Many people have never heard of panleukopenia virus, more commonly called "distemper," or have only heard of their cat getting a "distemper" vaccine but don't know why it's important. Others who have heard of it may think it's a disease of the past and no longer a danger, but unfortunately this is not true. My recent experience with this disease in two of my patients has prompted me to try to raise more awareness of why this problem is still relevant.
A virus with deadly consequences
Panleukopenia virus is a member of the parvovirus family. It is closely related to the disease called "parvo" in dogs; in fact, a strain of the feline panleukopenia virus mutated into canine parvovirus in the 1970s, leading to widespread outbreaks in the dog population. This particular strain is still capable of infecting both dogs and cats.
In both species, infection can lead to severe bone marrow suppression causing a very low white blood cell count and severe damage to the lining of the intestines. This damage to the intestines causes diarrhea and dehydration while also allowing intestinal bacteria access to the bloodstream of the infected patient. Meanwhile, the low white blood cell count makes it impossible for a cat to fight off these bacteria or any others they encounter in their daily life. Symptoms include fever, listlessness, severe dehydration, vomiting and diarrhea (which can lead to shock), hypothermia, and death. Some cats die so rapidly that they have almost no symptoms, while others get a milder form of the illness and are sick but eventually recover. Most cats die, with the virus having a 60-95% mortality rate in untreated patients, depending on the age and overall health of the infected individual.
Panleukopenia virus is very contagious, as it is shed in large quantities in the stool of cats (and dogs with the cat-contagious strain) with diarrhea. It is resistant to most disinfectants and can remain viable for over a year in moist environments. It doesn't require direct contact between infected animals and can easily be spread on bedding, people's hands, clothes, or shoes (particularly bad if you step in dog or cat diarrhea outside!), and farm or veterinary equipment. As you can imagine, barns are full of dark, moist places and this disease traditionally would lead to widespread die-offs of barn cat colonies, so many older farmers are familiar with this plague. Nowadays distemper can sweep through feral cat colonies and sometimes shelters, making it a very large concern for people who care for and manage these populations.
Some cats will survive panleukopenia with intensive nursing care, including IV fluids and antibiotics, but this care is very expensive and not always rewarding. It is difficult for individual owners to afford and very difficult to provide in the shelter setting.
Building early immunity
The good news is that there is a vaccine which is very effective at producing solid and long-term immunity to this horrible disease. The trick to good immunity is in the details, however.
Kittens should start on the vaccine for panleukopenia, which is often bundled in with two upper respiratory viruses, at their first vet visit and not later than 8 weeks of age. After that, they need to receive boosters every 3-4 weeks until they are at least 16 weeks of age, and ideally until they are 20 weeks old. This is because any antibodies in their circulation from their mother's immune system can block full effectiveness of the vaccine until they have naturally dissipated. For older kittens and adult cats, just two boosters 3-4 weeks apart are sufficient to induce immunity in 95% of cats. One year later, cats should receive another booster, and after that most only need a booster every 3 years or so.
Quality care in shelters is key
Cats and kittens that first enter a shelter or colony need a few weeks to acquire immunity from the vaccinations; these individuals are the ones most at risk for the infection. I had to care for two lovely 8-month-old boy kittens that were very healthy and robust, but were exposed to panleukopenia sometime around their first vaccination when they arrived at a shelter for adoption. Unfortunately, they did not have protection yet and they died of the infection, leaving behind a family who had fallen in love with them and adopted them just a week before.
Luckily this was a rare case, but it does illustrate an interesting trade-off for adopters. While the best case for the kittens is to get into the safety of a home, away from other cats, as soon as possible, you'll have less risk of heartache if you adopt kittens who have had at least two of the vaccine boosters. Shelters often try to reduce the risk of kittens being housed with older, potentially contagious cats, or keep adoptable kittens in foster homes until they've had a few vaccinations.
Adult cats entering a shelter environment should receive a distemper vaccination as soon as possible. With any luck, a stray might have received vaccines as a kitten and may have some pre-existing immunity that can be boosted, but it will take a few weeks for immunity to build up in a cat who hasn't been vaccinated before. Older cats whose immune systems are naturally declining with age can also be susceptible to infection. This, plus the contagious nature of the virus, is why older indoor cats should still continue to receive "distemper" boosters every 3 years or so at their regular checkups.
What you can do
Aside from making sure your pet cats receive their regular checkups and vaccinations, it's also important to take precautions when interacting with strange cats outdoors or when traveling to areas where vaccination is not routinely available to cat colonies. Make sure you wash your hands thoroughly before coming home to handle your own cats, and wash your clothing before allowing them to sniff it or picking them up. If you notice any stool in the tread of your shoes or boots, clean them thoroughly and allow them to fully dry before bringing them into the house.
With any luck, you'll never have to deal with this virus. Take precautions with your own cats and donate to organizations that provide vaccinations to feral and colony cats!
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