Panleukopenia Of Cats - What You Should Know About It

Feline Distemper
(aka FPLV, FPV, FP, Feline Parvovirus)

Ron Hines DVM PhD

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Feline Distemper (panleukopenia) is a disease US cat owners often hear or read about, but rarely see. That was not always the case. Not that many years ago, this disease was the leading cause of death of immature and young adult cats. That is no longer the case because since about 1950, veterinarians have a very effective vaccine to protect cats. But the virus is still around. It is still a significant problem in animal shelters, feral cat colonies and in areas of the World where cats are not routinely vaccinated against it. The virus is highly adaptable and constantly rearranging itself into new forms with novel disease potential. (You can read about that here.)

Dog distemper and feline distemper/panleukopena are entirely different virus - but dog Parvo and cat distemper/panleukopenia virus are very closely related. To avoid confusion, I will call the disease in cats, panleukopenia, a term that describes the virus’s effect on the body. Panleukopenia is a medical term describing a deficiency of all the types of white blood cells that are normally found in your cat’s circulation. The panleukopenia virus is a parvovirus – a relative of the parvovirus “Parvo” of dogs. Both these virus attack cells that divide rapidly – like the cells of the pet’s bone marrow that are responsible for producing white blood cells and the cells that line the intestines. White blood cells protect your pet against infection. With a deficiency of those defensive blood cells and a compromised, ulcerated intestinal lining, diarrhea, intestinal bleeding, dehydration and susceptibility to bacterial infections are the end results. The current panleukopenia virus is not a threat to humans and probably not a significant threat to dogs either. (ref) It will infect raccoons and all of the domestic cat’s relatives found in zoos and in the wild. (please read last paragraph of this article)

The panleukopenia virus is a tough, resistant virus. Once a cat has succumbed to it in a particular location, the virus often lurks there for long periods awaiting another unvaccinated, susceptible cat.

Most older, unvaccinated, outdoor or group-housed cats are survivors of panleukopenia and are no longer able to contract it. It is the young, unvaccinated cats and kittens that are at risk. Because most kittens arrive in the spring and summer and mature through the early fall, that is the time most panleukopenia cases occur.

What About The Future ?

Although vaccines have made panleukopenia-deaths uncommon in household cats in the United States and Europe in 2011, viruses are always ready to take advantage of new opportunities when they occur. There is some evidence that this might now be occurring as cats become infected with cat, dog, mink and perhaps other species parvovirus all at the same time. Here are some key articles in pdf that discuss that : (ref 1, ref 2, ref 3)

How Is Panleukopenia Transmitted Between Cats ?
How Would My Cat Catch It ?

Feline Panleukopenia is a very contagious virus. That is because the loose, watery stools (and, to a lesser extent, vomit) of infected sick cats fill the sick cat’s immediate environment with enormous numbers of infective virus that can persist in that environment for a very long time. Panleukopenia does not move through the air or transfer through insect bites. It can be carried from place to place by humans on contaminated objects, hands and shoes – but that is not how it routinely spreads. Cats are dedicated groomers, so any virus that come in contact with the cat’s fur are soon ingested as the cat preens itself. Cats are, by nature, very clean animals that guard their own space. But in animal shelter environments, that natural cleanliness and spacing can not occur.

Most kittens under 11 weeks of age have some residual protection against the virus due to the temporary immunity passed to them through their mother’s milk. But after that time and until about 16 weeks of age when their immune system is fully functional, up to three-forth of them will die if exposed to the virus. As the kittens mature more, the fatality rate drops due to their increased body reserves to weather the effects of infection as well as increased body mass to weather the dehydration that accompanies diarrhea. Exposure to massive amounts of panleukopenia may be able to over-ride the immunity of kittens that still have partial immunity derived from their mother and cause them to break with the disease – we really do not know.

The mortality rate in stressed and malnourished (immunocompromised) cats is higher than in those better prepared to weather the infection. Concurrent infection with other diseases can also make panleukopenia infection more severe. A living area that once housed an infected cat can look perfectly clean but still contain the virus. Only a thorough scrubbing of pre-cleaned areas with bleach or a phenolic disinfectant is likely to cleans surfaces satisfactorily.

Even after these precautions have been taken, unvaccinated cats should have a panleukopenia vaccination or booster vaccination a week or two before entering the premises.

The number of panleukopenia cases peak in late summer (July, August, September in the USA). That is because the majority of susceptible kittens are born a month or two before that. (ref)

Do Carrier Cats Exist ?

