Role of wild ruminants in the epidemiology of bluetongue virus serotypes 1, 4 and 8 in Spain

Abstract

Although the importance of wild ruminants as potential reservoirs of bluetongue virus (BTV) has been suggested, the role played by these species in the epidemiology of BT in Europe is still unclear. We carried out a serologic and virologic survey to assess the role of wild ruminants in the transmission and maintenance of BTV in Andalusia (southern Spain) between 2006 and 2010.A total of 473 out of 1339 (35.3%) wild ruminants analyzed showed antibodies against BTV by both ELISA and serum neutralization test (SNT). The presence of neutralizing antibodies to BTV-1 and BTV-4 were detected in the four species analyzed (red deer, roe deer, fallow deer and mouflon), while seropositivity against BTV-8 was found in red deer, fallow deer and mouflon but not in roe deer. Statistically significant differences were found among species, ages and sampling regions. BTV RNA was detected in twenty-one out of 1013 wild ruminants (2.1%) tested. BTV-1 and BTV-4 RNA were confirmed in red deer and mouflon by specific rRT-PCR.BTV-1 and BTV-4 seropositive and RNA positive wild ruminants, including juveniles and sub-adults, were detected years after the last outbreak was reported in livestock. In addition, between the 2008/2009 and the 2010/2011 hunting seasons, the seroprevalence against BTV-1, BTV-4 and BTV-8 increased in the majority of provinces, and these serotypes were detected in many areas where BTV outbreaks were not reported in domestic ruminants. The results indicate that wild ruminants seem to be implicated in the dissemination and persistence of BTV in Spain.

Figure 1

Map showing the location of Andalusia (southern Spain) and the provinces in which it is divided. Grey areas indicate the municipalities in which samples from wild ruminants were collected during the study period, 2006-2010. Sampling regions were grouped in western (including the Provinces of Huelva, Cádiz and Seville), central (including the Provinces of Córdoba and Málaga) and eastern regions (including the Provinces of Granada, Jaén and Almería).

Figure 2

Map of Andalusia (southern Spain) showing the spatial distribution of BTV serotypes in livestock and wild ruminants, period 2006-2010. The gradient of grey indicates the number of BTV-1 (A), BTV-4 (B) and BTV-8 (C) infected farms by domestic ruminants. Grey dots size is proportional to the number of BTV-1 (D), BTV-4 (E) and BTV-8 (F) seropositive wild ruminants detected and the black triangles indicate the presence of BTV-1 RNA (D) and BTV-4 RNA (E) positive animals. White areas indicate the regions in which wild ruminants were sampled.