Is Testing for FeLV and FIV in Feral Cats Always Necessary?
The protocol for veterinarians treating feral cats is relatively standard since most ferals are healthy and require only sterilization, vaccination, and worming. The hundreds of clinics across the country that treat ferals may differ only slightly in their procedures. Many people request a blood test for feline leukemia virus (FeLV) and/or feline immunodeficiency virus (FIV) prior to surgery. The veterinarian frequently offers euthanasia of cats testing positive as the only option, regardless of whether the cat is symptomatic (displaying signs of illness) or asymptomatic.
Contrary to common assumptions about feral cats, there is no evidence to suggest that the majority of feral cats are in poor health or are any more likely to be infected with FeLV or FIV than domesticated cats. Certainly, kitten mortality is high—at least half of all feral kittens born never reach adulthood. If they do, their immune systems are able to fight off most viral and bacterial infections. Studies show that between 1 and 5 percent of the domestic (socialized) cat population in the U.S. is infected with FeLV or FIV. When sick and “high risk” pets are tested, the infection rate is much higher: 13 percent for FeLV and 7 percent for FIV. Available data indicate that approximately 4 percent of feral cats are infected with FeLV and FIV. So how important is it to test feral cats for FeLV and FIV? The answer depends on a number of considerations.
The decision to test or not should be based both on the goals of the humane management program and the welfare of the individual cats. The enormous tragedy of overpopulation is what prompted rescue groups and individuals all over the country to start large-scale sterilization programs for feral cats. Controlling breeding through nonlethal means is and has always been the overriding goal of all of these programs. In addition to controlling breeding, neutering has the added benefit of improving the quality of the cats' lives by reducing or eliminating behaviors like fighting, mating, and roaming that put them at risk of becoming injured, getting killed, or contracting FeLV and FIV. Before making a decision about testing, it is important to assess the cats you are planning to trap and formulate a management plan. Are the cats truly feral or are they stray? Will the cats go back to the colony or, if stray or tamable, be homed? Clearly, tamable kittens and strays should be tested before being placed in foster or adoptive homes. But what about untamable adults who will be returned to the colony site? Testing may be warranted in some situations and not in others. Testing a colony with a high mortality or disappearance rate and/or obviously unhealthy members may be appropriate, whereas testing an apparently healthy, flourishing colony may be unnecessary. Also essential to the decision-making process is an adequate understanding of the nature of both viruses and the limitations of the tests used to detect them.
Feline Leukemia Virus\FeLV
Feline leukemia virus is a retrovirus belonging to the oncornavirus subfamily, which means it is a cancer-causing virus. In addition to causing feline leukemia, FeLV causes severe anemia and suppresses the cat's immune system, leaving the animal vulnerable to a variety of opportunistic diseases. Infected cats shed FeLV primarily in their saliva, although the virus is also present in the blood, tears, feces, and urine. Most cats acquire FeLV from their infected mothers. Other modes of FeLV transmission include mutual grooming, sharing food dishes, and fighting. Fortunately, FeLV cannot survive very long outside a cat's body. The virus loses its infectivity within minutes or hours if left at room temperature, and it can easily be destroyed with most disinfectants and detergents.
How FeLV exposure affects a cat
One of three things can happen when a cat is exposed to FeLV. The cat may experience a transient viral infection and then fight off the virus, developing future immunity. There is evidence that up to 70 to 80 percent of adults exposed to FeLV survive the initial stage of infection and acquire immunity. Kittens under 16 weeks are much less likely to overcome a viral attack. If the cat does not overcome the initial infection, the virus eventually moves to the bone marrow, and the cat becomes persistently infected, or viremic. Even though a persistently viremic cat may be asymptomatic for several years, he or she will usually develop FeLV-related diseases at some point. Persistently infected cats shed the virus throughout their lives, becoming a source of infection for other cats with which they come in contact.
A third possibility is that the cat is able to produce an effective immune response to the infection yet continue to harbor the virus somewhere in the body. A latently infected cat does not appear to be susceptible to FeLV-related diseases and does not shed the virus the way a persistently infected cat does, so there is no risk of infecting other cats. The latent phase of a FeLV infection seems to be temporary for most cats, which become free of the virus within a few years after the infection occurs. However, latently infected cats do occasionally become persistently viremic.
Testing for FeLV
There are two types of blood tests available for detecting FeLV: immunochromatic tests and the immunofluorescence assay (IFA). The immunochromatic tests, such as the ELISA, detects the presence of FeLV during the initial, or transient, stage of infection, whereas an IFA test detects the virus during the second stage, after the bone marrow has become infected (an ELISA can also detect the virus at this stage). Immunochromatic tests can be performed in a few minutes at a veterinary clinic.
Since it is possible for an ELISA to register a false positive result, a cat that tests positive should be retested in 8 to 12 weeks, using either an IFA test alone or a second immunochromatic test followed by an IFA test. A cat exposed to FeLV may test positive during the transient phase of the infection and then test negative if the virus is overcome. It is likely that some cats euthanized because of a positive test result were tested during this phase and would have eventually overcome the infection. A cat that tests positive using an IFA will likely remain positive for life. Note that a cat in the initial stage of FeLV infection may actually test negative. To avoid a false negative test result on an infected cat, test the cat at least 28 days after the cat's last possible exposure to the virus. Unfortunately, there is no test available to detect a latent FeLV infection.
