Introduction 

Feline Panleukopenia Virus (FPV, also known as “distemper” or “feline parvovirus”) is a highly contagious, deadly virus that can infect all felids. The name "panleukopenia" is derived from the Greek “pan” (all), “leuko” (white), and “penia” (insufficient amount). Because white blood cells (in the bone marrow and lymphoid tissues) and intestinal lining cells are among the fastest-replicating cells in a cat's body, they are disproportionately targeted by the virus. 

Similarly, when a pregnant cat is infected with the virus, it passes to her kittens in utero and attacks the rapidly dividing cells of the fetal cerebellum— the part of the brain responsible for balance, coordination and fine motor skills. This causes the cerebellum to be underdeveloped (called cerebellar hypoplasia or CH), leading to a characteristic ataxic (uncoordinated) gait in these kittens. The virus is incredibly robust and without appropriate disinfection can survive indoors for many months (upwards of a year) and even manages to survive freezing in outdoor environments. 

Researchers at Cornell University played a critical role in our early understanding of this impactful feline virus, and with improving our ability to diagnose and manage the disease it causes in cats.

Transmission

Unvaccinated cats have a lifelong vulnerability to contracting FPV. Because FPV is everywhere in the environment, almost all cats are exposed to it at some point in their lives. Although cats of any age may catch the virus, young kittens, sick cats and unvaccinated cats are most likely to become ill. Certain cat populations are more susceptible, such as those in pet shops, animal shelters, kennels, or boarding facilities, and unvaccinated feral cat colonies. 

Infected cats can spread FPV in their feces (stool) or vomit, and body fluids like urine and nasal secretions (made even more contagious when aerosolized through sneezing). Unvaccinated cats may become infected when they contact these substances, the infected cats themselves, or even fleas from infected cats. 

Other possible sources of infection are fomites (virus-contaminated items) such as bedding, litter boxes, cages, food and water bowls, toys, and sadly, even the hands or clothing of people who have handled infected cats and not properly washed their hands or removed contaminated clothing. Importantly, infected pregnant cats can also transmit the virus to their unborn kittens with devastating developmental consequences.

Clinical Signs

In adult cats, infection symptoms arise when FPV attacks cells that are rapidly growing and dividing, such as those in the lymph nodes, bone marrow and intestines; and it can attack rapidly dividing cells in developing fetuses within infected pregnant queens. Once the virus enters a cell, it triggers apoptosis (programmed cell death), essentially destroying the cell from the inside out. When it does this within leukocytes (white blood cells), the resulting decrease in their number diminishes a cat’s ability to fight off infection. When FPV causes the death of intestinal lining cells, the subsequent intense vomiting and diarrhea that results can cause severe dehydration that dramatically further weakens a cat.

Thanks to well-established vaccination protocols, most of our cats have strong immunity against this virus, though veterinarians still see outbreaks in densely populated cat communities, including feral colonies and animal shelters. Most cats exposed to FPV have immunity from vaccination or from previous infection that they managed to survive, and most show no signs of illness. Cats that do become ill—often those younger than a year old—most commonly show the following signs:

• Diarrhea
• Vomiting
• Fever
• Depression/lethargy
• Loss of appetite
• Dehydration (may appear as sunken eyes or dry gums)
• Painful belly
• Sudden death (most often observed in kittens under 5 months of age)

If your cat shows any of the above signs, immediately contact your veterinarian.

If a cat or kitten is strong enough to survive FPV infection, clinical symptoms generally abate in about a week. As mentioned earlier, kittens infected in utero will likely end up with CH, causing profound incoordination and significant tremors when moving, known as “wobbler cats.” 

Diagnosis

Guided by clinical signs, your veterinarian may suspect your cat has FPV and request to check white blood cell counts, along with other baseline health indicators. They may also have a FPV test they can run at their hospital. Clinical suspicion is increased if your cat has not been properly vaccinated or if your cat has been exposed to unvaccinated cats. If there’s any question as to the diagnosis, the Molecular Diagnostics Laboratory at the Cornell University College of Veterinary Medicine offers a specialized PCR test for FPV detection.

Treatment, Recovery and Long-term Care

There's no specific treatment for feline FPV, but veterinary intervention is crucial. Intensive care treatment for seriously ill cats includes aggressive IV (intravenous) fluid therapy to counter the significant fluid loss from the gastrointestinal tract, anti-nausea medications, nutritional support, antibiotics as indicated, vitamins and general supportive care until they improve. Cats with anemia and/or severe protein loss may also need a transfusion. It is very important that treatment is completed in isolation from other cats, including strict hygiene measures after contact with the affected cat, whether within the veterinary hospital or at home.

Recovery depends on a variety of factors, such as age and general health status, the severity of illness, and how quickly veterinary care is instituted. Serious clinical problems (as listed above) require early and consistent in-hospital intervention. If your veterinarian feels that your cat is strong enough to be managed at home, be sure to follow all treatment instructions and call the hospital with any questions or if you think your cat isn’t improving as advised. 

Once recovered, affected kitties have lifelong immunity and usually have no chronic effects from infection (the exception being the CH that can occur with in utero infection, as mentioned above). Recovered cats can continue to shed the virus in their feces for up to six weeks after recovery. It is important to keep them isolated from other unvaccinated cats during this time.

The good news about FPV is that even kittens with congenital CH can live happy, fulfilled lives. The neurological condition is non-progressive, non-contagious, does not shorten their life expectancy and is completely painless. These kitties can be neutered or spayed as usual with no greater anesthetic risk. If you are considering adopting a CH kitty, you should plan to dedicate lots of time for affection since these cats tend to be very lovable and bonded to their families. 

