The southern African nation of Angola has reported some 23 cases of yellow fever that resulted in seven deaths in Viana municipality, according to local media Friday.

Angola Image/CIA

Health minister, José Van-Dunem said during a press conference in Luanda that the first case was reported on 5 December 2015 in a Eritrea citizen. In addition, cases have been reported in Congolese citizens.

In all, Van-Dunem said of the 16 survivors, 13 were discharged and three are given special care. Among the victims, 22 are men and one is a woman, aged between 20 and 46 years old.

According to the US Centers for Disease Control and Prevention, Yellow fever virus is found in tropical and subtropical areas in South America and Africa. The virus is transmitted to people by the bite of an infected mosquito.

The majority of persons infected with yellow fever virus have no illness or only mild illness. In persons who develop symptoms, the incubation period (time from infection until illness) is typically 3–6 days. The initial symptoms include sudden onset of fever, chills, severe headache, back pain, general body aches, nausea, and vomiting, fatigue, and weakness. Most persons improve after the initial presentation.

After a brief remission of hours to a day, roughly 15% of cases progress to develop a more severe form of the disease. The severe form is characterized by high fever, jaundice, bleeding, and eventually shock and failure of multiple organs.

There is no specific treatment for yellow fever; care is based on symptoms. Steps to prevent yellow fever virus infection include using insect repellent, wearing protective clothing, and getting vaccinated.