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Roundworms in Cats: Toxocara cati

Toxocariasis is the term used to indicate infection with Toxocara roundworms. Toxocara cati and Toxascaris leonina are important roundworms in the cat belonging to the group of parasites known as ascarids. The main roundworm to affect cats is Toxocara cati. It is unclear whether this causes disease in humans as does the canine roundworm Toxocara canis. Due to this uncertainty I think it is best to assume that it may cause disease in humans and worm cats regularly to prevent human infection.


Infection with roundworms is much more of a problem in kittens than it is in adult cats. Kittens infected with Toxocara cati may fail to thrive and gain weight. They may develop a pot bellied appearance, suffer from vomiting and diarrhoea which may lead on to weakness, severe weight loss and then death if the kitten is not treated. Whole litters of kittens may be affected in this way. If the infestation with these roundworms is very severe then they may cause a blockage or intersusseption of the intestines in some individuals; both these conditions are serious and prompt veterinary treatment will be required. In adult cats roundworms are often carried in the absence of any clinical signs. Sometimes cats and kittens vomit these worms which are light brown in colour and are often coiled.


The life-cycle of the Toxocara roundworm is interesting and quite complex.

Toxocara roundworms have two main ways of infecting cats:

1: Adult worms living in the intestine produce eggs which are shed in the faeces of infected cats. Once shed the eggs take about 2 weeks to develop into the infective stage if the weather is warm or much longer in the cold, (the process is temperature dependent). These infective eggs are then eaten by an animal.

2: Toxocara may also form dormant cysts in the muscle of infected animals. Here it waits until the animal is killed or dies and the infected muscle tissue is eaten by a carnivore.

Once the worm eggs or dormant cysts are ingested by an animal the eggs will hatch or the larvae of the cysts will reactivate inside the intestines. The resulting first stage larvae will then penetrate the small intestine and enter the blood stream in which they are carried to various organs.

What happens next depends upon what type of animal has been infected:

In adult cats the larvae migrate in the blood to organs such as the muscles where they form cysts in the tissues. Larvae in the body tissues remain dormant unless a queen becomes pregnant in which case they will reactivate to go into the milk to infect the kittens.

In kittens the main route for the larvae is to go from the intestine to the liver then on to the lungs. From here they work their way up the bronchi to the pharynx and are then swallowed by the cat to enter the intestines again, where they develop into adult worms.

If eggs are swallowed by animals other than carnivores the larvae migrate to the muscles of that animal where they form dormant cysts and wait for the muscle tissue to be eaten by a cat so they can complete their life-cycle.

The process of the worm migrating through the body tissues is known as visceral larval migrans and this is a natural part of the life-cycle of this worm. Visceral larval migrans may occur in species other than cats if they happen to ingest Toxocara eggs. The larvae need to get back to a cat to complete their life-cycle. They attempt to do this by migrating to the muscles and residing there as a dormant form. Here they are likely to be eaten with the muscle tissue by a cat.


Cats should be wormed regularly to prevent problems associated with Toxocara spp. A drug called fenbendazole is the active ingredient in the preparations I usually recommend for this purpose. Products such as Panacur and Drontal Cat are effective treatments. If your cat or kitten has evidence of roundworm infection then it is wise to carry out at least two treatments about 4 weeks apart; since the life-cycle of this worm takes about 4 weeks you will kill the maximum number of adult worms in this way. (Eggs and larvae are not killed so you need to allow them time to develop into adults between treatments.)


To prevent anyone in your family catching toxocariasis it is wise to treat your pet for worms regularly as discussed above. Many owners only worm their cat every 6 to 12 months but I would suggest an interval of around every three months. Worm weaned kittens every two weeks until they are 12 weeks old then every month until they are 6 months old when they can begin the adult regime. Wash your hands well with soap and water after touching your cat or cleaning up faeces/ litter trays etc. Do not allow children to play in soil which may be contaminated; flower beds or other areas frequented by cats are likely to have soil contaminated with Toxocara eggs.


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