Internal Parasites in Pets – the hidden killer

Most of us are familiar with external parasites such as ticks and fleas, which are easy to detect on your pet. However, it is much more difficult to detect hidden internal parasites that can live inside your pet. In modern society, pets have a more intimate relationship with the family.

We pet them, carry them, kiss them and play with them. We bring them into our home, and sometimes even let them sleep in our beds! Because of the close relationship we have with our pets, it is extremely important to protect them against internal parasites, some of which can be transmitted to people. The most common internal parasites seen in our region are heartworms, roundworms, whipworms and tapeworms.

Heartworms are the most dangerous of all canine (and feline) internal parasites. Heartworms are spread by mosquitoes, so all dogs are at risk. If left untreated, heartworm infection causes fatal heart and lung disease. An infected dog can die within a few months. In rare cases an animal infected with heartworm may show no signs of infection.

More commonly, however, an infected animal will cough, find it difficult to exercise, have difficulty breathing, lose weight and have increased abdominal fluid. There are currently a number of products available that prevent heartworm. Oral medications include daily tablets and monthly chews or tablets.

There is also an annual injection available. The injection compares favourably on price with oral products but is much more convenient.

Although cats can be infected with heartworm, it is extremely uncommon.


The most common intestinal worms that infect pets are roundworms, hookworms, whipworms and tapeworms. Of these worms, only two are easily seen in faeces with the naked eye: roundworms and tapeworms. Hookworm and whipworm are too small to see without a microscope. Most worm infestations cause any or all of the following symptoms: vomiting, diarrhoea, weight loss, poor body condition, swollen abdomen, dull coat and reduced appetite.

Roundworms are probably the most common internal parasites found in dogs. A large percentage of puppies (and kittens) are born with microscopically small roundworm larvae in their tissues. The larvae are introduced to the developing fetus in the mother’s uterus. Larvae can also be transferred via the mother’s milk.

The larvae make their way to the intestinal tract, where they can grow up to 12 centimetres in length. Both mature worms (look like spaghetti) and eggs can be shed in the faeces. (Infestation of older animals is usually via ingesting eggs) Roundworms pose a health threat to humans, especially young children, via their ability to migrate to various human tissues. In rare cases, roundworm larvae can migrate to the eye!

Hookworms are much more common in dogs than cats. They are very small, thin worms that attach to the wall of the small intestine and suck blood. Similar to roundworms, hookworm larvae can be transferred to developing animals and neonates via the mother’s uterus and milk. Ingestion of stool-contaminated soil is also a route of infection. A severe hookworm infection can kill puppies by causing a life-threatening anaemia. Cutaneous larva migrans is a condition in people where hookworm larvae penetrate intact skin and migrate under the skin, causing an extremely itchy red eruption.

Tapeworms are transmitted to dogs and cats by two different routes. Most infections occur by the pet ingesting fleas. Less commonly, infection can occur by ingesting prey such as rodents and reptiles. Tapeworms can reach up to 20 centimetres in length.

Tapeworms crawl out of the anus, and are found crawling on fresh faeces, or in some cases segments are attached to the fur under the pet’s tail. Tapeworms are very itchy, and cause the pet to drag their rear end on the ground. The Echinococcus tapeworm is of particular concern as it can cause severe illness in people. Ingestion of infected material (usually uncooked sheep meat) can ultimately result in formation of life-threatening cysts in a person’s liver or lungs.

Whipworms are seen more often in dogs than cats. Ault whipworms are rarely seen in the stool, and relatively few eggs are shed into faeces, making diagnosis difficult. Whipworms cause chronic weight loss, and cause passage of mucous-covered faeces. Whipworms are not normally transmitted to people.

Prevention of intestinal worms is vitally important for you and your pet’s health. Oral medications are the most common, although some “spot-on” formulations also provide protection. Some oral preventatives (Sentinel, Interceptor) require monthly administration, whilst Drontal (our preferred product, and still regarded as the industry leader) is administered every 3 months to adult animals. Young animals require more frequent administration. Ensure that the product being used contains praziquantel, which is necessary to prevent tapeworm infection. Animals that hunt or ingest rodents and small reptiles may require higher doses of praziquantel to protect against Spirometra, a particularly hardy species of tapeworm.