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Which Vaccinations Should My Ferret Receive? How Often?  The Risks Of Over-vaccination

 

Ron Hines DVM PhD

All About Distemper In Ferrets

Ferrets need to be immunized against two important diseases: canine distemper and rabies.

1) Distemper

The distemper that affects ferrets is a disease of dogs and their wild relatives, foxes and wolves. Other wild carnivores can catch it too, but they are considered dead end, accidental victims of the disease. Distemper is a general term. To be accurate, the virus involved is the virus of canine distemper. The "distemper" of cats, panleukopenia, is not a threat to ferrets.

When a ferret catches canine distemper it is almost always fatal. Luckily, veterinarians have good vaccines to prevent that.

Distemper is spread when your ferret is exposed to an infected animal’s sneeze, cough or body fluids. The disease generally has an incubation period of about 6-9 days. There is no successful treatment. Early signs can be mistaken for human influenza to which ferrets are also susceptible. (ref)

Many authorities suggest that ferrets receive their first distemper vaccination at 6-8 weeks and a booster vaccination at 10-12 weeks with a third vaccination at 14-16 weeks of age. Many veterinarians then suggest that ferrets be given a yearly distemper booster vaccination throughout their lives. The companies that produce the vaccines agree. I do not believe there is any need for that. First of all, the risk of bad reactions to vaccines increase with the number of shots the pet receives over the years. These reactions can be fatal. I believe that that risk is much greater than the risks of a typically cared for indoor ferret developing distemper.

If your ferret already has the distemper virus in its system when you purchase or adopt it - the vaccine will not be helpful. If it does, the ferret was a rescue or bred by a disreputable source. If it doesn't - just keep the pet isolated until it is old enough to benefit most from its early vaccinations. The critical ones are at 10-12 weeks and 14-16 weeks and, when using Purevax®, a booster at the end of your ferret's first year. Older ferrets with unknown veterinary history just need two distemper vaccinations spaced 2-3 weeks apart.

 

What Are The Symptoms Of Distemper In Ferrets ?

Ferrets that catch the distemper virus generally become lethargic, depressed and have little or no interest in food – somewhat like the first days of your flu. But as the disease progresses, nasal and eye discharges/crusts, skin rash and fever commonly occur. It is also common for a variety of nervous system defects (from twitching, seizures to paralysis) to occur later in the disease. There is a second article of mine that deals specifically with distemper in ferrets. You can read it here.

When Should My Ferret Receive Distemper Vaccinations ?

Most ferrets sold in the United States received a distemper vaccination when they were 6-8 weeks old. Most veterinarians in the US give the ferret a booster distemper vaccination at 12 and 16 weeks of age (some 14wk+). Your veterinarian might suggest that an older ferret with an unknown vaccination history receive a distemper booster shot - perhaps two.

The two-shot series your veterinarian administers is similar to the two-shot series you child receives against measles. The measles virus is a very close relative of the dog distemper virus. (ref)The vaccination given at 6-8 weeks is ignored by me because several factors could conceivably prevent it from working. First, at that tender age, the ferrets immune system may not have reached its full potential to protect. And second, the mother’s immunity to distemper, passed on through its milk, might destroy live vaccine virus before they can have any effect. If this second event occurs in ferrets using current vaccines is unknown. (ref)

How Often Should My Ferret Receive A Booster Distemper Vaccination ?

Vaccine manufacturers suggest that ferrets receive a distemper booster vaccination every year. However, they have never run tests that confirm that yearly revaccination is actually required. In the case of canarypox-vectored vaccines like Purevax® Ferret, similar distemper vaccines given to dogs routinely give immunity that lasts at least 3 years (after a booster when the pet is 1 year old). (ref)

Two veterinarians at the University of Pittsburgh conducted similar studies in ferrets. They found that 4 years after their 1 year vaccination, 35 out of 38 ferrets still had protective antibody titers (>1:50) against distemper. (ref1, ref2)

That does not necessarily mean that your immunized ferret with a titer of less than 1:50 can catch distemper. Titer tests neglect to account for the persistence of cell-mediated immunity.  After a vaccination or natural encounter with a virus, the immune system’s memory cells are primed to rapidly produce protective antibodies against the same virus if it is ever encountered again.

