By Lynn Broom
Longmead Veterinary Practice.

INTERNAL worms are parasites that can live in various places within the body. Typically, they live alongside the host animal without causing too much damage, but some can cause significant harm and, in certain circumstances, death of the host.
Broadly speaking, in pet animals in the UK, the types of worms are divided into roundworms and tapeworms. Most roundworms live in the gut and live off the food passing through it as the animal eats. Some travel via the lungs or heart as part of their lifecycle and some live off the blood via blood vessels in the gut wall and, when present in large numbers, can cause anaemia.

Roundworm, particularly in dogs, can cause problems in growing children. The larvae of the worm can track to the developing optic nerve causing blindness. Roundworm eggs can survive in the environment and on infected animals’ fur, so it is essential that dogs in contact with children are wormed effectively.

Puppies can become infected from their mothers by trans-placental infection and puppies and kittens can get them from their mother’s milk. Even healthy, regularly wormed bitches are likely to carry low levels of roundworms. Puppies have no immunity to these worms so require regular worming from two to three weeks of age. Effective wormers will kill adult worms present at the time, but encysted stages present in the gut wall will then mature and a new adult population of worms will develop.

Other less common types of worm, such as lungworm and hookworm, can also be seen. Lungworm can cause a cough and a clotting disorder, as well as other less common symptoms, and are obtained by eating snails and slugs. The prevalence of lungworm is unknown but may be underestimated as a cause of clinical disease. Hookworm is a type of worm which burrows through foot pads and is more common in kennelled dogs such as greyhounds and can cause significant blood loss – and even death – in puppies.
Two commonly found forms of tapeworm are found in our pets. Infections are attained from eating raw meat and from fleas. Cats which eat wild-caught animals are commonly infected with tapeworm and can develop visible external segments three weeks after initial infection. Fleas commonly carry tapeworm eggs and pets grooming themselves when infested with fleas will often swallow fleas and the tapeworm eggs inside will develop inside the pet. Pets which do not have fleas and do not eat raw meat are at low risk of tapeworm infections.

There are many wormers on the market and they vary significantly in their effectiveness as well as which worms they treat, with most ‘off the shelf’ products not covering lungworm. If you want to ensure you are treating your pet correctly, please speak to your veterinary practice so they can assess the relative risk and advise you which wormer to use.