dr. Charles Rupprecht, Chief, Rabies Section, Centers for Disease Control (CDC) and Dr. Deborah Briggs, Director, Rabies Lab, Kansas State University (KSU) recommend that the Compendium of Animal Rabies Control recommendations be followed.

Veterinarians across the U.S. are advised to follow the current Compendium of Animal Rabies Control which recommends the protocol for post-bite exposure for the domestic ferret be the same as for dogs and cats.

S.R. Jenkins, Chair of the Compendium of Animal Rabies Control recommends that a decision on postexposure management on ferrets, be the same as for dogs and cats.

The CDC endorses the Compendium of Animal Rabies Control, 2001.

The Humane Society of the United States (HSUS) supports mandatory quarantine for ferrets that have been properly vaccinated and not exposed to potentially rabid animals.

Ferret Vaccination Schedule
Rabies - Imrab3
16 weeks of age (or first vet visit if older)
Then once yearly.

Distemper:
6-8 weeks of age, 12 weeks, 16 weeks
Then once yearly.

Distemper:
For older ferret or history unknown.
On first vet visit
Repeat in 4 weeks.

Ferrets have a tendency to develop more allergic reactions to vaccines as opposed to dogs and cats. You should stay at your veterinarians office for a minimum of 30 minutes after vaccination and closely monitor your ferret for several hours.

Vaccine reactions can be deadly! If your ferret has a severe reaction, you need to consider whether you should vaccinate your ferret at all. For minor reactions your ferret can be pre-treated with a pediatric antihistamine (such as Benadryl - 1/10 of a milliliter) 30 minutes before vaccination. Rhone Merieux (Imrab3) and many veterinarians recommend separating the rabies and distemper vaccinations by at least two weeks.