Fever of Unknown Origin in Cats Reviewing treatment options for cats with a Fever of unknown origin

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Fever of unknown origin (FUO) in cats is a prolonged fever and can be caused by a range of underlying illnesses. In this article, we will consider this condition in detail.

Fever of unknown origin (FUO) is a common clinical manifestation in cats that can be caused by a variety of underlying diseases. It is characterized as a prolonged fever (>39.5°C) lasting at least three weeks that is unidentified despite extensive diagnostic testing. As FUO necessitates a thorough workup and diagnostic tests, and because the underlying cause is frequently unclear, managing the illness can be difficult.

This article will give a general review of FUO in cats, covering its description, etiology, clinical symptoms, method of diagnosis, and treatment options.

What Causes Fever in cats?

There are numerous potential causes of sudden high fever in cats. Some of the known causes include:

  • Infectious diseases: Cats can get FUO from a variety of bacterial, viral, and fungal illnesses. They include, among others, illnesses spread by ticks, infections of the lungs, and infections of the urinary system.

  • Immune-mediated illnesses: Rheumatoid arthritis, systemic lupus erythematosus (SLE), and immune-mediated hemolytic anemia are a few examples of illnesses that can lead to FUO in cats.

  • Neoplasia: Cancerous growths such as lymphoma or leukemia can cause fever of unknown origin in cats.

  • Endocrine problems: Hormone abnormalities, including Addison's disease or hyperthyroidism, can cause FUO.

Other probable causes of FUO in cats include gastrointestinal disorders, medication responses, and tick paralysis.


If your cat has an unexplained fever, it may exhibit a range of other clinical signs, including:

  • Lethargy or weakness

  • Appetite loss or anorexia

  • Loss of weight

  • Dehydration

  • Nausea or diarrhea

  • Discomfort in the lungs (difficulty breathing)

  • Higher heart rate (tachycardia)

  • Pale or yellowish mucous membranes (anemia or jaundice)

  • Neurological signs (e.g., seizures or ataxia)


It might be difficult to identify the underlying cause of fever of unknown origin (FUO) in cats, and a complete diagnostic workup is necessary. The following diagnostic methods and tests may be suggested by the vet to determine the cause of FUO in cats:

  • Complete blood count (CBC): This examination of the platelets, white blood cells, and red blood cells might assist in finding indications of anemia, inflammation, or other blood-related illnesses.

  • Serum biochemistry profile: This test evaluates the levels of various enzymes and chemicals in the blood, like liver and kidney function tests, which can identify underlying systemic diseases.

  • Urinalysis: This examination looks for indications of infection or inflammation in the urinary system.

  • Testing for feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV): These tests are advised to rule out viral illnesses that might cause fever.

  • Imaging tests: Radiographs (X-rays), ultrasounds, or computed tomography (CT) scans might be useful in spotting structural alterations or anomalies in organs that may be causing fever.

  • Biopsy and culture: To find potential infectious organisms, inflammatory processes, or cancerous situations, tissue samples obtained through biopsy or aspiration can be sent for histopathology and culture.

Treatment and Management Options

The treatments and management of fever of unknown origin in cats depend on the underlying cause identified through diagnostic tests. Unfortunately, despite rigorous diagnostic testing, the underlying reason in certain situations might never be found. Therefore, if a kitten has a fever and is lethargic, some of the treatment and management options that may be recommended by the veterinarian include:

  • Fluid therapy: To help cats with FUO stay hydrated and prevent dehydration, Intravenous fluids may be advised.

  • Antipyretic medication: Medications such as Acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) may be used to reduce cat fever temperature.

  • Antibiotics: If a bacterial infection is suspected, antibiotics may be prescribed to treat the underlying infection.

  • Immunomodulatory therapy: In cases where immune-mediated diseases are suspected, immunomodulatory medications such as Corticosteroids or Cyclosporine may be prescribed.

  • Support with nutrition: To maintain appropriate nutrition, cats with FUO may occasionally need nutritional help, such as syringe feeding or the use of appetite stimulants.

  • Treatment for symptoms: Other drugs or therapies, such as antiemetics for nausea or anticonvulsants for seizures, may be advised to control certain clinical symptoms.

However, the course of treatment for feline FUO may be complicated and need constant evaluation and modification.

How to Prevent Unknown Origin Fever In Cats

Given the wide range of probable reasons for this illness, it may not always be possible to prevent fever of unknown origin (FUO) in cats. However, there are a number of actions cat owners may take to lessen the likelihood that their cats will acquire FUO:

  • Vaccination: Vaccinating cats regularly can help avoid several infectious disorders that might result in FUO.

  • Parasite prevention: Regular use of flea, tick, and heartworm preventatives can help protect cats from a range of parasitic infections that can cause FUO.

  • Good Hygiene: Frequent grooming, litter box cleaning, and hand washing all contribute to good hygiene and can help stop the transmission of infectious illnesses that can result in FUO.

  • Frequent veterinarian care: Wellness checks and preventative treatment can help find and address underlying health issues before they worsen and perhaps result in FUO.

  • Early treatment: Prompt treatment and response to any infections, injuries, or other health problems can help reduce the risk of developing FUO.

  • Diet and exercise: A healthy diet and regular exercise can help support a cat's overall health and immune system, reducing the risk of developing FUO.

While taking these precautions can help lower the incidence of FUO in cats, there is no 100% surefire way to avoid this ailment. As a result, cat owners should be on the lookout for any symptoms of illness or fever in their cats and seek veterinarian care as soon as possible.

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