No More Homeless Pets Forum April 11, 2005 Understanding Feline Leukemia and FIV

The truth might surprise you! Julie Levy, DVM of the University of Florida has studied Feline Leukemia and FIV (Feline Immunodeficiency Virus) extensively, and will answer your questions about how they are spread, the accuracy of tests, and the prognosis for cats who test positive.

Introduction from Dr. Julie Levy:

Are you confused about the difference between an ELISA, an IFA, and a PCR? How about the difference between antigen and antibody tests? What are the best tests for diagnosis of FeLV and FIV? How does vaccination influence test results? Can you ever be truly certain of a cat's infection status? What priority should you place on testing when funds are short and veterinary costs are high? Is there any way to reduce the costs of testing? Is it necessary for all cats to be tested? What is the responsible thing to do with cats who test positive? Is infection a death sentence?

These are common questions that face shelters, veterinarians, cat rescue groups, and feral cat sterilization programs. This week is your opportunity to learn about the science, politics, and urban legends that accompany retroviral infections of cats. We'll discuss how to develop responsible and cost-effective testing priorities that benefit the cats, protect pets, and control the spread of the diseases. We'll look at the challenges these infections raise for cat welfare organizations, which may have a very different perspective from individual cat owners.

It's your turn to ask about testing strategies, prevention, and treatment.

Questions

What percentage of cats are infected, and is testing of all cats necessary?
Does the FIV vaccine cause false positive test results?
How contagious is it?
Adopting out cats possible exposed to a virus
How accurate are diagnostic tests?
Is it okay to mix positive and negative cats?
What about using one SNAP test for multiple cats?
What's the story with all these feline leukemia tests?
Is it better to test or vaccinate?
Keeping infected cats as healthy as possible
Can a positive cat be sterilized, and are cheaper tests on the horizon?
Safe vaccines, and maybe a cure?

What percentage of cats are infected, and is testing of all cats necessary?

Questions from Christine and Char:

We vaccinate, sterilize and test each shelter intake for FIV/FeLV through our local vet with a blood test (at time of sterilization, which is usually 2 weeks to a month after they arrive depending on funding available). So we have tested hundreds and hundreds of cats at $40 per test. We do have a free roam room for social felines who have been tested, sterilized, vaccinated and dewormed.

We are not sure if we need to do this or if our money should be spent on trying to sterilize more. Is there is a cheaper screening test for the cats that seem like they are less at risk, like an owner relinquished declawed cat that has not gone outside but the owner moved? We raise all the money for helping felines through fundraising and donations, so our funds are very limited.

However, in the past 3 years we have had maybe 6 positive cats who were all large "tom" cats. Does Dr. Levy have any preliminary insights into the prevalence of these diseases from the research she recently completed?

Response from Dr. Julie:

Feline Leukemia Virus (FeLV) and Feline Immunodeficiency Virus (FIV) are among the most common infectious diseases of cats. Over the past 20 years, prevalence of FeLV has decreased, presumably as a result of widespread test and removal programs and immunization against FeLV. Testing for FIV is less common than for FeLV, and the recently introduced FIV vaccine is not widely used.

Last year, shelters and veterinary clinics joined us for a new study on FeLV and FIV prevalence. A total of 18,038 cats from the United States and Canada were tested, of which 446 (2.5%) were positive for FIV and 409 (2.3%) were positive for FeLV. Of these, 58 (0.3%) were co-infected with both viruses. Prevalence was significantly higher in cats tested at veterinary clinics than at shelters, in mature cats than in juveniles, in males than in females, and in diseased cats than in healthy cats. Cats with access to outdoors had higher infection rates than cats kept exclusively indoors.

How to get the biggest bang for your veterinary care buck is an important issue. After all, money (plus time and space) is directly related to how many cats you can save. With cat population out of control and a majority of cats admitted to animal control agencies still being euthanized, my personal opinion is that we are obligated to make our rescue programs as successful and efficient as possible.

You are right in thinking that a small minority of the cats that you test are likely to be positive. That means you can spend hundreds of dollars for each infected cat that you identify. Here are some strategies that rescue groups have used to make their budgets go as far as possible:

1. Purchase test kits through the IDEXX Shelter Program. IDEXX is the maker of the SNAP Combo test for FeLV and FIV. They generously offer their test kits at a 40% discount to non-profit groups (800-340-6296). Of course the tests are not very helpful if you cannot collect blood from the cats. Some groups have found a vet or vet tech who can draw the blood and run the tests. Others work out a deal for a discount with their veterinarians if the group provides the test kits.

2. The Tompkins County SPCA may be the country's premier example of how to set priorities to save lives. Tompkins County became the nation's only No Kill community saving 100% of healthy and treatable dogs and cats, and 100% of feral cats. One of the ways they accomplished this was to stop devoting resources to testing cats. While this might sound like heresy, the end result was that Tompkins County became the safest place in the country to be a dog or cat (http://www.bestfriends.com/nomorehomelesspets/pdf/feralcatcompassion.pdf).

