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In most cases, a roundworm infection doesn't cause any noticeable symptoms.

When symptoms occur, they usually follow a two-stage course, as described below:

Early-phase symptoms

The early-phase symptoms of a roundworm infection only affect a small proportion of people and are rare in the UK.

Symptoms usually begin 4-16 days after swallowing the eggs and last up to three weeks. They include:

Late-phase symptoms

The late-phase symptoms of a roundworm infection are even rarer in the UK, particularly in adults. If there are a lot of mature worms in the intestine, they can cause blockages. This won't occur before six weeks after the eggs have been swallowed.

Signs and symptoms associated with mature worms include:

However, most people have no symptoms.

If your intestines are blocked due to a large number of worms, you will probably experience vomiting and severe abdominal pain.