A fever of unknown origin in cats refers to a fever that persists for more than a few days without an identifiable cause. Fevers in cats can arise from infections, inflammation, immune-mediated disorders, or other health issues. While fever is typically a protective response by the body, it can become dangerous if it is prolonged or reaches a very high temperature.

Fever, also called pyrexia or hyperthermia, occurs in cats when their body temperature exceeds 39.2 degrees Celsius at rest. Fevers above 41°C are considered medical emergencies due to the risk of life-threatening complications.

What is a fever of unknown origin in cats?

A cat's normal resting temperature ranges between 38.3 and 39.2 degrees Celsius. Any temperature above this range is considered a fever. When a fever persists for several days without an obvious cause, it is referred to as a fever of unknown origin.

• A fever occurs due to the presence of a substance called a pyrogen, which can originate from either inside or outside the body.

• Pyrogens trigger a response from white blood cells, leading to changes in the body that raise its temperature.

• A fever acts as a protective mechanism, enhancing the immune system's function and inhibiting the activity of harmful invaders like bacteria. However, when a fever continues for several days, it can cause symptoms such as lethargy and reduced appetite.

• An extremely high fever, over 41.1°C, can result in life-threatening conditions like brain swelling, clotting disorders, and organ failure.

• It's important to note that fever is different from heat stroke.

Common causes of fevers include:

• Infections: bacteria (including abscesses), viruses (FeLV, FIV), fungi and parasites

• Inflammatory diseases, such as pancreatitis

• Autoimmune disease, such as immune-mediated haemolytic anaemia

• Reactions to medications such as vaccinations or antibiotics

• Reactions to poisons, toxins and stings or insect bites

• Cancer, such as lymphoma

A fever can lead to severe illness, particularly if it goes untreated for several days. If you suspect your cat has a fever, it's important to speak with a vet promptly. The Joii vets are available 24 hours a day to offer advice.

Symptoms of a fever of unknown origin in cats

The symptoms of fever are nonspecific and might go unnoticed initially. Common symptoms of a fever of unknown origin include:

• Lethargy

• Reduced appetite

• Hiding or reluctant to move

• Fast breathing or open-mouth breathing

• Shivering or trembling

• Stiffness

• Dehydration: dry, sticky gums and loss of skin elasticity

Are some cats more at risk of a fever of unknown origin?

A fever of unknown origin can affect cats of all ages, breeds, and sexes. Certain groups may have a higher risk of infectious causes, including:

• Young cats, especially males. Cat bite abscesses are common.

• Outdoor cats

• Unvaccinated cats

• Cats that have been abroad: Babesia, Leishmania, Ehrlichia, and Rabies

• Cats in households with many cats: FIP and FeLV

• Purebred cats: FIP, fungal infections

How is a fever of unknown origin diagnosed in cats?

A thorough physical examination is the ideal first step in investigating a fever. If this is your cat's first fever, the vet may recommend medication and close monitoring. However, if the symptoms do not improve or if your cat experiences repeated fevers, one or more of the following tests may be necessary:

• Blood and urine tests

• Faecal tests

• Biopsy of any lumps that are present

• Imaging: X-rays, ultrasound

• Heart scan

• Specialised tests for infectious diseases

Identifying the cause of a fever in cats can be difficult because of the wide range of potential causes and nonspecific symptoms. Diagnosing the underlying issue often involves extensive testing, which can take time. To assist your vet, it's important to follow their recommendations closely and provide a detailed medical history of your cat.

What is the treatment for a fever of unknown origin in cats?

Treatment of a fever of unknown origin can vary, depending on what the suspected underlying cause is. It may include:

• Antibiotics: if a primary or secondary bacterial cause is suspected

• Non-steroidal anti-inflammatory medication

• Immunosuppressants

• Pain relief

Severe symptoms

• Hospitalisation for monitoring and treatment

• Oxygen therapy

• Blood transfusion

• Fluids given via a drip

• Fever-reducing medication

How to look after a cat with a fever of unknown origin

You can support your cat at home when they have a fever by:

• Ensuring plenty of fresh water is readily accessible in an easy-to-reach spot.

• Offering highly palatable food. Moistening and slightly warming their food can make it more appealing. You can also provide small meals of bland food, like scrambled eggs or chicken, for up to 48 hours.

• Providing a comfortable and quiet place for your cat to rest and recover.

• Brushing your cat regularly. Often, they groom themselves less when they are unwell, and brushing will prevent mats from forming.

• Closely monitor their symptoms and promptly seek further veterinary care if they worsen.

Tips on how to prevent a fever of unknown origin in cats

There are many ways to protect your cat from developing a fever:

• Make sure your cat is up to date with their vaccinations and parasite preventatives.

• Remove any ticks as soon as you find them.

• Prepare well in advance for taking your cat abroad and make sure to follow your vet's advice.

• Treat any wounds promptly; ensure they don’t get infected, especially cat bite wounds.

• Never give your cat human medication.

• Prevent access to toxins and poisons in the house and outdoors.

Is my family at risk of catching a fever of unknown origin?

Many causes of a fever of unknown origin are not contagious, including autoimmune diseases, cancer, and reactions to medications. However, some conditions that cause fever, such as Salmonella, Campylobacter, and Toxoplasma, can be transmitted to other pets or humans. Therefore, it's important to have your cat examined by a vet if they show signs of fever.

When to worry about a fever of unknown origin in cats

Seek help from a vet in practice as soon as possible if:

• Your cat has been off their food or lethargic for more than 24 hours.

• Your cat has repeated signs of fever.

• Your cat has any symptoms such as collapse, breathing problems or dehydration.

Speak to one of our Joii vets if:

• You have any questions about which parasite preventatives you should use.

• Your cat has been off their food or lethargic for less than 24 hours.

• You need advice about removing or identifying a tick.