Ecological niche and geographic distribution of human monkeypox in Africa

Abstract

Monkeypox virus, a zoonotic member of the genus Orthopoxviridae, can cause a severe, smallpox-like illness in humans. Monkeypox virus is thought to be endemic to forested areas of western and Central Africa. Considerably more is known about human monkeypox disease occurrence than about natural sylvatic cycles of this virus in non-human animal hosts. We use human monkeypox case data from Africa for 1970-2003 in an ecological niche modeling framework to construct predictive models of the ecological requirements and geographic distribution of monkeypox virus across West and Central Africa. Tests of internal predictive ability using different subsets of input data show the model to be highly robust and suggest that the distinct phylogenetic lineages of monkeypox in West Africa and Central Africa occupy similar ecological niches. High mean annual precipitation and low elevations were shown to be highly correlated with human monkeypox disease occurrence. The synthetic picture of the potential geographic distribution of human monkeypox in Africa resulting from this study should support ongoing epidemiologic and ecological studies, as well as help to guide public health intervention strategies to areas at highest risk for human monkeypox.

Figure 1

Occurrence locations of human monkeypox. Circles show partitioning of the 156 point occurrences into Central African (red), West Africa (blue), and unclassified (green) monkeypox genotypes.

Figure 2

Overall predicted distribution of human monkeypox based on ecological niche modeling. Darker shades indicate areas with greater model agreement in prediction of suitability for monkeypox. Green points indicate input occurrences used in model development.

Figure 3

Summary of quadrant analyses of model robustness. (A) Central African human monkeypox occurrences divided into quadrants above and below the median longitude and latitude. (B) Modeled distribution created using only off-diagonal (b/d, red circles) input data. (C) Modeled distribution created using only on-diagonal (a/c, blue circles) input data. Darker shades indicate areas with greater model agreement in predicting area as suitable for monkeypox. Human monkeypox occurrence locations indicated by triangles were not used in model construction.

Figure 4

Ecological niche modeling results for West and Central African monkeypox. Eight West African and 146 Central African human monkeypox occurrences are indicated with green and blue circles, respectively. (A) Modeled distribution created using only Central African (blue) input data; (B) Modeled distribution created using only West African (green) input data. The vertical line (7.33°E longitude) denotes division between West and Central Africa. Nigerian occurrences were excluded from model development. Darker shades indicate areas with greater model agreement in prediction of potential suitability for monkeypox.

Figure 5

Visualizations of modeled monkeypox virus ecological niches in two-dimensional environmental spaces. Shown are all available habitat in the area of observation (dark blue diamonds); comprehensive monkeypox niche (pink); Central African niche (yellow), West African niche (light blue).