Cats with special needs
The FIV-positive Cat

Part 1

Anne Haughie

How is FIV transmitted?

Large amounts of the virus are present in an infected cat’s saliva and the most usual route of transmission is via a bite from an infected cat. The virus, once it has entered a cat’s blood stream, is able to use a particular type of enzyme (reverse transcriptase) to make a DNA copy of its genetic material – called the “proviral DNA – which is then permanently inserted into that of the host cell. A single bite can be enough to effect transmission. Once a cat is infected it will remain so for the rest of its life.

Cats with a history of cat bite abcesses are very much at risk. Casual, non-aggressive contact among cats does not appear to be an efficient route of spreading FIV. Sexual transmission seems to occur only very rarely. However, if the queen’s skin is punctured by an infected male when he grips her by the neck with his teeth during mating, the virus can enter her blood stream this way. An infected queen can transmit the disease to foetuses via the placenta during gestation, to unborn kittens during passage through the birth canal or when her newborn kittens ingest colostrums that is infected with the virus – around 30-50% of kittens will be thus infected. Because of the nature of the main route of transmission, the sector of the feline population most commonly at risk of infection are entire males that engage in internecine fights over territory and mates and therefore the most prone to receiving bites. As in HIV the virus can also be passed via an infected blood transfusion.

Diagnosing and testing for FIV

Accurate identification of FIV-infected cats has implications for the health of the feline population as a whole and for the management and veterinary care of sick cats. Diagnosis is based on the clinical signs and symptoms, the cat’s history (eg is it freeroaming and fighting with cats likely to be infected?) and results of an FIV antibody test on a sample of the cat’s blood. FIV produced a persistent infection from which cats do not recover and infected cats usually develop high amounts of FIV-specific antibodies.

IDEXX was the first manufacturer in 1988 to develop a commercial test known as an ELISA (enzyme-lined immunosorbent assay) for the diagnosis of FIV infection. In many cases, this test can be performed rapidly at a veterinary surgery (known as patient-side testing) giving an on-the-spot diagnosis of FIV infection. The presence of FIV antibody in “positive” blood test results indicates that a cat is infected with FIV and thus is capable of transmitting the virus to other cats. However, a false positive result is sometimes obtained.

A “negative” ELISA test result indicates that antibodies directed against FIV have not been detected. However, approximately 10% of cats infected with FIV do not develop antibodies so, in these circumstances, the test will give a false negative result. Another instance when this can happen is when a cat in the later stages of FIV infection tests negative because its immune system is so compromised that it no longer produces antibodies. Also, it takes 8-12 weeks after infection – sometimes even longer - before detectable levels of antibody appear. If the test is performed during this interval, inaccurate results can be obtained. Therefore, antibody-negative cats that have had possible exposure to FIV-infected cats prior to testing should be re-tested after 8-12 weeks in order to allow adequate time for development of anti-bodies. Sick cats should be re-tested for FIV, regardless of previous testing results.

For these reasons, many vets prefer not to rely on patient-side testing and will confirm the diagnosis by sending a blood sample to a commercial or university veterinary laboratory where there is a range of reliable confirmatory tests available that demonstrate the presence of antibodies or the virus itself. The more specialised tests include immonofluorescence, immunomigration (RIM) technology and western blotting (regarded as the gold standard) for the detection of antibodies to FIV and virus isolation and polymerase chain reaction (PCR) for the detection of the virus itself. Although these tests are more time consuming and expensive they are of great value in confirming a diagnosis, particularly in cases where the cat’s history and clinical signs suggest FIV but the antibody test is negative.

 

Should kittens be tested for FIV?

Antibody tests have to be interpreted carefully in kittens under the age of 6 months because they may have acquired FIV antibodies by passive transfer in colostrums from a mother that is infected. Young kittens may therefore produce positive test results from these maternally derived antibodies (MDA) for 12-16 weeks after birth – sometimes longer – without actually being infected with FIV; thus most kittens that initially test positive will eventually turn negative when their maternal antibodies wane. Kittens with positive antibody tests should therefore be re-tested when they are 6-8 months of age to determine their true infection status.

What is the prognosis for FIV-infected cats?

