Causes, Clinical Signs & Transmission of Feline Panleukopenia
Panleukopenia is caused by the feline parvovirus, which is an un-enveloped DNA virus. Another member of this virus family is responsible for causing canine parvovirus in dogs. (Feline parvovirus was present before the strain that affects dogs appeared. In fact, the first vaccination efforts to control canine parvovirus were made using feline panleukopenia vaccines.)
Feline panleukopenia is very stable in the environment and extremely resistant to most disinfectants—in fact, it can persist in the environment for more than a year.
Panleukopenia can spread from cat to cat in several ways. The virus is shed in all bodily secretions such as urine and vomit, and largely shed in the stool. Direct contact with an infected cat is one mode of transmission; the virus is also spread through contact with fomites (contaminated objects) such as hands, instruments, clothing, food and water dishes, toys and bedding.
Insects and rodents can also provide a means for disease spread. The virus can remain on a cat's hair coat long after recovery from clinical disease, which can also serve as a means of transmission.
The incubation period is the time from exposure to onset of symptoms, typically 5-7 days but can be as long as two weeks. Because the disease may be difficult for the shelter to detect during the incubation period, apparently healthy animals with panleukopenia may be adopted out only to become ill a few days later in their new homes, causing heartache for the shelter staff and the new owners.
It is very important to know the shedding pattern of panleukopenia in order to design an effective management, diagnostic and prevention strategy. Shedding is the period when virus is being excreted and thus can be transmitted. With feline panleukopenia, cats begin to shed virus often before clinical signs are obvious, during incubation, and can shed up to six weeks after clinical recovery.
On average, shedding is less than three weeks after clinical recovery. This means that it can be very hard to know just by looking which cats are infectious, and this is why shelters often have animals enter care that appear healthy, but are actually not. It is also why a strategy for control that only removes obviously clinically ill cats from an area will not be effective. Cats are very likely to still be incubating and shedding disease and thus perpetuate an outbreak.
Clinical Signs of Panleukopenia
Subclinical (no obvious signs)
The signs of panleukopenia can vary and may be similar to other illnesses. Infected cats may even show signs that resemble those seen when a cat has been poisoned or has swallowed a foreign object. The first visible signs might include generalized depression, loss of appetite, high fever, lethargy, vomiting, severe diarrhea and dehydration.
Sick cats may sit for long periods of time in front of their water bowls but not drink much water. Cats are very good at hiding disease and by the time a cat displays the signs of illness, it may be severely ill. In shelters, kittens and cats may simply be found dead in their kennel, when they were not previously showing any notable signs of illness.
Pathophysiology of Panleukopenia
The feline parvovirus infects and kills cells that are rapidly dividing, such as those in the bone marrow, intestines and the developing fetus. Infected cats usually develop diarrhea (which may or may not be bloody) because of the damage to the cells that line the intestines. They also develop the hallmark of the disease “panleukopenia” (shortages of all types of white blood cells) because the parvovirus infection damages the bone marrow and lymph nodes.
White blood cells are necessary for the immune system’s response to infection and panleukopenic animals are highly susceptible to infections that overwhelm the system.
When pregnant queens are infected in early to mid pregnancy, abortion or stillbirth is the usual result. When infection occurs late in pregnancy, the kittens may survive but the virus may affect their brain development, causing the kittens to be born with a condition called "cerebellar hypoplasia," which has effects on the kittens' coordination.
Diagnosis of Panleukopenia
Common laboratory tests include the Enzyme Linked Immunofluorescent Antibody (ELISA) and complete blood count (CBC). Some shelters also perform antibody titer testing in non-clinical cats to assess immunity.
Shelters should be prepared to run ELISA tests. The ELISA test is a useful screen for canine parvovirus as well as feline panleukopenia, both of which have significant population implication for shelters. This test utilizes a fecal swab to detect viral antigen, and can be run in 10 to 15 minutes.
While no test is 100% sensitive or specific, positive results in a symptomatic animal are worth heeding. Negative results may occur even when animals are infected depending on timing of sampling or excessive blood in stool, so an ill animal with negative test results may require further testing and care and should still be handled as though infectious. Results are most accurate with this test if it is administered the first few days after infection, or within five days after clinical signs appear.
A complete blood count or blood smear can be done in-house in many shelters, or sent out for a nominal fee. This can be done as further confirmation to look for low white cell counts, a hallmark clinical sign of the disease.
Finally necropsy and histopathology have value any time animals are dying or being euthanized—and are often the fastest and least expensive route to achieving a definite diagnosis. Any time a cat or kitten has died suddenly from an unknown cause in the shelter, panleukopenia should be high on the list of diagnoses to attempt to rule out.