Pinworms, roundworms, trichinella and tapeworms are the most common parasitic worms in Canada. Learn more about the symptoms and treatment of these unpleasant infections and how to prevent them.

What are worms?

Parasitic worms invade one or more organs of the body and prevent them from working properly. A parasite infestation is very unpleasant. Although worm infections are not all that common in Canada compared to other countries, they still occur here. The most common parasites in Canada are:

  • pinworms (small worms approximately 1 cm long)
  • roundworms (can grow up to 20 cm to 40 cm long)
  • trichinella (thread-like worms)
  • tapeworms (can grow from 4 m to 12 m)


A pinworm infection (oxyuriasis or enterobiasis) is the most common type of parasite infection in Canada. Pinworms are found in the large intestine. Children aged 5 to 10 years get these parasites most often, and 1 in 3 Canadians become infested during childhood.

Transmission and symptoms

The female pinworm lays eggs around a person’s anus during the night, which can cause itching in the anal region. If you then scratch this area, the eggs can stick to your hands and nails and then transfer to sheets and pyjamas. If you put your hand in your mouth, you’ll swallow the eggs and become reinfected. You can also infect other people indirectly from touching surfaces or objects or preparing food.

In addition to nighttime itching that disrupts sleep, pinworm infections can also cause stomach pain, a loss of appetite, nausea, and diarrhea. Girls and women can also experience itching on the vulva and in the vagina. Some people don't experience any symptoms.

It is best to see a doctor before getting an over-the-counter treatment, and children under 2 years old must see a doctor if infested. You should collect a worm to have it identified by a health care professional. For children, you can collect a worm in the evening when your child is asleep by searching for one around the anus (use a flashlight to see clearly). You can also carefully apply adhesive tape around the child's anus. Another method is to look for eggs in the stool. 


To treat the infestation, you will be given an antiparasitic drug that is available without a prescription, but you have to ask for it at the pharmacy counter (schedule II drug). This drug comes in the form of tablets or a liquid suspension. The pharmacist calculates the dose based on the person's weight. The treatment must be repeated after 2 weeks, as the first treatment won't kill all the eggs and larvae. In 14 days, the eggs and larvae will mature and will then be killed by the second treatment. You need to treat everyone who lives with the infested person, as pinworms are very contagious and the risk of reinfestation is high. Contrary to what you may think, laxatives are not recommended during the treatment.

You need to adopt specific hygiene measures for the duration of the treatment to avoid becoming reinfected and to prevent the worms from spreading.

  • Wash your hands and nails before eating or preparing food, after going to the bathroom, and after scratching the anal region.
  • Keep your nails short.
  • Have your child wear a onesie or tight-fitting pyjamas to keep them from scratching their anus in their sleep.
  • Wash sheets, pyjamas, underwear, towels and stuffed toys in hot water and detergent every day. Avoid shaking these items, as pinworm eggs can spread easily.
  • Frequently wash toilet seats, eating surfaces, and objects that are touched often (e.g., door handles, TV remotes, phones). Pinworm eggs can live up to 3 weeks on a surface at room temperature.
  • During the week following treatment, wear cotton underwear and change it 1 to 2 times a day.


Although more common in hot countries, a roundworm infection (ascariasis) can occur anywhere in the world. Children under the age of 10 are the ones who get it most often.

Transmission and symptoms

Roundworm eggs from contaminated feces can survive for 6 years in the ground and infect food grown in the soil. Sometimes eggs are found in such large quantities in the ground that they contaminate the air, and someone can breathe them in. The larvae then take 1 to 2 days to reach the lungs or liver. This causes fever, a cough and wheezing. The larvae then pass from the lungs to the throat and are swallowed. They move to the small intestine and grow to about 30 centimetres long.

A large number of worms in the digestive tract will cause stomach aches. Someone with roundworm may have symptoms of malnutrition, as the worms feed on what they eat. Sometimes the worms get so big that they can obstruct and even perforate the intestine.

A doctor generally diagnoses an infection of adult roundworms by looking for eggs in the stool, although adult worms themselves can also be found in the stool or vomit.


Some of the same medications that treat pinworms will also treat roundworms. The same hygiene precautions must be taken to get rid of these worms.


Trichinella is common around the world but is rare in North America. Outbreaks usually happen when people ingest raw or undercooked pork or wild game meat that has been infected with the parasite. Sausages and smoked or salted meats can also be contaminated even after they are processed.


Symptoms such as vomiting, chills and fever may appear 1 to 2 days after you ingest infected meat, but usually the signs of larvae infestation only appear after 7 to 15 days. Edema (swelling) of the upper eyelids, which becomes noticeable around the 11th day, is one of the earliest and most characteristic signs of trichinella infection (trichinosis or trichinellosis). This may be followed by a subconjunctival hemorrhage (blood in the white of the eye), pain, and intolerance to light. Muscle pain can be intense, particularly in the muscles used for breathing, chewing and swallowing. The myocardium, or the muscle envelope surrounding the heart, can also be affected.

The infested person can have major respiratory problems that can even be fatal. These problems start in the 2nd week, peak during the 3rd or 4th week, and then get better gradually. The fever will stay high (39 °C or more) for several days and then gradually get better. Most symptoms disappear in the third month, although some muscle pain may persist.


The body of an infested person most often gets rid of trichinella on its own. The goal of treatment will be to relieve symptoms. You can prevent this infection by taking specific measures; for example, cook wild game meat or pork to over 55 °C, or freeze the meat at -15 °C for 3 weeks.


Tapeworm infections aren't very common in North America. When they do happen, contamination sources are undercooked beef or pork or raw freshwater fish. This parasite makes its way to the small intestine of an infested person.


Although it often causes no symptoms, a tapeworm infection can cause stomach pain, diarrhea, decreased appetite and weight loss. The infection is diagnosed from the characteristic rings found in the stool or eggs in the perianal area.


This infection must absolutely be treated with antiparasitic drugs, but it can be easily avoided by properly cooking meat and fish.

A tip to remember

You can avoid the most common parasite problems in Canada by adopting good hygiene measures and sufficiently cooking meat and fish.

Don’t hesitate to talk to your pharmacist or doctor to get the right diagnosis and treatment for your situation.

Find a Pharmacy