The most common intestinal worms cats get are called roundworms and tapeworms.
Most infected cats do not show signs of having worms; however, heavy burdens of worms can cause weight loss, vomiting and diarrhoea, irritation around the anus and failure to thrive.
Importantly, while worms can sometimes cause problems for the cat itself, some worms can also be passed on to humans and on rare occasions can be a cause of serious human disease. For these reasons, regular treatment of cats and kittens to prevent or eliminate worms is very important.
Types of worms
Intestinal roundworms are the most common intestinal parasites in cats and occur in cats of all ages throughout the world. The two common roundworms of cats are called, Toxocara cati and Toxascaris leonina. Eggs from these worms are passed in the faeces and can remain viable in the environment for several years. These eggs can infect other cats in two ways. First, a cat may eat (ingest) eggs directly from a contaminated environment. Second, if another animal eats the eggs (eg, a mouse or rat), these can act as ‘intermediate hosts’ and pass on the infection to a cat if it preys on (and eats) the infected intermediate host.
Toxocara cati is also passed from queens (mother cats) to kittens through the milk she produces. Whenever a cat is infected with roundworms, some immature forms (larvae) remain dormant in tissues in the body. This usually causes no harm, but when a female cat becomes pregnant, these larvae migrate to the mammary glands and are excreted in the milk she produces for the kittens. This is a very common route of infection and we should assume that every kitten will be infected with Toxocara cati as a result.
In most cases, regular routine treatment for roundworms is recommended throughout a cat’s life. However, to determine if a cat is actually infected with worms, a faeces sample can be collected and examined in the laboratory to look for the presence of the worm eggs.
Other gastro-intestinal roundworms that may infect cats in various parts of the world include:
- Ollulanus tricuspis (found in the stomach)
- Gnathostoma spp
- Physaloptera spp
- Strongyloides spp
Hookworms are a type of small intestinal roundworm found in most countries throughout the world, but are more common in some countries than others. These worms can cause damage to the lining of the intestine where they attach to the surface, and this may result in weight loss, bleeding and anaemia.
Cats may be infected by ingestion (eating) eggs from the environment, from eating an infected intermediate host (as with Toxocara cati above) or by the larvae in the environment burrowing through the cat’s skin.
Common cat hookworms include Ancylostoma tubaeforme, and Uncinaria stenocephala, but other species occur in some countries.
Tapeworms are generally long flat worms composed of many segments. Mature segments containing eggs are released from the end of the tapeworm and are passed in the faeces. These segments often resemble grains of rice and can sometimes be seen on the hair around the anus of the cat, in the faeces and on the cat's bed.
To complete their life-cycle, all tapeworms require an intermediate host to first eat the eggs from the environment, and then the cat will become infected by eating the intermediate host. Animals that act as intermediate hosts vary depending on the species of tapeworm. The most common tapeworms that infect cats worldwide are Dipylidium caninum and Taenia taeniaeformis.
Dipylidium caninum is transmitted to cats by fleas. The immature fleas larvae ingest the eggs of the worm, but infection is then passed on to a cat when it swallows an infected flea during grooming. It should be assumed that any cat infected with fleas also has Dipylidium caninum (and vice versa).
Taenia taeniaeformis is passed on when they eat small rodents (rats and mice), the rodents having eaten eggs from the environment. This infection occurs very commonly in cats that hunt.
Other tapeworms that occur in some countries include:
- Diphylobothrium latum (fish are intermediate hosts)
- Spirometra spp (amphibian, reptiles and rodents are intermediate hosts)
- Diplopylidium spp (reptiles are intermediate hosts)
- Joyeuxiella spp (reptiles are intermediate hosts)
- Echinococcus multilocularis (rodents are intermediate hosts)
Worming your cat
Roundworms are extremely common in kittens, and as kittens can be infected from the mother’s milk it should be assumed that all kittens are infected and worming should be started at a young age. Common recommendations are to:
- Treat kittens for roundworms every 2 weeks from 3 weeks of age until 8 weeks of age, then monthly to 6 months of age
- Treat adult cats (greater than 6 months of age) every 1-3 months
Tapeworms are only usually a problem in older cats, unless a kitten also has fleas.
- Treat adult cats (greater than 6 months of age) every 1-3 months with a product that is effective against both tapeworms and roundworms.
A product active against Dipylidium caninum should also be used in kittens that have flea infestations.
Which worming products to use?
There are many different worming products available on the market, and drug availability varies between different countries. While worming products may be available from pet shops and even some supermarkets, these are often old or less effective products and some are even less safe to use in cats.
It is always better to seek the advice of your vet, who will know what types of worms occur commonly where you live, and will be able to recommend the most effective and safest treatments for your cat. Additionally, some treatments are available which may be easier to administer, such as an injection that your vet can give, a tiny tablet that can go in with food, or even some drops that can be applied to the skin.
See also our information on how to give your cat a tablet.
In addition to intestinal worms, cats can be infected with a variety of other worms in other sites of the body, although often these worms are not present in all regions of the world. These include:
- Dirofilaria immitis – heartworm
- Aelurostrongylus abstrusus – lungworm
- Capillaria spp– lungworm
- Thelazia callipaeda – eyeworm