Why does my cat have a fluctuating high fever with no clear cause?

Has he been tested for FeLV/FIV viruses? Sounds like he has what is called a FUO - fever of unknown origin. Many things can cause this. You need to start doing some testing to figure out what is going on. That being said, I have treated many cases where owners could not afford diagnostics and the cats eventually ended up getting better with supportive care......don't know why. Some relapsed later on, others not. We really do usually only consider a temp higher than 103.5F as a fever in cat. Are you taking rectal temps as that is the most accurate. Other ways (like ear, armpit, etc are not very accurate). Maybe this article will help clarify for you. ( https://vcahospitals.com/know-your-pet/fever-of-unknown-origin-for-cats ) Hope this helps. If you have more questions you can always opt for a private consultation where we can chat back and forth. That way you can ask as many questions as you'd like. Best wishes.

I strongly recommend getting your cat seen by your vet as soon as possible. Cats can sometimes get fevers with no known origin and it makes them not want to eat. A cat cannot go more than a couple days without eating before they develop liver damage. Your cat may need fluids and supportive care in order to lower his temperature back to normal and support him until his appetite returns.

Fever in cats usually indicates there is an infection present. Cats also can get fever from a flea parasite called Mycoplasma, which is treated with an antibiotic. There isn't anything you can do for either of these scenarios at home unfortunately. A vet visit is required to treat for these and hopefully get Snow back to normal. I would ask friends and family if they can assist you with getting Snow to the vet for further care. Here is also a website link with financial assistance if this is the reason why a vet visit isn't feasible for you. Best wishes and take care. http://m.humanesociety.org/animals/resources/tips/trouble_affording_veterinary_care.html Carecredit.com

Fevers can come and go with any ongoing infections including FIP in what is often referred to a 'waxing and waning' condition. This would not be definitive for any specific disease but does indicate that the condition is not being fully resolved and is triggering inflammatory responses

I typically don't recommend treating the fever specifically as fevers are a normal reaction to fight infection in the body. Like a cold in people, upper respiratory infections in cats can take several days to resolve. As long as she's eating and drinking normally, that is a good sign. If she stops eating and drinking or gets very congested and is breathing through her mouth, I would recommend taking her back to the vet. Occasionally upper respiratory infections get so severe that cats need to be hospitalized for IV fluids and syringe feeding until the symptoms improve.

It is unlikely she caught something from the kitten since the kitten is asymptomatic. If Lola's normal temperature isn't usually this high, then it may be best to have her bloodwork analyzed to see if there are any clues as to why she has a fever of unknown origin. Although infectious diseases do commonly cause fevers. I hope she feels better soon.

If your vet hasn't done blood work or x-rays, that may be the next step. Some cats can have a Fever of Unknown Origin, and it often responds to IV fluids. Inflammation of mucous membranes, such as the anus, can be caused by infectious or inflammatory disorders, and blood work may help to see if this is the cause, including CBC, chemistry, and testing for FeLV/FIV. Internal parasites or constipation can cause reddness of the anus.