Does My Cat's Flea Allergy Have Anything to do With My Cat's Sudden Weight Loss?

CatChannel and CAT FANCY veterinary expert Arnold Plotnick, DVM, explains the possible reasons for a cat's sudden weight loss, and whether flea allergy plays a part.

By Arnold Plotnick, DVM

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Q: My cat Crystal is about 13 years old. She was very overweight but otherwise healthy, then my cat suddenly lost weight and is very skinny. She has a flea allergy, and a month or so ago got fleas from our dog. We treated her for the fleas and they seem to be gone, but I'm worried about her because she is still scratching a lot and has sores on her face, ears and neck from scratching.

I know I should take her to the vet, but she is a very mean cat and, although I'm one of the few people she actually likes, I'm afraid of what's going to happen when we try to take her out of the house. I don't know if her weight loss is from being sick or if she's just old, but I'm very worried about her and don't know what to do.

A: I think the skin problem and the weight loss are unrelated. Cats with flea allergy are very sensitive to fleas. When the flea bites, it injects a small amount of saliva into the skin, and it is the saliva that allergic cats are reacting to. The bite of even one flea can trigger a severe skin reaction.

I'm not sure how you treated your cat for fleas, but I recommend that you use one of the once-a-month topical products that kill fleas before they bite the cat, for example, Frontline, Advantage or Revolution. To give your cat some relief, administer antihistamines in combination with an omega-3 fatty acid supplement. If this does not control the itching, a short course of an anti-inflammatory drug such as prednisolone, can be tried. Cats are initially given a higher dose, which is then quickly tapered as the itching comes under control.

As for the weight loss, older cats are at increased risk for diseases like diabetes, hyperthyroidism, and kidney disease, three disorders that can cause weight loss in cats. Your vet can diagnose these with simple blood and urine tests. I would put the skin disorder on the back burner for now, and have your vet focus on the weight loss.

I'm concerned because you describe the weight loss as occurring fairly suddenly. The disorders that I described tend to cause gradual weight loss. If the blood tests rule out the common disorders I described, it may be necessary to perform other tests, like abdominal ultrasound or chest X-rays, looking for other causes of weight loss such as gastrointestinal disease or cancer. Figure out the cause of the weight loss before ever considering steroids for the itchy skin, because steroids would be inappropriate for a cat with diabetes.
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