Spatio-Temporal Modelling of Culicoides Latreille (Diptera: Ceratopogonidae) Populations on Reunion Island (Indian Ocean)

Abstract

Background: Reunion Island regularly faces outbreaks of bluetongue and epizootic hemorrhagic diseases, two insect-borne orbiviral diseases of ruminants. Hematophagous midges of the genus Culicoides (Diptera: Ceratopogonidae) are the vectors of bluetongue (BTV) and epizootic hemorrhagic diseases of deer (EHDV) viruses. In a previous study, statistical models based on environmental and meteorological data were developed for the five Culicoides species present in the island to provide a better understanding of their ecology and predict their presence and abundance. The purpose of this study was to couple these statistical models with a Geographic Information System (GIS) in order to produce dynamic maps of the distribution of Culicoides throughout the island. Methods: Based on meteorological data from ground weather stations and satellite-derived environmental data, the abundance of each Culicoides species was estimated for the 2,214 husbandry locations on the island for the period ranging from February 2016 to June 2018. A large-scale Culicoides sampling campaign including 100 farms was carried out in March 2018 to validate the model. Results: According to the model predictions, no husbandry location was free of Culicoides throughout the study period. The five Culicoides species were present on average in 57.0% of the husbandry locations for C. bolitinos, 40.7% for C. enderleini, 26.5% for C. grahamii, 87.1% for C. imicola and 91.8% for C. kibatiensis. The models also showed high seasonal variations in their distribution. During the validation process, predictions were acceptable for C. bolitinos, C. enderleini and C. kibatiensis, with normalized root mean square errors (NRMSE) of 15.4%, 13.6% and 16.5% respectively. The NRMSE was 27.4% for C. grahamii. For C. imicola, the NRMSE was acceptable (11.9%) considering all husbandry locations except in two specific areas, the Cirque de Salazie – an inner mountainous part of the island- and the sea edge, where the model overestimated its abundance. Conclusions: Our model provides, for the first time, an operational tool to better understand and predict the distribution of Culicoides in Reunion Island. As it predicts a wide spatial distribution of the five Culicoides species throughout the year and taking into consideration their vector competence, our results suggest that BTV and EHDV can circulate continuously on the island. It implies significant limitations for any preventive or control actions targeting vector populations. To assess other control strategies, our model could be coupled with an epidemiological model of BTV and EHDV transmission.