Bad water and hygiene have led to an epidemic of hepatitis E that has killed 25 people over several months in a refugee camp in Diffa, a region in southeast Niger, Medecins sans frontieres said Wednesday.
"The current hepatitis E epidemic is closely linked to a lack of water, hygiene infrastructure and sanitation," said MSF in a statement.
The site of attacks from the jihadist group Boko Haram since 2015, Diffa sits on the border with Nigeria and harbours at least 300,000 refugees and displaced people living alongside an already poor population, according to United Nations figures.
The UN has called on the international community to increase financing of aid to the region.
Between December 2016 and April 23, 25 pregnant women died of the disease and 135 cases were identified in Diffa, according to MSF.
"Water and sanitary services clearly do not meet the needs of this population," said Elmounzer Ag Jiddou, who heads MSF's work in Niger.
MSF is focusing on early detection of the disease, treating people for free and running a campaign promoting hand washing in order to stem the epidemic.
Last week, Niger's health minister said the situation was under control while calling on anyone with symptoms of hepatitis E to visit a health centre immediately.
Pregnant women are especially vulnerable to the disease, which causes fever, headache, vomiting, abdominal pain and dark urine.
Hepatitis E is a liver disease caused by the infection of a virus transmitted through faecal-contaminated drinking water, according to the World Health Organization.