If your ferret received your veterinarian's 2-shot juvenile distemper series, a booster at one year of age and every three or four years thereafter, I believe it will remain well protected against the distemper virus should it encounter it. Considering the average lifespan of ferrets, that 3-4 year distemper booster is probably the only one it will need. Don't let the flu shots you get every year mislead you. Influenza mutates from year to year, requiring a different, custom engineered, vaccine every year. Distemper does not do that. That is why the same Purevax® vaccine formula has successfully protected ferrets against distemper for almost 25 years (ref)

I suggest you remain with your ferret at your animal hospital of choice for an additional 30 minutes after the shot is given so that you and your veterinarian's nurses can observe your pet to be sure that no vaccination reaction occurs.

If your ferret shows even the slightest post-vaccination reaction to any one of these distemper vaccinations, I suggest that the pet never again receive a distemper vaccination. Vaccine reactions tend to become more violent with every succeeding vaccination. There are many other physical ways to isolate your ferret from the threat of distemper.

There have been times when Purevax® Ferret distemper vaccine was unavailable from Merial Pharmaceuticals. (ref) During those periods, veterinarians in the USA shifted to using Nobivac® Puppy DPv vaccine made by Merck Animal Health. It is not a government-approved product for use in ferrets; but it has been used extensively in Europe and the UK to immunize ferrets against canine distemper. Besides a weakened distemper virus, Nobivac DPv also contains a weakened (attenuated) dog parvovirus. To the best of my knowledge, that has never presented a problem.

Nobivac® Puppy DPv use is still an option; but Boehringer Ingelheim, the current manufacturers of Purevax® Ferret, assured me October 2019 that future supplies of the Purevax® vaccine would be uninterrupted. I certainly hope so because it is the ferret distemper vaccine I am most comfortable using.

Never give vaccines of any kind to pregnant, ill, stressed or debilitated ferrets.

Vaccines should always be stored as indicated on their labels and given within 30 minutes of being reconstituted.  Not following those package instructions, exposing vaccines and syringes to chemical disinfectants, prolonged exposure to bright sunlight, heat or exposure to wild distemper virus before the shot has had time to work are the most common causes of vaccine failure. I cannot tell you how quickly sunshine inactivates the Purevax® pox/distemper or the Novibac® DPv attenuated virus distemper vaccines. Once inactivated, these vaccine are unlikely to work because the viruses in them must multiply in the ferret's body to generate sufficient antigen mass to trigger its immune system. But a close relative, the measles virus, is dead in less than two hours in bright sunshine.

What Are The Signs and Risks of Vaccine Reactions

When you give or are given a vaccine, you wake up a dozing immune system – a highly complex mix of mediating chemicals and cells with a variety of defensive functions. Vaccines are lifesavers. But giving them to an already-immunized individual is risky. Allergic reactions to vaccines are more common in ferrets than in dogs and cats. We do not know why. That is one of the risks of unnecessary vaccinations. Risks less discussed and less understood are later health issues related to overstimulation of the immune system. (ref1, ref2)

Many veterinarians (and physicians) believe that it is unlikely that the virus particles in vaccines are the actual cause of anaphylactic vaccine reactions. To produce vaccines, the weakened virus must be grown in tissue culture with various additives. They are often sold containing stabilizers, syringabilty agents and antibiotics as well. Since that information is proprietary, we rarely know what ingredients other than virus are in the vaccine. Suspicions fall on those additional ingredients as the probable cause of vaccine reactions when they occur. (ref)

Reactions that occur in the veterinarian’s office or shortly thereafter are called acute reactions or anaphylactic reactions. They range from facial puffiness, hives, itching, trembling, salivation, vomiting and diarrhea to more serious bluish gums (cyanosis), panting, weakness, life-threatening shock and collapse.

These reactions usually begin within a few minutes of the shot. The ferrets are usually still on my exam table when I notice that something is wrong. But they can take longer to occur - some say up to 8 hours before being noticed - although I have not observed that. (ref1, ref2

Tenderness at the site of vaccination and less activity after returning home are common. They are normal events.

