From the May-June 2001 Issue
Developing Immunity in the
In earlier times, panleukopenia was known as the “Cat Plague” because of its ability to devastate cat populations. There was no known prevention method, and no known cure.
Today, while cures for viral diseases are still mostly a pipedream, prevention is possible; the bully virus that can strike kittens dead without warning has met its match in the form of highly effective vaccines.
But administering these vaccines to shelter animals, especially very young ones, is more than just a matter of simple injection. Shelters must navigate a maze of logistical issues when vaccinating for panleukopenia.
Because panleukopenia can be especially deadly to baby cats, vaccination of kittens is particularly important. But it’s a tricky business: Maternal antibodies, which are absorbed through the mother’s milk during the first 24 hours of life, can interfere with the vaccine. “If the maternal antibody is at a certain level, it may be too low to protect [kittens] from infection, but too high to allow the vaccine to actually stimulate protection of its own,” says James Richards, DVM, director of the Cornell Feline Health Center at Cornell University. “And so if they’re exposed to enough of the virus during that stage, during that time that they’re getting vaccinated, they can easily come down with the infection.”
That’s why it’s a good idea to administer a series of vaccines a few weeks apart, says Richards. In general, kittens should start receiving their vaccinations at six to eight weeks, with a booster every three to four weeks until they reach about 12 weeks of age, when maternal antibodies have diminished to such a level that vaccinations will work. In the shelter environment, where there is a high risk of exposure to diseases like panleukopenia, kittens can start their vaccination series even earlier, Richards says.
“And I know that this is sometimes difficult to carry through with, but I like to vaccinate cats as soon as they get into the shelter,” says Richards. (The exception, of course, would be in cases in which cats are already exhibiting symptoms such as diarrhea.) “And I like to hold them in an area where they are not going to be exposed to other cats, at least as much as possible, for at least several days before I would put them into the general cat population. …When kittens come through the door, at least as far as panleukopenia virus is concerned, I would be inclined to vaccinate them at around four weeks of age, with a modified live vaccine. And then if they are still there three or four weeks later, then they would get a booster vaccine.”
But the modified live vaccine is probably not appropriate for kittens in the first month of life, says Richards. Shelters experiencing a panleukopenia outbreak may be wise to vaccinate kittens younger than four weeks, but administering modified live vaccines to these fragile little guys could be dangerous, says Richards. The vaccine, he explains, may actually attack their central nervous systems, just as the virus does. “But if we are in a situation where we’re even having kittens younger than four weeks of age succumb to panleukopenia in a shelter, then we could use …a killed product.”
For most animals in the shelter, though, modified live vaccines are superior to killed vaccines because they stimulate protection much sooner, says Richards. While modified live vaccines contain live disease-causing organisms that are altered slightly in order to stimulate antibodies in an animal without making him sick, killed vaccines contain dead organisms as well as special compounds known as “adjuvants,” or substances designed to enhance the immune-stimulating properties of the vaccine.
Killed vaccines take longer to produce an immune response, and they have to be administered more frequently. And although they were developed specifically as a potentially safer alternative to modified live vaccines, some killed vaccines have been linked to a kind of cancer in cats called fibrosarcoma.
Modified live vaccines also present a disadvantage in the shelter in that they can occasionally induce some of the symptoms of upper respiratory infection, says Becky Rhoades, DVM, an HSUS consultant who is also serving as the interim executive director of the Kauai Humane Society in Hanapepe, Hawaii. This can occur because some combination vaccines include protection not only against panleukopenia but also against URI bugs such as herpesvirus and calicivirus. “The hard part about using it is that sometimes [the animals] will sneeze and get runny eyes as a result of the vaccine,” says Rhoades, “and so it’s hard to tell a cat who’s getting sick from a cat who’s just showing reaction from the vaccine.”
Like Richards, Rhoades says much of the answer to protecting your cat populations lies in good medical management that takes into consideration the conditions of individual animals. “If you vaccinate a feverish animal, they may crash the next day,” she says. “So much of it is isolation, managing your population: When you see them get sick, get them out of the general population.”