FElV and FIV Testing: Important

All cats should be tested – and retested as necessary – for the presence of these viruses. Here is why. Among all causes of lethal feline disease, none should be taken more seriously by cat owners than those caused by two specific submicroscopic organisms: feline leukemia virus (FelV) and feline immunodeficiency virus (FIV). Although these viruses are somewhat different in appearance and in the manner in which they exact their toll on eline health, infection in either one of them, if undetected, is capable of causing a cat’s premature death.

All too Common. To make matters worse, FelV and FIV infections are by no means rare. Recent estimates indicate that two percent to four percent of the 83 million or so cats in the U.S. harbor one or both of these two viruses.

At present, several vaccines  prevent FelV infection are available, says Fres Scott, DVM, PhD, professor emeritus of virology at Cornell University’s College of Veterinary Medicine and the founding director of the Cornell Feline Health Center. With rare exceptions, all cats should be vaccinated against FelV as kittens and then revaccinated one year latr. However, notes Dr. Scott, “Sme veterinarians feel that, after these initial vaccinations, the benefits of the annual vaccinations are outweighed by the cat’s risk of developing cancer – sarcoma- at the vaccination site.” As for FIV, a vaccine has been developed, but its efficacy against all the strains of the virus remains to be determined. The key to combating the spread of these infections, therefore, is to identify infected cats and to prevent their coming into contact with uninfected animals.

Diagnostic Tests.  Diagnosis of FelV infections, says Dr. Scott, is based on a cat’s medical history and clinical signs and the results of tests to determine whener th virus is present in the blood. A positive test will identify the presence of FElV or its antigens – unique protiens that a cat’s immune system develops as a response to infection. Two tyoes of test commonly used for this purpose are the ELISA (enzyme linked immunosorbent assay), which can be performed in a veterinary clinic and is routinely carried out as the initial FelV screening test; and an IFA (immunofluorescent assay), a confirmatory test that, because of the technology required, must be done at a commercial laboratpry.

For the diagnosis of FIV infection in unvaccinated cats, the ELISA is used to detect specific antiviral antibodies circulating in the blood. The anti-FIV antibodies are produced during the normal immune response to a viral infection. The IFA is not used to confirm FIV infection, says Dr. Scott. Instead, the suspected presence of of FIV-associated antibodies cam be substantiated by means of a so-called Western Blot, in which specific antibodies to FIV can be identified. Thid procedure – like the IFA – must be carried out at a laboratory that is specifically equipped for the test; results will typically be available within a week.

Once cats have been vaccinated against FIV, the antibody assay for the virus is no longer useful, since the test cannot distinguish between antibodies produced as  aresult of infection and those produced following vaccination. Unfortunately there is no test available at present to diagnose FIV in FIV-vaccinated cats.

For a number of years, an innovative kind of assay called the IDEXX Combo test has been used routinely by veterinarians. The assay, which typically costs $60, can be performed in a local clinic and completed in a matter of minutes. Basically, Dr. Scott explains, the assay kit consists of a small piece of filter paper impregnated with various dots of test material: FelV-and FIV- positive controls, a negative control, and FelV sample test spot, and an FIV sample test spot.

When a few drops of cat’s blood, serum or plasma are put on the paper, either a change in the color the various dots – or no chnge at all – will indicate whether or not the animal is harboring one or both of the viruses. Various other commercial kit tests are available to diagnose FelV and FIV.

Artcle taken from the Cornell University’s College of Veterinary Medicine Feline Health Center’s Cat Watch Newsletter, Vol. 14, No.1, January 2010, page 5.

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