A model for the assessment of bluetongue virus serotype 1 persistence in Spain.

Cecilia Aguilar-Vega,Javier Lucientes,José Manuel Sánchez-Vizcaíno,Eduardo Fernández-Carrión

doi:10.1371/journal.pone.0232534

Cecilia Aguilar-Vega, Javier Lucientes + Show 2 more

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https://doi.org/10.1371/journal.pone.0232534

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Abstract

Bluetongue virus (BTV) is an arbovirus of ruminants that has been circulating in Europe continuously for more than two decades and has become endemic in some countries such as Spain. Spain is ideal for BTV epidemiological studies since BTV outbreaks from different sources and serotypes have occurred continuously there since 2000; BTV-1 has been reported there from 2007 to 2017. Here we develop a model for BTV-1 endemic scenario to estimate the risk of an area becoming endemic, as well as to identify the most influential factors for BTV-1 persistence. We created abundance maps at 1-km2 spatial resolution for the main vectors in Spain, Culicoides imicola and Obsoletus and Pulicaris complexes, by combining environmental satellite data with occurrence models and a random forest machine learning algorithm. The endemic model included vector abundance and host-related variables (farm density). The three most relevant variables in the endemic model were the abundance of C. imicola and Obsoletus complex and density of goat farms (AUC 0.86); this model suggests that BTV-1 is more likely to become endemic in central and southwestern regions of Spain. It only requires host- and vector-related variables to identify areas at greater risk of becoming endemic for bluetongue. Our results highlight the importance of suitable Culicoides spp. prediction maps for bluetongue epidemiological studies and decision-making about control and eradication measures.

Highlights

Bluetongue is an infectious, non-contagious, arboviral disease that affects primarily ruminants, both domestic and wild, and whose biological vector are midges of the genus Culicoides [1]
random forest for classification (RFC) is more balanced than the other algorithms when taking into account both recall and precision measures, which implies that RFC is good for identifying and predicting true positives
We applied RFC the same as for bluetongue virus (BTV)-1 model; for abundance models, mtry was set in order to obtain the minimum mean square error (MSE) (S1 Table) and 500 trees

Summary

Introduction

Bluetongue is an infectious, non-contagious, arboviral disease that affects primarily ruminants, both domestic and wild, and whose biological vector are midges of the genus Culicoides [1]. Bluetongue is caused by bluetongue virus (BTV), which belongs to the genus Orbivirus [1]. More than 30 BTV serotypes have been described [2]. Bluetongue is a listed disease of the World Organization of Animal Health because of its transboundary nature and major economic impact [3]. Prior to 1998, bluetongue was reported sporadically in Europe, but since numerous BTV serotypes have been reported in the continent, including in Spain [4].

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