The Lassa virus is a zoonotic virus, spreading to humans from Natal multimammate rats (Mastomys natalensis), most likely via their droppings. Although about 80 percent of infections are mild or even asymptomatic, the remaining 20 percent are quite severe, with symptoms including hemorrhaging from the mouth and gut, shock due to low blood pressure, and potentially permanent hearing loss. For patients hospitalized with Lassa fever, the fatality rate can reach a staggering 80 percent. So far, there are no approved vaccines or effective therapies against this virus.
Currently, several hundred thousand infections occur annually, mainly in Nigeria and other West African countries. However, by analyzing decades of environmental data associated with Lassa virus outbreaks, a team of scientists from Scripps Research has estimated that, due to changes in temperature, rainfall, and land-use, the virus may spread from West Africa into Central and East Africa over the next few decades. With this expansion and estimated African population growth, the human population living in areas where Lassa might 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,” said study first author Raphaëlle Klitting, a postdoctoral fellow at Scripps. “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.”
By considering projections of African population growth, the researchers discovered that the number of people potentially exposed to the virus could increase from approximately 92 million today to 453 million by 2050, and 700 million by 2070 – a more than 600 percent spike.
Fortunately, analyses of the dynamics of the spread of Lassa revealed that virus dispersal is rather slow, which may imply that – unless transmission dynamics change drastically in the new locations where the virus will circulate – its spread into new ecologically suitable areas over the following decades may also be slow.
According to the scientists, these findings should inform African public health policies by encouraging officials to add Lassa virus to lists of viruses under epidemiologic surveillance in parts of Central and East Africa.
“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,” concluded senior author Simon Dellicour, an expert in Population Dynamics at the University of Brussels.
The study is published in the journal Nature Communications.
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