Feline Leukemia Virus (FeLV) and Feline Immunodeficiency Virus (FIV) are both contagious viruses that attack the immune system of cats. Although FELV and FIV share many common characteristics, there are important differences, especially when it comes to how the viruses are spread and the long-term outlook for cats that become infected.
Cats infected with either FELV or FIV do not immediately appear to be sick. However, as the virus replicates and begins to weaken their immune systems, these cats can become susceptible to life-threatening infections by other viruses, bacteria, and fungi that under normal circumstances would have been relatively harmless. FELV and FIV infections also increase the risk of developing certain types of cancer.
Being outdoors increases a cat’s risk of exposure to both FELV and FIV. Recent estimates indicate that 2-4 percent of the approximately 83 million cats in the U.S. are infected with one or both viruses (yes, for some unlucky kitties it’s possible to contract both). And it’s not just feral cats who become infected; owned cats who go outside are infected with just as much frequency as ferals.
The viruses don’t survive for long in the environment, and both can be killed with common household disinfectants. Humans and other pets cannot become infected, as these viruses are only contagious in cats.
FeLV and FIV are often confused since their symptoms are so similar. Clinical signs can include:
- Poor appetite
- Weight loss
- Lethargy (low energy)
- Recurring respiratory infections
- Chronic dental, oral, and gum infections
- Pale gums
- Poor coat condition
- Chronic eye problems
- Skin infections
One of the biggest differences between FeLV and FIV is that a cat who is FeLV-positive will often exhibit these symptoms regularly throughout his life, while an FIV-positive cat may remain completely symptom-free for life.
In order to better understand the differences between these two viruses, here’s a quick summary of each.
The Feline Leukemia Virus invades special cells in the immune system called CD4 cells, found in lymph nodes and bone marrow. Once inside the cell, it begins to change the genetic characteristics of the cell, allowing the virus to replicate itself each time the infected cells divide.
About 70 percent of cats exposed to FeLV are able to successfully fight off the virus and never become sick. However, some cats can become carriers of the virus – although they are not clinically sick, they’re still able to infect other cats.
FeLV is transmitted through body fluids such as saliva, nasal secretions, and urine. It can be passed from one cat to another through bite wounds, shared food and water bowls, shared litter boxes, and mutual grooming.
Female cats can also transmit the virus to their offspring.
FeLV infections can be complicated to diagnose since every cat’s body reacts differently to the virus, and there are several stages of the disease. Blood tests are usually used to diagnose FeLV, but for some cats, their bone marrow must be examined to confirm the presence of the virus.
Antigen tests, which identify the presence of foreign proteins in the body, are used to diagnose FeLV. Since some cats are able to fight off the virus, a cat is not considered FeLV-positive until she’s tested positive on 2 different antigen tests done at least 90 days apart.
Progression of Disease
Every cat infected with FeLV reacts differently. As the virus progresses, some cats may develop lymphoma (cancer of the lymphatic tissues), leukemia (cancer of the bone marrow and white blood cells), and/or anemia (a shortage of red blood cells).
When a cat’s immune system becomes compromised, she may not be able to fight off infection from bacteria, protozoa, fungi, and other viruses. In adult cats, it may take months or years for these diseases to appear. However, in kittens and younger cats, the disease progresses much faster – around 80 percent of kittens diagnosed with FeLV do not live past 3 years, and most die within a year.
Since cats who go outside are at greater risk for exposure, you can greatly reduce the risk by keeping your cat indoors and away from other cats.
There are several vaccines available for FeLV, but there are downsides. First, the vaccine has not been shown to be 100 percent effective at preventing infection. Second, FeLV vaccines have been linked to an increased risk of cats developing “injection site sarcomas”, which are aggressive cancers that develop at the site of the injection. Be sure to discuss with your veterinarian whether the potential benefits of the vaccine outweigh the risks before you decide to vaccinate. If your cat is strictly indoors, and the other cats in your home are FeLV negative, the risk to your cat of being exposed to FeLV is extremely low.
Kittens are usually vaccinated against FeLV at around 8 or 9 weeks of age, with a booster given 3 to 4 weeks later. Annual boosters are given thereafter as long as the cat is at risk of exposure.
If you’re bringing a new kitten or cat into your home, until you’re certain that the new cat is FeLV-negative, keep it separated from all other cats and have it examined by a veterinarian as soon as possible.
The FIV virus is very similar to HIV (Human Immunodeficiency Virus) in humans. The virus is carried to the lymph nodes, where it reproduces and spreads to other lymph nodes throughout the body. In the first stage of FIV, an infected cat may experience temporarily enlarged lymph nodes and fever. Once that stage passes, the virus can become dormant for up to several years with the cat never showing any clinical signs of illness. The final stage is Feline AIDS, where the cat’s immune system becomes severely compromised and leaves him susceptible to numerous illnesses, some of which may be fatal.
