A new study has suggested that temperature, rainfall, and the presence of pastureland may contribute to an increase in outbreaks Lassa fever in Africa in years to come.
Researchers from the University of Brussels and the Scripps Research Institute have predicted areas hospitable to the Lassa virus may extend from West Africa into new regions of Central and East Africa. The researchers have warned that due to the expected population growth in Africa, the number of people vulnerable to Lassa fever may rise to over 600 million.
The study has been published in Nature Communications.
“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 first author Raphaëlle Klitting, PhD, a postdoctoral researcher at Scripps Research.
What is Lassa fever?
Lassa fever is a ‘zoonotic’ virus, meaning it is spread to humans from animals. It is believed that this Lassa virus stems from the droppings of the Natal multimammate rat. An estimated 80% of Lassa fever cases are mild or asymptomatic; however, some cases can become severe. Symptoms can include haemorrhaging from the mouth and gut, low blood pressure, and permanent loss of hearing. The fatality rate for hospitalised patients is high and reached 80% in the past.
Several hundred thousand cases of Lassa fever occur each year, mostly in Nigeria and other West African countries. There is currently no approved vaccine or effective drug treatment.
Although it has been established that the prime reservoir for the virus is the Natal multimammate rat, the virus does not exclusively occur in places where the rats are present. This suggests that it is possible that certain environmental factors are contributing to the spread of Lassa fever.
To identify the contributing factors, the researchers created an ‘ecological niche’ model of Lassa virus transmission, using data on the environmental conditions of the places where the virus had spread.
The researchers compared the model with projections of climate and land-use changes in Africa over the next several decades, and the known range of the Natal multimammate rat. Using this information, the researchers predicted the areas of Africa that could support the virus in the years 2030, 2050, and 2070. They have predicted a vast expansion of vulnerable areas during this time.
“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.
Population growth is a key factor in viral transmission
Africa is currently experiencing rapid population growth. The extent of this growth means the number of people potentially exposed to Lassa fever could rise from 92 million to 453 million by 2050, and 700 million by 2070.
However, the researchers examined the dynamics of the spread of Lassa fever using data on sequenced viral genomes samples taken from various locations in West Africa and found the viral dispersal of the disease appeared to be slow. The research stated that unless there is a drastic change in the transmission dynamics the spread of the virus into new regions of Africa will be slow in the coming decades.
The researchers hope their findings will inform African public health policies and encourage authorities to add Lassa fever to the list of viruses under epidemiologic surveillance in 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,” said Dellicour.
