On Oct. 18, 2018, an international team of researchers reported that a surge in Lassa fever cases in Nigeria in 2018 does not appear to be linked to a single virus strain or increased human-to-human transmission.

The Nigeria Centre for Disease Control (NCDC) reported an unusually large increase in Lassa fever cases in 2018, with 523 laboratory-confirmed cases and 135 deaths from January 1 through October 7. Lassa fever is endemic to West Africa, where Mastomys natalensis rodents, a primary animal reservoir of Lassa virus, are common.

The rodent is often found in or around human habitats, and people become infected with Lassa virus through direct contact with rodent urine and stool. People with Lassa fever also can transmit the virus to other people through close contact, although experts believe this is rare. The genomic analysis was published in The New England Journal of Medicine.