The Perils of Untreated Cat Flu. Should You Be Concerned?

What is Cat Flu?

Cat flu is an upper respiratory infection caused by viruses like feline herpesvirus, feline calicivirus, Chlamydophila felis. These viruses are highly contagious and spread easily between cats, especially in crowded conditions like shelters. The overall infection rate can be as high as 64.3%, with feline calicivirus being the most common at around 40.2% according to one study [1]. In household cats the prevalence is lower, between 0.2-33%, but still significant [2]. The viruses attack a cat’s upper respiratory tract, sinuses, and throat causing symptoms like sneezing, nasal discharge, eye discharge, ulcers, fever, and loss of appetite.

Symptoms of Cat Flu

The most common symptoms of cat flu include:

  • Sneezing – Cats with cat flu will often have sneezing fits that can last for minutes at a time. The sneezing is a response to irritation in the nasal passages caused by the flu virus.
  • Coughing – A dry, hacking cough is another typical symptom as the infection causes irritation in the throat. Cats may make a gagging sound as they try to clear their airways.
  • Eye/Nose Discharge – Cat flu often causes a thick nasal discharge from the nose and eyes. The discharge may be clear, yellow, or green.
  • Fever – Infection causes a fever, with cat body temperatures elevated above the normal 100-102°F range.
  • Lethargy – Sick cats tend to have little energy for play and interaction. They may isolate themselves and sleep more than usual.

According to the experts at BlueCross (, additional symptoms can include mouth ulcers, loss of appetite, and conjunctivitis. Cat flu symptoms tend to develop 1-5 days after exposure to the virus.

How Cat Flu Spreads

Cat flu is highly contagious and spreads primarily through direct contact between infected cats and susceptible cats. The viral pathogens can be transmitted through actions like nuzzling, grooming, sneezing, or sharing food bowls and litter trays 1. The viruses can also spread through the air from infected cats sneezing and releasing aerosolized droplets. Studies show the viruses can remain infectious in the air for up to 7 days 2.

The viruses have been shown to persist on objects and surfaces from days to weeks if not properly disinfected after exposure to an infected cat 3. Contaminated food bowls, litter boxes, bedding, toys, grooming tools, and carriers can all harbor the viruses. New cats brought into a household are at high risk of contracting flu from resident cats through contaminated environments.

Risk Factors

Certain cats are at higher risk of developing cat flu. Kittens under 12 weeks old are particularly susceptible as their immune systems are still developing. Shelters and catteries with a high density of cats in close proximity have an increased risk of outbreaks. Multi-cat households are also at risk, as the virus spreads easily between cats in close contact. According to the CDC, the viruses that cause cat flu can survive for 24 hours on surfaces, allowing for rapid transmission in group settings [1]. Keeping cats up-to-date on vaccines and reducing exposure to infected cats can help reduce the risk in these situations.

Dangers of Leaving Cat Flu Untreated

Left untreated, cat flu can lead to some serious health complications for cats. According to the Blue Cross, “Cat flu can cause life-threatening problems if left untreated,” including:

Pneumonia – The viruses that cause cat flu can spread to the lungs, causing a dangerous pneumonia infection. Pneumonia makes it difficult for cats to breathe and reduces oxygen supply in the blood (Source).

Dehydration – Sick cats often lose their appetite and stop drinking enough fluids. Vomiting and diarrhea can also contribute to dehydration. Without treatment, dehydration can become severe and jeopardize the cat’s health (Source).

Mouth Ulcers – The viruses that cause cat flu can lead to painful ulcers in the mouth that make it difficult for cats to eat. This exacerbates malnutrition and weight loss (Source).

Permanent Eye Damage – Eye ulcers and corneal scarring are common with cat flu. If not treated promptly, they can cause permanent vision impairment or blindness (Source).

Treatment Options

Cat flu is usually treated with antibiotics, antivirals, fluids, and rest. Antibiotics like doxycycline or amoxicillin are commonly prescribed to treat secondary bacterial infections that can occur with cat flu (Source). Antivirals may help reduce viral replication and shorten recovery time. Vets may administer intravenous fluids if a cat is dehydrated from decreased appetite and nasal discharge.