If you stop testing, I recommend that the cats be housed individually prior to adoption so that no new cats become infected. I also recommend that the new adopters receive clear instructions to have their cats tested by their own vet. Using this strategy, there may be a few sad families that have to deal with unpleasant news about their new family members, but there may also be a lot more cats that can be saved by your organization. It is imperative that the local vets and other rescue groups in your community have a clear understanding of the reasons for your unconventional policy or you could be the target of some bad PR.

3. Some groups choose an intermediate approach of testing only the highest risk animals: the sick, the fighters, the cats known to be exposed to infected cats.

4. FIV is less likely to make cats sick in the short term than FeLV is, and a large percentage of FIV-infected cats live long healthy lives. FIV infection is rare in kittens and males outnumber females 3:1. Therefore, many groups skip testing kittens for FIV or drop FIV testing altogether.

5. One thing that I do not endorse is testing "representative" cats, such as the just the mother of a litter or part of the litter. There are too many surprises in store to accurately extrapolate the results on one cat to another, no matter how closely related they are. If you advertise that "all cats" are tested, then they all should be. If you only test some, be straightforward about who has been tested and who has not.

Does the FIV vaccine cause false positive test results?

Question from Abby:

I'm a volunteer foster for a no-kill organization. We have one cat who tested positive for FIV only. He was a stray that started hanging around with some cats in someone's backyard. He was very friendly with people and other pets and already neutered. We retested two months after the initial test and it was negative. A third test showed positive results. (The tests were all SNAP combo tests.) He has been very healthy for the two years that I have fostered him. Is there a test available yet to tell if he has been vaccinated or if he really has FIV? And what are the chances of him passing it to other cats? Also, should he receive the same vaccinations as our other cats? I keep getting different answers from the several vets we use.

Response from Dr. Julie:

The mainstay of clinical screening for FIV infection is detection of circulating antibodies against FIV. Because FIV produces a persistent infection from which few cats recover, detection of FIV-specific antibodies in blood has been considered to be a reliable indicator of infection. Patient-side immunochromatic lateral flow antibody tests, such as the IDEXX SNAP test, are commonly used for screening cats, and the Western blot antibody test is recommended for confirmation of infection. Some cats fail to produce detectable antibodies against FIV following infection, and these cats will have false-negative results on antibody tests.

On a related side note, antibody tests are complicated in kittens that have acquired anti-FIV antibodies in milk from their infected mothers. It is uncommon for kittens to become infected from their mothers or from other cats, so most kittens that initially test "positive" will eventually turn out to be negative when their maternal antibody wanes.

The release of Fel-O-Vax FIV®, the world's first vaccine against FIV, was a scientific breakthrough. However, the vaccine also interferes with all of the currently licensed FIV diagnostic tests based on detection of antibodies. Vaccinated cats produce antibodies that are indistinguishable from those used for diagnosis of FIV infection. These antibodies are usually detected within a few weeks of vaccination and persist for more than a year. These antibodies are also passed to kittens that nurse on vaccinated queens. Passively acquired vaccine-associated antibodies persist past the age of weaning (8 weeks) in more than half of kittens but seem to be gone by 12 weeks of age.

Culture for FIV is an extremely accurate test, but is not currently available commercially and is primarily utilized in research laboratories. Although it would be the best test for your cat, you probably will not be able to get it.

The polymerase chain reaction (PCR) has been promoted as an alternative method for confirming the true FIV status of cats. Several reference laboratories now offer unlicensed PCR for diagnostic purposes, but virtually nothing is known about the sensitivity, specificity, and overall diagnostic performance of these tests. A recent study in our lab found false-negative rates of 7-59% in FIV-infected cats. False-positive rates of 0-10% were found in unvaccinated cats and 5-56% in vaccinated cats. The difficulty in distinguishing FIV-infected cats from FIV-vaccinated cats is a significant challenge for cat welfare groups. Right now, I am most confident in the PCR test offered by UC Davis.

The bottom line is that as long as various tests are discordant (conflicting) it is very difficult to know which one is correct.

As far as care, I would refer you to the guidelines established by the American Association of Feline Practitioners, http://www.aafponline.org/pdf/guidelines_retrovirus_testing_2001.pdf. The guidelines suggest that FIV+ cats should receive twice annual veterinary exams, once annual well-care blood tests, and routine vaccines (AAFP suggests vaccinating most cats every 3 years).

In my experience, FIV transmission within a household of cats that do not fight is uncommon, but not impossible.

How contagious is it?

Question from April:

Our feral cat spay/neuter program has met resistance in attempts to recruit host sites due to concerns about disease transfer. Can you briefly describe your cleaning/sanitizing/sterilizing procedures for your feral cat spay/neuter clinics? What are your techniques for preventing the spread of feline leukemia and FIV during your clinics and the holding times prior to and post sterilization?

Also, our volunteers transport feral cats to/from clinics in their cars - what are the best practices for preventing disease transfer to our own cat families? How long does the feline leukemia virus live outside of the body and how easily does is spread to other cats who come into contact with surfaces contaminated by a positive cat?