Also, be willing to make specific, important environmental adjustments to accommodate their lack of coordination:

• Keep them strictly indoors-- these kitties will not be able to fight or escape effectively when encountering another cat, larger predator, or motor vehicle.
• Create a soft, safe environment-- lots of padding and carpeted areas are the best support measures; restricting access to elevated surfaces and stairs to prevent injuries from falling is crucial.
• Optimize their food and litter areas-- use high-sided litter boxes (so they can comfortably lean against them for stabilization) with wide, low-entrances. Use wide, shallow, elevated food and water bowls so they can eat/drink without falling forward. Be prepared to make adjustments to these areas as they grow and offer individualized support as you evaluate your cat's particular challenges.
• Have patience for their special needs.

Prevention

Prevention is vital to avoiding this life-threatening or developmentally debilitating infection. Vaccination is the cornerstone.

Young kittens are especially susceptible to FPV infection. If a pregnant cat has already created antibodies against the virus either through natural disease or vaccination, she will share those antibodies with her newborn kittens through her milk. This “maternal immunity” provides important protection as kittens begin their lives, but this protection is temporary. Maternal antibodies raise the question of how many vaccine boosters kittens should receive. 

Kittens exposed to FPV while they have maternal antibody protection will be protected from FPV as if it was their own immunity. However, this immunity deteriorates at an unknown rate, so we cannot really rely on it beyond 6-8 weeks of age. This is why it’s important to start vaccination at 6-8 weeks old to be sure we don’t allow kittens to remain unprotected. Another issue is that the immune response (i.e. development of antibodies) to any vaccines administered before maternal immunity has declined to a certain level will be blocked by these maternal antibodies as if it was the real virus trying to enter, thereby leaving the kittens effectively unvaccinated and vulnerable to disease.

Over the years, various groups have worked to determine the optimal age window for administration of distemper vaccines. The Feline Veterinary Medical Association (Feline VMA) currently recommends a series of vaccines administered every 3-4 weeks beginning at 6-8 weeks of age and continuing through 16-20 weeks of age. This plan accounts for the variable rate of decline of maternal antibody and will provide the best protection against FPV during the first six months of life. Cats older than 16 weeks that have never been vaccinated or have an unknown history should receive one or two doses (depending on your veterinarian’s protocol), with the second dose given 3-4 weeks after the first.

To maintain protection, a booster dose of the vaccine is recommended at one year of age, with additional boosters every year (intranasal vaccine) or every three years (injectable vaccine) afterward. If your adult cat hasn't been vaccinated yet or is overdue for vaccination, it's not too late. Work with your veterinarian to follow a vaccination program based on your cat's age and needs.

The FPV vaccine is included in a combination vaccine (often abbreviated “FVRCP”) that also protects cats against two other common viruses: feline herpesvirus 1 and feline calicivirus. This vaccine is considered a "core" vaccine and is recommended for all cats—including cats that don't normally go outdoors or interact with other cats.

Vaccination protocols work best when paired with sensible environmental practices. These measures can help protect your cat from contracting FPV and other infectious agents:

• Avoid contact with known infected cats and their premises. 
• Keep your cat indoors to reduce the risk of exposure to potentially infected cats.
• Wash or sanitize your hands after handling other cats, especially if they appear sick.
• Avoid sharing toys, food bowls and other items between your cat and those of unknown health or vaccination status.
• When bringing a new cat or kitten into a home where other cats live, keep the new animal separated until your veterinarian has had a chance to examine the newcomer and they've received their necessary vaccines.
• Keep sick cats away from other cats and disinfect possible FPV-contaminated surfaces with a 1:32 dilution of household bleach (1/2 cup of bleach in one gallon of water) applied to all affected surfaces for at least 10 minutes. Dispose of any items that cannot be disinfected.

Human Health Concerns

There are no known human health concerns associated with FPV. The virus is strictly species-specific to felines and a few wildlife species. It does not infect humans, nor is it contagious to dogs.

History

The identification of panleukopenia as a cause of disease has an interesting history. The clinical disease was first recognized as early as the 1880s and until the 1960s was thought to be an inherited disorder, one that was very common in families of unvaccinated farm cats. It wasn’t until 1965, when Drs. Lawrence Kilham and J. Margolis at Dartmouth Medical College were studying a viral-induced cerebellar disorder in the rat and hamster, that the story of the contagious nature of the feline disease began to unfold. Their research demonstrated that a virus was causing cerebellar ataxia in newborn lab animals. As is often the case in research, a bit of unexpected coincidence led to a broader picture of the disease. When the laboratory’s lead veterinarian informed them that he had often witnessed a very similar congenital cerebellar ataxia in kittens on local farms, they included cats in their studies and proved that the feline condition was also caused by a virus. Collaborating with Dr. RH Johnson in the United Kingdom, they demonstrated that the virus was the feline panleukopenia parvovirus. 

Subsequently, Dr. Charles Csiza's doctoral thesis research at Cornell University further confirmed this viral agent as the cause of these specific congenital cerebellar lesions and examined exactly how the virus spreads and affects the tissues and immune systems of susceptible newborns. Within the next decade, the soon-to-be-established Cornell Feline Health Center’s very own Dr. Fredric W. Scott and his mentor Dr. James Gillespie worked to advance the critical task of developing a vaccine to address this wide-spread and devastating disease of cats. With the vaccine developed, veterinarians were finally able to reduce the suffering and mortality caused by this viral-induced feline disease and established that the disease could be prevented, even in at-risk populations, by vaccination of queens before pregnancy and following a structured vaccination protocol for all kittens and cats.