Probably not. Generally, viruses that provide lifetime immunity, such as parvovirus, do not persist for long periods in the body. So we do not believe that carrier cats play a major part in perpetuating this disease. It is much more likely that cats with relatively short, active infections but without apparent symptoms (asymptomatic) move the virus about as well as cats that have recently recovered from infection. It is almost impossible to rule the possibility of occasional panleukopenia virus carriers out. Carrier cats were reported in 1971 (ref) and are known to occur within the other members of the parvovirus family (ref 1, ref 2)

It can take a number of weeks (about 6) for a recovering cat to cease shedding the virus. These are not true carrier cats. There are veterinarians who believe that a small number of panleukopenia virus, or bits and pieces of its genetic instructions, might persist, hidden deeply within the cells of recovered cats. But as far as veterinarians know, cats once recovered from panleukopenia, are not susceptible to the disease a second time. Persistence is known to occur with other parvovirus infections in other species. (ref)

Some internet articles claim that long-term panleukopenia carrier cats do exist. Those ideas are probably based on a 1971 study of 6 kittens. In that study, the longest time the cats remained infectious was 43 days. You can read the article here.

About The Virus That Causes Panleukopenia

Panleukopenia virus evolved with cats as they evolved – it is not something new. All species of wild cats, and even raccoons, are also susceptible to it. Sometime, in the late 1970s, it jumped species attacking dogs, causing the very similar disease called canine parvovirus or just “Parvo”. (ref)

When a pet ingests the panleukopenia virus, it first multiplies within the lymphoid tissue that guards the cat’s throat (and thymus and spleen). Over the next few days, it spreads throughout the cat’s body entering and destroying cells that are dividing rapidly. Those rapidly dividing cells are found lining your cat’s intestines and within its bone marrow.

In that respect, it is similar to radiation sickness or poisoning and the signs one sees are very similar. That is why owners often assume the cat was poisoned.

Panleukopenia infections range from mild and insignificant to fatal depending on the general health and age of the cat, the number of virus it ingested and any degree of immunity it might already have. In serious infections, destruction (ulceration) of the cat’s digestive tract lining causes lack of appetite, vomiting, serious diarrhea, dehydration and shock. At the same time, destruction of the cats blood-forming bone marrow makes the cat susceptible to bacterial infections and internal bleeding. (The ulcerated intestines leak their bacteria and bacterial toxins into the cat’s system and the cat's bone-marrow-derived defense cells are no longer present to fight them) This is called septicemia or endotoxemia. It usually takes 3-5 days before the cat appears severely ill.

The combination of fluid and salt (electrolyte) loss through diarrhea and a lack of desire to drink cause rapid, and often fatal, dehydration and shock.

What Are The Symptoms Of Panleukopenia ?

We tend to think of a severe disease with dramatic symptoms when we think of panleukopenia. It is easy to forget that many cats suffer only mild to moderate signs, go on to recover completely without treatment, and remain immune to the disease for the rest of their lives. The dose of virus that the cat is exposed to, the cat’s general health, and , most importantly, its age and immune status determine the severity of panleukopenia infections.

The younger a cat is when it develops panleukopenia, the more severe the disease is likely to be. Kittens that lack maternal protection usually develop the disease 2-7 days after exposure. This is panleukopenia in its peracute form – severe and rapidly fatal. These kittens are extremely uncomfortable. Their tummies are bloated, gassy and painful. Their body temperature rapidly drops and they drift off into shock, and collapse, often dying before diarrhea or dehydration develops. Those that survive 3 days or longer often have a short spike of high fever, vomiting and diarrhea before fading. Some rest motionless in a praying position with their head extended between their paws.

The diarrhea of panleukopenia can be explosive and its smell is usually very odorous and quite objectionable. Diarrhea often becomes bloody and combined with their general reluctance to drink, these cats rapidly become dehydrated. Dehydration causes their third eyelid to extend over the nasal side of their eyes (the medial canthus) and their skin to have a clay-like consistency when pinched. Elevated fevers (up to 104F) rapidly are replaced by sub-normal temperatures (less than 100.F). Body temperature below 100F is a particularly disturbing and grave sign.

Older cats that develop the disease sometimes sit in front of their water bowls or food dishes drooling – as if interested but reluctant to eat. These cats are often severely depressed and apathetic to their environment. Their hair coat is usually matted and they show no interest in grooming.

