Cat Flu (Upper Respiratory Tract Infection)

Last Updated on January 6, 2021 by Julia Wilson

Cat flu at a glance

Also called: Respiratory tract disease, influenza

About: Cat flu is an upper respiratory infection, similar to the flu in humans. It is caused by several viruses and bacteria; feline herpesvirus and calicivirus account for 80% of cases, other pathogens include bordetella, chlamydophilia, and mycoplasma.c

Symptoms: Symptoms are similar to that of a human cold or flu and may include eye and nasal discharge, sneezing, fever, loss of appetite, dehydration, eye and mouth ulcers and lethargy.

Transmission: Direct contact with nasal, eye and mouth secretions, indirect contact such as bowls, bedding and toys (fomites) and chronic shedders.

Diagnosis: Most veterinarians can make a tentative diagnosis based on symptoms. Samples may be necessary to determine the exact pathogen.

Treatment: Supportive care such as fluids, nutritional support, antiviral medications and antibiotics to treat secondary infection.

What is cat flu?

Image courtesy Patricia Towne, Flickr

Cat flu is a general term used to describe a common set of symptoms of the upper respiratory tract and is similar to the colds and flu that affects people.

It is seen mostly in young kittens, senior cats, crowded environments such as cat shelters where close proximity to other cats as well as increased levels of stress increases the rate of transmission.

Cats with weakened immune systems are also at increased risk. If healthy adults do contract cat flu, they usually recover quickly; however, kittens, senior cats and those with weakened immune systems can become quite sick.


Cat flu is caused by several pathogens (disease-causing organisms) which include viruses, bacteria, and mycoplasma. The most common pathogens are:

Feline herpesvirus and feline calicivirus are the most common pathogens and are responsible for 80% of cat flu cases. Feline herpesvirus typically is the most severe of the two. Co-infections and secondary bacterial infections are also common.


The pathogens responsible for cat flu are highly contagious and can be spread via direct or indirect contact

Direct contact: Infection is passed from a sick or carrier cat via eye, nasal, and mouth discharges. It is possible for infected dogs to pass bordetella on to cats and vice versa.

Indirect contact (fomites): Contaminated food bowls, bedding etc. Calicivirus is resistant to many disinfectants and can live in the environment for long periods.

Chronic carriers/shedders: Cats who have been exposed to feline herpesvirus or calicivirus can shed the virus even after they have recovered, there is more information on carriers/shedders later in the article.


Two stray kittens with signs of cat flu
Two stray kittens with signs of cat flu

Many of the causes of cat flu have overlapping symptoms. However, some causes have individual symptoms. For example, mouth ulcers are common with feline calicivirus and eye ulcers with feline herpesvirus. Cats with FCV may also develop a limp due to transient arthritis.

Cat flu symptoms are similar to those seen in humans and can be acute (lasting ten days or less) or chronic (longer than ten days).

Generalised symptoms:

  • Nasal discharge: Thin and clear or thick and purulent if a bacterial infection is present.
  • Sneezing: Accompanying nasal discharge is sneezing.
  • Fever: When an infection takes hold, the body responds by increasing its temperature. This can make your cat feel generally unwell.
  • Anorexia (loss of appetite): A cat with the flu will often lose his appetite, which can be exacerbated by nasal discharge which affects the sense of smell.
  • Dehydration: Sick cats can quickly become dehydrated as they don’t tend to drink as much when they are feeling unwell. If you lift the skin directly above the shoulders and release, it should spring back quickly. The skin is slower to move back into place if the cat is dehydrated.
  • Lethargy and depression. Lack of interest in surroundings, not as active, playful or attentive as he may normally be.
  • Calicivirus can cause transient arthritis in cats which can result in limp, which is known as limping syndrome as well as ulceration of the paws.


Mouth ulcers in a kitten's mouth due to cat flu
Mouth ulcers in a kitten’s mouth due to cat flu

Ulcerations of the mouth and tongue may develop, making eating painful and is usually associated with calicivirus. Gums may be inflamed (gingivitis) and red, and the cat may salivate (drool) excessively due to ulcers.


A cat's eyes affected by feline herpes
Cat’s eyes affected by feline herpes

A thick, sticky eye discharge also occurs with cat flu. Eyes become red and inflamed (conjunctivitis). Pain, squinting, sensitivity to light can develop if your cat has developed corneal ulcers due to herpesvirus infection.


Sneezing and nasal discharge are common symptoms of cat flu. The virus causes inflammation of the mucous membranes (rhinitis), accompanied by nasal discharge, which may be clear, thick and mucopurulent (containing pus and mucus). This can make breathing difficult.


Lung inflammation can lead to secondary bacteria taking hold and pneumonia developing.

Pneumonia symptoms:


The veterinarian will perform a complete and thorough physical examination of your cat and in many cases can make a diagnosis based on clinical signs. To determine the exact pathogen, he/she may take a throat or eye swab to send off to a laboratory for testing.

  • Fluorescein is an orange dye which the veterinarian may put in the cat’s eyes to look for corneal ulcers.
  • X-rays to evaluate the lungs for pneumonia.

Cats with chronic upper respiratory tract infection will require a more thorough workup to look for other causes such as a foreign object, fungal infection, cancer or parasites.

Diagnostic workup:

  • Nasal cavity swab.
  • Bacterial culture and sensitivity to determine the bacteria present and the most appropriate antibiotic.
  • Rhinoscopy is an examination of the inside of the cat’s nose.
  • Xrays of the nasal cavity.

What is the treatment for cat flu?

