Until recently, bluetongue (BT) virus (BTV) serotypes reportedly causing transplacental infections were all ascribed to the use of modified live virus strains. During the 2007 BT epidemic in Belgium, a significant increase in the incidence of abortions was reported. A study including 1348 foetuses, newborns and young animals with or without suspicion of BTV infection, was conducted to investigate the occurrence of natural transplacental infection caused by wild-type BTV-8 and to check the immunocompetence of newborns. BTV RNA was present in 41% and 18.5% of aborted foetuses from dams with or without suspected BTV involvement during pregnancy, respectively. The results of dam/calf pairs sampled before colostrum uptake provide evidence of almost 10% transplacental BTV infection in newborns. Apparently immunotolerant calves were found at a level of 2.4%. The current study concludes that the combined serological and real-time PCR (RT-qPCR) result of pregnant dams gives no indication of the infection status of the offspring except in the case of a double negative result. In a group of 109 calves with clinical suspicion of BT, born during the vector-free period, 11% were found to be RT-qPCR positive. The true prevalence was estimated to be 2.3%, indicating the extent of transplacental infection in a group of 733 calves of one to 4 months of age without BT suspicion. Moreover, virus isolation was successful for two newborn calves, emphasizing the need for restricting trade to BT-free regions of pregnant dams possibly infected during gestation, even if they are BTV RT-qPCR negative.

In 2006 bluetongue (BT) emerged for the first time in North-Western Europe. Reliable diagnostic tools are essential in controlling BT but data on the diagnostic sensitivity (Se) and specificity (Sp) are often missing. This paper aims to describe and analyse the results obtained with the diagnostics used in Belgium during the 2006 BT crisis. The diagnosis was based on a combination of antibody detection (competitive ELISA, cELISA) and viral RNA detection by real-time RT-PCR (RT-qPCR). The performance of the cELISA as a diagnostic tool was assessed on field results obtained during the epidemic and previous surveillance campaigns. As the infectious status of the animals is unknown during an epidemic, a Bayesian analysis was performed. Both assays were found to be equally specific (RT-qPCR: 98.5%; cELISA: 98.2%) while the diagnostic sensitivity of the RT-qPCR (99.5%) was superior to that of the cELISA (87.8%). The assumption of RT-qPCR as standard of comparison during the bluetongue virus (BTV) epidemic proved valid based on the results of the Bayesian analysis. A ROC analysis of the cELISA, using RT-qPCR as standard of comparison, showed that the cut-off point with the highest accuracy occurred at a percentage negativity of 66, which is markedly higher than the cut-off proposed by the manufacturer. The analysis of the results was further extended to serological and molecular profiling and the possible use of profiling as a rapid epidemiological marker of the BTV in-field situation was assessed. A comparison of the serological profiles obtained before, during and at the end of the Belgian epidemic clearly showed the existence of an intermediate zone which appears soon after BTV (re)enters the population. The appearance or disappearance of this intermediate zone is correlated with virus circulation and provides valuable information, which would be entirely overlooked if only positive and negative results were considered.

An EDTA-blood sample from a cow without clinical signs, which gave early birth to a newborn calf that died soon after delivery, was shown to be positive for bluetongue virus (BTV)-RNA using a group-specific real-time RT-PCR (RT-qPCR). In-house serotype-specific RT-qPCR assays for bluetongue virus serotype 1 (BTV-1), -6 and -8 all gave negative results. Subsequent assays were carried out using conventional (gel-based) RT-PCR primers for all 25 BTV serotypes and only two primer sets, both specific for BTV-11, gave bands of the expected size. The cDNAs generated were sequenced and comparisons of the genome segment 2 sequence with that of the modified 'live' vaccine strain of BTV-11 from South Africa showed 100% identity. A survey of all ruminants in a 1-km area around the first positive farm using a BTV-11 serotype-specific RT-qPCR revealed five other holdings with in total nine BTV-11 positive animals. A cross-sectional monitoring of dairy cattle in Belgium showed an overall prevalence of 3.8% on herd level and 0.2% on animal level. A BTV-11 has been introduced into the Belgian cattle herd during the 2008 vector season. The source of the infection and the way by which the virus was introduced are unknown.

BackgroundIn northern Europe, bluetongue (BT) caused by the BT virus (BTV), serotype 8, was first notified in August 2006 and numerous ruminant herds were affected in 2007 and 2008. However, the origin and the time and place of the original introduction have not yet been determined.Methods and Principal FindingsFour retrospective epidemiological surveys have been performed to enable determination of the initial spatiotemporal occurrence of this emerging disease in southern Belgium: investigations of the first recorded outbreaks near to the disease epicenter; a large anonymous, random postal survey of cattle herds and sheep flocks; a random historical milk tank survey of samples tested with an indirect ELISA and a follow-up survey of non-specific health indicators. The original introduction of BTV into the region probably occurred during spring 2006 near to the National Park of Hautes Fagnes and Eifel when Culicoides become active.Conclusions/SignificanceThe determination of the most likely time and place of introduction of BTV8 into a country is of paramount importance to enhance awareness and understanding and, to improve modeling of vector-borne emerging infectious diseases.

shown to be widely but unevenly distributed throughout Belgium, with a gradient 48 decreasing towards the south and the west of the country. The analysis has shown 49

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Bluetongue (BT) is an arthropod-borne viral disease of ruminants. In August 2006, domestic ruminant populations in Northern Europe became infected with BT virus serotype 8 (BTV-8). The first BTV-8-case of the year 2007 in Belgium was notified in July. This case was the starting point of a second wave of BT outbreaks. The main objective of this study was to describe the evolution and the clinical impact of the second episode of BT in Belgium. In addition, the main differences with the previous episode (August-December 2006) are reported. Both outbreak and rendering plant data were analysed. Overall cumulative incidence at herd level was estimated at 11.5 (11.2-11.8) and 7.5 (7.3-7.8) per cent in cattle and sheep populations respectively. The findings went in favour of a negative association between within-herd prevalence in 2006 and the risk of showing clinical signs of BT in 2007 (via protective immunity). A high level of correlation was demonstrated between BT incidence and small ruminant mortality data when shifting the latter of 1-week backwards. This result supports the hypothesis that the high increase in small ruminant mortality observed in 2007 was the consequence of the presence of BT. For cattle, the correlation was not as high. An increase in cattle foetal mortality was also observed during the year 2007 and a fair correlation was found between BT incidence and foetal mortality.