Response from Dr. Julie:

This is an easy one! FeLV and FIV are very fragile viruses that do not survive well in the environment. On a dry surface, they are inactivated within an hour or so. Routine disinfectants, such as quaternary ammonium, are also effective. However, the viruses can remain infectious for a while longer if they are protected by body fluids such as blood and saliva.

What this means is that it is virtually impossible to transmit these viruses by placing cats one after the other in a clean cage, car, carrier, or via contaminated skin and clothing of the handlers. Even a simple screen is all that is necessary to prevent transmission between cats.

It also means that the viruses can be transmitted by using contaminated instruments, endotracheal tubes, tattoo equipment, etc. Even though our feral cat Trap, Neuter, Return (TNR) program, Operation Catnip, is extremely frugal, we observe "universal precautions" to prevent spread of blood-borne pathogens. This includes a new set of sterile instruments (we autoclave everything and do not rely on cold sterilization), blades, suture, gloves, needles, etc., for each cat. If we use dental equipment or endotracheal tubes, these are cleaned and disinfected before the next use. If we give a blood transfusion, it is from a negative cat. We used to tattoo cats, but found it was impossible to sterilize the equipment between cats, so we gave it up.

Although it is common for vets and cat welfare groups to try to save money by reusing contaminated instruments on multiple cats, I do not think this is appropriate. As a specialist, I sometimes diagnose FeLV or FIV in older indoor cats that have been negative in the past. I often wonder if shoddy infection control practices in veterinary clinics might explain some of these cases. Not all infected cats test positive all of the time and there are likely more diseases yet to be discovered that we should be guarding against as well. The best practice is to treat all the cats as you would like your own pet or yourself to be treated.

While FeLV and FIV present little challenge, other infectious disease that clinics might be wary of are a lot tougher. Herpes lives for days, calicivirus can survive for more than a week, and panleukopenia and ringworm are capable of infection after more than a year. And then there are all the creepy crawlies like fleas that may hitchhike in on the cats.

Protecting the volunteers, their pets, and the veterinary clinics from these other infections is very important. I recommend that volunteers keep the trapped cats in completely separate areas from their pets, such as a garage. The floor under the traps can be lined with plastic that is sprayed with a cat-safe flea spay to reduce flea infestation. Separate clothing and gloves should be worn when working with the feral cats. Hand-washing and then disinfection after the cats are gone (it's hard to beat bleach for that) cannot be overemphasized. I think the biggest threat to a car is that a cat might urinate during a car ride. There is nothing as enduring as feral tomcat pee on upholstery. Preemptive plastic lining is highly encouraged. At the clinic, the volunteers should stay away from the other cats in the clinic, wear gloves and protective clothing, confine their activities to the minimum area possible, and disinfect well after use.

Even with all of these precautions, both feral and pet cats can bring in diseases, even if they are not outwardly sick. The new virulent form of calicivirus took its deadly rampage through several clinics, homes, and welfare groups because it was hardy enough to be transmitted by personnel and other cats.

Adopting out cats possible exposed to a virus

Question from Lyla:

I recently had a cat that was euthanized after testing positive for FeLV (having tested negative 3-4 months earlier). It was a hard decision to put him down (and even harder for the vet office where the cat had spent half his life practically), but given how sickly he had been the whole six months I had him, it seemed the right thing to do.

I run a small cat shelter with open caging and this cat was mixed in with numerous other cats, all of whom have received FELV vaccinations. Should I take any special precautions in adopting out these cats? I do not normally test for FELV/FIV unless a cat is sickly and my vet recommends it. I do not want to get a reputation of giving out sick cats, and don't know how one leukemia positive cat is likely to have affected the other 30 cats in the room.

Response from Dr. Julie:

I am very sorry for your loss. It's hard to let them go, even when you know it is the kindest thing for them.

In general, kittens are much more susceptible to FeLV than adults. However, this resistance in adults can be overcome by concurrent diseases, crowding, and stress, which are frequent factors in rescue groups.

For these reasons, my recommendation is to test all cats that are going to be housed in groups. If you rescue enough cats, you are going to have some that are positive. Since most infected cats are outwardly healthy, you can't be confident of their status without a test.

Your situation is a difficult one. I think you are obligated to tell potential adopters that the cats have been housed with at least one FeLV+ cat. That is likely to scare off some of the adopters, so your placement rate might fall, leading to fewer rescues. FeLV vaccination does not protect all cats, so you cannot rely on that as a substitute for testing. On the other hand, a bad reputation is difficult to shake, even if you take corrective measures.

We never want to inadvertently hurt our rescued cats in our efforts to help them. As you've experienced, FeLV can cause severe illness and tragically shortened lives. For this reason, I believe it is important to use husbandry practices that prevent the transmission of FeLV and FIV in our rescue facilities.

I would suggest that you test all the cats now, segregate any positives, and test again in two months. Although you can never be 100% sure that a cat is not a latent carrier of FeLV, the vast majority of cats will test positive within two months of effective exposure. Future cats should be tested before entering the general population.

