Liza Cahn, DVM
Ah, acronyms, veterinary medicine is full of them. While these abbreviations may save your vet time, they can certainly be confusing for pet parents. Here, we will explore three big feline viral diseases that you may have heard of: Feline Immunodeficiency Virus (FIV), Feline Leukemia Virus (FeLV), and Feline Infectious Peritonitis (FIP). Beyond their acronyms, these conditions share several similarities. In the past, these viral diseases were considered a death sentence for cats, but new advances in vaccinations and treatments are on the horizon.
Overview of Feline Viral Diseases
Viruses are microscopic infectious agents composed of genetic material (DNA or RNA) inside of a protein coat. Viruses can’t replicate on their own, so they hijack the cellular machinery of their hosts to produce more copies of themselves. In cats, viral infections can lead to a wide range of health problems, ranging from mild symptoms to severe illness and death. Unlike bacteria, viruses do not respond to antibiotics (yep, this is why your doctor won’t prescribe antibiotics for a common cold). Treatment focuses instead on prevention through vaccination (when possible), antiviral medications, and supportive care to manage symptoms.
Feline Immunodeficiency Virus
What is FIV?
FIV has been likened to HIV (the virus causing AIDS) in humans; however, it only affects cats. FIV is classified as a lentivirus (a type of RNA retrovirus) that attacks and slowly weakens the immune system. This makes cats susceptible to other illnesses, allowing a variety of normally harmless organisms to cause severe disease.
In North America, FIV is found in approximately 2.5-5% of healthy cats. While FIV can occur in any cat, it is most common in intact (un-neutered) male outdoor cats, as they are most likely to get in fights with other cats. FIV is a serious condition without a cure. However, with proper care and management, most infected cats can live normal lives for many years.
How Do Cats Get FIV?
FIV is primarily spread via saliva or blood, through a bite wound from an infected cat. For this reason, it is often known as the “unfriendly” cat disease, as opposed to FeLV, which can be spread from “friendly” behaviors such as mutual grooming and sharing of food and water bowls. It is also possible for kittens to become infected by their mother during pregnancy or through nursing. Less commonly, a cat could become infected by receiving a blood transfusion from an infected blood donor.
Symptoms of FIV
FIV attacks a cat’s immune system, making them vulnerable to other types of disease, such as infection and cancer. There are three stages of disease:
Acute Phase
As the virus begins to replicate in the body, it can lead to mild and temporary symptoms such as enlarged lymph nodes, fever, loss of appetite, and lethargy. In many cases, there are no obvious symptoms, and pet parents don’t even notice that their cat is ill.
Latent Phase
In this next stage of disease, cats appear completely healthy for months to years. However, the virus is still replicating within the cells of their immune system, slowly weakening it.
Acquired Immunodeficiency Syndrome
At this point, the immune system is weakened and vulnerable to disease, and other types of infection or cancer are likely to occur. Symptoms are often nonspecific or vary depending on the secondary disease. Pet parents may notice:
- Recurrent infections: Including upper respiratory infections, skin infections, urinary tract infections, and eye infections
- Poor fur coat: Dull, matted, or thinning fur
- Weight loss and decreased appetite
- Lethargy
- Dental disease: Including gingivitis, stomatitis, and tooth loss
- Persistent fever
- Diarrhea or vomiting
- Respiratory issues: Such as coughing, sneezing, and difficulty breathing
- Neurological problems such as seizures
- Behavioral changes
- Bleeding or blood disorders
Diagnosis of FIV
FIV is diagnosed through bloodwork. The most common test, called an ELISA, detects antibodies to the virus, and can be run in the vet clinic on a small sample of blood while you wait. However, in some cases this test can be inaccurate, such as in young kittens (who obtain antibodies from an infected mom), cats who have been vaccinated for FIV, or a cat who was only recently exposed (the body has not had time to make sufficient antibodies).
For these reasons, if your cat tests positive for FIV on an ELISA, your vet may recommend retesting them in approximately eight weeks or having a laboratory run another type of test, such as a PCR.
