The role of drought as a determinant of hemorrhagic disease in the eastern United States

Abstract

Bluetongue virus and epizootic hemorrhagic disease (HD) virus are globally distributed, vector‐borne viruses that infect and cause disease in domestic and wild ruminant species. The forces driving increases in resulting HD may be linked to weather conditions and increasing severity has been noted in northerly latitudes. We evaluated the role of drought severity in both space and time on changes in HD reports across the eastern United States for a recent 15 year period. The objectives of this study were to: (a) develop a spatiotemporal model to evaluate if drought severity explains changing patterns of HD presence; and (b) determine whether this potential risk factor varies in importance over the present range of HD in the eastern United States. Historic data (2000–2014) from an annual HD presence–absence survey conducted by the Southeastern Cooperative Wildlife Disease Study and from the United States Drought Monitor were used for this analysis. For every county in 23 states and for each of 15 years, data were based on reported drought status for August, wetland cover, the physiographic region, and the status of HD in the previous year. We used a generalized linear mixed model to explain HD presence and evaluated spatiotemporal predictors across the region. We found that drought severity was a significant predictor of HD presence and the significance of this relationship was dependent on latitude. In more northerly latitudes, where immunological naivety is most likely, we demonstrated the increasing strength of drought severity as a determinant of reported HD and established the importance of variation in drought severity as a risk factor over the present range of HD in the eastern United States. Our research provides spatially explicit evidence for the link between climate forces and emerging disease patterns across latitude for a globally distributed disease.

Tracking Community Timing: Pattern and Determinants of Seasonality in Culicoides (Diptera: Ceratopogonidae) in Northern Florida

“…In general, the wider scales are more dynamic and better suited to environmental filtering than seasonality. Moreover, temporal patterns in HD occurrence are strongly dependent on the spatial hierarchy since between years and periods, HD is nested at county and biogeographical scales [132,133]. Thus, we suggest that regional patterns in HD can also be predicted by surveying local scenarios of Orbivirus transmission in Culicoides community data.…”

“…In the panhandle, the pattern of HD occurrence is supported by the enzootic stability hypothesis [69] as the relationship between high BTV/EHDV transmission rate and herd immunity [27] is associated with low mortality [69]. Christensen et al [132] shows that the increase in drought severity has a protective effect on HD mortality occurrence within the counties in the top 20% of wetland cover and bellow 30 • latitude, which define our study location. Therefore, drought-flooding dynamics may lead to the enzootic stability of HD in association with Culicoides community change.…”

“…Here, we describe the annual variation at the Culicoides community level for the first time in Florida (Figure 2; RDA 2,3 ) and that it is strongly related to the fluctuation in the environmental conditions. Importantly, the annual incidence of HD also correlates with environmental variables, especially drought severity, weather conditions and land cover change in the USA [25,132,133]. We speculate that the annual temporal scale is related to how species recruitment and the local environment are shaped by global-scale weather patterns.…”

The importance of long‐term studies on wildlife diseases and their interfaces with humans and domestic animals: A review

“…Long‐term approaches are aimed at providing the necessary perspective to understand processes that operate over long temporal scales (Christensen et al., 2020; Nugent et al., 2012; Vicente et al., 2013). We can discern what the drivers of infection dynamics are, and how pathogens become endemic or fade out in host communities and populations (Gordo & Avilés, 2017; Nugent et al., 2012; Strayer et al., 1986), and generate (or evaluate) well‐informed strategies for effective risk management (Delahay et al., 2013; Portier et al., 2019).…”

“…The relevance of long‐term studies in the field of ecology and evolutionary biology has been widely recognized, and an increasing body of knowledge is available, both individual‐ and population‐based (Gordo & Avilés, 2017; Likens, 1989; Strayer et al., 1986). In contrast, long‐term wildlife disease research (LTWDR) in free‐living hosts is scarce (Barroso et al., 2020; Christensen et al., 2020; Delahay et al., 2013; McDonald et al., 2017; Vicente et al., 2013) despite its relevance to human, livestock and wildlife health, and conservation of biodiversity. Some reviews and meta‐analyses on wildlife diseases have assessed the quantity and scientific quality of the articles published and their temporal trends, paying special attention to a particular geography and the time trend of the number of studies on specific pathogens or hosts, including the livestock–wildlife interface (Wiethoelter et al., 2015).…”