Testing for FIV and FeLV – What the Tests Can and Cannot Tell Us

Why testing is not the end-all-be-all of retrovirus management in cats.

by Brittany Roth, Calvin’s Paws Medical Care Coordinator and FIV/Felv Advisor

It seems simple enough – you go to the vet with your new furry friend, and the vet recommends testing her for the two common retroviruses in cats – FIV and FeLV (for the difference between the two viruses and more information, read our previous blog post here). You get the test results back, and they’re either positive or negative, and that’s that, right? Well, not really.

Why not?

A positive test result may indicate that your cat has one of the two viruses…but it might not. How can this be? There are two main factors that play into this: the age of the cat or kitten and the virus that they’re testing positive for.

Kittens

As we explained in our previous blog post, My Kitten has FIV, any kitten younger than 6 months testing positive for FIV most likely does NOT actually have the virus. The test for FIV looks for antibodies to the virus, not the actual virus itself. Kittens get antibodies from their mother while they are nursing, so if the mom has antibodies to FIV, she can pass those on to the kittens. Once the maternal antibodies clear out of the kitten’s system, the kitten will test negative.

The test for FeLV looks for an antigen (protein on the surface of the virus) of FeLV. A kitten testing positive for FeLV is a little trickier, but still not a sure thing. Yes, mothers can pass the virus on to their kittens in the womb or after birth, but just because a kitten gets a few virus particles in their system does not mean it will definitely become persistently infected. Kittens born to positive mothers should be separated from mom as soon as safely possible (6 weeks or so) and retested at 3-6 months of age. We have had several cases (including one just this year!) where kittens testing faint FeLV+ later cleared it from their system and tested negative within about 2 months.

FIV+ versus FeLV+

Adults testing positive are a somewhat different story, depending on which virus they’re testing positive for. Adults testing positive for FIV are usually actually infected, but a second test should ALWAYS be performed to rule out test error. If a cat tests positive with Calvin’s Paws, we always immediately do a second test, and then retest the cat in a month. If all tests agree that the cat is positive, then the cat is probably positive. But here’s the kicker – as mentioned above, tests for FIV look for antibodies to the virus, and current tests can’t tell the difference between an infected cat and a cat that was vaccinated for FIV! So even if all tests agree that your adult cat is positive for FIV, there is still no way to determine if he actually has the virus itself.

Adult Cats

Adults testing positive for FeLV simply cannot be diagnosed with FeLV based on one test. FeLV is a very complex virus and is still not well understood. When a cat is exposed to FeLV, there are 3 possible outcomes:

  1. Some cats will not be infected due to inadequate exposure and a good immune response. These cats may initially test positive for FeLV after exposure, but will test negative once they clear the virus from their system.
  2. Some cats will develop a latent or regressive infection; these cats will not be able to destroy all of the virus, but will be able to hold it in check. The virus integrates into the cat’s own DNA but is not active. These cats show no signs of infection and usually do not shed virus in their saliva or other body secretions. However, the infection can later become active again, especially if the cat becomes stressed or immunocompromised. These cats may or may not ever test positive, depending on when they are tested.
  3. Some cats will become persistently infected; these cats will not develop an adequate immune response and will remain permanently infected with FeLV. This is called a progressive infection. These cats will shed large amounts of virus in their saliva and often develop FeLV-associated diseases within a few years. These cats should always test positive.

If a cat is tested only once for FeLV and comes up positive, it doesn’t tell you much. One positive test does not tell you which of the 3 outcomes above that the cat will have – they might be able to clear the virus completely, they might suppress it and never have symptoms, or yes, they might actually be persistently infected. To actually diagnose a cat with FeLV, you must do more testing. When an adult cat tests FeLV+ in Calvin’s Paws, we immediately repeat the in-house test to rule out test error. If that is also positive, we then take blood and send it off for an IFA lab test – this gives us a better picture of the stage of the disease. If the IFA test is also positive, it means that outcome #1, clearing the virus completely, is extremely unlikely, and we can officially diagnose the cat with FeLV. If the IFA test is negative, it means that the cat is still in the stage of infection where they might be able to fight the virus off completely. In this case, we isolate the cat and retest them in one month. Theoretically, you keep retesting until the test results agree, but it is possible for a cat to have an atypical infection and consistently have discordant results on the in-house test and IFA test. This is the case with one of our FeLV cats, Ice Dream, who has been with us since 2007 and STILL tests positive on the in-house test and negative on the IFA test.

