Feline upper respiratory infections (cat flu)

Written by Small Door's medical experts

Feline upper respiratory infections describe a group of viral, bacterial, fungal, and parasitic infections that affect your cat’s upper respiratory tract. You might refer to them generally as “cat flu.” Your cat can have one or a combination of upper respiratory illnesses, the most common of which are feline herpesvirus and feline calicivirus. Upper respiratory infections are very contagious among cats, but they usually have a good prognosis when properly diagnosed and treated.

In this article: 

What are upper respiratory infections in cats? 

Upper respiratory infections can be viral, bacterial, fungal, or parasitic in nature. Feline upper respiratory infections generally affect your cat’s eyes, nose, sinuses, mouth, and throat. The acute infections can cause symptoms in your cat for a week or more.

Symptoms of upper respiratory infections in cats

If your cat is showing any of the following symptoms, consult your veterinarian immediately: 

  • Coughing

  • Sneezing

  • Nasal discharge/runny nose

  • Sniffling 

  • Congestion

  • Eye swelling

  • Eye discharge/watering eyes/squinting

  • Ulcers in the mouth

  • Ulcers on the nose

  • Hoarse voice

  • Fever

  • Fatigue

  • Difficulty breathing or open-mouth breathing

  • Loss of appetite

Causes of upper respiratory infections in cats

Feline upper respiratory infections are highly contagious between cats, and they can have different underlying causes. 

Causes include:

  • Viruses

  • Fungal infections

  • Bacterial infections

  • Protozoal (a single-celled parasite) infections

While each of these causes have different methods of transmission, the main way this illness is spread is through inter-cat socialization, sharing the same food and water bowls, toys, or by contact with a human caretaker who has been exposed to an infected cat.

Kittens are more likely to become infected because of their immature immune system.

Some of the infections below will resolve on their own after treatment, but two of the most common viruses, calicivirus and herpesvirus, can be lifelong and may recur at times of stress.

Some of the most common causes of feline upper respiratory infections are: 

  • Feline calicivirus: Calicivirus is a very contagious virus spread through nasal discharge from sneezing. Able to survive outside of its host for up to 30 days, calicivirus can be killed by disinfecting with a diluted bleach solution. Most cats infected with calicivirus will experience upper respiratory symptoms such as coughing, sneezing, and ocular and nasal discharge, or they will develop oral ulcers. Calicivirus can also spread to the lower respiratory tract, causing viral pneumonia. In extremely rare cases, cats can develop systemic calicivirus, which can cause swelling of the limbs and head, liver damage, and gastrointestinal bleeding. Calicivirus can remain in some cats for many years, causing them to shed virus at any time, and symptoms can emerge at times of stress.

  • Feline herpesvirus: Also referred to as feline viral rhinotracheitis, this is a highly contagious virus, and up to 97% of cats are exposed to this virus at some time during their lives. Herpesvirus can only survive 18 hours outside of its host and is inactivated through cleaning with bleach-based products. Symptoms of this virus are sneezing, coughing, congestion, fever, eye discharge, eye swelling, or ulcers on the surface of the corneas (keratitis). Once infected with herpesvirus, cats will carry this infection for the rest of their life and may experience recurrent episodes. Recurrences are often triggered by stressful events such as moving to a new home, introduction of a new pet, boarding, or undergoing surgery. 

  • Bordetella bronchiseptica: This is a bacteria spread through nasal or oral discharge and is commonly found within shelters or other colonies that contain a large number of cats. Dogs infected with B. bronchiseptica can also transmit this illness to cats. Clinical signs include coughing, trouble breathing, sneezing, and eye discharge.

  • Chlamydophila felis: Formerly known as Chlamydia psittaci, this is a bacterial infection transmitted through eye discharge. Clinical signs of infection include yellow or green eye discharge, and red or swollen eyes. 

Can cats get flu from humans?

The human flu is not a disease that can be transmitted from humans to animals. If you’re sick with the flu, you cannot spread the illness to your cat.

However, you can spread an upper respiratory infection from one cat to another cat. If you are exposed to a sick cat, you could transmit the infectious organisms to another cat through contact with your clothing, shoes, or unwashed hands. 

Ways to avoid spreading disease between cats include changing your clothes and shoes, and thoroughly washing your hands after being in contact with a sick cat.

Diagnosing upper respiratory infections in cats

How your veterinarian diagnoses an upper respiratory infection may differ depending on your cat's symptoms and how severely ill they are. Typically, infection is diagnosed by your veterinarian based on recognizing the clinical symptoms. 