Although it is not always practical, it would be ideal to quarantine new arrivals and retest them two months after the first test in case there was a recent exposure. Our rescue group tried to rehome cats as quickly as possible, but our adoption forms recommended that the new owner have the cats tested one more time "just to be sure." We group-housed our cats as well, and although quarantining cats for two months was not possible, we did retest cats if they were still with us after 6 months to help assure nothing slipped by the pre-admission screening.

How accurate are diagnostic tests?

Question from Michelle:

About three years ago, I sought to find a home for a tame cat that had been left to fend for himself in my parents' neighborhood. After several tests at the vet, the cat came up "weakly positive" and "positive" for FeLV and "weakly positive" and then "negative" for FIV. The rescue who had offered to adopt the cat out wouldn't take any cats that tested positive for FeLV or FIV, so I decided to keep him. Since I first got Chester, he has put on some much-needed weight. He wheezes a bit, shakes his head from time to time and drools sometimes, but other than that is pretty much the picture of health.

I was speaking to a fellow rescuer recently who said that there have been studies about the "reverse" rates for cats who have been tested with pretty high numbers of cats who test positive and then when retested a while later, test negative. Have there been such tests and, if this is the case, are we doing cats in our care a disservice by using tests that are largely inaccurate? Can cats be carriers, but not be infected or affected healthwise?

Response from Dr. Julie:

The tests for FeLV and FIV, when properly used, are very accurate. We can miss infections on the first test if there was a recent exposure to infection, and sometimes the infection level is too low to detect on the tests. These are exceptions, however, and the vast majority of cats have clear results.

I believe the SNAP test is harder to "mess up" than the multiwell plates or the wand tests. The SNAP test does its own "washing" while the others require the user to wash the test. Inadequate washing is probably the most common cause of false positive results. I also believe that testing saliva or tears is so fraught with potential for errors that I wouldn't use them at all.

It is possible to misuse the SNAP test as well. The most common mistake is not to "SNAP" it soon enough so that there is excessive blue background color that confuses interpretation.

Other practices that can cause misinterpretation of results are mixing samples from several cats to perform a single test, improper storage of test kits, and mixing reagents from different batches of tests.

Some cats can be transiently infected with FeLV (test positive) and then clear the infection with a good immune response (test negative). Whether these cats are truly uninfected or have only reverted to a latent infection state is unknown. It is believed that most cats that test positive for 3 months will remain positive for the rest of their lives. The chances that the first test will take place in the brief 3 months of the cat's life when it was transiently positive are low, but not zero. That is why we always recommend retesting cats after a first positive test, however, in my experience, they almost always stay positive.

FIV antibodies can be transiently present in uninfected cats in two situations. One is in kittens that nurse on FIV-infected or FIV-vaccinated queens. Although most of the kittens are actually free of FIV, these antibodies will show up in the FIV test for up to 12-20 weeks of age. The other is in the case of cats that have been vaccinated against FIV. Vaccinated cats will have detectable antibodies for more than a year.

Cats can be carriers capable of infecting other cats without any sign of disease themselves. Being a "carrier" is equivalent to being "infected."

Is it okay to mix positive and negative cats?

Questions from Mary and Christie:

I belong to a group that does Trap, Neuter, Return (TNR). Some in our group want to buy land/buildings and turn this land into a refuge for feral cats who cannot be returned to their colonies. These people do not plan to test any of these cats before releasing them on the refuge. What range of problems could we expect to happen from this action?

Also, in doing TNR programs with feral colonies, should positive cats be put down instead of being placed back into the free-roaming colony?

Response from Dr. Julie:

The first part of your question is fairly easy. If you are planning to confine cats for the rest of their lives in a sanctuary, I think they should be tested and segregated based on their infection status.

Although transmission among adult cats that do not fight is relatively low, it is not zero. The risk of transmission is higher among cats that are housed in large groups and that are under physical or psychological stress, which might be expected to occur when translocating cats to a sanctuary.

In most cases, sanctuaries quickly fill up to the holding capacity and then the sanctuary is virtually closed to new admissions. It would be more difficult to care for the cats over many years if infectious diseases are circulating among them. An excellent model for a feral cat sanctuary is at Best Friends Animal Sanctuary (WildCats Village, buttons #10 and #11 at http://www.bestfriends.com/atthesanctuary/animals/cats.cfm).

The second question is harder and is likely to generate more disagreement. It also might seem like my answer to the first question is contradictory to my answer to the second one.

Here are the facts that affect my opinion:

1. Feral cats have infection rates of FeLV and FIV of approximately 4%. This is similar to the rate in pet cats, suggesting that feral cats are no more of a threat to pets than the neighbor's pet is. (Lee IT, Levy JK, Gorman SP, Crawford PC, Slater MR. Prevalence of feline leukemia virus infection and serum antibodies against feline immunodeficiency virus in unowned free-roaming cats. J Am Vet Med Assoc 2002;220:620-622.)

2. A reasonable estimate of a community's stray and feral cat population is about 0.5 cats/household. That means our TNR programs have to be massive in scale (thousands of cats each year, not hundreds) if there is a reasonable expectation to reduce their overall numbers. We must make sure that every penny and every volunteer minute is put to the best possible use.

