Marburg virus has killed five people in Tanzania’s north-western Kagera region, according to the health ministry.
High fever is a common symptom of the deadly Ebola-like virus, often followed by bleeding and organ failure.
Tanzania’s health minister Ummy Mwalimu said the disease had been contained and she was confident it would not spread further.
No vaccines or anti-viral treatments have been approved to treat the virus, according to the WHO, but it adds that rehydration with oral or intravenous fluids has improved survival.