These reactions almost never occur during the administration of the initial series of vaccinations to your recently purchased ferret. They are much more likely to occur when later booster shots are given and they tend to increase in severity with every succeeding vaccination. (ref) One publication suggested that the frequency of reactions to distemper shots in ferrets is about 5.9%. But they noted that older ferrets, those likely to have had many distemper shots, had considerably more vaccine reactions than younger ones. So I believe that if they had presented the percentages separately, the incidence of reactions in older ferrets would be higher than 5.9%. How much higher I cannot tell you.
(ref)

I never give two different vaccinations to a ferret at the same time. I like to wait about 2 weeks after the last of the ferrets 2-shot initial or later single booster distemper vaccination before I give its rabies shot. I know that every additional visit to big chain veterinary hospitals is accompanied by a sales pitch. But not giving multiple vaccinations during a single visit is important enough to suffer through them multiple times. Be patient, be nice, smile and say you will consider the products or procedures when you get home.

Don’t rush in for your appointments and then rush out. After the vaccination, wait 25-30 minutes in the waiting room with your ferret safely confined to a carrier. Observe its behavior. Inform the veterinary nurses if you become concerned that your pet's behavior is abnormal or unusual.

Some veterinarians routinely have their clients administer Benadryl just before they leave home for a vaccination appointment.  Others administer it upon arrival. That might account for some of the post-vaccination drowsiness you might observe. Diphenhydramine, the active ingredient in Benadryl, can also cause hyperexcitability in people. If that also occurs in ferrets is unknown.

I would also think twice before giving vaccines to older ferrets that are already battling serious health issues.

How Will My Veterinarian Deal With A Vaccine Reaction :

Vaccine reactions (anaphylactic reactions) come in all degrees of seriousness. All acute vaccine reactions are thought to begin with a sudden release of histamines, the cause of hives and itching. So Most veterinarians administer an injectable antihistamine to block these negative effects of histamine. That and a period of observation at your animal hospital is often all it takes to get a ferret through a mild to moderate vaccine reaction. To me, a reaction like that is a flashing message not to give that vaccine again. Be sure it gets noted on your ferret's records.

More serious vaccine reactions include difficult breathing in various degrees and/or circulatory collapse leading to low blood pressure and low blood oxygen. Those ferrets need immediate supplemental oxygen until the antihistamine injection takes effect. The more seriously affected ferrets also need supplemental intravenous fluids and perhaps epinephrine. These post-vaccination circulatory issues are often accompanied by a drop in body temperature (hypothermia). When that is the case, your vet will provide a source of warmth.
 
Metoclopramide injections (ref) usually block the nausea that sometimes accompanies vaccine reactions in ferrets.

Some veterinarians include corticosteroid injections in their vaccination reaction treatment plans. Corticosteroids have been phased out of the suggested treatment for anaphylactic reactions in human medicine. But perhaps these steroids are still useful in preventing other longer-term issues a vaccine reaction might generate. We do not know.

I don’t include lumps and bumps at the site of the vaccination as vaccine reactions. Those problems probably occur when a tiny plug core of skin, hair, bacteria or foreign substance enters the hollow of the needle used and is deposited under the skin. These lumps usually clear up on their own or with the help of some oral antibiotics. If fluid or pus accumulates, they need to be lanced and drained. But they may also be implicated in the development of fibromas tumors that occasionally occur where an injection was given. (ref)  We do not know. Injection site tumors are considerably more common in cats. (ref) In cats, it is vaccine ingredients that generate them. As in cats, it is wise to give the distemper shot always on one side of the ferret’s body and their rabies vaccination on the other side (at a different visit). Note which side and which vaccine and lot number in your ferret’s records. That way, should a lump occur, one knows which vaccine was responsible.