The goal of treatment is to provide medical therapy as well as supportive care, and in some cases, it will be necessary to hospitalise the cat.

Medical therapy:

Feline Chlamydophila:

  • Antibiotic eye ointment (usually tetracycline).

Feline herpesvirus:

  • Antiviral drugs can include oral tablets or eye ointments. Common antivirals used to treat herpes include trifluridine, ganciclovir, famciclovir, idoxuridine and vidarabine.
  • L-lysine is an over the counter amino acid has been shown to suppress viral replication and inhibit cytopathogenicity.

Feline calicivirus:

  • Antibiotics to treat secondary bacterial infections.
  • Corticosteroids and/or anti-inflammatories to treat transient arthritis.

Supportive care:

  • Encourage food and water intake; if the cat is not showing an interest, try offering small gourmet canned food. Warming it up a little can also help make it more appealing. There are also high-calorie products available from your veterinarian to use with sick and recuperating cats. These are usually in paste form. Cats with mouth ulcers benefit from soft food. If the cat cannot be encouraged to eat, a feeding tube will be necessary.
  • Nasal decongestants and vaporisers to clear discharge and ease breathing. If you don’t have a vaporiser, run a hot shower for 10 minutes, so the room gets steamy and leave the cat in the bathroom for 10-15 minutes can help loosen up congestion.
  • Oxygen therapy for cats who are having difficulty breathing.


This depends on the severity and the overall health status and age of your cat. But typically you can expect the cat to recover within 7-10 days.

Some cats may go on to become chronic shedders and during these periods may develop clinical signs again, although typically milder, or in some cases, no symptoms at all but they can pass on cat flu to other cats during the period of shedding. Test cats for FIV and FeLV who fail to respond to treatment.


Generally, the prognosis is very good with prompt treatment. Young kittens are at increased risk, but healthy adult cats usually have an uneventful recovery after a week or so.

Some cats infected with feline herpesvirus will develop chronic rhinosinusitis as a result of damage to the nasal mucosa. Symptoms include chronic nasal discharge and sneezing. Antivirals and antibiotics can manage symptoms.

What is a carrier/shedder cat?

Once a cat has contracted feline herpesvirus, he has it for life. Once he recovers from the initial infection, small numbers of the virus lie dormant in the nerves. Cats who have previously been exposed to feline herpesvirus can occasionally shed the virus when it re-activates. This is usually during periods of stress such as stress (caused by pregnancy, lactation, overcrowding, poor nutrition, new family member, etc.) or another sickness.

They may or may not show symptoms while they are shedding depending on their overall health. Calicivirus can be shed for up to 3-18 months after infection, but most cats have eliminated the virus by 18 months. It is possible for other cats to catch feline herpesvirus or calicivirus if they come into contact with a cat who is shedding the virus. Take care to avoid stress in carrier cats.


The F3 vaccination protects against FHV and FCV.

A vaccine is available for Chlamydophila felis; however, side effects can occur in a small percentage of cats. This can include lethargy, lameness, depression, anorexia, and fever; therefore, it is best for high-risk cats. The American Association of Feline Practitioners does not recommend routine use of this vaccination. Speak to your veterinarian about this vaccination.

Wash hands and change clothing after handling sick cats to prevent infecting other cats.

Also, as a courtesy, if you are visiting multiple breeders or shelters in one day, advise them beforehand. Some breeders will ask you not to visit them if you have been to another cattery, to reduce the chances of transmitting diseases.

Quarantine new cats for two weeks before introducing them to resident cats.

Home care

  • Administer all medications as prescribed and always complete the entire course.
  • If you have other cats in your household, isolate the sick cat to avoid spreading the disease.
  • Wash your hands thoroughly before and after handling cats with cat flu.
  • Never give cold medications for humans to a sick cat.
  • Keep a close eye on your cat’s food and water intake and contact your veterinarian if the cat cannot be encouraged to eat or drink.
  • Keep the eyes and nose clear of discharge by wiping with cotton or gauze soaked in saline solution.
  • Confine indoors and allow to rest.
  • Help to loosen up mucus by putting your cat in a steamy bathroom for 15 minutes.

Cat flu FAQ

How long does cat flu last?

The duration of cat flu depends on a number of factors which include the age and health status of the cat and the pathogen involved. Typically, cats have clinical signs for one to two weeks.

Can cat flu kill cats?

Cat flu can kill. Young kittens, senior cats and cats who are immunosuppressed are at greatest risk.

How common is cat flu?

Cat flu is one of the most common infectious diseases of cats.

Is cat flu contagious?

Cat flu is extremely contagious to other cats, the viruses responsible are airborne and also transmitted via body secretions as well as fomites (objects such as bedding, clothing, brushes, food bowls etc).

Can I catch colds and flu from my cat?

No, it is not possible to catch a cold or flu from your cat, nor can your cat catch a cold or flu from you.

Update December 2016: An American veterinarian has caught a rare strain of bird flu from a Manhattan shelter. This is the first time that the strain H7N2 has infected cats and then infected a human. The good news is that the veterinarian and all but one of the cats had mild symptoms and recovered quickly. Please remember, this is a strain of bird flu, and not the usual pathogens such as feline herpesvirus, calicivirus etc., typically associated with flu in cats.

Can humans pass on cat flu?

The viruses responsible for cat flu are not contagious to humans, as we cannot catch cat flu, we cannot transmit cat flu to cats. Certain other strains of flu can be transmitted from humans to cats and cats to humans, but this is extremely rare.

Is FIV cat flu?

FIV stands for feline immunodeficiency virus and is similar to HIV in humans.

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