25703178_ice_dream

But if my cat is negative and has ALWAYS been negative, then he’s negative, right?

Not necessarily. Remember outcome #2, where cats can have a latent or regressive infection? If cats have a regressive infection, their immune system has cleared all traces of the virus from the blood, but the virus’ DNA has integrated into the cat’s own DNA, which the immune system can’t do anything about. These cats will test negative on the in-house tests AND the IFA lab test! The only way to identify them is through a PCR test, which looks for FeLV DNA and magnifies any fragments it finds until it’s at a detectable level. Because PCR technology is relatively new, there is still a lot of ongoing research on what the results of it mean in terms of the health of a cat. We do know that regressive infections can become active again if the cat is stressed or immunosuppressed, but there is very little data on how often this happens. The most current research has found that somewhere between 5% and 10% of cats that test negative for FeLV actually test positive on a PCR test, indicating a possible regressive infection.

Aside from all of this, tests cannot detect infections immediately after exposure. If a cat was recently exposed to either virus (less than a month or so before testing), they may test negative simply because they were tested too soon after exposure. Then when you take into account the fact that the tests themselves do have a known error rate for both false positives and false negatives…well, you can see why interpreting tests gets tricky.

In conclusion, a positive test result does not always mean the cat has the virus, and a negative test result does not always mean the cat does not have the virus. This doesn’t mean that testing isn’t worth doing – it just means that testing should be a starting point, not the one and only step of retrovirus management. Unfortunately, many shelters (and even vets!) treat each individual test as undeniable fact, and the results of that test are literally life-or-death.


Calvin’s Paws is a 501(c)(3) rescue. We work through a network of foster homes throughout the Triangle area to save homeless cats and dogs. We are a dedicated group of volunteers with common goals: rescuing animals (both positives and non-infected felines), finding the best fitting homes for each animal, and educating the public on animal health and responsible pet ownership.
www.calvinspaws.com

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Testing for FIV and FeLV – What the Tests Can and Cannot Tell Us

Chase – An FIV Adoption Success Story

Years ago before I was a volunteer/foster Mom for a Rescue group, my daughter wanted a cat for her Birthday. We had just moved into a rental home and I DID NOT want any animals.

Chase
Chase

She literally forced me to go see this beautiful cat at Petsmart. I did, and fell in Love through the glass window. I read his BIO and was concerned that it said he was special needs having FIV. I had no idea what FIV was and I knew that I would not be able to afford a cat that needed a lot of medical attention. I asked the Vet on duty at Banfield what all is involved with this condition. They were very helpful by telling me all about FIV and gave me information to take home and read about. I decided to adopt the kitty cat after I felt I would not be in over my head with Vet bills. I knew he should not be allowed outside ever and he can spread the virus to another cat if he were to cause a DEEP bite, he needs no special food, humans and dogs cannot catch this virus, he can live a normal life and nobody would ever know that he is FIV positive, not even he knows.

I did try an adopt another FIV kitty for Chase to have a friend, but those kitties were not the right fit for me. Chase was fine with any friend!!! Then one day a friend from work needed to rehome her male gold cat named George real fast. So, I brought him home and they were BFF’s!!!! They were so good to each other and played and never any big arguments.

I hope that people are educated about FIV cats and know that they are just as normal as any other cat and live a normal life.

Today, 5 years later we still have Chase and he is what we call our Cat/Dog. He is playful and loving to our dogs and any foster dog that comes in the house.

Chase and friend


Calvin’s Paws is a 501(c)(3) rescue. We work through a network of foster homes throughout the Triangle area to save homeless cats and dogs. We are a dedicated group of volunteers with common goals: rescuing animals (both positives and non-infected felines), finding the best fitting homes for each animal, and educating the public on animal health and responsible pet ownership.
www.calvinspaws.com

Chase – An FIV Adoption Success Story

The Beginning of a Beautiful Friendship

by Teri P

I went to Petsmart on the idea I would donate to Calvins’ Paws on behalf of my cat Cheetah who had passed away a few months before. She was 19 and lived a good long life. I missed her deeply, but felt I needed to pay forward some of what she was able to give me.

