Lassa virus endemic area could significantly grow in coming decades

 Researchers examined decades' worth of environmental data related to Lassa virus outbreaks for their study, which was published on September 27 in Nature Communications.

They found that temperature, rainfall, and the existence of pastureland areas are the main factors influencing viral transmission. In the coming decades, the researchers predicted, the Lassa virus could spread from West Africa into Central and East Africa. The human population residing in the regions where the virus should, in principle, be able to circulate might increase by more than 600 million as a result of this spread and anticipated population increases in Africa.

Raphalle Klitting, PhD, the study's primary author and a postdoctoral researcher at Scripps Research at the time, states that "our analysis demonstrates how climate, land use, and population changes in the next 50 years could drastically raise the danger of Lassa disease in Africa."

Klitting works in the lab of Kristian Andersen, PhD, a professor at Scripps Research and a research co-author. Simon Dellicour, PhD, of the University of Brussels, was the study's principal author.

The Natal multimammate rat (Mastomys natalensis) is the source of this "zoonotic" virus, which spreads to people most likely through its excretions. The remaining occurrences of infections are more severe, with signs and symptoms that can include bleeding from the mouth and gut, low blood pressure (shock), and potentially irreversible hearing loss. While an estimated 80% of infections are minor or asymptomatic. Hospitalized patients typically have a high death rate, which can occasionally reach 80%.

Numerous hundred thousand infections are thought to occur annually, mostly in Nigeria and other West African nations. There isn't a highly effective drug cure or a vaccination that has been licenced as of yet.

Although it is known which species serve as the main Lassa virus reservoir, the virus only spreads in some of the places where these animals are found. As a result, it's possible that the environment also influences whether and where the considerable viral transmission can happen. In the study, the researchers used information on the environmental circumstances at places of known spread to build an "ecological niche" model of Lassa virus transmission.

The researchers calculated the regions of Africa that could support Lassa virus transmission right now as well as in the years 2030, 2050, and 2070 by combining the model with predictions of climate and land-use changes in Africa over the following several decades as well as the known range of the Natal multimammate rat. The estimated present areas matched up well with the known endemic regions of West Africa, but the projections for the following decades implied significant growth both within and beyond West Africa.

"We found that various locations in Central Africa, including Cameroon and the Democratic Republic of the Congo, and even in East Africa, in Uganda, will likely become environmentally conducive for virus propagation," said Knitting.

The population of Africa is currently expanding quickly, so the researchers took population forecasts for the regions where the Lassa virus is currently and potentially circulating into account. They discovered that there might be a more than 600% rise in the number of people who could be exposed to the virus from the current 92 million to 453 million and 700 million by the years 2050 and 2070.

More encouragingly, the researchers used information on sequenced viral genomes gathered in different areas in West Africa to analyse the dynamics of the virus's propagation and discovered that dispersal appeared to be gradual. They came to the conclusion that the virus's spread into new biologically suited places in the coming decades may also be gradual unless transmission dynamics substantially alter in the new location where it circulates.

The findings, according to the authors, could guide African public health policy, pushing officials to include the Lassa virus on lists of viruses being monitored epidemiologically in some regions of Central and East Africa, for instance.

The study is the outcome of an interdisciplinary effort that included ecological and climate modelling, as well as molecular and evolutionary investigations.

"Further thorough 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," says Dellicour. "With the ongoing climate change and increasing impact of human activities on the environment."