Monthly variation in the probability of presence of adult Culicoides populations in nine European countries and the implications for targeted surveillance

Background: Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are small hematophagous insects responsible for the transmission of bluetongue virus, Schmallenberg virus and African horse sickness virus to wild and domestic ruminants and equids. Outbreaks of these viruses have caused economic damage within the European Union. The spatio-temporal distribution of biting midges is a key factor in identifying areas with the potential for disease spread. The aim of this study was to identify and map areas of neglectable adult activity for each month in an average year. Average monthly risk maps can be used as a tool when allocating resources for surveillance and control programs within Europe. Methods : We modelled the occurrence of C. imicola and the Obsoletus and Pulicaris ensembles using existing entomological surveillance data from Spain, France, Germany, Switzerland, Austria, Denmark, Sweden, Norway and Poland. The monthly probability of each vector species and ensembles being present in Europe based on climatic and environmental input variables was estimated with the machine learning technique Random Forest. Subsequently, the monthly probability was classified into three classes: Absence, Presence and Uncertain status. These three classes are useful for mapping areas of no risk, areas of high-risk targeted for animal movement restrictions, and areas with an uncertain status that need active entomological surveillance to determine whether or not vectors are present. Results: The distribution of Culicoides species ensembles were in agreement with their previously reported distribution in Europe. The Random Forest models were very accurate in predicting the probability of presence for C. imicola (mean AUC = 0.95), less accurate for the Obsoletus ensemble (mean AUC = 0.84), while the lowest accuracy was found for the Pulicaris ensemble (mean AUC = 0.71). The most important environmental variables in the models were related to temperature and precipitation for all three groups. Conclusions: The duration periods with low or null adult activity can be derived from the associated monthly distribution maps, and it was also possible to identify and map areas with uncertain predictions. In the absence of ongoing vector surveillance, these maps can be used by veterinary authorities to classify areas as likely vector-free or as likely risk areas from southern Spain to northern Sweden with acceptable precision. The maps can also focus costly entomological surveillance to seasons and areas where the predictions and vector-free status remain uncertain

PCR prevalence of rodent-borne Ljungan virus across Europe

Since its discovery in Swedish bank voles (Myodes glareolus) in the 1990s (Niklasson et al., 1999), interest in the Ljungan (picorna-)virus (LV) has grown as a result of a suggested association of the virus with some human pathologies, and because serological and neutralization tests have confirmed that humans are exposed to LV (38% in Jääskeläinen et al., 2013). LV infection induces fetal malformations and diabetes-like symptoms in laboratory mice, and since LV also causes disease in some wild rodents, it may have a role in small mammal cycles. Hence, LV epidemiology is potentially of global interest. Although LV has been noted in single populations of several rodent species in Denmark, the USA, Germany, Italy, Finland and the UK (Johansson et al., 2003; Hauffe et al., 2010; Kallies, 2010 and references therein; Jääskeläinen et al., 2013; Salisbury et al., 2014), this is the first systematic screening of LV across the EU, especially in the bank vole, but also in other small mammals, including shrews and commensal species. In all, 15 different species from nine European countries were sampled as part of the EU FP7 project EDENext. Using an LV-specific RT-PCR method (Donoso-Mantke et al., 2007), 1509 liver samples stored at -80°C were screened for LV, including 831 bank voles. All amplified fragments were sequenced for confirmation. LV-positive samples were found in all countries with significant sample sizes, and in most species, including house mice, but not black rats. Overall PCR prevalence in bank voles was about 16% (range 0-50% per population). We added eight new species to the list of LV hosts, including the red squirrel (Sciurus vulgaris), and a number of voles and shrews. Our study suggests that LV has a wide geographical and host distribution

PCR prevalence of rodent-borne Ljungan virus across Europe

Since its discovery in Swedish bank voles (Myodes glareolus) in the 1990s (Niklasson et al., 1999), interest in the Ljungan (picorna-)virus (LV) has grown as a result of a suggested association of the virus with some human pathologies, and because serological and neutralization tests have confirmed that humans are exposed to LV (38% in Jääskeläinen et al., 2013). LV infection induces fetal malformations and diabetes-like symptoms in laboratory mice, and since LV also causes disease in some wild rodents, it may have a role in small mammal cycles. Hence, LV epidemiology is potentially of global interest. Although LV has been noted in single populations of several rodent species in Denmark, the USA, Germany, Italy, Finland and the UK (Johansson et al., 2003; Hauffe et al., 2010; Kallies, 2010 and references therein; Jääskeläinen et al., 2013; Salisbury et al., 2014), this is the first systematic screening of LV across the EU, especially in the bank vole, but also in other small mammals, including shrews and commensal species. In all, 15 different species from nine European countries were sampled as part of the EU FP7 project EDENext. Using an LV-specific RT-PCR method (Donoso-Mantke et al., 2007), 1509 liver samples stored at -80°C were screened for LV, including 831 bank voles. All amplified fragments were sequenced for confirmation. LV-positive samples were found in all countries with significant sample sizes, and in most species, including house mice, but not black rats. Overall PCR prevalence in bank voles was about 16% (range 0-50% per population). We added eight new species to the list of LV hosts, including the red squirrel (Sciurus vulgaris), and a number of voles and shrews. Our study suggests that LV has a wide geographical and host distribution

PCR prevalence of rodent-borne Ljungan virus across Europe

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