It is impossible to predict accurately the life expectancy of an infected cat. Although a terminal disease, FIV is not usually an immediate death sentence and there is a very long incubation period – possibly five or six years – during which time a cat can lead a normal life. With good veterinary care and owner support and under ideal conditions, such as isolation of the FIV-infected cat from other cats – thereby reducing the risks from secondary infections – quality of life is often high over a long period of time. Many cats will remain in apparent good health for months or even several years after the initial infection and, in fact, many die in older age from causes completely unrelated to their FIV infection. The majority of health problems in FIV-infected cats are due to secondary diseases; these not only cause clinical illness but also play a major role in the progression of the disease and are the major cause of death in FIV-infected cats.

How does the disease progress following infection?

Following initial infection the virus is carried to regional lymph nodes where it may replicate in white blood cells known as T-lymphocytes. The virus then spread to lymph nodes throughout the body resulting in a generalized enlargement of the nodes. This stage of the disease frequently passes unnoticed by an owner unless the nodes are greatly enlarged and so veterinary advice is not usually sought. Some time later – possibly days but usually weeks or moths – the cat may develop a fever and a drop in its white blood cell count. This decrease in white cells is due primarily to a lack of neutrophils (the white blood cells that help protect cats against bacterial infections) and to a loss of certain types of lymphocytes called T-helper cells, which play an important role in almost every aspect of immune protection. Anaemia (low red blood cell count) may also develop, especially as the disease progresses.

Eventually, signs of immunodeficiency begin to appear and the cat’s ability to protect itself against infection is compromised. The same bacteria, viruses, protozoa and fungi that are found in a cat’s everyday environment – where they usually do not affect healthy animals – can cause severe illness in cats with a weakened immune system. Many infected cats have a history of recurrent bouts of illness with non-specific signs such as swollen lymph nodes, poor coat condition, persistent fever and lethargy. Loss of appetite is common, accompanied by slow but progressive weight loss, followed by severe wasting late in the disease process.

Gingivitis (infection and inflammation of the gums) and stomatitis (infection and inflammation of the mouth) are present in many cats infected with FIV. Chronic or recurrent skin problems such as dermatitis and eczema may occur and urinary and bladder infections and upper respiratory tract infection often develop. Persistent diarrhoea can be a problem. Conjunctivitis (inflammation of the mucous membrane that lines the inner surface of the eyelid and exposed surface of the eyeball) and uveitis (inflammation of the tissues of the eye) occur frequently. Rhinitis (inflammation of the mucous membrane of the nose) is a common problem causing sneezing, snuffling and a persistent nasal discharge. Kidney failure is common in the later stages of the disease. FIV-infected cats have an increased risk of developing certain types of cancer, such as lymphomas.

Some infected cats experience seizures, mental deterioration and other neurological disorders. Some cats have recurrent episodes of illness interspersed with periods of relative health in between; in these cases, low white blood cell counts and anaemia appear to cycle with recovery to nearly normal levels. However, the overall trend seems to be progressive, with white blood cell counts dropping lower with each subsequent episode. Abortion of kittens and other reproductive failures have been noted in infected queens. Almost inevitably, there will be deterioration over time to a point where euthanasia will eventually become necessary on humane grounds.

Prevention and Control?

Pet cats that are kept indoors on in an enclosed garden away from free-roaming cats are highly unlikely to contract FIV-infection. Spaying and castrating cats that do go outdoors will limit transmission of the virus by decreasing roaming, mating and fighting behaviours. Cats that go out should therefore be neutered and not be exposed to contact with untested homeless stray or feral cats.

As FIV attacks the immune system leaving an immunosuppressed cat with a reduced ability to fight disease, FIV-infected cats are at high risk from infectious agents carried by other cats they come into contact with; for this reasons, they are best confined to home, run or an enclosed garden. An amenable cat may adjust to hearing a harness and lead but this will not be appropriate where dogs run free because of the risk of attack and injury. FIV-infected cats that have a tendency to become involved in fights should definitely not be allowed to roam both because of the risks they pose to other cats and the risk that they will pick up further infections themselves.

However, total confinement is not always possible and some cats that have previously been allowed free access to the outside world do not adjust easily to an indoor life and this in itself can place their immune system under stress. Where total confinement is not a practical option, keeping the cat in at night is a god compromise, as this is when most cat fights occur. For the cat that is reluctant to come in as darkness approaches, experience has shown that the certainty that a couple of prawns or another tasty treat will appear as soon as they poke their head in through the cat-flap is an inducement that works like a dream with even the most intrepid of adventurers.

To be continued …..