ABUJA, Feb. 21 (Xinhua) -- The death toll from Lassa fever in Nigeria, Africa's most populous country, has risen to 85 since the beginning of the year, local health authorities said on Monday.

In its latest update on Lassa fever, the Nigeria Center for Disease Control (NCDC) said 15 dead cases were recorded between late January and mid-February, taking the count so far this year to 85.

The NCDC said 68 cases were recorded within the period, bringing the tally this year to 531.

The public health agency put the fatality rate at 16 percent, saying 79 local government areas across 20 states had so far recorded at least one confirmed case this year.

"The predominant age group affected is 21-30 years while the male-to-female ratio for confirmed cases is 1:0.9," NCDC said.

According to the World Health Organization, Lassa fever is caused by the Lassa virus. Humans usually contract the virus through exposure to food or household items contaminated by the urine or feces of infected Mastomys rats. The disease is endemic in the rodent population in parts of West Africa.

In some cases, Lassa fever has similar symptoms to malaria, appearing between one and three weeks after exposure to the virus. In mild cases, the disease causes fever, fatigue, weakness, and headache.

The death toll of Lassa fever in Nigeria topped 170 from nearly 1,000 cases last year till November, amid intensified measures by the government to reduce infections.