Tanzania's health ministry on Tuesday confirmed that five people have died and three others are being treated for the Ebola-like Marburg disease.
Health Minister Ummy Mwalimu said the cases were identified in the western region of Kagera and the government had managed to control its spread to other regions.
Like Ebola, the Marburg virus originates in bats and spreads between people via close contact with the bodily fluids of infected people, or surfaces, like contaminated bed sheets. Without treatment, Marburg can be fatal in up to 88% of people.
Marburg outbreaks and individual cases have in the past been recorded in Angola, Congo, Kenya, South Africa, Uganda, and Ghana, according to the World Health Organization.
Kenya and Uganda are on high alert due to the recent cases in Tanzania.
WHO representative Zabulon Yoti, who spoke during the Tanzania health ministry press briefing, praised the government for what he called its swift response and transparency.
The acting director of the African Union's public health agency, Ahmed Ogwell Ouma, tweeted that Africa CDC would deploy immediately to strengthen response and limit the spread of the disease.
The rare virus was first identified in 1967 after it caused simultaneous outbreaks of disease in laboratories in Marburg, Germany, and Belgrade, Serbia. Seven people died who were exposed to the virus while conducting research on monkeys.
There are no authorized vaccines or drugs to treat Marburg, but rehydration treatment to alleviate symptoms can improve the chances of survival.