What determines the location and severity of Ebola virus outbreaks? According to Tulane University School of Public Health and Tropical Medicine researcher Daniel Bausch, lead author of "Outbreak of Ebola Virus Disease in Guinea: Where Ecology Meets Economy," a new article in PLOS Neglected Tropical Diseases, the causes are a composite of biological and ecological circumstances superimposed on populations made vulnerable by social and political strife.
The outbreak addressed in Bausch's article is currently occurring in West Africa, impacting the neighbor countries of Guinea, Sierra Leone, and Liberia, with over 1,000 cases and a fatality rate over 60 percent to date.
Bausch, who has spent much of the last few months in Guinea and Sierra Leone as part of the outbreak response team, poses the questions why the outbreak is occurring there and why now?
There have never been any cases of Ebola virus disease observed in these countries before, observes Bausch. There are five varieties of the Ebola virus, and until this time, each has been found only in well-defined geographic areas in three Central African countries, Democratic Republic of the Congo, Republic of the Congo, and Gabon, all of which are over two thousand miles from West Africa.
Bausch contemplates two possible mechanisms behind the current West African outbreak. The first is that the virus actually has been in West Africa all along. "The virus is likely maintained in fruit bats, with which humans normally have little contact, thus providing limited opportunity for infection," says Bausch.
The second possibility is that the virus was carried from Central Africa to West Africa. In this case, Bausch believes that introduction by a human traveler is unlikely. "There is little regular travel or trade between Central Africa and Guinea, and Guéckédou, the remote epicenter and presumed area of first introduction, is far off the beaten path..." says Bausch. An Ebola virus-carrying bat flying from the original territory of the virus in Central Africa to West Africa is more likely, Bausch concludes.
Regardless of what biological and ecological factors may have resulted in introduction of Ebola virus into the area, human social and political conditions of the impacted countries play a significant role in facilitating an outbreak, Bausch says. "The sites of attack are far from random; large hemorrhagic fever virus outbreaks almost invariably occur in areas in which the economy and public health system have been decimated from years of civil conflict or failed development." All three of the West African countries currently experiencing the spread of Ebola have histories of civil conflict and political unrest.
Bausch notes three specific effects of these socio-political conditions. First, "poverty drives people to hunt deeper into the forest for food, and to find wood for fuel, and to go deeper into mines to find minerals, all of which can bring them into risk of exposure to Ebola," he says. Secondly, the impoverished condition of such countries results in a lack crucial healthcare resources such as protective gloves, masks and gowns, as well as clean needles and disinfectants, allowing diseases to spread. Thirdly, the countries lack intergovernmental coordination needed to monitor the movement of people, including infected persons, across their borders, frustrating efforts to contain the spread of disease.
As to the question why the outbreaks are occurring now, Bausch believes that the advent of the dry season may be a factor, as has been noted in other outbreaks. "At present, we can only speculate that these drier ecologic conditions somehow influence the number or proportion of Ebola virus - infected bats and/or the frequency of human contact with them," he says.
When an outbreak such as the current Ebola virus epidemic occurs "the focus is often on the rapidity and efficacy of the short-term international response," says Bausch. Nevertheless, "attention to these admittedly challenging underlying factors - economic, cultural, political - will be required for long-term prevention and control."