3. Most of the FeLV+ and FIV+ feral cats that we detect are outwardly healthy. Many of these cats can be expected to live for a number of years.

4. There is no opportunity for confirmatory testing if cats are euthanized at the first test.

Given all of these facts, my opinion is that we should devote all of our resources toward sterilizing more cats via TNR and cutting back on anything that might detract from that effort. This is "herd health" medicine, and we should focus what is best for the group. We no longer routinely test cats in the Operation Catnip TNR program. Sometimes we will test a debilitated cat and use the information as a "tie-breaker" in a decision to euthanize or not.

I don't think it is necessarily wrong to test feral cats, but groups should have a clear understanding of the cost:benefit ratio if they choose to do so. How much does it cost to find those few infected cats vs. could that money be spent more effectively elsewhere? They should also have their policies in place so everyone agrees on what will be done with cats that test positive.

Comment from Laura:

I am involved in trap-alter-release efforts for feral cats. I do not euthanize FeLV positive cats since I've heard that the risk of transmission is actually quite difficult and is mostly from mother to kitten. Since I am altering, this mother to kitten mode of transmission will be stopped. And as Dr Levy mentioned this week, most cats who aren't vaccinated show natural exposure and subsequent immunity. In other words, cats are usually exposed to it and show natural resistance. It's not like the positive feral that I return to his or her feeding grounds will be any greater risk to the colony than before being fixed. In fact, they'll be less of a risk, because they won't be mating or bearing young.

I've also heard that only a 1/3 of those that test positive will die from getting full-blown FeLV within a couple years. The others will live longer or will simply be a carrier and never get the full-blown disease. Since most of the cats can live for a few years or even a full life, I think this is the most humane thing to do. Sure, many will die of FeLV, but they could also die of a host of other threats on the street. In my mind, that the cats have a "chance of having a painful ending" is not reason enough for me to euthanize. I am aware that many other groups working with ferals will euthanize FeLV positive cats.

What about using one SNAP test for multiple cats?

Question from Gerry:

In regards to Feline Leukemia (FeLV) testing, the shelter I work with tests every cat when it first comes in and again after approximately 30-60 days (for example all January incoming cats are retested March 1). We also test all cats once a year, in case a cat comes in which is positive but does not test as such but has spread FeLV to the other cats.

When testing several cats from the same household (up to five), We pull a blood from each cat, place it separately in a labeled test tube and after all the samples are gathered, we take some from each tube, mix these together and then run the IDEXX test on this "batched" blood. We have found the IDEXX test able to find a positive sample done like this. While we did not have good luck with blood mixed like this when sent to an outside lab (ANTECH) we have found the IDEXX snap tests pick up the positive mix every time. We also "batch" test when doing the retest and yearly checks.

We also vaccinate with Solvay EC4+FeLV, first dose given upon arrival, followed by a second dose 21 days later. This is standard for every cat coming in. We have picked up a positive at the first retest, (this cat was tested solo upon admission, we believe it was a case of exposure before admission in too short of a time frame to show as positive at first testing). We retested the entire population every month for three months and had no additional positives. We now firmly believe that the vaccine does give protection.

As for vaccination, we have found using Felomune CVR on every cat upon admission has cut incoming Upper Respiratory Infection (URI) to less than one percent. One dose of this may be shared by three to four cats using only one drop in each eye and nostril to cut costs while not harming effectiveness. Even if each cat is given the full dose, the cost saving are huge when compared to treating 20 to 40 percent of the new cats for URI.

Response from Dr. Julie:

I think this is a good example of a rational and thorough testing program that screens cats at admission, then does a follow-up to catch any recent converters. Testing annually for any cats still in the program is a good safety net for any infection that might have slipped through the cracks.

The only thing I would quibble with is pooling samples. While you are correct that a strong-positive sample can be diluted several fold and still be detected, a weak-positive sample can be diluted below the level of detection.

I agree that colony-housed cats should be vaccinated against FeLV (again, seeking to protect against any FeLV infections that snuck past our testing program). However, most resistance against the virus in adult cats is due to natural immunity. That is why FeLV infection research is usually performed in kittens. It is relatively hard to get adults infected.

What's the story with all these feline leukemia tests?

Question from BJ:

We have a feral male cat that was shot by neighborhood punk with a bb gun. He lost an eye because of this act. We trapped him and obtained medical help for him only to learn that he was positive for leukemia (ELISA test).

The cat has recovered from this injury and appears to be doing all right at the moment. We have him in an outdoor enclosure (with shelter, of course) separate from our other cats. He will not let us have any contact with him, but we are trying to spend a few moments a day in the cage with him, talking softly, etc. We don't want to upset him.

We want to do all that we can for him, although he is feral and will not let us touch him. We are currently feeding him Purina One kitten formula with yogurt. He had thrown up a couple of times initially throughout all the trauma, but this food seems to be something he likes and he hasn't thrown up at all in over a week. We give him a little wet food in the morning and in the evening to give him a little variety.

