Spatial and temporal distribution of Culicoides species in mainland Portugal (2005-2010). Results of the Portuguese Entomological Surveillance Programme.

Rita Ribeiro,Lara E Harrup,Telmo Nunes,Javier Lucientes,Fernando Boinas,David W Ramilo,Rita Amador,Anthony J Wilson,Sara Madeira,Filipa M Baptista

doi:10.1371/journal.pone.0124019

Abstract

Bluetongue virus (BTV) is transmitted by Culicoides biting midges and causes an infectious, non-contagious disease of ruminants. It has been rapidly emerging in southern Europe since 1998. In mainland Portugal, strains of BTV belonging to three serotypes have been detected: BTV-10 (1956-1960), BTV-4 (2004-2006 and 2013) and BTV-1 (2007-2012). This paper describes the design, implementation and results of the Entomological Surveillance Programme covering mainland Portugal, between 2005 and 2010, including 5,650 caches. Culicoides imicola Kieffer was mostly found in central and southern regions of Portugal, although it was sporadically detected in northern latitudes. Its peak activity occurred in the autumn and it was active during the winter months in limited areas of the country. Obsoletus group was present at the highest densities in the north although they were found throughout the country in substantial numbers. Culicoides activity occurred all year round but peaked in the spring. A generalized linear mixed model was developed for the analysis of the environmental factors associated with activity of the species of Culicoides suspected vectors of BTV in the country. For C. imicola Kieffer, the most important variables were month, diurnal temperature range (DTR), the number of frost days (FRS) and median monthly temperature (TMP). For the Obsoletus group, the most important factors were month, diurnal temperature range (DTR), and linear and quadratic terms for median monthly temperature (TMP). The results reported can improve our understanding of climatic factors in Culicoides activity influencing their distribution and seasonal pattern.

Highlights

Bluetongue (BT) is an infectious disease of ruminants caused by bluetongue virus (BTV), an arbovirus with 26 recognised serotypes [1]
The Afrotropical species C. imicola Kieffer is considered to be the most important vector in most parts of Africa and southern Europe, species in the Obsoletus group and group Pulicaris have been implicated as efficient vectors of certain strains of BTV during recent outbreaks in northern Europe [2,7]
This study has shown that what determines the presence of C. imicola is strongly correlated with middle infra-red reflectance, and correlated with vegetation structure and surface temperature, and how much each varies throughout the year

Summary

Introduction

Bluetongue (BT) is an infectious disease of ruminants caused by bluetongue virus (BTV), an arbovirus with 26 recognised serotypes [1]. Clinical disease is most common in sheep and certain species of deer [2] but is seen in cattle [3,4]. Since 1998, BTV activity in Europe and in Mediterranean basin has increased substantially [5] and since 2006 the virus has emerged in northern Europe. Vertical transmission in cattle has been observed for at least one field strain of BTV [8,9] and oral transmission is suspected [10], possibly explaining the observed ability of BTV to “overwinter” for long periods in the absence of vector activity [11]

Methods

Results

Discussion

Conclusion