Moderate severity
Coccidiosis (Coccidia)
An intestinal infection with tiny single-celled coccidia parasites that causes watery, sometimes bloody diarrhoea — mainly in kittens, in shelters and in crowded or unhygienic conditions. Most healthy adults cope, but young kittens can become dangerously dehydrated.
⚠️ Common symptoms
Coccidia are microscopic single-celled parasites that live in the lining of a cat's intestine, and the illness they cause — coccidiosis — is above all a problem of kittens and of places where cats are kept close together. Many adult cats carry the parasite quietly, their mature immune systems keeping it in check with no outward sign at all. It is the young, the stressed and the crowded who fall ill.
The hallmark is diarrhoea. In a mild case it may just be soft, but a heavier infection produces watery, sometimes mucousy or blood-flecked stools, straining, a fading appetite and a kitten that is not growing or thriving as it should. Because kittens are small and lose fluid quickly, the real danger is dehydration, which can turn a grumbling gut infection into a genuine emergency over a day or two.
The parasite spreads through faeces. An infected cat sheds tough little eggs called oocysts, which contaminate litter trays, bedding and the ground, survive well in the environment, and are swallowed by the next cat during grooming or exploring — or eaten along with an infected mouse. This is why coccidiosis loves a busy shelter, a breeding cattery or a litter of kittens sharing one tray, and why cleaning is as much a part of beating it as the medication is.
Diagnosis is straightforward for a vet with a fresh stool sample and a microscope, and the treatment — a prescribed course of anti-parasite medicine, plus fluids for any kitten that has dried out — usually clears it well. The condition is not something to treat at home with shop-bought wormers, which do not touch coccidia. If you have a kitten with diarrhoea, or an adult cat whose loose stools are not settling, a prompt vet visit with a sample in hand is the quickest route to the right answer.
🔍 Causes
Cats pick up coccidia by swallowing the microscopic oocysts, which are shed in the faeces of infected cats and can survive a long time in the environment; they may also be caught by eating an infected prey animal such as a mouse. The parasite thrives where cats are crowded and hygiene is hard to keep on top of — shelters, breeding catteries and litters of young kittens — and stress or a weak immune system makes an infection more likely to cause illness. Kittens are especially vulnerable because their immune systems are still immature.
🛡 Prevention
Good hygiene is the mainstay. Scoop and clean litter trays daily, disinfect and dry them regularly, and keep the number of cats sharing a space sensible so trays are not overwhelmed. Remove faeces promptly, wash your hands and keep food away from toileting areas. New or newly-adopted kittens should have a faecal check, and keeping a cat from hunting reduces one route of infection. In a household where a cat has been diagnosed, cleaning up after every toilet trip helps stop it spreading to others.
💊 Treatment
Coccidiosis is diagnosed by your vet finding the parasite's eggs (oocysts) under the microscope in a fresh faecal sample. Treatment is a prescription anti-parasitic medication given as a course — often for a week or two, because the drugs stop the parasite multiplying and the cat's own body clears the rest — and repeat samples may be checked to confirm it has gone. A kitten that has become dehydrated needs fluids and supportive care, sometimes on a drip, alongside the medication. Thorough cleaning of the environment is part of the cure, because the eggs are hardy and reinfection is easy.
⚕️ Medical disclaimer
- This information is educational only and is not a substitute for veterinary advice.
- Symptoms overlap between conditions — only a vet can diagnose accurately.
- Never withhold treatment or self-medicate based on information found online.
- When in doubt, call your vet. Early intervention almost always leads to better outcomes.