Parasites in cats: worms, protozoa and the hitchhikers (and what you can catch)

Nobody likes to think about it, but here it is: if your cat has never been dewormed, something is probably living rent-free inside them. Most cat parasites are easy to deal with. A few are not. And some can move in with you, too.

A large European survey found that owners deworm their cats about 2.2 times a year on average, while most cats in the study fell into risk groups for which vets recommend deworming much more often. So this is worth five minutes of your time. His Majesty has asked us to point out that he, personally, has never had a worm in his life. His Majesty has also never seen his own bottom.

Not every parasite is a worm

This is the most important thing to understand, because it explains why "I gave him a dewormer" doesn't always solve the problem.

• Worms (roundworms, tapeworms, hookworms, lungworms) are animals. The usual dewormers from your vet are made to kill them.
• Giardia, coccidia, Toxoplasma and Leishmania are not worms. They are protozoa: tiny, single-celled parasites. Most standard dewormers don't touch them. They need a diagnosis from your vet and specific treatment, sometimes for weeks.
• External parasites (fleas, ticks, mites, sandflies, mosquitoes) live on the outside or bite from the outside. They need their own products, and some of them also carry other diseases.

The internal parasites, by name

Worms

• Roundworms (Toxocara cati): the most common worm in cats, especially kittens, who can catch them through their mother's milk. Look like spaghetti. A kitten with a pot belly and a dull coat often has roundworms.
• Tapeworms (Dipylidium caninum, Hydatigera taeniaeformis): flat, segmented worms. The segments look like grains of rice around the bottom or in the bedding. One type comes from swallowing an infected flea while grooming; the other from eating mice.
• Hookworms (Ancylostoma): small blood-sucking worms that can cause anaemia, especially in kittens.
• Lungworms (Aelurostrongylus abstrusus): caught by hunting snails, slugs, birds or lizards. They live in the lungs and can cause coughing. Present in Spain.
• Whipworms exist too, but they are rare in cats in Europe.

Protozoa (not worms)

• Giardia: causes greasy, smelly, on-and-off diarrhoea. Stubborn, because cats easily reinfect themselves from their own coat and environment.
• Coccidia (Cystoisospora): especially dangerous for kittens and weak cats: watery diarrhoea, dehydration, weight loss. Treated with specific anti-coccidial drugs or sulfonamide antibiotics.
• Toxoplasma: usually harmless in cats, but important for humans (see below).
• Leishmania: spread by sandflies, not by other cats (see below).

External parasites

• Fleas: itching, scratching, flea allergy, and they carry tapeworm. For every flea you see on your cat, many more are living in your home as eggs and larvae.
• Ticks: attach to the skin and can transmit infections. Common in rural Catalonia from spring to autumn.
• Ear mites: dark, coffee-ground wax and constant head-shaking. Very contagious between cats.
• Lice: less common, mostly in weak or neglected cats.
• Mosquitoes: can transmit heartworm, which is present in Spain and can affect cats too.
• Sandflies: tiny biting flies that transmit Leishmania (see below).

Can people catch them? Yes, some of them

Several cat parasites are zoonotic: they can pass to people. And some of them you can catch without ever owning a cat.

• Toxoplasma: people mostly catch it from raw or undercooked meat and unwashed fruit and vegetables, and sometimes from soil or a litter tray. It matters most for pregnant women and people with a weakened immune system. Good news for litter duty: Toxoplasma eggs only become infectious 1 to 5 days after the cat passes them, so scooping the litter every day really helps.
• Roundworm: eggs from soil, sandpits or unwashed vegetables, swallowed by accident, mostly by children. The larvae can wander through the body (toxocariasis).
• Hookworm larvae: can burrow into bare skin, for example when walking barefoot on contaminated soil or sand, causing an itchy, wandering rash.
• Tapeworm (Dipylidium): only by swallowing an infected flea, which is why it's mostly seen in small children.
• Leishmania: through the bite of an infected sandfly. Cats don't pass it to you directly.
• Giardia from cats rarely infects people, but good hygiene is still wise.

And humans: do we need a dewormer too? It's not mandatory, and health authorities don't ask healthy adults to deworm routinely. What protects you is hygiene: wash your hands after the litter tray, gardening or handling raw meat; wash fruit and vegetables; cook meat well; wear shoes and gloves in the garden; cover sandpits. If you have symptoms, are pregnant, or have small children who play in the dirt, talk to your doctor.

Leishmania: the Mediterranean one

Leishmania is a single-celled parasite spread by the bite of sandflies: tiny, silent flies that bite from dusk to dawn in the warm months. It thrives in Mediterranean climates with hot summers and mild winters, which makes much of Spain, including Catalonia, an endemic area. Cases have been documented in Lleida province, including Pyrenean areas where the disease was once unknown.

Dogs are the main victims, but cats get it too. In a Spanish study, about 40% of stray cats tested in Zaragoza had antibodies showing they had been exposed. Many infected cats show no signs; others develop skin sores and nodules, eye problems, weight loss or kidney disease, especially cats with weakened immunity (for example FIV-positive cats).

How to protect your cat:

• In the warm months, keep your cat indoors from dusk to dawn when you can, and use fine mosquito nets on windows.
• Ask your vet about cat-safe repellent options.
• Warning: never use a dog's product on a cat. Many dog spot-ons and collars against sandflies and fleas contain permethrin, which is highly toxic to cats and can kill them. Even contact with a recently treated dog can poison a cat. If you have both, ask your vet for a permethrin-free product for the dog.

Tino's story: when a dewormer isn't enough

Tino came to us from the street, and he was in a bad way: so heavily infested that he had become weak and really ill. Tests found not one but two of the most stubborn parasites there are: giardia and coccidia. Neither is a worm, so an ordinary dewormer would have done nothing.

It took us two months of treatment, rechecks and patience to get rid of them. The parasites had badly damaged his gut flora, so alongside the medicines Tino ate a fibre-rich diet to help his gut recover.

Tino's story shows why diarrhoea that doesn't go away needs a vet and a test, not just another dewormer.

How often should you deworm?

The European parasitology experts (ESCCAP) base it on your cat's lifestyle:

Cats that hunt or eat raw meat, live with small children, or go to catteries or shows may need more. Your vet can also test a stool sample instead of deworming blindly. And remember: if your cat has fleas, treat the fleas too, or the tapeworms will be back.

Signs your cat may have parasites

• worms or rice-like segments in the poo or around the bottom
• diarrhoea (sometimes on and off), soft or smelly stools, mucus or blood
• vomiting, sometimes with worms in it
• weight loss despite a good appetite; a pot belly in kittens
• a dull, scruffy coat
• itching, scratching, hair loss, black dirt in the fur (fleas)
• head-shaking and dark ear wax (ear mites)
• coughing (lungworm)
• in Leishmania: skin sores or nodules, eye problems, weight loss

Many cats show no signs at all, which is exactly why regular prevention matters.

A simple routine

1. Deworm on schedule, using products from your vet, at the right dose for your cat's weight.
2. Protect against fleas and ticks, with cat-only products.
3. Scoop the litter every day and wash your hands afterwards.
4. Test, don't guess, if diarrhoea doesn't stop: giardia and coccidia need a vet.
5. Keep cats in at dusk in sandfly season.

His Majesty would like it noted that he tolerates all of the above. Under protest.