Can you suggest anything more that we might be able to do for him (i.e., something we could put into his food that he would not smell or taste perhaps) that might boost his immune system?

Also, at what point should we have him retested? And should we have the IFA test done, or have a Western Blot test done? Testing will entail trapping and transporting to the vet and he will probably have to be sedated for them to be able to work with him, so we don't want to do it too soon before the results might be conclusive. The ELISA test was approximately one month ago.

Response from Dr. Julie:

This poor little kitty is lucky he found you. We'll discuss a testing and treatment plan for him, but first, a little virology . . .

Detection of the FeLV core protein p27 (antigen), which is produced abundantly in most infected cats, is the mainstay of clinical FeLV testing. Immunochromatic lateral flow devices and microtiter ELISA can be performed in clinics. Commonly used tests in the US include the IDEXX SNAP and Synbiotics Witness tests.

The immunofluorescent antibody test (IFA) detects p27 antigen in infected blood cells. Because it requires special processing and fluorescent microscopy, the IFA must be performed by a qualified reference laboratory. This test requires an experienced technician to interpret, and poor laboratory quality control can lead to inaccurate results. The laboratory that I prefer to use is the National Veterinary Laboratory in New Jersey. They invented the FeLV IFA test decades ago.

Antibody tests are not useful because of the high rate of exposure to FeLV in the environment. In surveys conducted prior to the development of FeLV vaccines, most free-roaming cats acquired anti-FeLV antibodies, evidence of at least transient exposure and infection with the virus.

The polymerase chain reaction (PCR) test has been used for the diagnosis of FeLV infection. This test detects viral DNA instead of protein antigens. PCR may be useful in helping to determine the true status of cats with discordant results from other testing techniques and may be the most sensitive test available. The PCR must be performed by well-equipped and trained laboratories. At this time, I believe that the PCR laboratory at UC Davis is a good choice.

Virus culture for FeLV is not routinely available in the US, but is considered to be the confirmatory test of choice in Europe. However, not all cats with FeLV infection are positive on virus culture. Because FeLV generally replicates in lymphoid tissue and other sites before the bone marrow, immunochromatic tests may detect infection a few weeks earlier than the IFA. Some cats are apparently able to clear the infection at this stage and may revert to negative status within a few weeks to months. IFA-positive tests indicate that the bone marrow is infected with FeLV. In this case, most cats remain persistently infected for life.

That was a long-winded introduction for a testing plan for your cat. In my experience, most cats with positive FeLV tests remain positive. I think that is because it is statistically unlikely that you will test very many cats that just happen to be in their brief "transient" infection phase. Still, to be safe, we like to wait 2-3 months before testing again. Cats that are still positive at that time are likely to remain positive for life.

If you do elect to sedate him for retesting, I would probably go the extra step to collect samples for SNAP and IFA (and PCR if you are really want to be as thorough as possible).

The next question is how will the results affect your management of him? Is he going to be released if he is negative? If he (and you) thrive in the current situation, then there may not be an urgent need to do further testing.

As far as trying an oral supplement to enhance his immune system, I am going to go out on a limb to say that there are no products that have shown any benefit in FeLV+ cats. While there are literally dozens of folk remedies that have their earnest supporters, there are no well-designed controlled studies that address this question. We all know FeLV+ cats that live full healthy lives without any special care. The response to infection is so individual that without controlled studies, we'll never learn if there is something out there that can really help these cats. A classic example is a German product called Baypamune, which was proposed to save hundreds of FeLV+ cats from their deathbeds. When a large placebo-controlled study was done, there was no benefit in the treated cats. In fact, a higher percentage of the cats that received the placebo (sugar pill) were alive at the end of the study than the cats that received Baypamune.

An injectable product, Feline Interferon Omega, is available in Europe and did show increased survival in treated cats. It can be imported via Internet pharmacies, but requires a USDA permit specifically for each cat to be treated. More information about studies for FeLV therapy can be found at http://www.vetcontact.com/interferon/index.htm and http://www.virbagenomega.com.

Is it better to test or vaccinate?

Question from Frances:

We have run a shelter of about 300 cats for the last 10 years. Upon entry, new cats are placed in cages for a period of 2 weeks or more (depending on their health status) in order to test, vaccinate and sterilize as appropriate.

Due to cost issues, we only test for FIV/FeLV those cats that are either unknown origin or whose origins make them likely to have FIV/FeLV. Cats who test positive for FIV are placed in a free-roaming FIV room. Those who test positive for FeLV are placed in a free-roaming leukemia room. We also have rooms based on special diets (e.g. CD or PH Control). Other healthy, no-issue cats are placed in general rooms, again free-roaming.

In the last 3 months, we are seeing a steadily rising incidence of FeLV in the 'healthy' rooms, which has us concerned. I understand that in some cats, the FeLV may lie dormant for months and even up to 2-3 years, showing as negative on tests.

If this is true, I am wondering if testing will be a cost-effective way to control the problem now, and prevent it in the future, as we cannot afford to test all the cats now, then in 3 months (and still not know if we've caught all of them).

