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Ask a Vet: Can Parasites Make Old Cats Seriously Ill?

Many parasitic infestations in senior cats are opportunistic, pointing to a broader problem.

Dr. Eric Barchas  |  Apr 12th 2016


A concerned cat owner named Roopa recently contacted me. What she wrote worried me.

My 14-year-old cat has been diagnosed with Isospora species through a routine stool test. Her vet has asked me to give her Kiwof (one tablet, to be repeated after 15 days). Her weight is four kilograms. She used to be five kilograms and has lost one kilogram in the last month. She had stopped eating for 12 days and is now eating a little bit of fish a day. She is listless and frail.

My questions are: 1. Is the dosage of Kiwof recommended by my vet correct?
2. How soon after my giving her this first dose of medicine will I begin to see improvements? 3. Should I force feed her by syringe (a little dry food gruel) to stimulate her appetite?

My first thought was: What on earth is Kiwof? A web search revealed that it’s a drug known in the USA as Drontal for cats, an anti-parasitic medication that contains two active ingredients: pyrantel pamoate and praziquantal. Together, these two drugs eliminate roundworms, hookworms, and tapeworms from cats’ intestines.

Photo of Dr. Eric Barchas by Liz Acosta

Photo of Dr. Eric Barchas by Liz Acosta

Isospora is not a roundworm, hookworm, or tapeworm. It is not a worm at all. It is a microscopic intestinal parasite that belongs to a group of organisms collectively known as coccidia. Coccidia infestation is poorly treated by many vets. However, the prescribed treatment for Roopa’s cat went well beyond poor treatment, into the realm of incompetence.

I didn’t mention that to Roopa; instead, I suggested that she seek further testing to try to find out the real reason her cat was sick. Although I don’t know why Roopa’s cat has become so gravely ill, I do know that Isospora are not a likely culprit.

Coccidia are ubiquitous organisms. They can be found almost anywhere, and they are a common cause of diarrhea in kittens.

In kittens less than six months old, coccidia often cause prolific, watery, malodorous diarrhea. In fact, when I see a kitten with really bad diarrhea, I assume that coccidia are playing a role, and appropriate anti-coccidial treatment is always a part of my protocol.

Kittens with severe coccidiosis can suffer from weight loss, poor appetite, lethargy, dehydration, and unkempt coats. Their diarrhea may become incessant; I once treated two patients, whom I shall forever remember as the “shittin’ kittens.” They passed diarrhea every few minutes, and they had a knack for hitting the walls with their waste. The owner elected to hospitalize them until the symptoms resolved — her home was becoming uninhabitable as a result of the mess. The kittens’ presumed diagnosis was coccidiosis.

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Treatment of coccidia used to be very tricky. The standard medication was sulfadimethoxine, also known as Albon. Albon inhibits the reproduction of coccidia, but in my experience it doesn’t work well.

Fortunately, another medication is available that, in my experience, works much better. This medication, called ponazuril, usually can clear coccidia with just a couple of doses. Sadly, many vets haven’t learned about this medication (which has been in use in kittens for at least 10 years). I frequently receive pleas from owners whose cats have been prescribed Albon and who are trying to cope with diarrhea for weeks.

If Rooopa’s cat had been 14 weeks old, rather than 14 years old, Isospora might have been a possible cause for the weight loss and poor appetite. However, mature cats very rarely suffer from clinically relevant coccidiosis, and I have never seen an adult cat become severely sickened by the parasite. Coccidiosis in older cats is opportunistic. It occurs in cats whose immune systems are compromised. It is more likely to be a symptom of a problem than the main source of the problem.

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Fourteen-year-old cats aren’t predisposed to coccidia, but organic diseases are rife in that demographic. Kidney failure, diabetes, thyroid problems, pancreatitis, triaditis, and cancer all may cause the symptoms and weight loss that Roopa has described. A cat that has gone 12 days without eating probably also has developed hepatic lipidosis. I’m guessing that Roopa lives in a part of the world where FIV/feline AIDS might be common; other exotic feline diseases also may be prevalent in her area.

For Roopa’s cat to have a good chance, the real problem needs to be identified. The cat needs comprehensive bloodwork and X-rays. She may require an abdominal ultrasound to get an answer. If hepatic lipidosis has set in, a feeding tube may be necessary.

I am happy to report that Roopa’s cat is likely to get the tests and treatments that she needs. Roopa responded favorably to my e-mail beseeching her to seek further treatment.