In most people, a roundworm infection does not cause any noticeable symptoms.
It is unclear why some people are particularly sensitive to the effects of roundworms while most people are unaffected. One theory is that most people have a natural immunity (resistance) to roundworms, which prevents the parasites from reproducing and moving through the body.
When symptoms occur, they usually follow a two-stage course:
- Early-phase symptoms are caused by the larvae (newly hatched worms) moving from the small intestine to the lungs.
- Late-phase symptoms are caused by adult worms moving back from the lungs to the intestine, where they begin to reproduce (see Roundworm - causes for more information about the life cycle of the roundworm).
Early-phase symptoms
The early-phase symptoms of a roundworm infection usually begin 4 to 16 days after swallowing the eggs. They include:
- high temperature (fever) of 38C (100.4F) or above
- a dry cough
- shortness of breath
- wheezing
Late-phase symptoms
The late-phase symptoms usually develop six to eight weeks after the eggs have been swallowed. The severity of your symptoms will depend on the number of roundworms inside your body. A low number of worms is known as a ‘light worm burden’ and a high number of worms is known as a ‘heavy worm burden’.
Signs and symptoms associated with a light worm burden include:
- mild abdominal (tummy) pain
- nausea
- vomiting
- diarrhoea (you may also notice blood in your stools)
Signs and symptoms that are associated with a heavy worm burden include:
- passing a worm in your vomit, stools or through one of your nostrils
- severe abdominal pain
- nausea
- vomiting
- feeling like you have a lump in your throat
- unexplained weight loss
Blocked intestine
If your worm burden is particularly heavy, the worms can cause a blockage in your intestine. This is usually more common in children aged one to five years because their intestines are smaller and at greater risk of becoming blocked. Children between these ages account for 85% of cases of blocked intestine.
The symptoms of blocked intestine include:
- a severe, sharp abdominal pain
- vomiting (the vomit may contain worms)
- high temperature (fever) of 38C (100.4F) or above
- diarrhoea