Or given the costs, are we better off to just vaccinate all the cats whose status is either negative or unknown? Then upon adoption, advise 'adoptive parents' of the possibility of FeLV, particularly in rescued cats, and strongly recommend (and subsidize) a test.

I understand that vaccinating an FeLV+ cat will not help it, but can vaccinating without prior testing hurt a cat?

Response from Dr. Julie:

Far and away, most cats with FeLV infection will have a positive test. The ones that slip by our testing programs because they have just recently been infected or because they have very low levels of infection are rare.

I am a firm believer that group-housed rescue cats should be tested. How bad would you feel knowing that a cat who came to you for help contracted a deadly, but preventable, disease while under your care? Testing for FeLV and FIV is so straight forward that it makes prevention of new infections almost 100% avoidable. There are few other diseases that are so easy to prevent.

Remember also, it is very difficult to recover from a bad reputation. One heartbroken and angry pet adopter who inadvertently brings an infected cat into their home (possibly exposing their other cats) can spread a lot of distrust about your organization. Ultimately, adopters may steer clear of your cats, which would reduce the number of cats that you can save.

So what are your alternatives? One is to house the cats individually and then recommend that the new adopter have the cats tested when they take them home. This keeps all of the cats safe from infection. However, if cats tend to stay in your program a long time, it can be difficult to assure a good quality of life for the kenneled cats.

The other alternative is to test all cats at admission before they enter the group-housing area. The special discount prices on test kits for non-profit groups can make this quite affordable. Shelters can sign up to purchase the discounted test kits by calling IDEXX at 800-248-2483 and asking for the Inside Sales Department.

Immune response to vaccination is quite variable among cats. Immunity is not immediate and develops over a period of weeks to months. Not all vaccines are equally effective. Although I advocate FeLV vaccination in group-housed rescue cats, it should never be thought of as a safe alternative to testing. They are complimentary to each other for a best overall effect.

Keeping infected cats as healthy as possible

Question from Karen and Carol:

I have two FeLV positive cats and one FIV positive cat. I tried switching them over to raw food diets but was not successful. Has a basic protocol for caring for these cats been developed yet? Have any supplements been shown to be effective in keeping these cats healthy? One author strongly opposes the feeding of dry commercial cat food to cats – not just immune-system-impaired cats. I feed high quality dry food as well as some canned foods. Should I be moistening the dry food even though the cats like it the way it is?

Is FeLV anything like human leukemia? Do any of the human-type treatments work with cats?

What treatment do you suggest for a cat with FeLV? My cats have been taking Interferon for over a year now and have had no symptoms. What is a typical life span for these cats?

Response from Dr. Julie:

The goal of caring for FeLV and FIV infected cats is to keep them healthy, detect emerging problems early, and treat associated diseases promptly and aggressively so that the cats can enjoy the maximum quantity and quality of life.

The American Association of Feline Practitioners has developed guidelines for caring for infected cats, both in the healthy stage and when disease occurs. The full report can be read at www.aafponline.org/pdf/guidelines_retrovirus_testing_2001.pdf

In summary, the AAFP suggests twice annual veterinary examinations, twice annual blood tests for FELV+ cats and once annual blood tests for FIV+ cats, spaying and neutering, feeding of cooked balanced diets, routine parasite control, and routine vaccinations with inactivated vaccines ("routine" for the AAFP is every 3 years).

The AAFP is also quick to point out that not all medical problems that occur in infected cats are related to their virus infections. In many cases, these cats just have ordinary diseases just like other cats and are equally likely to respond to appropriate therapy. I always approach treatment of FeLV and FIV infected cats with optimism and see how they respond.

Unfortunately, there are very few studies that rigorously compare any of the proffered treatments for FeLV and FIV. Anecdotal claims about antiviral drugs, immunomodulators, nutrition, herbal therapies, crystals, massage and others abound. Each kind of therapy has its ardent supporters. There is a serious need to study treatments scientifically so that the truly beneficial ones can be identified and offered to all cats. So far, we've mostly relied on our own personal experiences. Since so many infected cats thrive for many years without any therapy at all, it is very hard to know if anything we do try is making a difference.

Currently, the best scientific evidence for a beneficial effect exists for feline interferon omega. It is given by injection at a high dose, as opposed to the oral microdosing that is commonly used with the human interferon alpha. Unfortunately, it is not available in the US. Some Internet pharmacies will arrange importation and complete the USDA importation permits. More information about interferon omega is available at www.virbagenomega.com.

Comment from Michelle:

I have obtained feline Interferon for my cats, as have several other people on the www.felineleukemia.org list serve. A vet simply needs to send a letter to the FDA asking for special dispensation to import it. The FDA takes about a month to approve these, then sends a letter for the vet to include when ordering the drug from overseas. The drug is very expensive, but seems to help. Anyone interested in getting information about this process can join www.felineleukemia.org and either look in the archives or post a request.

Can a positive cat be sterilized, and are cheaper tests on the horizon?