Treatment and Prevention for FIV
While there is no cure for FIV, many FIV-positive cats do well and live normal lives long-term. Of the three viral diseases discussed here, FIV has the best long-term survival. Some FIV-positive cats may die from age-related issues, while others succumb to complications from secondary diseases, such as infection or cancer.
In some cases, antiviral medications (such as the human AIDS medication, AZT) may be recommended. However, treatment is generally focused on preventing and treating secondary infections as they arise.
As FIV is mainly spread from bite wounds, keeping your cat indoors is the best way to protect them. Vaccinating cats against FIV is no longer recommended.
Feline Leukemia Virus
What is FeLV?
FeLV is a retrovirus that weakens the immune system, resulting in infection, anemia, and cancers such as leukemia (cancer of the white blood cells). In the United States and Canada, FeLV affects approximately 2-3% of healthy cats. Luckily, these numbers have decreased since the development of the FeLV vaccine.
How Do Cats Get FeLV?
FeLV is transmitted through saliva, urine, feces, and milk. It is known as the “friendly” cat disease, because it is spread via long-term close contact between cats, such as mutual grooming and sharing of litter boxes, food, and water bowls. Like FIV, it can also be spread through bite wounds and from mother to kittens.
Young cats or kittens are at higher risk of developing disease after exposure. However, there are three possible outcomes that can occur after a cat is exposed to the FeLV virus:
- Abortive infection (20-30% of cats): In this best-case scenario, a cat’s immune system successfully fights off the virus, eliminating it entirely. The cat remains uninfected and does not test positive for FeLV.
- Regressive infection (30-40% of cats): In this case, a cat initially becomes infected, but their immune system manages to suppress the virus. While the virus will linger in the cat’s body, it’s not actively replicating and does not cause symptoms. However, intermittent shedding of the virus is possible, and stress or immune system weakening can trigger the virus to reactivate.
- Progressive infection (30-40% of cats): In this case, the virus is actively replicating in the bone marrow and spreading throughout the body. These cats often develop clinical signs, are contagious to other cats, and have a poor prognosis.
Symptoms of FeLV
Possible symptoms of FeLV may include but are not limited to the following. It’s also important to note that many of these symptoms can be caused by less serious medical conditions. If your cat is feeling sick, it’s important to see your vet for a diagnosis and appropriate treatment.
- Loss of appetite
- Weight loss
- Lethargy or weakness
- Poor fur coat
- Fever
- Enlarged lymph nodes
- Vomiting and diarrhea
- Behavioral changes
- Recurrent infections: Including upper respiratory, urinary tract, eye, and skin
- Dental disease: Including gingivitis, stomatitis, and tooth loss.
- Anemia: pale gums, weakness
- Bleeding disorders
- Leukemia and other cancers
- Reproductive problems such as infertility and abortion
- Neurological problems such as seizures
Diagnosis of FeLV
FeLV is diagnosed through blood testing. A rapid ELISA test can detect viral particles in the bloodstream. Cats with abortive infections will test negative and those with progressive infections will test positive. However, regressive infections can be more difficult to pinpoint. For this reason, a vet may recommend retesting your cat in approximately eight weeks, or running additional tests such as IFA or PCR.
Treatment and Prevention for FeLV
Unfortunately, at this time, there is no cure for FeLV, and it is considered a fatal disease. Treatment focuses on managing symptoms and treating secondary conditions such as anemia and infection. The average survival time for FeLV-positive cats is 2.5 years, however, cats with regressive infections can do well for much longer.
The good news is that there is an effective vaccine available for FeLV, which is recommended for all kittens and then yearly for cats who go outdoors.
Feline Infectious Peritonitis
What is FIP
FIP is a complex and fatal viral disease in cats, caused by a specific strain of the feline coronavirus. Most strains of coronavirus (known as enteric coronavirus) are asymptomatic or cause only mild symptoms affecting the intestines and upper respiratory tract. In fact, coronavirus is found in the intestines of the majority of healthy cats. However, in approximately 5-10% of infected cats, the virus mutates into a more dangerous form that leads to FIP. This mutated virus spreads throughout the body and triggers an intense inflammatory response, causing a range of severe symptoms.
