Intestinal Worms in Cats and Dogs


Most animals will become infected with internal parasites at some point in their life. In fact, the majority of animals become infected with worms before they are even born. Dogs and cats can be infected by a variety of different worms, such as roundworms, tapeworms, lungworms, and heartworm.

With the exception of heartworm and lungworms, most of these parasites are generally found in the gastrointestinal tract. Parasitic worms can significantly contribute to ill-health and disease in your pet. Pet owners should regularly worm their animals and have their stools checked for parasites to ensure that their pet is healthy.

Tapeworms (Cestodes, Dipylidium caninum, Echinococcus granulosa)

Tapeworms are segmented flatworms that rely on animal hosts to complete their life cycle. The most common tapeworm of cats and dogs is Dipylidium caninum. Cats and dogs become infected with tapeworms by accidentally ingesting fleas (that have eaten tapeworm eggs) while grooming, or by hunting other animals that are infected with tapeworm.

Segments containing worm eggs are passed in the faeces or “crawl” out onto the hair coat of an infected animal. Most cases of tapeworm are diagnosed by seeing these tapeworm segments, which look like little grains of rice, adhered to the pet’s hair around the anus or the tail.

Generic, over-the-counter drugs are rarely effective against tapeworm infections. A wormer containing praziquantel and/or epsiprantel can be prescribed by your veterinarian as an effective means of ridding your pet’s tapeworm infestation. Flea control is also an important factor in tapeworm control. Other tapeworms can be avoided by restricting your pet’s access to garbage and raw meat, and by preventing it from hunting.

Roundworms (Ascarids, Toxocara spp.)

Roundworms are white or cream coloured worms that inhabit the small intestine of cats and dogs. Roundworms are transmitted by eggs passed in the faeces of infected animals, in the milk of infected mother animals, or transplacentally from the mother to her unborn puppies and kittens. Thus, a high incidence of roundworms is common in neonatal animals born to infected mothers.

Worm larvae make their way to the small intestine, where they mature into adults and begin shedding large numbers of eggs. If the animal consumes some of the egg-laden faeces, it will re-infect itself. Larvae hatch from the eggs in the intestines, and migrate through the liver to the lungs, where they enter the airways. The larval worms are coughed up, swallowed, and return to the small intestine where they mature into adult worms. Thus, the life cycle of the roundworm continues, increasing the parasite load of the affected animal.

When large amounts of roundworms accumulate in the small intestine, this can lead to obstruction of the intestine, intussusception, and even rupture of the gut. Puppies and kittens with high worm burdens typically have a pot-bellied appearance.

Roundworms are diagnosed by seeing the worms in the faeces, or identifying the eggs during a microscopic examination of the faeces.

Hookworms (Ancylostoma, Uncinaria)

Unlike tapeworms and roundworms, it is unlikely that pet owners will ever see evidence of these worms in their pet’s faeces. Hookworms are small, threadlike parasites that use their sharp teeth to attach themselves to the lining of the small intestine. Once attached to the intestinal lining, they suck blood from blood vessels within the wall of the small intestine. Hookworm infestations can lead to anaemia and even death if they go untreated.

Hookworms can be transmitted in a number of ways: by ingestion of eggs in infected faeces, penetration of the skin (usually via the footpads), from mother to offspring in the womb, or through nursing infected milk.

Hookworms are diagnosed by examining a stool sample for eggs under a microscope.

Whipworms (Trichuris vulpis)

Whipworms are more commonly seen in dogs than cats. As opposed to tapeworms, roundworms, and hookworms, which inhabit the small intestine, whipworms are usually found in the large intestine and are a frequent cause of chronic colitis in dogs. They live in the caecum, the section of the large intestine equivalent to the appendix in humans.

The life cycle of the whipworm is similar to that of other intestinal worms. Pets become infected by ingesting faeces containing whipworm eggs. The eggs hatch in the gut and the whipworms grow to maturity in the large intestine. The adult worms produce eggs in the large intestine that are passed in the faeces. Unlike, other intestinal worms, whipworms do not migrate through the tissues.

Whipworms are difficult to diagnose because they are seldom seen in the faeces and produces few eggs.

What signs should I look for if I suspect my pet has worms?

The symptoms of a worm infestation are variable – they depend on factors such as the age of the animal, the type of worm, the quantity of parasites, any other concurrent disease, etc. Common signs include:

• Loss of appetite
• Lethargy or depression
• Distended abdomen (pot-bellied appearance)
• Vomiting
• Diarrhoea (may contain blood, mucus, worms)
• Ill thrift and/or stunted growth
• Weight loss
• Anaemia
• Poor hair coat
• Scratching or licking around the anus
• Breathing difficulties or coughing
• Inflammation or bleeding at sites of hookworm penetration (e.g. foot pads)

If you suspect your pet has become infected with worms, make an appointment with a veterinarian. Worms can be a potentially life-threatening condition for very young animals – they can cause severe anaemia, intussusception, gut obstruction, rupture of the intestine, and pneumonia.

Why should a veterinarian examine a stool sample?

Adult pets should have a stool check as part of their annual examination. Puppies and kittens should have a stool check at their first veterinary exam. The faeces are examined under a microscope for the presence of worm eggs. By identifying the eggs of a specific worm, a vet can determine the best medication to treat those worms. For instance, if your cat has tapeworms, it may be given a different wormer than if it had roundworms.

How do I decide on the best wormer for my pet?

Always consult your veterinarian when choosing a wormer for your pet. Generally, prescription wormers are much more effective than over-the-counter wormers at eliminating worm burdens. Pets that are on heartworm prophylaxis may be covered for some of the intestinal worms. A veterinarian can suggest a treatment regime that effectively covers heartworm, intestinal parasites, and fleas.

Are people at risk if their pets have worms?

Some worms are a potential health hazard for humans. Penetration of the skin by hookworms is known as “cutaneous larva migrans”, a disease that results in itchiness, dermatitis, and scarring. If roundworms eggs are ingested, they can cause a disease syndrome known as “visceral larva migrans”, which occurs as a result of roundworms migrating through human tissue.

Kids playing in sandboxes where animal faeces are present are most at risk of ingesting infective eggs. Always, adopt strict hygiene measures if you are in close contact with pets.

How can I reduce the risk of intestinal worms?

There are a number of steps pet owners can take to prevent themselves and their animals from becoming infected with intestinal parasites:

• Worm your pet regularly (at least every 3 months)
• Only use wormers under veterinary supervision
• Prevent your animal from hunting or eating garbage
• Have your veterinarian perform a stool check at least once a year
• Remove animal faeces from your back yard – worm eggs can survive for a long time in the environment
• If you are walking your dog in a public area, clean up any faeces so as not to contaminate the soil with worm eggs
• Pregnant animals may need to be wormed more frequently so as to prevent transmission of worms to their offspring
• Puppies and kittens require a different worming regime than that of an adult animal – ask your vet about wormers that are appropriate for young animals

(photo: nickmitha)