Questions from Kristine and JoEllen:

If a cat tests negative for IFA (positive ELISA), is it safe for that cat to be spayed or neutered? I understood that surgeries on Feline Leukemia cats was disadvised because the recovery from the surgery is difficult given their circumstances.

Is it safe to place a healthy cat with an IFA negative cat?

Instead of waiting to repeat the ELISA test for verification, is it better to just move on and perform the IFA test?

Is there any indication on the horizon that the more expensive tests will eventually become lower priced so they can be used as the definitive test the first time around?

Response from Dr. Julie:

In my experience, FeLV and FIV infection does not impact recovery from sterilization surgery. The American Association of Feline Practitioners recommends that infected cats be routinely sterilized to avoid the stress of constant estrous cycling, territorial defense, etc. Also, the metabolic rate of sterilized cats goes down, which makes it easier the keep weight on them.

Of course, debilitated cats are another story, but most of the FeLV and FIV infected cats that I see are pretty robust.

There is no difference in the health of a cat that tests positive with the ELISA vs. the IFA.

There is also a common misconception (even among veterinarians) that the IFA test is more reliable than the ELISA. That is not true. The ELISA is actually more sensitive than the IFA, turns positive sooner after infection, and can detect cats that do not have infection in the bone marrow. Thus some infected (and contagious) cats test positive on ELISA and negative on IFA. The IFA detects infected blood cells, which generally means that the bone marrow is infected and the cat is likely to remain infected for life.

We call the IFA a "confirmatory test," and this likely contributes to the confusion. It is recommended because it is a different technology than the ELISA. This allows us to test a cat two ways. If both of the tests agree, then we can very confident (but not always absolutely certain) that we know the true status of the cat. However, if the tests disagree (discordancy) we can't know which is right. The ELISA is more sensitive (will detect more infected cats) than the IFA, but is reported to have a higher rate of false positives (I have not found this to be true if it is properly performed).

The bottom line is that any cat with a positive test (regardless of the technology) should be segregated from other cats.

I think the confirmatory tests, including IFA, PCR, and culture, are likely to remain somewhat expensive. In addition, there are costs associated with shipping the samples to outside laboratories. The National Veterinary Laboratory (NVL, 201-891-2992), which invented the FeLV IFA test, is considered to be an excellent laboratory and charges less than $20 for the IFA.

Safe vaccines, and maybe a cure?

Questions from Dawn, John, and Evelyn:

Many people still do not vaccinate for FeLV due to concerns about it causing a malignant sarcoma (a type of tumor) at the vaccination site. There is also controversy about how safe and effective the vaccine actually is. Is there any hope that a FeLV vaccine will be made in the future that is safe and effective?

Also, what kind of progress is being made in curing FeLV/FIV? Is anyone out there studying them and making any progress?

Response from Dr. Julie:

Vaccine-associated sarcomas have been associated with most kinds of vaccines, as well as other injections such as steroids and antibiotics. Even subcutaneous fluids have been implicated. Some studies suggest that FeLV and rabies vaccines are riskier than other vaccines such as FVRCP, but other studies have not found this to be true.

That means that we should use vaccines judiciously. We should not unnecessarily vaccinate cats, but we should also use them to prevent serious and fatal infectious diseases. The diseases kill far more cats than the tumors do. It is estimated that the tumors occur in about 2 per every 10,000 vaccines given. Compare that to about 5 of every 100 cats having FeLV or FIV. The actual risk of tumor formation and its cause remain a hotly debated and unsolved mystery. Excellent information is available at http://www.avma.org/vafstf/default.asp and http://www.geocities.com/~kremersark/newhope.html

Judiciously means that vaccine protocols should be developed for each cat according to its risk. Thus, house cats with little exposure to other cats should receive less intensive vaccines than cats kept in large groups or that fight. As a starting point, the American Association of Feline Practitioners has established guidelines for typical house pets, at http://www.aafponline.org/pdf/guidelines_vaccine.pdf.

Recently, the vaccine company Merial introduced a "needleless" vaccine system for FeLV in cats. The hope is that tumor formation will be avoided, but until it is widely used in the field, that can't be known for sure. Tumors have not been associated with intranasal vaccines to date, but there are no intranasal FeLV vaccines.

In my opinion, shelter and rescue cats fall into the high-risk group for infectious disease transmission, including FeLV. The high turnover of our cat populations, cats housed in groups, concurrent diseases such as URI, and a large number of kittens all add up to higher exposure than the average pet cats for whom the guidelines were developed. For this reason, I recommend routine FeLV vaccination for most rescue groups.

By the way, I put all my injections in the lower hind limb of cats (except for the feral cats who get their injections "intracat"). That way, if a tumor develops, I have the best chance of getting the wide surgical borders needed to have the best chance of a cure.

Alas! There is no cure in sight. These are retroviruses, the same as HIV that causes AIDS. Once these viruses become entrenched, it is virtually impossible to eradicate every infected cell. The viral load can be suppressed (either by the cat's immune system or by drugs), which reduces the damaging effects of infection, but cure is an uncommon event. In HIV, more resources are being directed at developing prevention and treatment than in trying to find a cure, because scientists are more optimistic about the first two.

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