FIP can occur worldwide in any cat, but is most commonly seen in young cats under two years of age. It is also notoriously difficult to diagnose. New drugs offer some hope for treatment, but are not yet readily available in the United States. FIP in cats has nothing to do with COVID-19 affecting people.
How Do Cats Get FIP?
Coronavirus is very common, affecting 50-90% of cats at some point in their lifetime and is shed in the feces. However, it’s important to remember that the majority of cats infected with coronavirus will NOT go on to develop FIP. The development of FIP is a complex process involving viral mutation and an exaggerated immune response.
So why do some cats get FIP and not others? The answer is unclear. It may be due to a combination of age, genetics, and environmental factors. FIP is more common in cats who live in multi-cat households, shelters, or catteries. Male cats and certain breeds, including Bengals, Abyssinians, and Birmans, may also be more susceptible.
Symptoms of FIP
There are two forms of FIP, with different symptoms. Both can cause lethargy, depression, loss of appetite, weight loss, intermittent fever, and failure to thrive.
Wet FIP
Along with the symptoms above, wet (effusive) FIP will also cause:
- Abdominal Distension: Fluid buildup in the abdomen leads to a swollen, pot-bellied appearance.
- Difficulty Breathing: Fluid may accumulate in the chest cavity or around the heart, causing labored breathing or rapid respiration.
Dry FIP
Along with the symptoms above, dry (non-effusive) FIP may also cause:
- Neurological Symptoms: Seizures, incoordination, head tilt, circling, behavior change, sensitivity to touch, or vision problems.
- Eye Lesions: Inflammation in the eyes can cause uveitis (inflammation of the uvea), retinal detachment, or blindness.
- Granulomas: Inflammatory masses form in various organs, including the liver, kidneys, lymph nodes, and intestines, causing organ dysfunction.
Treatment and Prevention for FIP
Until recently, FIP was considered a devastating and fatal disease. Now, there is hope for treatment, but medications are still costly and hard to come by in the US. Medications, such as GS-441525 and Remdesivir, target the replication of the feline coronavirus and appear to be remarkably effective in treating both forms of FIP. These medications are becoming more available, and some vets may be able to prescribe them or guide owners on how to obtain them. Sadly, without treatment, most FIP-positive cats die or are euthanized within days to weeks of diagnosis.
As we do not understand exactly what causes the normally harmless coronavirus to mutate and lead to FIP, it is difficult to prevent. Keeping up on basic health care, providing plenty of enrichment to reduce your cat’s stress levels, and keeping their litter box clean to reduce fecal contamination and house soiling are all recommended. While there is a vaccine available for coronavirus, it is not considered effective against FIP and is generally not recommended by the American Association of Feline Practitioners.
Protecting Cats Against Viral Disease
While it’s not always possible to prevent viral disease in cats, the following guidelines are considered best practices. If you are living with an FIV, FeLV, or FIP-positive cat, these are especially important for both keeping your cat as healthy as possible and preventing spread of disease to other cats.
- Keep them indoors only
- Have them spayed or neutered
- Feed a high-quality quality complete and balanced diet
- Keep up to date on wellness exams, vaccines, and preventative care as recommended by your vet.
- Follow your vet’s recommendations on when to screen your cat for viral disease – this generally includes at a kitten’s first veterinary visit, before bringing a new cat into your home, before vaccinating for FeLV, after possible exposure, and if your cat is sick.
- Treat any secondary illnesses that arise promptly
- Use good litter box hygiene – Clean your litter boxes and the surrounding area frequently. Be sure to provide enough litter boxes for your cats (a good rule of thumb is the number of cats in your home plus one) and make sure they are easily accessible and separate from food and water dishes. Good litter box hygiene can help decrease urinating and defecating outside of the litter box and reduce fecal contamination.
- Keep your home clean – Many viruses do not survive for long outside of their host and can be killed with traditional cleaning products, including bleach.
- If you have multiple cats, talk to your vet about the best way to prevent disease spread between them.