Fine-scale wetland features mediate vector and climate-dependent macroscale patterns in human West Nile virus incidence

Abstract

Context Mosquito-borne diseases in the United States are notorious for their seemingly erratic temporal and spatial outbreak patterns in humans. Identifying linkages between fine-scale phenomenon and macroscale outbreak patterns can improve the understanding of these complex socio-ecological systems. Objectives Using West Nile virus (WNV) as a model system, we examine whether fine-scale wetland characteristics-wetland size, connectivity, and inundation regime-have an important effect on macroscale human disease outbreak in the northeastern and midwestern United States. Methods We take a spatially explicit GIS-based approach, derive new macroscale wetland metrics based on fine-scale wetland characteristics, and use county-level annual human WNV incidence data over 11 years to evaluate linkages between the fine and macroscales (1.6 million km 2 ). Results In regions dominated by the Culex tarsalis WNV vector, U.S. counties with a small average wetland size had more than 100 % higher human WNV incidence than counties with a large average wetland size. In regions dominated by the Cx. pipiens and Cx. restuans vectors, a low proportional area of connected wetland was associated with at least 50 % higher human WNV incidence than a high proportional area of connected wetland. Finally, Cx. tarsalisdominated counties with a high proportional area of semi-permanent wetland that were experiencing drought conditions had over 300 % higher annual WNV incidence than drought-affected counties with a low proportional area of semi-permanent wetland. Conclusions Our results suggest that phenomena occurring at the individual wetland scale may aggregate to influence macroscale human WNV outbreak patterns and may be mediated by the interplay of other factors such as vector species-specific traits and climate.

Increased Human Incidence of West Nile Virus Disease near Rice Fields in California but Not in Southern United States

“…27,28 Several studies at the national scale have argued that regional differences in land covers associated with increased WNV disease incidence roughly correspond to the distributions of major Culex vectors. [19][20][21]29 However, the broad classification of grassland and agriculture land cover encapsulates a wide diversity of crop types, each with variable effects on mosquito abundance and WNV risk. 27 In addition, none of the broad-scale studies correlating land cover with WNV disease incidence include quantitative data on mosquito abundance or infection to support the different regional correlations and conclusions.…”

Wetland characteristics linked to broad-scale patterns in Culiseta melanura abundance and eastern equine encephalitis virus infection

“… Wetland inundation classification: A wetland’s inundation classification combined with changes in hydrological wetness (water table depth) may alter host density and mosquito infection. Research on West Nile virus (WNV) and St. Louis encephalitis virus (SLEV) indicates that drought-driven reductions in water table depth reduces the availability of aquatic habitats forcing vectors and avian hosts onto a few remaining aquatic refuges [ 30 – 34 ]. This may result in increased contact between important vectors and hosts and subsequent increases in vector infection.…”

Public health impacts of drought in high-income countries: a systematic review

“…One study examined differences in environmental factors (wetland con guration and hydrological regime) and their association with higher incidence of WNF during periods of drought in the USA. This study found that drought-affected areas with a high proportion of semi-permanent wetland had over 300% higher annual incidence of WNF incidence than drought-affected areas with a low proportion of wetland (Skaff and Cheruvelil 2016). This study highlights the complexities involved with assessing the relationship between weather patterns, vectors and subsequent health outcomes.…”