Fever in Cats: Causes, Recognition, and Welfare Management

Fever (pyrexia) in cats is a common sign of underlying illness that causes significant discomfort. Recognising fever early and identifying its cause enables targeted treatment that resolves both the symptom and its source.

Key Facts

Normal feline body temperature is 38.1-39.2°C; pyrexia is defined as a rectal temperature above 39.5°C sustained beyond transient stress response.
Fever is an active immune response — a regulated rise in body temperature that impairs pathogen replication and enhances immune cell function.
Common causes include bacterial and viral infections, immune-mediated disease, neoplasia (particularly lymphoma), and idiopathic causes (fever of unknown origin, FUO).
Feline infectious peritonitis (FIP) and feline panleukopenia are among the viral causes of severe pyrexia; FIP has become treatable with GS-441524 antiviral therapy.
Cats with fever typically show lethargy, anorexia, hunching, and reduced grooming — the behavioural "sickness response" serves an adaptive role but causes significant discomfort.
Never give paracetamol (acetaminophen) to cats — it is highly toxic and can cause fatal haemolytic anaemia and liver failure.
Meloxicam or other licensed feline NSAIDs can be used to reduce fever under veterinary direction when the cause is identified and there are no contraindications.
Fever of unknown origin (FUO) in cats often requires extensive investigation including blood cultures, imaging, and sometimes bone marrow or lymph node biopsy.

Welfare Considerations

Fever causes genuine suffering in cats through the sickness response it activates: lethargy, anorexia, muscle aches (myalgia), and a general state of malaise that is uncomfortable and prevents normal behaviour. While mild fever has adaptive value, high fevers (above 41°C) cause organ damage and are medical emergencies. The welfare obligation is to investigate the cause of fever while providing symptomatic support — hydration, appropriate analgesia where indicated, and a comfortable quiet environment. Providing warmth for cats with fever may paradoxically worsen discomfort, as the fever-set-point is elevated — offering a cool space allows the cat to self-regulate. Persistent unexplained fever warrants thorough investigation rather than repeated symptomatic treatment, as underlying causes like lymphoma or immune-mediated disease cause progressive welfare harm if unidentified.

What You Can Do

If your cat is lethargic, not eating, and feels warm to the touch, check temperature rectally — seek veterinary care if above 39.5°C.
Never give paracetamol, ibuprofen, or human pain medication to cats — these are toxic and can be fatal.
Provide a quiet, comfortable space with access to water; allow the cat to choose a cool or warm spot according to its preference.
Request thorough investigation of persistent fever — repeated symptomatic treatment without diagnosis delays appropriate management.
Follow your vet's treatment plan for identified causes; most bacterial and many viral fevers resolve rapidly with appropriate targeted therapy.