In my experience, the course of a panleukopenia infection is usually a steady ski slope downward. If the cat’s condition plateaus (levels out) for 12 hours, the cat will almost certainly recover. It is not a disease that has ups and downs.

So the symptoms of panleukopenia can be very mild or very serious. When they are serious or fatal, it is because the virus has destroyed the cells that line your cats intestine and the defensive white cells of its blood. No other sudden, infectous disease causes the extensive white blood cell loss that panleukopenia does.

The Special Case Of Kittens Exposed To Panleukopenia Virus In The Womb Or Shortly After Birth = Cerebellar Hypoplasia

You already know that the panleukopenia virus prefers to attack cells that are rapidly dividing. In very young kittens, there are other populations of rapidly dividing cells outside of its intestines and bone marrow.

In early pregnancy, all the fetal tissues are dividing and growing rapid. So a pregnant momma cat, exposed to the virus in early pregnancy often loose those infected fetuses. Sometimes they are just reabsorbed, and no one notices. At other time, the fetuses are aborted or still-born. It is common for these mother cats to show no signs of illness themselves.

Pregnancy in cats lasts 62-67 days. When mother cats become infected with panleukopenia in the last two or three weeks of their pregnancy, or when kittens are infected in the first few weeks after their birth, their brains are still growing rapidly. We do not know why the other rapidly growing portions of their bodies are protected, but the virus often does it damage in these kittens brains – particularly in a portion of their brain called the cerebellum, that controls coordination.

Newborn kittens are all uncoordinated. But it soon becomes noticeable that these particular kittens are much too wobbly (ataxic). Portions of their cerebellum have not developed properly. A particularly telling sign is a jerky (tremors) , exaggerated (hypermetric) , mechanical motion when the kitten is focused to some action or on moving from one location to another (intention tremors). Occasionally, these kittens are blind. Some twitch and sway. Many elderly humans show similar tremors when attempting to write or hold a spoon (action tremors).

These kittens have excellent appetites and grow normally. They may adjust, somewhat, to their problem, but they do not get physically better (or worse) with time. If they can master simple tasks, like using the litter box and successful eating; they can live happy, long lives.

Vaccine-induced Cerebellar Hypoplasia In Kittens

The threat of cerebellar hypoplasia and of abortion is why veterinarians do not vaccinate pregnant cats with the live-virus vaccines we routinely use on non-pregnant animals. Kittens under 4 weeks of age, or mother cats with kittens under 4 weeks of age, should not receive these vaccines either. If young or pregnant cats must be vaccinated (as during an outbreak in a shelter or cattery) they need to be vaccinated with a vaccine that contains only killed (attenuated) panleukopenia virus.
If you are faced with this decision in an individual pet, an alternative to revaccination is to test the cat's blood levels of protective antibodies and only vaccinate if they are too low.

If My Veterinarian Suspects Panleukopenia, What Tests Will Be Run ?

When a young cat is brought to a veterinarian showing sudden signs of diarrhea, vomiting, dehydration and, perhaps, fever, no doubt panleukopenia will cross your vets mind. This suspicion will grow if the cat has no vaccinations against the disease and it will be even stronger if the cat is determined to have a low white blood cell count.

Things like poisons, feline leukemia, feline aids and salmonella can produce similar signs, but it is rare for them to be accompanied by a dramatically low white blood cell count. By the end of the first week, it can be hard to find any white blood cells (leukocytes) in blood films examined under the microscope. The term “pan” means “all” and “Leukopenia” means lack of white cells – hence the name of the disease. The worse the leukopenia, the graver the prognosis. It is a particular white blood cell, the neutrophil, that is found in lower than normal numbers. Any evidence that white blood cell numbers are beginning to increase is almost certain evidence that the cat is on the road to recovery.

Sudden, unexplained death of kittens and young cats will also bring panleukopenia to mind. In those cats, a PCR test will identify that the virus is present. (ref)
This test can also be run on sick or recovering cats if the diagnosis is unclear. (ref)
A simpler method is for your veterinarian to use the in-office dog Parvo test. Dog parvovirus and cat panleukopenia virus are similar enough in structure for the test to identify the presence of panleukopenia virus in most cats (a stool sample). (ref)

A recent vaccination can also yield a positive result by either test and the in-office dog-parvo test will miss a few infected cats. (ref 1, ref 2)

In cats that die from panleukopenia, the pathological changes in the intestinal tract bone marrow and lymphoid tissue are quite distinctive. (ref) If you have been unfortunate enough to loose a kitty, veterinary pathologists should have no difficulty confirming your veterinarian's diagnosis.

