Ebola virus disease outbreaks in West and Central Africa have been linked to spillover from potential disease reservoirs such as bats, apes, and duikers (an antelope-like animal). Spillover has been thought to be related to population density, vegetation cover, and human activities such as hunting, poaching, and bushmeat consumption. In this study, forest data from satellites coupled with disease outbreak records identify a nexus between forest fragmentation and Ebola.
The researchers identified 11 sites of the first human infection of Ebola from a wild species having occurred since 2004. Changes in forest cover between the year 2000 (baseline year) and the years of first infection for each of these outbreaks were determined using high-resolution satellite data on tree cover. All 11 centers of infection were found to be located in forested areas where the rate of forest fragmentation was greater than the regional average. Similarly, forest fragmentation decreased with increasing distance from the centers of infection.
All 11 centers of infection were found to be located in forested areas where the rate of forest fragmentation was greater than the regional average.
The centers of first infection … tend to occur in areas where on the outbreak year the average degree of forest fragmentation (e.g., within a 25 km, 50 km or 100 km distance from the infection center) was significantly higher than in the rest of the region [Rulli 2017: 2].
Furthermore, eight of the 11 centers of infection were located in fragmentation “hotspots,” meaning within a cluster of highly fragmented forest areas.
Bats are the commonly accepted host to filoviruses such as Ebola and tend to increase in population in fragmented habitats. The geographic distribution of potential bat hosts was consistent with the distribution of the zoonotic niche of Ebola. A decline in the population of insectivorous bats and an increase in the frugivorous (fruit-eating) bat species as a result of forest fragmentation was observed. Reshaping forest boundaries, habitat disruption, and biodiversity loss may enhance the likelihood of zoonotic infection by increasing the abundance of a particular species and thus the prevalence of that species’ pathogens.
The fact that spillover tends to occur in hotspots of forest fragmentation rather than in clearcut areas suggests that chances of human interactions with host wildlife are higher in areas where human encroachment leaves forest fragments that provide habitat for reservoir species [Rulli 2017: 5].
Pressure on land and its products is increasingly pushing people into forested areas. Given the danger of zoonotic disease outbreak, any evaluation of the costs, risk, and benefits of forest loss and fragmentation should include global health considerations.
Rulli, Maria Cristina, et al., 2017, The nexus between forest fragmentation in Africa and Ebola virus disease outbreaks, Scientific Reports 7, https://www.nature.com/articles/srep41613.