cat flu shelter

Feline Upper Respiratory Tract Infections (Cat Flu)

Feline upper respiratory tract infections are a common health problem amongst cats. Infections of the feline upper respiratory tract are described as ‘cat flu’. Unlike human flu, which is caused by the influenza virus, cat flu can be caused by a number of different viruses and bacteria.

The two most common causes of feline upper respiratory tract infections are feline herpesvirus (FHV-1) and feline calicivirus (FCV), together these viruses account for more than 80% of all instances of cat flu.

See below for more about the symptoms of cat flu or the treatment of cat flu.

The Feline Respiratory System

The primary role of the respiratory system is to take in oxygen and remove the waste gas, carbon dioxide. In cats, the respiratory system also plays a role in temperature regulation.

Feline Respiration System
Fig. 1 Upper and lower feline respiratory tract

The respiratory system can be divided in to two sections; the upper respiratory tract and the lower respiratory tract.

In this article, we are discussing infections of the upper respiratory tract (shown in red in figure 1), which includes:

  • Oral/Nasal cavity
  • Pharynx (upper throat)
  • Larynx (lower throat)

Infections of the Feline Respiratory System

Feline upper respiratory tract infections are usually described with the single term ‘cat flu’. Cat flu can be caused by both viruses and bacteria, however, there are two viruses in particular that are associated with cat flu, these are:

  • Feline herpesvirus (FHV-1)
  • Feline calicivirus (FCV)

Feline Herpes Virus (FHV-1)

Feline herpes virus is a major causative agent of cat flu. The virus is highly contagious and will cause persistent infection in over 80% of cats exposed to the virus.

Although the majority of infected cats will make a full recovery, the virus persists in a dormant state in nerve cells and can be reactivated during times of stress. Reactivation will result in the development of cat flu symptoms again.

Cats not displaying symptoms of an active upper respiratory tract infection can still shed the virus in discharge from the eyes and nose. This makes them an infection risk to other cats. Shedding of the virus can increase during periods of stress or following medication. This is a particular problem in catteries, shelters and multicat households, as an individual cat can appear healthy, but is able to spread the virus unknowingly.

Read more about FHV-1. 

Feline Calicivirus (FCV)

Feline calicivirus is the second major causative agent of feline upper respiratory tract infections. In a similar manner to FHV-1, the virus is highly contagious and can be shed for long periods of time even after an individual cat recovers from the infection.

Cats infected with FCV typically experience ‘milder’ cat flu symptoms compared to FHV-1 infected cats. However, cats infected with calicivirus will likely develop noticeable mouth ulcers, which can be painful.

Read more about FCV.

Primary and Secondary Bacterial Infections

Cats with a viral upper respiratory tract infection are more likely to develop secondary bacterial infection. A secondary infection can cause further inflammation to the upper respiratory tract and prolong the recovery process.

Two species of bacteria that are also commonly reported to have a primary role in causing cat flu are:

  • Bordetella bronchiseptica (the bacteria responsible for kennel cough in dogs)
  • Chlamydophila felis (causes conjunctivitis and mild respiratory disease)

Symptoms of Feline Upper Respiratory Tract Infections

The exact symptoms of cat flu can vary slightly on an individual basis and also depending on which virus or bacteria is responsible for the infection.

cat flu
Conjunctivitis and nasal discharge
Nottingham Vet School
  • Sneezing
  • Discharge from the eyes and nose
  • Conjunctivitis
  • Eye ulceration
  • Loss of appetite
  • Fever, depression and lethargy
  • Ulceration in the mouth (including tongue, gums and lips)
  • Painful joint inflammation causing limping (Limited to some FCV infections)
  • Skin inflammation (dermatitis) and ulceration (rare symptom in long term FHV-1 infections)

Treating Cats with Upper Respiratory Infections

Treatment for feline upper respiratory tract infections mainly involves providing supportive care until the cat flu symptoms pass. This includes:

  • Encouraging cats with lost appetite to eat – This can be achieved through providing highly palatable, warm, blended food
  • Wiping away nasal discharge
  • Bathing eyes
  • Encouraging movement of mucus

Other methods for managing the acute infection include:

  • Antibiotics – For the treatment of bacterial infections, but also given to prevent secondary bacterial infections
  • NSAIDs – To reduce fever and pain, particularly in cases where there is ulceration in the mouth/eyes
  • Mucolytics – To break down excess mucus
  • Eye Drops – For lubricating the eye, as inflammation can cause dry eyes
  • Appetite Stimulants – An option for cats who are not eating because of cat flu

Antivirals may be an option in some extreme cases, but usually they are avoided for the treatment of cat flu due to price. No cat-specific antivirals are currently available, so human antivirals are used off-label.

We’ve also previously discussed the benefits of Lysine supplementation for cat flu.

Vaccination and Prevention of Infections Spreading


Core vaccinations for cats include FHV-1 and FCV (the two most common causes of cat flu). For maximum protection, cats should be vaccinated at 9 and 12 weeks of age and again 12 months after the first vaccination. See here for more information on vaccinating your cat.

Preventing the Spread of Infection

In the majority of cases, cats infection with either FHV-1 or FCV will carry the virus for life. Carriers of the virus can experience ‘flare-ups’, where the virus will become active again, causing cat flu symptoms. There are ways to manage infection however, to reduce the occurrence of flare-ups and minimise the spread of the virus.

Stress Reduction – Stress is the main reason for flare-ups and can also increase the amount of virus that is shed by an infected cat. Steps should be taken to minimise stress, particularly in multi-cat environments such as shelters and catteries.

Management – In places with large cat populations, steps should be taken to keep infected cats separate from healthy cats. This also applies in the multicat home environment. Vaccinate existing cats against the virus and considering isolating the new cat for 1-2 weeks in case symptoms of cat flu develop.

Sanitation – Standard disinfectant is enough to remove the majority of cat flu causing bacteria, as well as FHV-1. FCV however, is a more hardy virus that can last for a while in the environment and requires stronger detergents, such as bleach, to remove.

Image Credit | Jennuine Captures

About James Watts

BSc Bioveterinary Science. Editor of PetSci. When I'm not writing, learning, discussing, or reading about animals, you know it's the weekend! Currently developing PetSci HealthTrak, the fast and easy way to monitor your pet's weight and calorie intake. HealthTrak offers a simple way to track your pet's progress, helping them achieve a healthy weight and a long, happy life.

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