Spatial parasitology and the unmapped human helminthiases

Abstract

Helminthiases are a class of neglected tropical diseases that affect at least 1 billion people worldwide, with a disproportionate impact on resource-poor areas with limited disease surveillance. Geospatial methods can offer valuable insights into the burden of these infections, particularly given that many are subject to strong ecological influences on the environmental, vector-borne or zoonotic stages of their life cycle. In this study, we screened 6829 abstracts and analysed 485 studies that use maps to document, infer or predict transmission patterns for over 200 species of parasitic worms. We found that quantitative mapping methods are increasingly used in medical parasitology, drawing on One Health surveillance data from the community scale to model geographic distributions and burdens up to the regional or global scale. However, we found that the vast majority of the human helminthiases may be entirely unmapped, with research effort focused disproportionately on a half-dozen infections that are targeted by mass drug administration programmes. Entire regions were also surprisingly under-represented in the literature, particularly southern Asia and the Neotropics. We conclude by proposing a shortlist of possible priorities for future research, including several neglected helminthiases with a burden that may be underestimated.

Keywords: Bayesian modeling; ecological niche modeling; helminth parasites; medical geography; parasite biogeography; spatial statistics; systematic review.

Graphical abstract

Fig. 1.

(A) Efforts to map the human helminthiases have increased over time. (B) Spatial data for a few helminthiases make up the majority of all human helminth spatial data. The 45 helminth species with spatial data were grouped together by the conditions they cause (e.g. Wuchereria bancrofti and Brugia malayi are grouped as lymphatic filariasis).

Fig. 2.

Existing human helminth spatial data predominantly comes from small-scale prevalence mapping studies. Studies containing spatial data on human helminthiases were characterized by spatial scale and methodology, with several studies employing more than 1 methodology.

Fig. 3.

Most published spatial research on human helminthiases describes incidence and burden in sub-Saharan Africa (particularly Kenya and Uganda), China and Brazil.

Fig. 4.

Among studies that map other helminth hosts or helminth vectors, studies mapping less mobile hosts and vectors predominate. Baboons, antelopes and wild boars were classified as wildlife hosts; some studies mapped multiple non-human hosts.