If your cat’s symptoms are not resolving or become severe, your veterinarian may recommend performing one or more of these tests (but they are not needed often):

  • PCR testing: Polymerase chain reaction (PCR) tests use swab samples taken from the mouth, nose, or eyes to identify the viral DNA of herpesvirus. 

  • RT-PCR testing: Reverse transcriptase polymerase chain reaction (RT-PCR) tests use blood samples or use swab samples taken from the mouth, nose, or eyes to identify calicivirus. 

  • Radiographs: Radiographs can be used to visualize your cat’s respiratory tract and other organs if your veterinarian is concerned about pneumonia. 

  • CBC: A complete blood count (CBC) will measure your cat’s white and red blood cells and platelets.

  • Chemistry: A blood chemistry panel will check the function of your cat’s organs, such as the liver and kidneys. 

Treatment for upper respiratory infections in cats

The treatment your veterinarian recommends will depend on the symptoms your cat is having. Mild symptoms may not require any treatment, whereas cats with moderate to severe symptoms will need treatment, and, in some cases, hospitalization.

Treatments for an upper respiratory infection could include one or a combination of the following:

  • Antibiotics, taken orally

  • Eye antibiotic drops or ointment

  • Subcutaneous or intravenous fluid therapy

  • Nebulization or saline nose drops

  • Antihistamines

  • Antiviral medications

  • Antifungal medications

  • Immune supplements

Is there a cure for upper respiratory infections in cats?

There is no cure for viral feline upper respiratory infections, only treatment and preventative measures to help your cat feel better until symptoms resolve. Usually there’s a cure for bacterial and fungal infections.

Are upper respiratory infections contagious to humans or other pets?

Feline calicivirus and feline herpesvirus are both specific to cats and cannot be transmitted from cat to humans or other pets.

What is the cost of treating upper respiratory infections in cats?

The cost of treating an infection can vary depending on the severity of symptoms and what treatment is needed. It may cost about $150 for a basic examination and medications to upwards of $500 to $1,000 or more if further testing and supportive care is needed.

How long do upper respiratory infections in cats last?

In general, upper respiratory infections in cats usually last approximately 7 to 10 days. Healthy and vaccinated adult cats will generally have a good prognosis. However, some older cats, young kittens, and unvaccinated cats and kittens can experience prolonged or more severe illness and may need extra supportive care. 

While acute respiratory symptoms usually resolve in about a week, two common viral infections, calicivirus and herpesvirus, can stay silent in your cat’s system for years and come out from time to time.

What can happen if cat flu goes untreated?

If severe respiratory symptoms are left untreated, cat flu can become serious and lead to hospitalization. Untreated illness can cause a cat to stop eating and drinking, which leads to dehydration. An infection can also progress into the lower respiratory tract, causing bronchitis or pneumonia. In severe cases, the illness can even progress to affect the central nervous system or become life-threatening.

Recovery & management of upper respiratory infections in cats

Most cats will recover well if appropriately diagnosed and treated. Cats who have received the FVRCP vaccine will have a significantly lower risk of experiencing severe symptoms. 

You can help to manage chronic upper respiratory infections by minimizing stress for your cat and treating episodes of flare-ups with antibiotics or antiviral medications as recommended by your veterinarian. 

Prevention & vaccines for upper respiratory infections in cats

While vaccines may not prevent infection, they will minimize the severity of symptoms should your cat contract an upper respiratory infection.

Is there a vaccine for upper respiratory infections in cats?

There are vaccines available that can help protect your cat against upper respiratory infections. These include:

  • FVRCP vaccine: This is one of your cat’s core vaccines and is recommended for all cats. It protects against feline viral rhinotracheitis (feline herpesvirus), calicivirus, and panleukopenia.

  • Bordetella bronchiseptica vaccine: Not considered a core vaccine for cats, this nasal vaccine is most often considered only for cats entering high-volume housing situations (such as a shelter or for boarding).

Summary of upper respiratory infections in cats

Feline upper respiratory infections, or “cat flu,” are common among cats and can have varying underlying causes, with two viruses – calicivirus and herpesvirus – as the most common causes. Severe illness is preventable through vaccinations. If you notice any symptoms of an upper respiratory infection, consult your veterinarian. For chronic upper respiratory illness, stress management can help reduce the number of episodes your cat experiences within their lifetime. 

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