Toxocara cati (syn. of Toxocara mystax), also called the feline roundworm or the cat roundworm, is a parasitic nematode very common in cats and other felids (e.g. lynxes, big cats). It can also infect humans.

Toxocara cati is not a bloodsucking worm. Depending on its developmental stage and location it feeds on body fluids of the host or on the intestinal content in its gut.

Toxocara cati is found worldwide. Eggs and larvae of Toxocara cati can survive for months and even years in the environment (see life cycle below). Therefore it must be assumed that most places regularly visited by cats (gardens, parks, playgrounds, etc.) are more or less contaminated.

Toxocara cati, adult worms. Picture from Wikipedia Commons

The disease caused by Toxocara cati is called toxocariasis. Toxocara canis, a related species infects dogs and other canids (e.g. foxes, coyotes, wolves, etc.); and Toxocara vitulorum infects cattle. All belong to a group of roundworms called ascarids (maw worms), together with other nematodes of veterinary importance, e.g. Ascaris suum and Toxascaris leonina.

Toxocara cati does not affect cattle, sheep, goats, swine, horses or poultry.

Are cats infected with Toxocara cati contagious for humans?

  • YES. If humans ingest eggs of Toxocara cati shed with the feces they can become infected as well. This can happen through direct or indirect contact with the droppings of infected cats, but also indirectly through eggs in their hair coat. For additional information read the chapter on the life cycle below.

You can find additional information in this site on the general biology of parasitic worms and/or roundworms.

Final location of Toxocara cati

Predilection site of adult Toxocara cati is the small intestine, but migrating larvae can be found in the abdominal cavity and in several organs (lungs, eyes, heart, liver, etc.).

Anatomy of Toxocara cati

Adults of Toxocara canis have the typical slender shape of worms, with thinner head and tail. They are about 7 to 11 cm long and 2-3 mm wide, whereby females are larger than males. They have a whitish-yellowish color.

The anterior end has two wing-like projections (alae). The head has three prominent lips armed with small teeth. The worm's body is covered with a cuticle, which is flexible but rather tough. The worms have no external signs of segmentation. They have a tubular digestive system with two openings. They also have a nervous system but no excretory organs and no circulatory system, i.e. neither a heart nor blood vessels. The female ovaries are large and may contain up to 30 million eggs. Males have simple chitinous spicules for attaching to the female during copulation.

The eggs are almost spherical, brownish, measure about 65x75 micrometers, have a thick wall with a rough surface, and contain a single cell.

Life cycle and biologyof Toxocara cati

Detail view of the cervical end with the typical alae (=wing-like) projections. Picture from Wikipedia Commons

Toxocara cati has a direct life cycle, with cats and other felids as final hosts, but particularly complex, because other mammals (e.g. rats and mice), but also earthworms, cockroaches, beetles and even chicken can act as transport hosts (also called paratenic hosts). In these transport hosts the worms do not complete development to adults, but can be rather harmful and are infective for cats if they east these intermediate hosts.

The eggs are shed with the cat's feces and once outside the host L2 larvae develop inside the eggs in 2 to 3 weeks depending on weather conditions. These eggs containing the L2 larvae are infective for cats and other transport hosts. A single infected cat or kitten can shed more than 100'000 eggs per gram of feces. By suitable conditions these eggs can survive and remain infective for months and even years in the soil.

In young kittens, ingested eggs release the L2 larvae in the intestine. These larvae cross the gut's wall and migrate to the lungs through the portal vein and the liver. One in the lungs thy molt to L3 larvae, migrate to the trachea (windpipe) and further to the mouth (e.g. after coughing or sneezing). This migration takes about 10 days. From the mouth L3 larvae are ingested, reach the intestine, complete development to adult worms and start producing eggs, about 25 to 30 days after infection. Nursing queens can become infected with these eggs when licking their kittens. 

In older kittens and adult cats the hatched L-2 larvae undertake a somatic migration that can lead them to numerous organs (liver, lungs, heart, brain, muscles, gut's wall, etc.) where they encyst and start a period of dormancy that can last for years. Part of these dormant larvae can migrate back to the gut, complete development to adults and star producing eggs. In lactating queens dormant larvae in the tissues become activated and reach the mammary glands. Suckling kittens become infected through the milk. These larvae do not undertake a somatic migration inside the kitten, but go directly to the gut and complete development. A single infection is enough for the queens to transmit the worms to all their successive litters.

In contrast with the dog tapeworm Toxocara canis, there is no intrauterine transmission of Toxocara cati larvae from the pregnant mother to the fetuses.

In transport hosts (often small rodents such as rats, mice, but also earthworms, beetles, cockroaches, chicken, etc.) that ingest infective eggs, L2 larvae hatch after digestion and migrate to various organs where they encyst without completing development. If a cat or another suitable final host ingests such infected hosts, after digestion the cysts release the L2 larvae, which go directly to the gut where they complete development to adults and start producing eggs.

