By Dial A Vet Veterinary Team
In cats, one of the most common reasons for a sudden fever is a bite abscess from a neighbourhood fight that the owner never saw. In dogs, it might be a tooth root infection, a tick-borne problem, or an inflamed pancreas. Fever is the body deliberately turning up its thermostat to fight a threat, which makes it a useful signal: it tells your vet something is going on and starts the search for what.
Key takeaways
- A fever is a controlled rise in body temperature, triggered by infection, inflammation, immune disease, some cancers or certain medicines.
- Heatstroke is different. It is overheating from the environment or exercise and needs urgent cooling.
- Cats often hide fever, showing it mainly as hiding, poor appetite and lethargy.
- Never give human fever medicines. Paracetamol can be fatal to cats, and ibuprofen can cause kidney failure and ulcers in dogs and cats.
- Finding the cause is the key to treatment, and sometimes needs several tests.
Fever versus heatstroke
In a true fever, the brain resets its temperature set point upwards on purpose. The pet may shiver to generate heat and seek warm places. In heatstroke, the set point is normal but the body cannot shed heat fast enough, often after exercise on a hot day, being left in a car, or in flat-faced breeds in humid weather. A heatstroke patient pants heavily, may have bright red gums, and can collapse. Heatstroke needs immediate cooling with tepid water and urgent vet care. Fever does not respond to external cooling in the same way and should not be treated with ice.
Common causes of fever
In dogs
- Bacterial infections: wounds, abscesses, tooth roots, urinary tract, uterus (pyometra in entire females), lungs
- Viral infections such as kennel cough complex, or parvovirus in unvaccinated dogs
- Tick-borne diseases. In Australia these include ehrlichiosis, first recognised in northern Australia in 2020
- Pancreatitis and other inflammatory conditions
- Immune-mediated diseases affecting joints, blood cells or other tissues
- Some cancers
- Reactions to certain medicines or vaccines (usually mild and short-lived)
In cats
- Cat bite abscesses, which are very common in outdoor cats
- Upper respiratory infections (cat flu)
- Feline infectious peritonitis (FIP), a serious coronavirus-related disease, mainly in young cats
- Infections linked to feline immunodeficiency virus (FIV)
- Pancreatitis, inflammation and some cancers
When a fever has no obvious cause even after initial testing, vets call it a fever of unknown origin. This needs a more detailed workup.
Signs to watch for
Dogs tend to be lethargic, off their food, sometimes shivering and reluctant to move. Cats often become withdrawn, hide, stop grooming and refuse food. Both may have faster breathing and seem sore. A home thermometer reading above about 39.5°C supports a fever (our guide to checking a dog's temperature walks through how), though many cat owners find it hard to take one safely and rely on their vet instead.
When to see a vet
Emergency now: collapse, seizures, laboured breathing, very high temperature (above about 41°C), suspected heatstroke, or a pet with fever plus repeated vomiting or pale gums.
Same day: any cat that has not eaten for 24 hours, a swelling or wound that is hot and painful, a dog or cat with fever lasting more than a day, or fever in very young, old or chronically ill pets.
Monitor with advice: a pet who is a little flat after vaccination but is eating and improving.
What to avoid at home
- Do not give paracetamol, ibuprofen, aspirin or any other human medicine. These cause severe poisoning in pets, and cats are especially vulnerable. Our article on paracetamol and cats explains why.
- Do not use ice baths for fever.
- Do not leave a feverish pet without water, and keep them in a comfortable, quiet room.
How vets investigate a fever
The search usually goes step by step:
- A full history, including outdoor access, fights, travel, tick exposure, diet and vaccinations.
- A careful examination, checking teeth, lymph nodes, joints, the abdomen, skin and any wounds.
- Blood tests to look at white blood cells, organ function and inflammation markers.
- Urine tests, and imaging such as X-rays or ultrasound.
- Further tests if needed, such as joint fluid samples, infectious disease tests or biopsies.
Treatment is aimed at the cause: draining and cleaning an abscess, treating infection with medicine your vet prescribes, managing pancreatitis, or treating immune disease. Supportive care such as fluids and nutrition helps pets recover.
Prevention
- Keep vaccinations current (C3 or C5 for dogs, F3 or F4 for cats, as your vet advises).
- Keep cats indoors or in an enclosure at night to reduce fights and bite abscesses.
- Use year-round parasite prevention, including tick control where relevant.
- Desex pets that are not intended for breeding, which removes the risk of pyometra.
- Schedule regular dental checks.
FAQ
Is a mild fever good for my pet?
A moderate fever helps the immune system, but the underlying cause still needs to be found and treated.
Can I take my cat's temperature at home?
Some cats tolerate it, many do not. Do not force it. Your vet can take it safely.
Why is paracetamol dangerous for cats?
Cats cannot break it down properly, so it damages red blood cells and the liver. Even a small amount can be fatal.
Can stress cause fever?
Stress can raise temperature slightly, for example during a vet visit, but it does not usually cause a sustained fever.
Talk with a vet
If your dog or cat seems feverish and you are not sure how urgent it is, a Dial A Vet veterinarian can help you weigh up the signs and plan the next step. Talk to a vet at Dial A Vet. Collapse, breathing difficulty or suspected heatstroke needs an in-person emergency vet straight away.
References
- Merck Veterinary Manual: Fever and hyperthermia in small animals
- Cornell Feline Health Center: Feline infectious peritonitis
- International Cat Care: Paracetamol poisoning in cats
- Australian Government Department of Agriculture, Fisheries and Forestry: Ehrlichiosis in dogs
- WSAVA Vaccination Guidelines for Dogs and Cats
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If you are worried about your pet right now, contact your local vet or nearest emergency animal hospital.
