SummaryA serological survey to detect Schmallenberg virus (SBV)-specific antibodies by ELISA was organized in the Belgian sheep population to study the seroprevalence at the end of the epidemic. One thousand eighty-two sheep samples which were collected from 83 herds all over Belgium between November 2011 and April 2012 were tested. The overall within-herd seroprevalence and the intraclass correlation coefficient were estimated at 84.31% (95% CI: 84.19-84.43) and 0.34, respectively. The overall between-herd seroprevalence was 98.03% (95% CI: 97.86-98.18). A spatial cluster analysis identified a cluster of six farms with significantly lower within-herd seroprevalence in the south of Belgium compared with the rest of the population (P = 0.04). It was shown that seroprevalence was associated to flock density and that the latter explained the presence of the spatial cluster. Additionally, 142 goat samples from eight different herds were tested for SBV-specific antibodies. The within-herd seroprevalence in goats was estimated at 40.68% (95% CI: 23.57-60.4%). The results of the current study provided evidence that almost every Belgian sheep herd has been in contact with SBV during 2011 and should be taken into consideration as part of comprehensive SBV surveillance and control strategies.

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.

A cross-sectional survey was conducted in the Belgian cattle population after the first period of infection of the emerging Schmallenberg virus. A total number of 11 635 cattle from 422 herds sampled between 2 January and 7 March 2012 were tested for the presence of Schmallenberg-specific antibodies using an ELISA kit. Between-herd seroprevalence in cattle was estimated at 99.76% (95% CI: 98.34-99.97) and within-herd seroprevalence at 86.3% (95% CI: 84.75-87.71). An Intraclass Correlation Coefficient of 0.3 (P < 0.001) was found, indicating that the correlation between two animals within a herd with respect to their serological status was high. Those results corroborate the conclusion that the Schmallenberg virus was widespread in Belgium during winter 2011. Seroprevalence was shown to be statistically associated to the animal's age (P < 0.0001): with 64.9% (95% CI: 61.34-68.3) estimated for the 6-12 months of age, 86.79% (95% CI: 84.43-88.85) for the 12-24 months of age and 94.4% (95% CI: 93.14-95.44) for the animals older than 24 months. Based on the results of the described serological survey, we can conclude that after the first Schmallenberg virus episode, almost every Belgian cattle has already been in contact with the virus. In consequence, the vast majority of the host animals should have developed post infection protective immunity against the virus.

Schmallenberg virus (SBV), which emerged in Northwestern Europe in 2011, is an arthropod-borne virus affecting primarily ruminants. Based on the results of two cross-sectional studies conducted in the Belgian ruminant population during winter 2011-2012, we concluded that at the end of 2011, almost the whole population had already been infected by SBV. A second cross-sectional serological study was conducted in the Belgian cattle population during winter 2012-2013 to examine the situation after the 2012 transmission period and to analyse the change in immunity after 1 year. A total of 7130 blood samples collected between 1st January and 28 February 2013 in 188 herds were tested for the presence of SBV-specific antibodies. All sampled herds tested positive and within-herd seroprevalence was estimated at 65.66% (95% CI: 62.28-69.04). A statistically significant decrease was observed between the beginning and the end of 2012. On the other hand, age-cohort-specific seroprevalence stayed stable from 1 year to the other. During winter 2012-2013, calves between 6 and 12 months had a seroprevalence of 20.59% (95% CI: 15.34-25.83), which seems to be an indication that SBV was still circulating at least in some parts of Belgium during summer-early autumn 2012. Results showed that the level of immunity against SBV of the animals infected has not decreased and remained high after 1 year and that the spread of the virus has slowed down considerably during 2012. This study also indicated that in the coming years, there are likely to be age cohorts of unprotected animals.

Neosporosis caused by Neospora caninum, paratuberculosis (or Johne's disease) caused by Mycobacterium avium subspecies paratuberculosis (MAp), and Q fever caused by Coxiella burnetii are three infectious cattle diseases that have significant health and economic impacts (Woldehiwet 2004, Haddad and others 2005, McKenna and others 2006). Whereas Neospora and Q fever in cattle are mostly associated with reproductive disorders, such as abortion (Woldehiwet 2004, Dubey and others 2007), MAp causes chronic enteritis and progressive weight loss (Tiwari and others 2006). Q fever, moreover, is a zoonotic disease. For MAp, a possible relationship has been suggested with Crohn's disease in humans, although this remains controversial (over and others 2011). in Belgium, a cross-sectional serological survey of cattle, the winter screening, is carried out during the housing period in winter every year. This winter screening provides an ideal opportunity for the simultaneous monitoring and surveillance of several infectious diseases in the Belgian cattle population. As no recent seroprevalence data were available for N caninum, MAp or Q fever at the regional or national level in Belgium, it was decided to test for those diseases during the winter screening conducted between November 2009 and February 2010. For this survey, a total of 1100 cattle herds were selected for sampling by simple random sampling using the