2) Rabies Vaccination

It is unlikely that your pet ferrets will contract rabies. But it is a disease that terrifies and demands our attention.  Besides, in most of the developed world it is the law that pet ferrets be immunized against rabies. Catching rabies requires being bitten or exposed to the saliva of a rabid animal – often a skunk, a bat, a raccoon or a dog. As far as I know, the few cases that have occurred in ferrets in North America were of strains of rabies virus found in skunks and raccoons. In Europe, it has been the fox strain of rabies virus that caused sporadic cases in unvaccinated ferrets and wild polecats. The period between the time a ferret is bitten and the time rabies symptoms begin is highly variable in ferrets. It has been reported as being as short as two weeks and greater than 3 months. Once symptoms do begin they rarely survive more than a week. (ref1, ref2)

Should I Have My Ferret Vaccinated Against Rabies And How Often ?

Yes, your ferret should receive a rabies vaccination as frequently as your state requires. By law, most states and federal public health authorities require a yearly rabies vaccination for ferrets (even though studies have shown that many of the rabies vaccines give pets longer protection).

The most commonly used rabies vaccine in ferrets in 2019 is Imrab3®, produced by Merial/Boehringer Ingelheim. It gives a 3 year immunity to dogs and cats, but the Company suggests that it be given yearly to ferrets, cows and horses. I assume that some of their early studies found that those three species had trouble maintaining the protective antibody levels that the CDC demanded.  As I may have mentioned before, we really do not know what titer protects against rabies. I also care for injured and immature wild freetail bats - a known reservoir of rabies. So after having an initial 3-shot series of the old duck human rabies vaccine, I have had many yearly preventative rabies booster shots that contain the same rabies virus strain found in IMRAB®3. I have never in my life been able to attain a 1:50 titer either.

Most veterinarians administer the ferret’s rabies shot at about 16 weeks of age and yearly thereafter. There are liability issues if those shots are not at least offered.

Do Rabies Vaccinations Sometimes Produce Bad Reactions ?

Yes. For long periods of time, veterinarians tended to give both distemper and rabies vaccinations during the same office call. So when a vaccine reaction occurred, they could not tell which of the two shots caused the problem. However, in hindsight, it appears that rabies vaccinations caused more frequent vaccine reactions than distemper vaccinations when the distemper vaccine used was Merial/Boehringer Ingelheim’s Purevax® Ferret. Before Purevax®  was available, I had to rely on Fervac-D® distemper vaccine to immunize ferrets against distemper. At that time, Fervac caused more vaccine reactions in my client’s ferrets that Imrab3®. So things appear to have reversed – probably because Purevax®, a subunit canarypox-vectored vaccine, contains considerably less reaction-causing impurities than Fervac-D® did.

A second problem is that given yearly, your ferret has more opportunities to develop a rabies vaccine allergy. We know that the number of vaccine reactions following rabies vaccination goes up as the number of rabies shots your ferret has received in its lifetime goes up. (ref) That leaves veterinarians and ferret owners in a quandary: give annual rabies vaccine boosters and comply with the laws of your state and the vaccine manufacturers or go your own way and risk having your pet put down by your health department should it ever nip a stranger or family member. How those situations are handled varies from country to country, state to state and municipality to municipality. Inquire.

The signs of a vaccine reaction following a rabies vaccination are the same as they would be following a reaction to a distemper vaccination: hives, itching, respiratory distress, vomiting, diarrhea, internal bleeding and collapse  - generally occurring within the first thirty minutes following the vaccination.

Determining The Need For Booster Vaccinations By Serum Titer :

It is possible for your veterinarian to withdraw a blood sample from your ferret and have the serum tested for its antibody content (titer) against distemper and rabies.

If the antibodies are there in sufficient quantity, scientifically, the ferret does not need a booster vaccination against that disease. Veterinary laboratories like Antech offer this service.

Removing blood from a ferret in the quantities necessary to run the test today without sedation is not an easy task. I think that this is a procedure that will be more widely used when the amount of blood required becomes smaller and hopefully as authorities become more comfortable accepting the procedure as an alternative to rabies vaccination. (ref) When it comes to rabies titer today, I do not believe that finding evidence of protective rabies titer in your ferret in lieu of yearly vaccination or subsequent to a bite frees you from obeying your local laws. Most public health departments are resistant to change and function on the basis of "better safe than sorry". Few are fond of ferrets.