Then I saw this:

Mr Big

Oh crap. I wasn’t there to adopt, I wasn’t, I WAS NOT. He was just looking out the window in the adoption room and I swear I heard “Whazzup” from that gorgeous face. OMG is this dude HANDSOME! I was in love already. I read the tag attached to his kennel “Mr. Big” was his name, charm was his game. A big fluffy, green eyed love bug. I think he knew already we were destined to be together. We both heard the violins!

He was listed as special needs, FIV in fact. Wait WHAT?!?!? FIV?! That sounds a lot like HIV. What’s this all about. Special needs indeed I thought. There he was, the love of my life (in fur terms of course) and he’s got a bad disease?!?!? NOOOOOOO!!!!

I’ll admit, I freaked a little. What does this mean to his life expectancy, his health, my health, his care, special meds, food, diet, exercise…was I looking at a bubble boy in cat form?

But you don’t understand, I LOVE him already! He’s MY guy, what am I going to do?!

The thought NEVER crossed my mind to NOT adopt him. Oh he was mine, we were ours, you’re coming home with me buddy, but info, I needed info.

Onto the website I went. Whoa…check out all the info on Calvin’s Paws about FIV. I read and reread, asked about 1.2 million questions, read some more.

Will it shorten his life? No

Does he require special meds? No

Special food? No (just lots of food, dude is BIG!)

Can he go outside? No (for the record, my other cat never did, and lived to be 19 so yeah, you’re inside buddy boy)

Is he going to be ‘sick’ all the time? No

Can I catch this? No

Can he spread this? Yes and no…yes, if he bites another cat deep in the muscle. No cuz he’d never do that (he’s a gentleman) and he’s indoors

Can my other cats catch this? Not through casual contact or use of same litterbox, food or water dishes.

What about a dog, can a dog catch this? No, no interspecies jumping does this disease do.

Do I clean the litter box differently? No, just more often cuz dude is BIG!

What else should I know? Lysine helps boost the immune system, give him a treat with Lysine to help him out. Make sure if he gets the sniffles, he sees the vet so anything is brought under control quickly. Regular vet checks and watch his teeth, they might start hurting him as he gets older.

Will he train me in under a week where I will do his bidding whenever he feels I need to? YES

Will be beg for treats like Puss N Boots with those giant eyes and watch me crack under pressure? YES

Will he burp and fart and demand belly rubs and to sit in the sunshine? Hell yes!

Will he take up the majority of a queen sized bed without batting an eyelash at me? YESSIR

Ok, I felt better, questions were answered and I filled out the application. Please oh PLEASE let this go through! He’s my boy, we cannot be kept apart. Then I got the best phone call ever

“When are you coming to pick up your new baby?”

WOOHOOOOOOO!!!! Here I come Handsome!

I ‘may’ have exceeded speed limits to get to Petsmart, but let’s move on. I did the proper signing, oaths (I promise to not declaw you, give you daily brushes, rub your Buddha belly when asked, kiss your forehead and cheeks far too many times a day and love you unconditionally forever and ever amen), got Lysine recommendations, bought some food, treats, litterbox, water and food bowls. We were OUTTA there!! The cardboard pet carrier was too small for my robust guy, he got out and rode in my lap all the way home, purring the whole time. This is what it’s like, this love at first sight thing. Sigh. I will love him and pet him and call him Bunny! He adapted to his new home in an HOUR. No kidding, an hour.

During his time with me, until his passing in November of 2014, he had a few sniffles here and there, but that was it. He was a lovely, sweet, generous cat (generous with his love) and gave me smiles and laughs and love. He was truly the best. In my heart I know this…FIV+ cats just KNOW. They take NOTHING for granted. They appreciate everything, they give more than they receive, they are loving and kind and happy babies. Every. Single. One.

Had I the chance to do this all over again, same outcome, I would.

And guess what, he KNOWS I would. Cuz, FIV+ babies, they KNOW.

Bunny Relaxing

To read more about Bunny’s adventures and the life he led, please check out his personal blog at http://bunnyboy-terip.blogspot.com.


Calvin’s Paws is a 501(c)(3) rescue. We work through a network of foster homes throughout the Triangle area to save homeless cats and dogs. We are a dedicated group of volunteers with common goals: rescuing animals (both positives and non-infected felines), finding the best fitting homes for each animal, and educating the public on animal health and responsible pet ownership.
www.calvinspaws.com

 

The Beginning of a Beautiful Friendship