Roundworms may be carried by a cat which shows no obvious sign of ill health. However they may sometimes be noticed in a pet's vomit or in faeces. They are about 5-15 cm long, off-white in colour and are sometimes coiled. In kittens they can cause gastrointestinal problems; this most often manifests as vomiting and diarrhoea. In adult cats they do not seem to cause problems very often. Cats catch roundworms from other cats and infected animals will constantly re-infect themselves when they groom around their bottom and tail.
Tapeworms vary in length but can be up to 30 cm long. Usually the worm itself is not seen but the mobile tapeworm segments may be observed around the cat's anal region or on its bedding. They are white in colour and look a bit like grains of rice about 1 cm in length. Tapeworms are not passed from one cat to another but are carried by fleas and small prey mammals such as mice. Therefore tapeworms do not tend to affect kittens but are more of a problem for the adult cat. Cats are especially at risk from tapeworms if they have fleas or they are regular hunters. Housecats kept free of fleas are less at risk from tapeworms. If an adult cat has tapeworms they may not cause any noticeable problems but sometimes they may cause irritation around the anus or diarrhoea.
Ideally your adult cat should be wormed regularly whether you see worms or not. There are a wide range of different products available. Wormers commonly come as tablets, powders or pastes, but there are newer spot-on products available as well. Different products control different worms; some products such as Drontal control roundworms and tapeworms, other products may control either roundworms or tapeworms or both; many of the spot-on preparations control fleas as well as worms. Remember that by controlling fleas you will also help to control tapeworms because they are the most common source of tapeworm infection for the cat. In many situations the spot on products are the easiest to use since it can be very difficult to get a cat to take any medication by mouth.
During pregnancy a cat should be wormed every two weeks in the final third of the gestation period, then after the birth until the kittens are weaned. Speak to your vet about products suitable for use during pregnancy. Kittens will often get roundworms from their mother so they should be wormed with a product such as Panacur from around 6 weeks of age. Treat them every 2 weeks until they are 12 weeks old then monthly until they are 6 months old. After this treat them as adults. If you see roundworms in a young kitten it would be advisable to see your vet as they may have a very heavy infestation. As adults, cats who hunt frequently or that often have fleas will need to be wormed more frequently than cats that spend most of their time indoors and don't suffer from fleas; but as a rough guide the average cat should be wormed every three months. Ask your vet for a product suitable for your cat and worm at an interval suitable for your cat and the product you use.