FIV differs from FeLV in that FIV-positive cats can live relatively normal lives after becoming infected. FIV-infected cats don’t become ill due to the virus itself, but rather due to secondary infections (bacterial, viral, parasitic, or fungal) that occur because of their weakened immune systems.
FIV is transmitted through contact with an infected cat’s saliva. However, unlike with FeLV, FIV is usually only transmitted through deep bite wounds and NOT from casual contact or shared food bowls or litter boxes.
This means FIV-positive cats can live safely alongside FIV-negative cats, as long as the cats get along and there is no fighting resulting in bite wounds.
Female cats can pass FIV to their offspring. However, unlike FeLV, it’s sometimes possible for an FIV-positive cat to give birth to kittens without passing the virus on to them.
Testing for FIV is done with a blood test, usually a combination test that also tests for FeLV at the same time.
The FIV test looks for the presence of antibodies (small proteins manufactured by white blood cells in response to the presence of an invader) that a cat’s body produces in response to the virus.
It takes 60 days after exposure for antibodies to FIV to show up in the blood. Therefore, if you believe your cat has been exposed, be sure to wait at least 60 days before testing, or you could get a false-negative result.
Because infections with both viruses can be complex, veterinarians often recommend re-testing at different intervals depending on the test results.
Progression of Disease
Once a cat has been infected with FIV, the cat will always have the virus. Unlike with FeLV, cats aren’t able to fight off FIV and develop immunity to it.
The health of an FIV-positive cat may progressively deteriorate, or the cat may experience recurrent illnesses followed by periods of relatively good health. Signs of immunodeficiency can appear anywhere in the body.
However, if the cat remains healthy and receives good medical care, he may not experience any clinical symptoms, and may never reach the Feline AIDS stage.
There is a vaccine available against FIV, but most veterinary professionals do not recommend giving it. There are several reasons for this.
First, the vaccine is not 100 percent effective. There are 5 strains of FIV, and the vaccine was only tested on one strain.
Second, once you administer an FIV vaccine to a cat, that cat will test positive for the virus for the rest of his life since the FIV test is unable to distinguish between FIV infection and FIV vaccination. This could be a problem if your FIV-vaccinated cat ever becomes lost and is picked up and taken to a shelter, as he could be falsely identified as having the FIV virus. Also, any subsequent FIV test you give to that cat will never be accurate, so you’ll never be able to tell for sure if he ever actually becomes infected.
Third, like the FeLV vaccine, the FIV vaccine has also been linked to injection site sarcomas.
Since an FIV-positive cat can live a long time without symptoms, the risks of the current FIV vaccine are greater than the benefits – at least until a more effective vaccine is developed.
Prognosis and Treatment for FeLV and FIV
There is no cure for FeLV or FIV. Of the two, FeLV has the bleaker prognosis – 85 percent of cats infected with FeLV usually die within 3 years of diagnosis, whereas an FIV-positive cat can live for many years without showing any signs of illness. However, as long as an infected cat is kept indoors, given proper veterinary care and good nutrition, and treated immediately for any illnesses that may arise, it’s possible for the cat to live a long and healthy life. This is why the American Association of Feline Practitioners recommends against routine euthanasia for cats testing positive for either virus.
If you are the caretaker of a cat with FeLV or FIV, there are several things that can be done to help extend the life of your kitty:
- Keep your cat indoors to reduce risk of exposure to parasites and to keep him from becoming injured (as well as to prevent the spread of the virus to other cats).
- Be sure your cat is spayed or neutered.
- Feed your cat a healthy, palatable diet that is nutritionally complete. Do NOT feed a cat with FeLV or FIV a raw diet. Bacteria in uncooked meat and eggs can be dangerous for a cat with a weakened immune system.
- Take your cat to see a veterinarian for a complete checkup at least twice a year.
- Watch for any changes in your cat’s health and behavior, no matter how minor, and report them to your veterinarian.
If your FeLV- or FIV-positive kitty does become sick, your veterinarian can prescribe medication for secondary infections, fluid and electrolyte-replacement therapy, anti-inflammatory drugs, and other medications to boost your cat’s immune system.
Not An Automatic Death Sentence
Although FeLV and FIV are serious illnesses in cats, a positive diagnosis is not necessarily a death sentence. With proper care, many infected cats (especially those with FIV) can live reasonably normal lives.
If you’re considering adopting a cat with FeLV or FIV and you have other cats, adopting a cat with FeLV is not recommended. However, it’s possible for a cat with FIV to live safely with other cats who are FIV-negative, as long as everyone gets along.
Your veterinarian is an excellent resource for any additional questions you may have about FeLV and FIV.
Have you ever cared for a cat with either FeLV or FIV? Please tell us about it in the comments below!