If you’ve ever browsed the cat rows at the shelter, you may have noticed a sign on a cat’s enclosure stating that they are FELV+ or FIV+. The cat behind the sign is perfect for you, but those big letters next to that plus sign can be pretty scary for a new pet owner! Don’t pass over that friendly face just yet – first, let’s understand what having FELV or FIV means for a cat, and their owner.
Feline Retroviruses
FIV (Feline Immunodeficiency Virus) and FELV (Feline Leukemia Virus) have a few things in common. For one, they are both retroviruses – this class of virus is able to incorporate itself into the DNA of the host’s body, where it can then replicate inside of the host’s cells. Once it is incorporated into the host’s DNA, it cannot be cleared by the immune system, and the host will remain infected for the duration of its life: once a cat is infected with either of these viruses, they will always have it.
FELV and FIV are two of the most common retroviruses that affect felines – each of them affects roughly 3% of the cat population in the US. These viruses are only transmissible between felines – they cannot infect humans, dogs or other non-feline pets. They can both cause compromised immunity, but they do have some significant differences in both transmission and prognosis for infected felines.
FELV
Transmission
Feline Leukemia Virus is transmitted through saliva, feces, urine and milk. It does not survive for long outside of the host’s body, and it’s not as highly infectious as, say, an upper respiratory infection, but any prolonged close contact between felines can result in transmission: bite wounds, mutual grooming, or even sharing litter boxes can all result in a new infection. It can also be transmitted from a queen to her kittens during pregnancy, or through her milk when nursing the kittens.
Diagnosis
There are several different blood tests used to test for evidence of FELV infection. Due to the nature of the virus and the different types of infection, which we’ll discuss below, no one test at any one time can be used to definitively diagnose infection.
Types of FELV Infection
Exposure to the FELV virus can result in 3 different infectious outcomes: an abortive infection, a regressive infection, or a progressive infection.
According to Cornell University’s Feline Health Center, the cat’s immune system clears the body of the virus before the virus’ genetic material can be incorporated into the host’s DNA approximately 20-30% of the time. In these cases, the immune system develops antibodies against the virus, and the cat is functionally immune to infection in the future. This is what is called an abortive infection. These cats do not test positive on any of the previously mentioned diagnostic tests, and do not experience any clinical symptoms of FELV.
In 30-40% of exposed felines, they develop what is called a regressive infection. This happens when the virus is able to incorporate itself into the cat’s DNA, but the cat’s immune system develops enough antibodies to partially eliminate the virus. Cats with regressive infections can go long periods of time with no symptoms of infection, and can test negative on ELISA and IFA tests while asymptomatic. The infection can, however, become progressive at any time, at which point the cat will be infectious to other cats and experience clinical symptoms of disease. Progression is usually triggered by immunocompromisation of the cat through stress, age, reproduction or other diseases.
The final 30-40% of exposed felines develop a progressive infection. Young kittens with incomplete immune systems are at the greatest risk of developing progressive infections when exposed to FELV. In progressive infections, viral genetic material makes its way into the bone marrow (where most of the body’s blood cells are made), and is continuously replicated. These cats are infectious to other cats, and are at a high risk of associated fatal diseases. The FELV virus is best known for its ability to trigger the development of cancers such as leukemia or lymphoma, but more commonly causes moderate to severe suppression of the immune system, resulting in secondary bacterial or viral infections with their own sets of risks and symptoms.
Prognosis
Unfortunately, at the time of this writing, there is no cure for FELV. There is a vaccine, but it is not 100% effective – the only way to fully prevent FELV is to prevent exposure to cats who carry the virus. For this reason, combined with FELV+ cats’ compromised immune systems, these cats should live indoor-only lives, and should not be housed with FELV- cats. While the life expectancy of FELV+ cats is greatly reduced, FELV+ cats can live relatively normal lives for years before experiencing negative effects. These cats deserve dignity and care during the time they have left, and no one wants to see them spend that time here in the shelter. For this reason, there is no adoption fee for FELV+ cats.
FIV
Transmission
FIV is significantly less communicable than FELV. The main mode of transmission is deep bite wounds; non-aggressive, casual contact such as mutual grooming or sharing a litter box presents a low risk for transmission. In homes with stable social structures, an FIV+ cat can live and thrive amongst FIV- cats with a low risk of new infection. Transmission from a mother cat to her kittens is rare, but possible.
Diagnosis
FIV tests are sensitive to antibodies produced by the immune systems of infected cats, so there are a few opportunities for false positive and false negative results. It takes up to 6 months for the body to produce these antibodies after infection – testing performed before these antibodies form will result in false negatives. Conversely, FIV- kittens may have antibodies from their FIV+ mothers and test positive, without actually having the virus. For this reason we generally do not test kittens for FIV until they have reached 6 months of age.
Stages of Infection
FIV infection comes in three distinct stages: acute, latent, and progressive. The acute stage of infection comes 1-3 months after exposure, and presents with symptoms such as enlarged lymph nodes, fever, lethargy and a reduced appetite. After this, cats will enter the latent stage of the disease. During this stage, the virus replicates very slowly, and cats may show no outward signs of illness. Some cats never leave this stage, and never show any outward signs of illness. Those who do enter the progressive stage will experience immunocompromisation, and their bodies will be less effective at fighting off secondary viral and bacterial infections.
Prognosis
FIV positive cats can and often do live full, normal lives. Even those who experience progressive infection can be managed with increased wellness checks and hygiene, a high quality diet and an indoor lifestyle. FIV+ cats can be introduced to FIV- cats provided extra caution is taken to introduce cats slowly and judiciously to prevent the deep bite wounds that carry the highest risk of disease transmission.
Takeaways:
- FELV+ cats should not cohabitate with FELV- cats, and may experience a reduced lifespan. In order to help them find homes, they are made available for adoption free of charge at CASPCA.
- FIV+ cats can live normal lives, and can be integrated into a multi-cat household with appropriate precautions taken.
- Both FELV+ and FIV+ cats should live indoor-only lifestyles to prevent the spread of disease and protect them from secondary viral and bacterial infections if immunocompromised.
Don’t let stigma stand in the way of you and your next best friend! If you’re interested in providing an FELV+ cat a safe place to land, check out our adoptable animals here and look for “Elderberry”, “Blank Space” and “Doily”. For FIV+ cats, check out “Madagascar”, “Lane” and “Hamlet”!
For more information about FELV and FIV, check out Cornell University’s articles below:
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