Parents can usually tell if their child has a fever by feeling their forehead. People have tried similar methods with their cat, by feeling their ears or nose. Alas, if it were only this simple. As a feline practitioner, I’ve examined thousands of cats with fevers.
Although some cats with fevers clearly have ears that feel noticeably warmer to the touch, the majority of febrile cats have normal temperature ears, while some normal cats appear to have overly warm ears (probably due to being nervous in the exam room). As for the nose, there is no correlation between the degree of wetness or dryness and body temperature.
Most febrile cats are weak or lethargic, have a poor appetite and may appear to have an increased respiration rate, but there are no consistently telltale signs. The only sure way to know if a cat has a fever is to take his temperature. This is best performed with a pediatric rectal glass or digital thermometer. I prefer digital thermometers because cats are impatient, and these thermometers are faster. Avoid mercury thermometers.
Taking a cat’s temperature is a two-person job. One person gently restrains the cat while the other person inserts the thermometer about 1 inch into the rectum. Use liberal amounts of petroleum jelly, and leave the thermometer in for two minutes (or until the digital thermometer beeps). The normal temperature for a cat at home is 100 to 102.5 degrees Fahrenheit. Anything higher than that should be discussed with your veterinarian. Never give a cat aspirin, acetaminophen, or ibuprofen, under any circumstances.
Common causes of a fever
1/ Infectious disease(s)
2/ Inflammatory conditions
3/ Immune-mediated disorders
5/ Adverse drug reactions
Infectious causes are the most common reason for a fever of unknown origin (FUO). Cancer is less common, and FUO due to immune-mediated diseases is rare in cats. Most cases of FUO are caused by a common illness presenting in an unusual fashion.