Other blood test changes are usually associated with the severe dehydration that accompanies the often-violent diarrhea (azotemia, etc).

How Will My Sick Cat Be Treated ?

If you would rather read current guidelines on how veterinarians treat panleukopenia, you can read my copy of the ABCD guidelines here as well as my copy of the 2006 Edition of Dr. Norsworthy’s text on the subject here.

There are no medicines that kill the panleukopenia virus when it is in your cat’s body. It is your cat’s own immune system that will destroy the virus if the cat’s life can be sustained long enough. To keep your cat alive long enough for its immune system to produce specific antibody, we need to counteract the dehydration and shock that accompany its intestinal damage and to give it antibiotics to ward off secondary bacterial infection until its white blood cell numbers have sufficiently increased.

All that is called supportive treatment. It consists of intravenous fluids to replaced lost water and electrolytes, proper warmth and all forms of TLC one can provide. Your veterinarian has medications that will lessen the vomiting and diarrhea and make your cat more comfortable. But it is not advisable to give cats in the midst of panleukopenia any nourishment by mouth. These nutrients can be added to the intravenous fluids your veterinarian administers (total parenteral nutrition)

Cats that have become anemic due to blood loss can be given transfusions from donor cats.

I also recommend giving young cats with possible panleukopenia signs or exposure 2- 4 ml of blood serum (intraperitoneally) from a healthy, vaccinated cat. Preferably a hospital blood donor cat. Those cats are routinely tested for other infectious diseases and their hospital environment tends to keep there antibody levels high.

Panleukopenia is a rapidly progressing crisis. Every 8-12 hours the pet survives in a stable state greatly improves it chances for total recover. The key factors that indicate if a cat will survive appear to be the extent of its white blood cell depression (leukopenia, thrombocytopenia), how low its blood albumin has become (hypoalbuminemia), the extent of its blood potassium depletion (hypokalemia) and dehydration. (ref)

If this cat recently came from a shelter or group home, its chances of having several disease problems occurring and compounded by panleukopenia are greater. It is common for these shelter kittens to be battling, upper respiratory virus, parasites, flea anemia ,malnutrition and panleukopenia all at the same time. That is another big reason so many of them do not make it. (succumb).

Will My Cat Fully Recover
?

Yes.

Cats that are fortunate enough to survive panleukopenia usually do not suffer any permanent damage. Both intestinal lining and white blood cells replace very fast. They are immune to panleukopenia for life and require no further vaccination.

But Neonatal (kittens)cats that develop cerebellar hypoplasia will remain disabled for the rest of their lives.

How Should I Clean Up After An Outbreak ?

The panleukopenia virus is a tough cookie. It is showered around the environment in the diarrhea that accompanies the disease. In this foul mix, it sticks to all surfaces it comes in contact with and the fecal residues shield and encapsulate it. The virus is resistant to heat (the virus can survive about 130F or 56C for a half an hour or so and is similarly stable at cold temperatures).

Many products are sold as disinfectants for this and dog parvovirus. None are more effective than ordinary household bleach. I generally dilute my bleach 1 part bleach in twenty parts warm water, but a 1:30 dilution is said to be effective. I add a few drops of dishwashing detergent to help the solution penetrate and disburse on surfaces. Let it sit on surfaces 30 minutes before rinsing it off.

No disinfectant works well when applied to grimy surfaces or areas or anything that is porous or has a high content of organic material. So one needs to clean all surfaces as scrupulously as you can before applying the bleach solution.

Bleach solution is great for indoor, smooth surfaces or when applied in sufficient quantity to get down into cracks, crevices and porous surfaces. When in doubt, leave it on longer or increase the strength of the solution. I gather up all small bleachable items, fill a 55 gallon plastic trash can with solution, and leave these pre-cleaned objects in it overnight. If they are rustable items, I remove them sooner, rinse them, wipe them dry or blow them dry with a hair dryer and spray them with WD40.

The problem occurs with items and areas than can not be bleached or pre-cleaned. Things like carpets, wood flooring, sofas and the like. If you have access to a steam jenny, they work well. Some of these jennys reach 325F at the nozzle – so test a small piece of carpet or sofa material to be sure you do not ruin them.
If you utilize a profession steam cleaning service, they need to use a machine that reaches 240-270F at the nozzle tip , not the wimpy rental units.