Rest is crucial for recovery, so vets recommend keeping cats isolated in a warm, stress-free environment during treatment. Severely affected cats may need to be hospitalized for more intensive care like oxygen therapy or feeding tubes. Most cats recover within 2-4 weeks with appropriate treatment, but some may require extended care if secondary infections develop.

Recovery Timeline

The recovery timeline for cat flu can vary depending on the severity of the infection. In mild cases, cat flu symptoms typically resolve within 2-4 weeks. Cats may start to show improvement within the first week as their immune system fights off the infection. However, it can take a full 2-4 weeks for cats to fully recover from mild cat flu.

In more severe cases of cat flu, full recovery can take 4-6 weeks. Severe cases are often characterized by high fever, lethargy, loss of appetite and pneumonia. With aggressive treatment and supportive care, most cats will start to show gradual improvement after the first 1-2 weeks. However, it takes time for the respiratory tract inflammation to fully heal and for the cat to regain strength and energy. Full recovery in severe cases will usually take a full 4-6 weeks.

Key factors that influence recovery time include the cat’s overall health and immune function, virulence of the flu strain, how quickly treatment was initiated, and the presence of any secondary infections. Monitoring the cat closely and following veterinary recommendations can help ensure the most prompt recovery possible.


There are several ways to help prevent the spread of cat flu:

Vaccines: Getting your cat vaccinated is the best way to protect against cat flu. The vaccine helps prevent infection from the most common viruses that cause cat flu symptoms. Kittens should receive an initial vaccine series starting around 6-8 weeks old, with boosters every 2-4 weeks until 16 weeks old. Adult cats need annual vaccine boosters to maintain immunity. [1]

Isolate infected cats: If you have multiple cats and one develops symptoms of cat flu, isolate the sick cat in a separate room. This helps prevent spreading the infection to other cats in your home. Any objects the infected cat touches should also be thoroughly disinfected. [2]

Minimize stress: Stress can weaken a cat’s immune system and make them more susceptible to illness. To help avoid cat flu, minimize stressful events like adding new cats to a household or moving homes. Keep litter boxes clean and try to stick to a routine for feeding times and playtime. [3]


The outlook for cats diagnosed with cat flu is generally positive, with most cats making a full recovery within 2-4 weeks when proper treatment is administered [1]. However, in some cases, especially if left untreated, the virus can become deadly.

According to one study, the fatality rate for feline influenza infections is under 1% when cats receive veterinary care and treatment [1]. However, experimental studies have found fatality rates as high as 70% in untreated cats infected with novel or highly virulent strains [2].

Proper treatment and nursing care are critical, as cats can rapidly decline and even die if cat flu is left unchecked. Dehydration, pneumonia, and secondary bacterial infections are common complications that can prove fatal [1]. That’s why vigilance and prompt veterinary care are vital, especially in kittens, senior cats, or those with compromised immune systems.

With attentive home care and veterinary treatment, most cats fully bounce back from cat flu. But in severe cases, negligence can lead to permanent damage or death, making early intervention and proper care essential.

When to See a Vet

If your cat is experiencing symptoms of cat flu, it’s important to monitor them closely and seek veterinary care if their condition seems to worsen or persists longer than expected. According to experts, you should take your cat to the vet if they have any of the following symptoms:

  • Difficulty breathing – Labored breathing, wheezing, or open-mouth breathing could signal pneumonia or other complications.
  • Not eating or drinking – Cats need adequate nutrition and hydration. Lack of appetite for more than a day warrants attention.
  • Lethargy – If your cat seems overly tired and inactive, it could mean their body is working hard to fight infection.
  • Fever over 104°F (40°C) – High fever indicates a serious infection or illness.

According to experts, if lethargy persists beyond the first 2 days of illness, you should contact your veterinarian. Respiratory infections like cat flu can turn serious if left unchecked. It’s better to seek help sooner rather than later.

Your vet will examine your cat and may run tests to determine the cause of infection. They can provide medications, supplements, and supportive care to help your cat recover. With prompt treatment supervised by a vet, most cats bounce back from cat flu within 1-2 weeks.

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