Treatment
Although there is no known cure for FeLV, supportive care—including good nutrition, minimization of stress, and prompt treatment of illness—can improve the health of and prolong the life of FeLV-infected cats. New treatments known as immunotherapies are said to boost an infected cat’s weakened immune system. These therapies are popular, but their effects are largely unproven.
Feline Immunodeficiency Virus\FIV
Feline immunodeficiency virus, like FeLV, is a retrovirus. FIV is in the lentivirus subfamily. FIV results in suppression of the cat's immune system, compromising the animal's ability to fight off infection. FIV-infected cats are vulnerable to a wide array of bacteria, viruses, and fungi that normally are harmless to a healthy animal. Fortunately, FIV does not seem to be transmitted as easily as FeLV. Evidence suggests that the primary mode of transmission is through bite wounds. This explains why the cats most likely to become infected are free-roaming, unneutered males prone to territorial fighting. FIV does not appear to spread easily through casual contact among cats, so it is possible to keep an FIV-infected cat in the same household as a healthy cat with little risk of transmission, provided the cats tolerate each other and are not fighting. It is important to note that kittens are unlikely to acquire FIV from an infected queen, either through in utero transmission, maternal grooming, or nursing.
Progression of the virus
After initial infection, the virus spreads to the cat's lymph nodes, causing them to become enlarged. The cat may develop a fever that lasts for several days and may experience a drop in the white blood cell count. During the second stage of infection, the cat can be completely asymptomatic and remain healthy for up to several years. During the third, chronic stage, the cat begins to develop signs of immunodeficiency and may suffer from a number of secondary conditions and opportunistic infections, including stomatitis, ocular inflammation, cancer, and respiratory tract infections. FIV-infected cats can also develop persistent intestinal and urinary tract infections, neurological problems, kidney disease, and tumors. A diagnosis of FIV is not necessarily cause for alarm. Since the virus has a relatively long incubation period, a cat that tests FIV positive may live happily and healthily for several years.
Testing for FIV
Infection can be detected by testing for the presence of FIV antibodies. In some cases, detectable FIV antibodies may not appear until 8 to 12 weeks after exposure. The IDEXX SNAP test can be used to detect FIV antibodies (a SNAP combination kit can test for both FeLV and FIV using the same blood sample). Since false positive results do occur, a positive test should be confirmed with a second test, preferably with a more specific test like the Western blot (WB). The WB (or immunoblot) test also detects the presence of FIV antibodies, but is more timeconsuming than the ELISA and requires laboratory analysis. Remember that kittens that test positive are not necessarily infected. If a kitten tests positive, the test is probably detecting antibodies passed from an infected mother to the kitten through colostrum. Positive kittens should be retested between 4 and 6 months of age, when any antibodies obtained from the mother cat will have disappeared.
In 2002, the first FIV vaccine was approved. Fel-O-Vax FIV results in antibodies that are indistinguishable from those that occur with natural infection. Therefore, it has become difficult to know which cats are infected with FIV, vaccinated against FIV, or both infected and vaccinated.
Care and treatment
Although there is no cure for FIV, veterinarians can treat or at least alleviate the secondary conditions and opportunistic infections associated with the virus. And good supportive care can improve the quality of an FIV-infected cat's life. Holistic veterinarians recommend nutritional support, herbs, vitamins, homeopathy, and other alternative treatments such as acupuncture to help strengthen an animal's impaired immune system. For more information about holistic treatments, see The New Natural Cat, by Anitra Frazier (also provides information about treating FeLV) and Dr. Pitcairn's Complete Guide to Natural Health for Dogs and Cats by Richard Pitcairn, DVM, and Susan Hubble Pitcairn.
FeLV And FIV Testing in High Volume Spay\Neuter Programs
In 1991, manyrescue organizations formed guidelines for veterinarians and caregivers working with feral cats that included a recommendation to test the first 20 to 25 percent of the colony and to test a mother cat to determine the status of her kittens. Many programs have evolved since that time, including large-scale feral cat spay days like those run by Operation Catnip in North Carolina and Florida, AzCATs in Arizona, the Feral Cat Coalition in San Diego, and ACA in the Washington, DC area. Experience has led many of those involved in these and similar programs to question the efficacy of testing feral cats for FeLV and FIV. Some have even chosen to discontinue testing of feral cats altogether. The factors they considered in deciding not to test included:
- The percentage of feral cats infected with either FeLV or FIV is low. Approximately 4 percent are infected with FeLV and 4 percent with FIV. This is similar to the infection rate in pet cats.
- Sterilization contains the spread of viruses like FeLV and FIV. Since neutering reduces or eliminates the primary modes of transmission, such as fighting and breeding, infected cats pose little risk to other cats.
- Infected cats are often asymptomatic and can remain healthy for several years. In addition, because testing is not always accurate, healthy cats may be euthanized unnecessarily when positive test results occur. Moreover, removing and euthanizing a cat that tests positive will not necessarily prevent spread of the infection within the colony since it's likely that the other colony members have already been exposed to the virus.
- In some circumstances, the cost of testing may outweigh its effectiveness and even hinder the success of a sterilization program (see interview with Dr.Levy, following). The effectiveness of these large-scale sterilization programs indicates that the goal of spaying and neutering as many ferals as possible can be met without compromising the health or well-being of the cats. It is important to remember that we are in the midst of a crisis. Shelters all over the country are killing stray and feral cats at an alarming rate. We need to focus our energy and resources on preventing the births of more homeless kittens, most of whom don't survive their first year of life. Increasing the number of animals who are spayed and neutered is the single most effective way to help control the crisis and reduce the suffering of stray and feral cats.