What Causes Cats to Catch the Flu?

Just like humans, cats can catch the flu, a respiratory illness that affects their overall health and well-being. Cat flu, also known as feline viral respiratory disease, is a condition caused by various viruses and bacteria that infect the upper respiratory system. While it's not the same as the flu humans get, it can still be highly contagious among cats and cause symptoms that can range from mild to severe.

In this article, we'll explore the causes of cat flu, how it spreads, and what cat owners need to know to keep their furry friends healthy.

1. Viral Causes: Feline Herpesvirus (FHV) and Feline Calicivirus (FCV)

The most common causes of cat flu are viral infections, specifically Feline Herpesvirus (FHV) and Feline Calicivirus (FCV). These two viruses account for the majority of cat flu cases, and they are highly contagious, spreading quickly from cat to cat.

Feline Herpesvirus (FHV): This virus primarily causes upper respiratory infections in cats. It attacks the cat’s nasal passages, throat, and eyes, leading to symptoms like sneezing, coughing, nasal discharge, and conjunctivitis (inflammation of the eyes). FHV can remain in a cat’s system even after the initial symptoms have subsided, meaning that some cats become chronic carriers of the virus and may experience flare-ups during times of stress or illness.
Feline Calicivirus (FCV): While it also affects the respiratory system, FCV can have a broader range of symptoms. In addition to causing flu-like symptoms such as sneezing and nasal congestion, FCV can lead to mouth ulcers, drooling, and difficulty eating. In more severe cases, FCV may affect a cat’s joints, causing lameness or pain.

Both FHV and FCV are spread through direct contact with an infected cat or through shared items like food bowls, bedding, and litter boxes. Cats that live in close quarters, such as multi-cat households or shelters, are especially vulnerable to contracting these viruses.

2. Bacterial Causes: Bordetella bronchiseptica and Chlamydophila felis

In addition to viral infections, bacteria can also play a role in causing cat flu. Two of the most common bacterial culprits are Bordetella bronchiseptica and Chlamydophila felis.

Bordetella bronchiseptica: This bacterium is closely related to the one that causes kennel cough in dogs, and it can infect cats as well. Cats that contract Bordetella typically experience mild symptoms, including sneezing, coughing, and nasal discharge. However, kittens, elderly cats, or those with weakened immune systems may develop more serious respiratory issues.
Chlamydophila felis: This bacterium primarily causes conjunctivitis and eye infections in cats. It can accompany other respiratory symptoms such as sneezing and nasal discharge. Although it’s not as severe as some viral infections, Chlamydophila can still cause discomfort and is easily spread between cats.

Both bacterial infections are often secondary to viral infections, meaning that cats with an existing viral infection are more susceptible to developing a bacterial infection as well. These bacteria can be spread through direct contact with infected cats or contaminated environments.

3. Environmental Factors and Stress

While viruses and bacteria are the primary causes of cat flu, environmental factors and stress can also play a significant role in a cat's susceptibility to illness. Cats that live in overcrowded or unsanitary conditions are at higher risk of contracting cat flu due to the increased exposure to infectious agents.

Stress can weaken a cat’s immune system, making them more vulnerable to viral or bacterial infections. Common stressors for cats include:

Changes in their environment (such as moving homes)
Introduction of new pets or people
Loud noises or disruptions to their routine
Traveling or visiting the vet

When a cat is stressed, its immune system becomes less effective at fighting off infections, increasing the chances of catching the flu. Cats with chronic conditions or weakened immune systems, such as elderly cats or those undergoing medical treatment, are also more prone to flu-like illnesses.

4. Age and Vaccination Status

Kittens and senior cats are more likely to catch the flu due to their weaker immune systems. Kittens, in particular, are highly vulnerable if they haven’t yet been fully vaccinated. Since their immune systems are still developing, they are less capable of fighting off viruses and bacteria.

On the other hand, vaccinated cats are generally better protected. Vaccinations for Feline Herpesvirus and Feline Calicivirus are part of the standard kitten vaccination schedule, and regular booster shots are recommended throughout a cat's life. However, no vaccine is 100% effective, so even vaccinated cats can occasionally contract milder forms of the flu.

5. Close Contact with Infected Cats

Direct contact with an infected cat is one of the fastest ways for the flu to spread. Cats can catch the flu by:

Sharing food or water bowls: If an infected cat sneezes near or drinks from the same bowl, the virus can easily be passed on to other cats.
Using the same litter box: Cats that use a shared litter box may come into contact with contaminated surfaces.
Grooming each other: Cats that groom or touch each other are at risk of spreading infectious agents through their saliva or nasal discharge.
Being in close proximity: In shelters or multi-cat households, where cats are often in close quarters, the flu can spread rapidly from one cat to another through airborne droplets or contaminated surfaces.

Cats that have recovered from flu can still spread the virus for weeks after they no longer show symptoms. In the case of Feline Herpesvirus, cats can become lifelong carriers and experience recurring episodes of illness, particularly during times of stress.

Preventing and Treating Cat Flu

Vaccination: The best way to prevent your cat from catching the flu is by keeping them up-to-date on their vaccinations. Regular booster shots can help protect them from the most common viral causes of cat flu.
Isolating Infected Cats: If one of your cats shows signs of the flu, it’s essential to isolate them from other pets to prevent the infection from spreading. Keep their food and water bowls, bedding, and litter box separate from those of healthy cats.
Good Hygiene: Regularly cleaning your home, especially areas where cats eat, sleep, and play, can reduce the risk of spreading infections. Disinfect shared items and keep litter boxes clean.
Reducing Stress: Providing a calm, stable environment for your cat can help strengthen their immune system and reduce the chances of flu outbreaks. Ensure they have access to a safe, quiet space and minimize changes to their routine when possible.

Conclusion

Cat flu is a common illness caused by a combination of viruses and bacteria, most notably Feline Herpesvirus and Feline Calicivirus. Cats are particularly vulnerable to catching the flu in environments where they are in close contact with other cats or when their immune systems are weakened by stress, age, or lack of vaccinations.

By understanding the causes and taking preventative measures, such as vaccinations and reducing stress, you can help keep your cat healthy and reduce the risk of them catching the flu.