What is Cat Flu?
Cat flu is a highly contagious upper respiratory infection in cats caused by viruses like feline herpesvirus (FHV-1) and feline calicivirus (FCV) (Kang et al., 2008). The infection primarily affects the upper respiratory tract, causing symptoms like sneezing, eye discharge, conjunctivitis, ulcers in the mouth, fever, and lethargy (Veterinary Vision Center). Cat flu is very common in cats, especially young kittens and cats living in crowded conditions like shelters.
Transmission
Cat flu is primarily transmitted through direct contact between infected cats and susceptible cats. The virus spreads via saliva, mucus, tears, and other bodily secretions from infected cats. Direct face-to-face interactions like nuzzling, grooming, playing, and sharing food bowls can facilitate transmission (CDC).
The virus can also spread indirectly through contaminated objects and surfaces. If an infected cat sneezes on a toy, bed, food bowl, or other object, the virus can survive there for 1-2 days. Any susceptible cat that comes in contact with the contaminated fomite can then pick up the infection (Cats Protection).
For these reasons, cat flu is especially problematic in crowded, high-density environments like animal shelters and catteries. When large groups of cats are housed together in close quarters, direct contact and environmental contamination greatly facilitate viral transmission and outbreaks (RSPCA).
Prevalence
Estimates vary widely regarding the prevalence of cat flu among domestic cats. According to Cats Protection, around 80% of cases of cat flu are caused by feline herpesvirus (FHV-1) or feline calicivirus (FCV). However, other sources cite prevalence between 10-40%.
The prevalence is likely higher among stray cats and cats in shelters, where cats live in close proximity and viruses can spread more easily. One study found over 90% of shelter cats tested positive for exposure to FHV-1 or FCV. For pet cats, annual prevalence has been estimated between 6-20%.
Risk Factors
Certain cats are at higher risk of developing cat flu or experiencing more severe symptoms. According to the Cats Protection organization, kittens and older cats tend to be the most susceptible to cat flu infections (https://www.cats.org.uk/northherts/feature-pages/about-cat-flu). Kittens have undeveloped immune systems, making it harder for them to fight off the infection. Older cats often have weaker immune systems as well.
Stress and concurrent illnesses can also trigger outbreaks in cats previously exposed to cat flu viruses according to Purina (https://www.purina.co.uk/articles/cats/health/symptoms/cat-flu). The viruses remain dormant in the cat’s body and activate when the cat’s immunity is lowered. Multi-cat households are at higher risk since the viruses spread easily between cats in close contact.
Symptoms
The most common symptoms of cat flu include sneezing, eye and nasal discharge, fever, and lethargy. Cats may experience a significant amount of sneezing along with a thick nasal discharge from the eyes and nose. This can range in color from clear to yellow or green. Eye discharge in particular can be copious. Affected cats often run a fever ranging from 103 to 105°F. They tend to be lethargic and have diminished appetite. In severe cases, cat flu can progress to pneumonia as the infection spreads to the lungs. This causes additional symptoms like labored breathing and coughing.
According to the Blue Cross, common symptoms of cat flu include “runny eyes and nose; sore throat; mouth ulcers; dribbling; sneezing; loss of voice; cat fever.” The Trudell Animal Health resource lists “lethargy (no energy to play)” and sneezing as key symptoms. WebMD also notes that medications called mucolytics can help “clear their airways and remove mucus” if a cat is having trouble breathing due to a runny nose.
Diagnosis
Diagnosis of cat flu is typically based on the cat’s symptoms and exposure history. Vets will look for common symptoms like sneezing, nasal discharge, eye discharge, mouth ulcers, fever, and lethargy. If the cat has been exposed to other cats with flu symptoms, that further raises suspicion of cat flu.
Vets may run viral tests on nasal, eye, or mouth swabs to identify the specific virus causing the infection. Common viruses include feline herpesvirus, feline calicivirus, feline coronaviruses, and feline reovirus. These lab tests help confirm the diagnosis and allow the vet to choose the most effective treatment.
According to the Blue Cross, diagnosis to identify which type of cat flu they have may be made by taking swabs and looking for the virus but, in most pet cats, the diagnosis is made on the typical clinical signs. (https://www.bluecross.org.uk/advice/cat/health-and-injuries/cat-flu)
Treatment
Treatment for cat flu typically focuses on supportive care and managing symptoms. This includes providing fluids, appetite stimulants, and soft foods that are easy to eat if your cat is not feeling well (Source).
Antibiotics may be prescribed by a veterinarian if a secondary bacterial infection develops. They help clear up infections that can make cat flu symptoms worse (Source).
In severe cases, antiviral medication may be administered to cats with weakened immune systems. However, there are no antiviral drugs that can cure cat flu itself (Source). The main focus is keeping the cat comfortable and nursing them back to health.
Prevention
There are several ways to help prevent cat flu in cats:
Vaccination is key. Kittens should receive vaccines for FHV-1 and FCV starting as early as 6-8 weeks old, with boosters every 3-4 weeks until 16 weeks old. Adult cats need yearly booster vaccines to maintain immunity. While the nasal vaccine does not provide complete protection against infection, it can reduce the severity and duration of symptoms if a cat does get sick. Vaccination is highly recommended by veterinarians as a critical preventative measure. https://www.bluecross.org.uk/advice/cat/health-and-injuries/cat-flu
Reducing stress and exposure to the viruses can also help prevent infection. Keep cats indoors and away from strays or cats with unknown vaccine history. Reduce stress by providing adequate space, proper nutrition, environmental enrichment, and minimizing changes to routine. Proper hygiene like washing hands before and after contact, using separate food bowls, and disinfecting shared litterboxes, toys, bedding can help stop the spread of germs between cats. New cats should be kept separate from resident cats for at least 2 weeks. https://www.trudellanimalhealth.com/learn/further-reading/cat-flu-signs-symptoms-treatments
Prognosis
Most cases of cat flu resolve within 2-4 weeks with proper treatment and care[1]. However, in some cases, cat flu can lead to lasting effects like corneal ulcers if not treated promptly and properly. Corneal ulcers are open sores on the surface of the eye which can cause significant pain, impaired vision, and even blindness if not addressed. With aggressive treatment from a veterinarian, most corneal ulcers will heal within a few weeks. But they do require diligent care from the owner at home with medicated eye drops and ointments. So while cat flu itself often clears up within a month, secondary effects like corneal ulcers may linger longer without dedicated treatment. Overall, with attentive veterinary care and at-home nursing, most cats make a full recovery from a bout of cat flu. But owners should closely monitor their cat even after acute symptoms subside, as lingering effects are possible.
The Bottom Line
Cats can easily contract feline herpesvirus, calicivirus, and Chlamydia through direct contact or indirectly through contaminated objects and environments. Though prevalence rates are high, with an estimated 80-90% of cats exposed, many cats never show symptoms or have mild symptoms that resolve on their own. About 25% of exposed cats become persistently infected. The viruses remain dormant in nerve cells and may reactivate during times of stress. For cats in shelters, multi-cat households, or with compromised immune systems, the risks of symptomatic illness are greater.
Prevention is key to protect cats from contracting or spreading cat flu infections. Kittens are most vulnerable and need a series of vaccines starting as early as 6 weeks old. Annual boosters are recommended for adult cats, especially those at higher risk. Keeping cats indoors, reducing stress, maintaining proper hygiene, and isolating infected cats can further reduce transmission. While cat flu cannot be cured, symptoms can often be managed through supportive care, antibiotics, antivirals, and immune system boosters under a vet’s supervision. With prompt treatment, most cats go on to live normal, healthy lives.
