Doctors Without Borders says a cholera outbreak in the West African country of Niger killed 20 people and has sickened nearly 1,000 people.

The medical aid group said Friday that several districts in the country's south have been affected. Cholera is caused by the ingestion of infected food or water and often occurs in places with poor sanitation. It causes severe diarrhea and vomiting and can lead to death by dehydration, sometimes within a matter of hours.

Doctors Without Borders began working with Niger's Health Ministry to stamp out the cholera outbreak when the first cases were identified last month. In addition to treating the sick, teams from the group are handing out chlorine to treat water, disinfecting homes and teaching people how to avoid becoming infected.