In the study, which appeared on September 27 in Nature Communications, scientists analyzed decades of environmental data associated with Lassa virus outbreaks, revealing temperature, rainfall and the presence of pastureland areas as key factors contributing to viral transmission. The researchers projected that areas hospitable to Lassa virus spread may extend from West Africa into Central and East Africa in the next several decades. With this expansion and expected African population growth, the human population living in the areas where the virus should — in theory — be able to circulate may rise by more than 600 million.

“Our analysis shows how climate, land use, and population changes in the next 50 years could dramatically increase the risk of Lassa fever in Africa,” says first author Raphaëlle Klitting, PhD, a postdoctoral researcher at Scripps Research during the study.

Klitting is a member of the laboratory of study co-author and Scripps Research professor Kristian Andersen, PhD. The study’s senior author was Simon Dellicour, PhD, of the University of Brussels.

Lassa virus is a “zoonotic” virus that spreads to humans from other animals — in this case, the Natal multimammate rat (Mastomys natalensis), most likely via its droppings. While an estimated 80% of infections are mild or asymptomatic, the remaining cases are more severe, with signs and symptoms that can include hemorrhaging from the mouth and gut, low blood pressure (shock), and potentially permanent hearing loss. The fatality rate for hospitalized patients is generally high, sometimes reaching 80%.

An estimated several hundred thousand infections occur each year, chiefly in Nigeria and several other West African countries. So far there is no approved vaccine or highly effective drug treatment.

Although the primary animal reservoir for Lassa virus is known, the virus spreads in only some — not all — areas where these animals are present. Thus, it is possible that environmental factors also help determine whether and where significant viral transmission can occur. In the study, the researchers developed an ‘ecological niche’ model of Lassa virus transmission, using data on environmental conditions at sites of known spread.

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