Mammalian biogeography and the Ebola virus in Africa

Abstract

Ebola virus is responsible for the fatal Ebola virus disease (EVD). Identifying the distribution area of the Ebola virus is crucial for understanding the risk factors conditioning the emergence of new EVD cases. Existing distribution models have underrepresented the potential contribution that reservoir species and vulnerable species make in sustaining the presence of the virus. In this paper, we map favourable areas for Ebola virus in Africa according to environmental and zoogeographical descriptors, independent of human‐to‐human transmissions. We combine two different biogeographical approaches: analysis of mammalian distribution types (chorotypes), and distribution modelling of the Ebola virus. We first obtain a model defining the distribution of environmentally favourable areas for the presence of Ebola virus. Based on a review of mammal taxa affected by or suspected of exposure to the Ebola virus, we model favourable areas again, this time according to mammalian chorotypes. We then build a combined model in which both the environment and mammalian distributions explain the favourable areas for Ebola virus in the wild. We demonstrate that mammalian biogeography contributes to explaining the distribution of Ebola virus in Africa, although vegetation may also underscore clear limits to the presence of the virus. Our model suggests that the Ebola virus may be even more widespread than previously suspected, given that additional favourable areas are found throughout the coastal areas of West and Central Africa, stretching from Cameroon to Guinea, and extend further East into the East African Lakes region. Our findings show that the most favourable area for the Ebola virus is significantly associated with the presence of the virus in non‐human mammals. Core areas are surrounded by regions of intermediate favourability, in which human infections of unknown source were found. The difference in association between humans and other mammals and the virus may offer further insights on how EVD can spread.

Pathogeography: leveraging the biogeography of human infectious diseases for global health management

“…Mammalian chorotypes in Africa were employed as surrogates of the types of distributions shown by reservoirs and any wildlife species implicated in the virus spillover cycle. Olivero et al (2017a) found that a model based on a number of diversity patterns, each one associated with a different mammalian chorotype, defined favourable areas for the presence of Ebola virus with higher accuracy than did a model based on environmental variables alone (i.e. climate, forest type), concluding that mammalian biogeography contributes significantly to explaining the distribution of Ebola virus in Africa.…”

“…Ebola virus, Leroy et al 2004, Groseth et al 2007, Olival and Hayman 2014, imposing restrictions to the selection of host or vector species considered in a model might under-represent the zoological substrate conditioning a pathogen's transmission and distribution (Roche et al 2012). Olivero et al (2017a) thus addressed the mapping of favourable areas for the Ebola virus in the wild by combining two biogeographical approaches: SDM and chorotype analysis. Mammalian chorotypes in Africa were employed as surrogates of the types of distributions shown by reservoirs and any wildlife species implicated in the virus spillover cycle.…”

“…Some estimates of disease 'risk' (or, perhaps more accurately, 'hazards') are based on these (e.g. tick nymphal abundance as a measure of Lyme disease risk) and their ecologies may contribute directly or indirectly to disease patterns (Civitello et al 2015), such that data on their potential occurrence can improve biogeographically-informed risk mapping of disease outcomes in humans (Messina et al 2015, Pigott et al 2016, Olivero et al 2017a. One major challenge for biogeographic analyses of human infectious diseases, however, is the availability and utility of appropriate data, which we discuss further in Box 1.…”

“…detailed assessments of G and E for diseases/hosts/vectors in regions of interest relevant to single diseases or disease assemblages) (Eisenberg et al 2007), disease trait profiling (classifying epidemiological features of diseases, such as the presence or absence of the E, V, R and H elements as sources of pathogen transmission (see Box 3), and the species known to be implicated in each), and human profiling (assessments of the human population distribution, density and movement patterns and the existing management and observation landscapes). Intersection of these geographic, disease trait or human profiles will ultimately yield yet deeper understanding or management relevant insights (Semenza et al 2016). when several species are involved in the analytical design; for example, when using models for deriving indices based on multiple species (Estrada et al 2008), and for the study of biogeographical relationships between species (Real et al 2009, Acevedo et al 2010, including relationships between pathogen and host complexes (Olivero et al 2017a).…”

“…Although we are aware of no studies examining chorotypes of human infectious diseases, mammalian chorotypes have been recently incorporated into an infectious disease distribution model (Olivero et al 2017a). When the ecology of a pathogen is complex and unresolved (e.g.…”