Study hypotheses is that Antiparasitic therapy in patients with chronic diarrhea after travel to a developing country, with a negative stool findings, will be significantly effective in eliminating diarrhea and other gastro-intestinal complaints compared to similar patients receiving placebo.

It is common to encounter travelers from developing countries who suffer from persistent diarrhea after returning home. In many cases repeated stool samples are negative for bacteria, parasites and helminthes and the cause of the diarrhea is not found.

The main debate is whether this condition is a persistent parasitic infection (unidentified) or post-infectious irritable bowel syndrome.However, clinical experience suggests that some of these travelers respond to antiparasitic therapy.

This study aims to answer the question whether antiparasitic treatment in these cases is beneficial.

Inclusion Criteria:

• Diarrhea (3 or more soft stools per day) for at least two weeks after a trip to a developing country in the past year
• Stool sample negative for bacteria, parasites and helminthes at least once
• Has not received, until now, antiparasitic or antihelminthic therapy

Exclusion Criteria:

• Bloody diarrhea
• Fever during enrolment 5. Allergy to the offered medication