Lassa Fever Reported in US Traveler Returning from West Africa
A micrograph of Lassa virus next to some cell debris.
Credit: CDC / C. S. Goldsmith, P. Rollin, M. Bowen

A Minnesota man who recently returned home after visiting West Africa has tested positive for Lassa fever, health officials have confirmed.

The man went to a hospital in Minnesota on March 31, complaining of fever and confusion. Blood samples sent to Centers for Disease Control and Prevention tested positive for Lassa fever on April 3. The man is recovering and is in stable condition, according to the Minnesota Department of Health.

Lassa fever is a severe viral disease that causes fever and bleeding, and is common in West Africa but rarely seen in the United States. Only seven other cases of Lassa fever cases have been identified in the U.S., with the last one reported in Pennsylvania in 2010, according to the CDC. All cases were likely imported from other countries, 

Preliminary information indicates that the patient flew from West Africa to New York City, and then caught another flight to Minneapolis.

"This imported case is a reminder that we are all connected by international travel. A disease anywhere can appear anywhere else in the world within hours," said CDC director Dr. Tom Frieden. [7 Devastating Infectious Diseases]

About 20 percent of people infected with Lassa fever need hospitalization, and about 1 percent die due to the disease, according to the CDC. The disease first causes flulike symptoms such as fever, sore throat and cough, which means it can easily be confused with other common diseases in Africa, such as typhoid fever and malaria. 

In West Africa, Lassa virus is carried by rodents and transmitted to humans through contact with the animals' urine or droppings. In rare cases it can be transmitted from person to person through direct contact with a sick person’s blood or bodily fluids, or through sexual contact.

About 100,000 to 300,000 cases of Lassa fever occur yearly in West Africa, and 5,000 people there die of the disease each year, according to the CDC.

The CDC is now working with public health officials and airlines to determine the patient’s travel route, and identify any passengers or crew who were seated near the infected person and may have had close contact with him.

However, the risk to other passengers is considered extremely low, because Lassa fever is not transmitted through casual contact, investigators said.

"People will not get this infection just because they were on the same airplane or in the same airport," CDC's researcher Dr. Barbara Knust said.

Email Bahar Gholipour or follow her @alterwired. Follow us @LiveScience, Facebook & Google+. Original article on Live Science.