Population changes could dramatically increase the risk of Lassa fever in Africa

Lassa virus is a "zoonotic" virus that spreads from other animals to humans. According to health scientists, the virus spreads from 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 low blood pressure (shock), hemorrhaging from the mouth and gut, and potentially permanent hearing loss. It is noteworthy that the fatality rate for hospitalized patients is generally high, sometimes reaching 80%.

A study led by Scripps Research and the University of Brussels shows that the risk of exposure to Lassa virus, which can cause a severe and often lethal hemorrhagic fever disease, known as Lassa fever may expand substantially in the next several decades and could soon become a much bigger public health problem in Africa due to climate change and other factors suitable for Lassa virus.

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. In the next several decades, areas hospitable to Lassa virus spread may extend from West Africa into Central and East Africa, according to the researchers' projections. With this expansion combined with 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. Now at Marseille University, he was a postdoctoral researcher at Scripps Research during the study.

"We found that several regions will likely become ecologically suitable for virus spread in Central Africa, including in Cameroon and the Democratic Republic of the Congo, and even in East Africa, in Uganda," Klitting said.

"With the ongoing climate change and increasing impact of human activities on the environment, further comprehensive studies of the ecology and spread of zoonotic and vector-borne diseases are needed to anticipate possible future changes in their distribution as well as their impact on public health," Dellicour says.

Several hundred thousand infections are estimated to occur each year, primarily in Nigeria and several other West African countries. There is no approved vaccine or highly effective drug treatment as of yet.

Currently, Africa's population is undergoing rapid growth. Therefore, the researchers considered projections of this population growth for the areas of current and potential future Lassa virus circulation. They found that the number of people potentially exposed to the virus could increase from about 92 million today to 453 million by 2050, and 700 million by 2070—a more than 600% jump.

The study was funded by the National Institutes of Health (U01AI151812, R01AI153044, U19AI135995), the European Union, the Wellcome Trust, the German Federal Ministry of Health, the Global Health Protection Program, the German Research Foundation, the Research Foundation – Flanders, and the Belgian Fonds National de la Recherche Scientifique.