Harm caused by Toxocara cati infections, symptoms and diagnosis

Infections with a few worms are usually benign for cats and kittens and cause no clinical signs other than reduced weight gains. But these benign infections are important for disease transmission to other cats or to humans.

Heavy infections can cause intestinal inflammation (enteritis) with subsequent diarrhea, mucous feces, vomiting and weight loss, which can be particularly serious for kittens. Fatalities can happen due to intestinal obstruction and even rupture. Affected animals often show a dull hair coat and inflated bellies. Migrating larvae in various organs can also cause coughing, nasal discharge, constipation, jaundice, and allergic reactions.

Humans can become infected through ingestion of infective eggs, which can be picked mostly through direct or indirect contact with contaminated cat feces, but occasionally also from the hair coat by petting a cat. Humans act as transport hosts, i.e. the larvae will not complete development to adult worms in the human intestine, but will migrate (therefore called larva migrans) through the intestinal wall towards various organs causing two types of syndromes: visceral larva migrans if several internal organs are effected (mainly the liver, the lungs and the intestinal wall, but sometimes also the central nervous system, i.e. the brain), and ocular larva migrans if the eyes are affected.

Children are especially at risk because they are more likely to ingest eggs from contaminated environments. Human infections with a few worms are usually benign and resolve spontaneously with a few weeks. But untreated heavy ocular infections can cause blindness and severe visceral infections can be even fatal in extreme cases.

Diagnosis in dogs is done by fecal examination for detection of eggs. In heavy infections full worms or larvae may be found in the vomit or even in the feces of kittens. Diagnosis of larval infections in body organs can be accurately done with ELISA, PCR (Polymerase Chain Reaction) or other serological assays, but the are not available in some countries. 

Prevention and control of Toxocara cati infections

It is highly advisable to prevent pets and puppies from eating or licking soil or other substrates potentially contaminated with eggs, but this is often very difficult to achieve. In catteries and boarding houses it is essential to follow strict sanitation and disinfection of cages, boxes and any places used by adult cats or kittens. Droppings must be eliminated daily.

Kittens younger than 3 months should be preventatively treated with a wormer approved for roundworm control every 2 to 3 weeks starting 3 weeks after birth. It is advisable to treat their mother as well.

Based on the local epidemiological situation and the cats' specific environment (rural, urban, contact with other dogs, season, climate, etc.) it can be advisable to periodically treat adult cats of both sexes with appropriate wormers as recommended by your veterinary doctor. If available and affordable it can make sense to regularly perform a fecal examination of the cats' droppings.

After acquiring a kitten or an adult cat, it is highly advisable to preventatively deworm it and, if possible, to get whatever clinical information from the previous owner.

All these measures are especially important in families with young children in close contact with cats or kittens. In addition children must be instructed to frequently clean their hands with soap before eating, to avoid contact with the pets' droppings, not to lick their hands after contact with the pets, etc. These measures are obviously very advisable for adults as well. On the other side it is also important to train the pets not to defecate in places where the children use to play.

There are numerous anthelmintic products (also called wormers or dewormers) effective against Toxocara cati and other roundworms. They contain active ingredients of various chemical classes such as benzimidazoles (e.g. fenbendazole, febantelflubendazole, mebendazole), tetrahydropyrimidines (e.g. pyrantel), macrocyclic lactones (e.g. milbemycin oxime, moxidectin, selamectin), emodepside, levamisole, piperazine derivatives, etc. They are often used in mixtures, sometimes with specific taenicides (mostly praziquantel) to control tapeworms as well.

Most of these pet wormers are available in formulations for oral delivery either as solids (tablets, pills, etc.) or as liquids (drenches, suspensions, etc.). In some countries there are also a few spot-ons (= squeeze-ons = pipettes) and a few injectables that are effective against Toxocara cati.

Most wormers kill the worms shortly after treatment and are metabolized and/or excreted within a few hours or days. This means that they have a short residual effect, or no residual effect at all. As a consequence treated animals are cured from worms but do not remain protected against new infections. To ensure that they remain worm-free the pets have to be dewormed periodically, depending on age and the local epidemiological, ecological and climatic conditions.

Excepting a few spot-ons, other antiparasitics for external use (shampoos, soaps, sprays, powders, insecticide-impregnated collars, etc.) are not effective against Toxocara cati or other roundworms.

There are so far no true vaccines against Toxocara cati. To learn more about vaccines against parasites of livestock and pets click here.

Biological control of Toxocara cati (i.e. using its natural enemies) is so far not feasible.

You may be interested in an article in this site on medicinal plants against external and internal parasites.

Resistance of Toxocara cati to anthelmintics

So far there are no reports on resistance of Toxocara cati to anthelmintics.

This means that if an anthelmintic fails to achieve the expected efficacy, chance is very high that it was not due to resistance but to incorrect use, or the product was unsuited for the control of these parasites. Incorrect use is the most frequent cause of failure of antiparasitic drugs.

Ask your veterinary doctor! If available, follow more specific national or regional recommendations for Toxocara cati control.