Infectious Diseases Affecting Cats

By Johnny D. Hoskins and John D. Rhoades.

The most important infectious diseases affecting cats are feline panleukopenia, feline viral respiratory diseases, feline infectious peritonitis, and the feline leukemia virus disease complex. Other infectious diseases affect cats, but do not occur as frequently.

Feline Panleukopenia also is variously termed feline infectious enteritis, or cat distemper. It is caused by a parvovirus (DNA virus).

The virus infects cats of any age but is a disease principally of young cats, with worldwide distribution.

Transmission of the virus usually is by direct contact among susceptible and infected cats. Transmission also can occur by way of contaminated food and water dishes, bedding, litter containers, and the hands and clothing of owners.

Recovered cats may shed the virus in their feces for long periods and act as carriers of the disease. The main route of infection to a susceptible cat is the ingestion of contaminated feces.

Infected cats usually will experience fever first, followed by decreased interest in eating, vomiting, and diarrhea. The diarrheal stools are large quantities of liquid feces that are dark with partially digested blood. Frank blood with a lot of mucus in the feces may be seen occasionally.

Severely affected cats will show marked dehydration and depression with their mucous membranes appearing pale.

The virus is capable of passing the placental barrier in pregnant cats. Infection of the fetus results in abortion, stillbirth, early fetal death, or permanent structural brain damage.

Diagnosis of feline panleukopenia depends on recognition of the signs of illness and demonstration of the decrease in the white blood cell numbers.

The virus will affect production of white blood cells formed in the bone marrow and a severe decrease in circulating white blood cells will be seen. If the cat recovers, the white blood cells will quickly return to normal numbers and the diarrhea stops.

Cats that die of panleukopenia generally die of bacterial infection which has complicated the viral infection.

Immunization is the preferred method of preventing feline panleukopenia. Both killed-virus and live-virus vaccines are available and either will induce good protective immunity in cats.

Because colostral antibody interferes with vaccination, cats should be vaccinated repeatedly. In most cases, a minimum of 2 vaccinations are required.

Kittens should be vaccinated at 9 weeks and 12 weeks of age. Because of antibody loss, annual revaccinations are recommended throughout the cat's life.

Vaccinated cats can develop panleukopenia several years after receiving vaccinations as kittens if annual booster injections are not given.

Respiratory Infections Two viruses, feline herpesvirus and feline calicivirus, have been implicated in respiratory infections in cats. These viruses have been isolated with approximately equal incidence and account for the majority of feline respiratory diseases.

It has been acknowledged for many years that it is not possible to distinguish these viral diseases on grounds other than virus isolations.

Feline herpesvirus is a DNA virus and feline calicivirus is a RNA virus. Shedding of both viruses occurs in all discharges from the nose, eye, and throat, but transmission is largely by direct nose-to-nose contact or by droplets from sneezing cats.

The viruses may persist in cats for a long period after infection, hence infected cats become carriers of the viruses. Infected carriers excrete virus intermittently from the nose and throat.

Infection generally remains in the upper portion of the respiratory tract, although the viruses may cause infection of fetuses and abortion in pregnant cats.

Early in the course of the disease infected cats usually will experience depression, sneezing and coughing. Progression to serous ocular and nasal discharges with elevated body temperature is rapid. Both viruses may cause ulcers in the mouth but corneal ulceration appears only in feline herpesvirus infections.

When the herpesvirus infection is confined to the upper respiratory tract, it generally is referred to as feline viral rhinotracheitis.

Pneumonia is more likely to occur with calicivirus infections.

Diagnosis of feline viral respiratory disease is made on the basis of signs of the illness, especially the pronounced sneezing and the ocular and nasal discharges. Definitive diagnosis of the viral cause of the infection depends solely on virus isolation and identification.

Immunization for both viruses produces significant protection following vaccination. Vaccines against the viruses are included in combination with the panleukopenia virus.

Two vaccinations are required for all ages. Kittens should be vaccinated at 9 weeks and 12 weeks. There should be a 3-week interval between vaccinations for adult cats. Annual revaccination is recommended.

Some vaccinated cats may sneeze, and an occasional one may have watery eyes for one to two days. Severe disease does not occur in properly immunized cats.

Infectious Peritonitis

This disease was first seen in the early 1950's in various parts of the United States and named in 1966. The disease has been reported throughout North America.

Cause of feline infectious peritonitis is a coronavirus. coronavirus infections are relatively common in domestic cats but the majority of these infections do not produce signs of disease.

Feline infectious peritonitis affects cats of all ages, though the prevalence is highest in animals one to two years old. There appears to be no apparent breed predisposition. Initial exposure to the virus may result in mild respiratory disease as indicated by runny eyes and nose.

The majority of cats with this mild respiratory disease recover, with some of them serving as carriers of the virus. An even smaller number of cats will not recover but experience the primary disease. The viral infection spreads from an infected cat to a susceptible cat by direct contact.

Two Forms. The disease occurs in two forms. In one form the abdomen and chest accumulates fluid as part of the infection. As a result the cat experiences fever, reluctance to eat, depression and weight loss.

As body cavities continue to fill with the fluid, organ systems will become compromised and cause signs of specific organ failure such as jaundice from severe liver involvement or breathing problems from fluid pressing on the lungs. Eventually the disease process becomes so extensive the cats die of organ failure.

The other form of feline infectious peritonitis is more insidious and frequently is associated with involvement of specific organs. Signs of kidney and/or liver failure, pancreatic disease, and nervous system disease may be observed in cats with severe organ impairment.

Lesions affecting the infected cat's eyes are very common and may be the first sign of a problem seen with the disease.

In both forms the disease process becomes so extensive that affected cats die of organ failure.

The mechanisms of disease with feline infectious peritonitis have been studied for many years but the explanation as to how an infected cat recovers or develops one or the other form of disease is not well understood.

The coronavirus may serve as a stimulator of the body immune system which leads to immune complexes being formed. These complexes then collect in blood vessels in the various body organs and cause severe vascular damage to occur.

Organ failures occur as a result of the complexes damaging the blood vessels and interfering with vital organ function. Also, the coronavirus has the capability of altering various parts of the immune system causing either the fluid accumulation or forms of the disease in which specific organs are attacked.

Diagnosis of feline infectious peritonitis is made by evaluation of history and signs of disease and the results of supportive laboratory tests. Considering the grave prognosis associated with diagnosis of this disease and the lack of curative therapy, it is essential to differentiate the disease from other conditions with similar symptoms.

Laboratory tests used include analysis of chest and abdominal fluids, measurements of total serum protein, clinical chemistry profiles, and serum coronaviral antibody titer and biopsies of affected organs.

Routine immunization against feline infectious peritonitis is not possible currently. Newly acquired cats can be tested for coronaviral antibodies. Tested cats that are negative for coronaviral antibodies 3 to 4 weeks apart are considered free of infection. Only those cats that test coronaviral antibody negative should be used for breeding.