Ebola is a “zoonotic” disease: the virus starts out in animal populations – believed to be fruit bats – and then spills over into humans. Now, a new study that investigates landscape features of where spillover occurs suggests human population density and vegetation cover may be important factors.
The study is the work of two researchers from SUNY Downstate Medical Center in Brooklyn, NY, who write about their findings in the open-access journal PeerJ.
First author Michael G. Walsh, assistant professor of epidemiology and biostatistics in SUNY Downstate’s School of Public Health, says they found significant interaction between density of human populations and the extent of green vegetation cover in the parts of Africa that have seen outbreaks of Ebola virus disease (EVD).
However, he also warns that because of the observational nature of the data, the study cannot prove that the specific pattern of interaction between human populations and forested land causes the spillover of Ebola from animal reservoirs into humans. The most it can do is suggest that they may help it along.
We first got to know about EVD in 1976 when it broke out in today’s Democratic Republic of the Congo and South Sudan. Since then, there have been 24 outbreaks of EVD in 10 countries in Central and West Africa.
Due to its high rate of fatality – ranging from 32-90% – EVD causes fear and disruption when it strikes. “Never has this been more apparent than during the 2014 EVD outbreak in West Africa, which is currently underway,” write the authors.
The current outbreak in West Africa is the largest EVD event ever documented. The latest
For their study, the authors used precise geo-locations of where EVD had spilled over from animals into humans in West and Central Africa. They applied what they call an “inhomogeneous Poisson process model” to the locations.
Even after accounting for other potential influencing factors, such as climate and altitude, the analysis showed that while population density was strongly associated with spillover from animals to humans, there was significant interaction between population density and green vegetation cover.
In locations where human populations were sparse, increasing vegetation cover was linked to a decrease in risk of spillover. But as human population density increased, increased vegetation cover was linked to increased risk of spillover of EVD from animals to humans.
Prof. Walsh comments on what they found:
“The reservoir species of the Ebola virus is believed to be fruit bats, with a secondary source being non-human primates. As human populations increase and move into forested areas that are home to these animals, the risk of humans contracting EVD appears to increase, judging from our analysis of EVD outbreaks in Central and West Africa.”
Meanwhile, Medical News Today recently learned how a new epidemic model predicts Ebola in Liberia could end by June. Researchers have developed a computer model that not only takes into account features of Ebola virus and how it transmits, but also what is being done to halt its spread.