Outdoors, cleanup is more difficult. First off, your cats should not be out-and-about. But there are some things you can do. Open up the area to sunlight and drying by clipping back tree limbs and close mowing. Remove trash and stored junk from your yard. Encourage lawn growth and close mowing. Spread a fresh layer of sand or topsoil over the area that the cats inhabited. Wait 5 (warm) months, if you can, before allowing cats to re-access the area.

Do not bring new cats into the recovered cats environment until two weeks have passed since the new cat’s vaccination.

How Can I Prevent Panleukopenia In My Cat ?

If you cats do not go outdoors, and you do not introduce new, young cats to your household, you will not see panleukopenia. If you have your cat properly vaccinated when it is 12 and 16 weeks old, it will not develop panleukopenia. Once a cat recovers from panleukopenia, it will not develop the disease a second time. If you are in doubt as to your cats level of protection – have its antibody titer determined. There is no need for yearly booster vaccinations. The cat will probably be protected for life by the vaccination given at 16 weeks of age, but many veterinarians suggest a booster every 7 years.

There is no benefit in giving household kittens panleukopenia shots at an earlier age. Just don’t expose them to virus until two weeks after their 16 week vaccination. Transient parental immunity in the kitten, derived from the mother’s milk, blocks the action of vaccines given at an earlier age and if the kitten was already exposed when you obtained it, the vaccine will not alter the course of the disease.

Never vaccinate pregnant cats or mothers of kittens with a live-virus vaccine (MLV vaccine) until the kittens are 4 weeks old. In special circumstances such as shelters, younger cats might require vaccination. In that case, killed (inactivated) vaccines, such as Intervet’s Panagen® are an option. They might also be a better option if immuno-suppressed cats with FLV or FIV must be vaccinated. In susceptible kittens over 4 weeks of age, a single vaccination gives rapid protection. One study found that kittens were immune 72 hours after the shot. (ref) a more recent one found all kittens solidly immune 7 days after a single PLV inoculation. (ref)

I prefer an intranasal vaccine - like Heska’s UltraNasal . I prefer these, and trans-dermal, needle-less vaccination systems for other cat diseases because there is the possibility they will prevent vaccination-related tumors later in life (injection site tumors).

There are veterinarians who believe that injectable vaccines provide better immunity in cat shelter situations and I do see more transient sneezing and eye irritation when intra-nasal vaccines are used.

How Often Should My Cat Be Vaccinated Against Panleukopenia ?

Most veterinarians now recommend a booster panleukopenia vaccination every three years. That is generally the suggested interval given on the bottle instructions. We know that immunity last much longer – probably for life – so I recommend your cat receive a booster panleukopenia vaccination every 7 years. I have never seen the disease in a vaccinated cat. You always have the option to have your cats antibody/immunity level to panleukopenia determined through a blood test.

The risks of more frequent vaccination – such as cancer at the injection site – greatly outweigh any benefits you cat might obtain.

Cats That Show PCR evidence of prior FLV Infection

In the last several years, very sophisticated tests have become available that can find the remnants of prior virus infections in animals that have, supposedly, completely recovered from infection. One study, conducted in Germany, purported to find the remnants of feline leukemia virus deep and dormant within the bodies of cats that had successfully fought of the disease years before. That same study found that cats with these inactive, viral code snippets within their cells, were more susceptible to a variety of health problems later in life – including panleukopenia. You can read that article here.

Another 1995 study found panleukopenia-like symptoms in feline leukemia positive cats from which the panleukopenia virus could not be isolated by normal techniques. (ref)
Most vets are still sitting on the fence regarding the significance of those two studies, but keep them in mind when dealing with perplexing cases.

More Perplexing Information

A 2000 study found evidence of panleukopenia virus in the heart muscle of one third of the cats that had died of acute heart failure (cardiomyopathy, myocarditis). So there may be more to this virus than veterinarians have traditionally believed. (ref) We will just have to wait and see.

More disturbing to me is a recent Chinese study. In 2008, an epidemic of severe diarrhea occurred at a monkey research facility in Beijing, China. Two hundred monkeys became ill and over half of them died in a 3–5 day period. Feline panleukopenia virus was isolated from these monkeys. To confirm that this was really feline panleukopenia, the virus was injected into 20 cats. All the cats died with typical panleukopenia-like signs. I do not know what to make of that article. If it is indeed true, it signals a very serious new threat - transfer to monkeys is a giant step closer to transfer to humans. Lets hope it is not true or that it is only a one-time aberration of Nature. You can read the article here.