Avoiding the Panic
By Dr. Bronwyn Dawson, DVM
Sometimes I think it’s something in the air. In the last two months I have had several clients ask me about Aleutian disease [AD] in ferrets. The ferret folks on the Internet are talking about it the way they talked about ECE years ago; a local pharmacist calls to ask if I know anything about a vaccine; veterinarians who treat ferrets are dusting off their veterinary school notes to review this old, but little known disease. Let me state right up front that I’m very skeptical about the supposed wide-spread prevalence of this disease and I do not think this is the next ferret plague. However, this is a deadly virus with no vaccine and no treatment: and I think ferret owners certainly need to know as much about it as possible.
AD is caused by a parvovirus which was first reported in ranch-bred mink in the 1950’s. The parvovirus clan is a nasty one; its diverse members cause disease in dogs, cats, swine and wild mammals such as raccoons and coyotes. Like all viruses, parvoviruses can mutate into new strains and, if the mutation is great enough, have the potential to jump species lines. Those of us who owned dogs in the late 1970s remember when canine parvovirus suddenly emerged as a new disease: no vaccine, no treatment; dogs developed severe diarrhea and vomiting and usually died. Canine parvovirus, still one of the most feared puppyhood diseases, was a mutated form of feline panleukopenia, caused by the feline parvovirus.
AD, although originally a disease of mink, now has at least one strain which is specific to ferrets. Ferrets can also be experimentally infected with the mink strains.
Unlike the acute, severe disease caused by the feline and canine parvoviruses, active AD in ferrets usually manifests itself as a chronic wasting disease. Ferrets lose weight, become quite lethargic and weak, sometimes showing neurologic signs (everything from in coordination to seizures). Affected ferrets can become anemic, sometimes with dark tarry stools, and can develop kidney or liver failure. As stated before, antibiotics and all other treatments tried so far are ineffective. Good nursing care with supplemental fluids, feedings, even transfusions, can support a ferret sick with AD, but nothing will cure it.
“Wait a minute!!” You are saying as you read this. “Neurologic signs? Incoordination? Don’t we see that with insulinomas? Anemia? Dark, tarry stools? I thought intestinal ulcers caused that! A big liver and spleen? Couldn’t that be lymphoma?”
A resounding “YES” to all of the above, astute ferret owners! Not to mention that lethargy goes along with just about any illness that effects ferrets! Deciding that AD is actually the cause of illness in a ferret requires some specific diagnostic tests. There are two blood tests for ferrets that look for antibodies to the AD virus; the CEP tests used to screen mink and an Immunofluorescent Antibody test that [is] more sensitive. It is crucial to realize that a ferret can test positive on these tests yet be perfectly healthy. In fact, a positive reactor on these tests may never develop clinical disease. In the 1980s, Dr. Susan Brown, a well-known ferret veterinarian, screened over 500 shelter ferrets; 10% tested positive on the CEP test. Of these, only two animals developed disease signs compatible with AD.
There is another test that can help confirm whether a sick Aleutian-positive animal is sick due to the virus or due to concurrent disease. Serum plasma electrophoresis is a blood test that separates different protein fractions in the blood according to their molecular weights. Sick ferrets with more than 20% of their total proteins represented in the gamma globulins who have tested positive to AD are quite likely to be sick because of the virus. Sick ferrets with a normal electrophorectic pattern are likely to be sick due to some other illness, even if they test positive for AD. Necropsy with tissue samples submitted to a pathologist familiar with ferret diseases is the old standard for confirmation of AD in mink; however, this is not the way we like to diagnose disease in any pet.
Research is ongoing in the areas of vaccine intervention and treatment of AD, but right now, ferret owners are restricted to being familiar with the signs of this virus and distinguishing it from other ferret illnesses. The virus is shed in all bodily secretions; any ill ferrets suspected of AD should obviously be kept away from other ferrets. It is believed that asymptomatic carrier ferrets [usually] do not shed the virus, but even this has not been proven beyond a doubt. What is very difficult for ferret owners is the long incubation period possible with this virus and the problem of what to do with asymptomatic AD positive ferrets. Mink owners cull their animals, but these are livestock to them. I would never recommend euthanasia for a healthy AD positive ferret; however, I would have to caution the owner against bringing that ferret into contact with AD negative ferrets.
I am glad AD is being discussed; it is a poorly understood virus that has been completely unknown to most ferret owners. However, I caution ferret owners not to assume that any sick ferret with signs compatible with AD [automatically] has the disease. Lymphoma, insulinoma, eosinophitic enteritis, and cardiomyopathy are all far more common among American ferrets than Aleutian disease. Remember, in our country, if we hear hoof beats it is much more likely to be a herd or horses than a herd of zebras. A sick ferret is much more likely to have one of the more common metabolic diseases than the relatively rare parvovirus.
Dr. Bronwyn Dawson, DVM is a veterinarian at the Animal House Veterinary Hospital in Monrovia, CA.