Distribution of Schmallenberg Virus and Seroprevalence in Belgian Sheep and Goats

A 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.     

Large‐Scale Cross‐Sectional Serological Survey of Schmallenberg Virus in Belgian Cattle at the End of the First Vector Season

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.     

Evidence of extensive renewed Schmallenberg virus circulation in Belgium during summer of 2016 – increase in arthrogryposis‐hydranencephaly cases expected

A seroprevalence study carried out between June and September 2016 in the Belgian sheep population showed a significant increase in overall (from 25% to 62%) and between‐herd (from 60% to 96%) seroprevalence against Schmallenberg virus (SBV) during this period, indicating the most extensive recirculation of SBV since its original emergence in 2011. SBV recirculation was confirmed by the detection of SBV RNA‐positive Culicoides obsoletus complex midges collected in the region of Antwerp in August 2016, reaching a minimum infection rate of 3%. The recirculation of SBV in the largely unprotected ruminant population during summer 2016 will likely cause an increase in the number of arthrogryposis‐hydranencephaly cases in newborn ruminants during the coming months.     

Two Years After the Schmallenberg Virus Epidemic in the Netherlands: Does the Virus still Circulate?

Two years after the introduction of the Schmallenberg virus in north‐western Europe, it is unknown whether the virus is still circulating in countries that were the first to be confronted with it. When the population‐level immunity declines in Europe, reintroduction or the re‐emergence of SBV in Europe might eventually result in an outbreak of similar magnitude of that seen in 2011–2012. The Netherlands was part of the primary outbreak region of SBV in 2011. The aim of this study was to determine whether SBV circulated amongst dairy herds in the Netherlands in 2013, and if so, to which extent. For this purpose, the presence of SBV‐specific antibodies in naive cattle was investigated. A total of 394 dairy farms were sampled between October and December 2013 by collecting five serum samples per herd. Antibodies were detected in 1.1% [95% confidence interval (CI): 0.7–1.7)] of the animals. All seropositive animals were single reactors per herd and were at least 8 months old at sampling. As these results were inconclusive in demonstrating freedom of SBV circulation, a more in‐depth investigation was initiated to provide more insight: an additional sample of 20 youngstock within the same age category (including the five initially sampled animals) was collected from 17 of the 21 positive herds and tested for SBV‐specific antibodies. This resulted in 9 antibody‐positive test results of 316 samples. Again, the positive samples were single reactors within the sample obtained from each farm, which is unlikely given the characteristics of SBV. Therefore, assuming the single reactors as false‐positive, this survey showed with 95% confidence that the maximum possible prevalence of herds with SBV circulation in the Netherlands was <1% in 2013.     

Post‐epidemic investigation of Schmallenberg virus in wild ruminants in Slovenia

Schmallenberg virus (SBV) is a vector‐borne virus belonging to the genus Orthobunyavirus within the Bunyaviridae family. SBV emerged in Europe in 2011 and was characterized by epidemics of abortions, stillbirths and congenital malformations in domestic ruminants. The first evidence of SBV infection in Slovenia was from an ELISA‐positive sample from a cow collected in August 2012; clinical manifestations of SBV disease in sheep and cattle were observed in 2013, with SBV RNA detected in samples collected from a total of 28 herds. A potential re‐emergence of SBV in Europe is predicted to occur when population‐level immunity declines. SBV is also capable of infecting several wild ruminant species, although clinical disease has not yet been described in these species. Data on SBV‐positive wild ruminants suggest that these species might be possible sources for the re‐emergence of SBV. The aim of this study was to investigate whether SBV was circulating among wild ruminants in Slovenia and whether these species can act as a virus reservoir. A total of 281 blood and spleen samples from wild ruminants, including roe deer, red deer, chamois and European mouflon, were collected during the 2017–2018 hunting season. Serum samples were tested for antibodies against SBV by ELISA; the overall seroprevalence was 18.1%. Seropositive samples were reported from all over the country in examined animal species from 1 to 15 years of age. Spleen samples from the seropositive animals and serum samples from the seronegative animals were tested for the presence of SBV RNA using real‐time RT‐PCR; all the samples tested negative. Based on the results of the seropositive animals, it was demonstrated that SBV was circulating in wild ruminant populations in Slovenia even after the epidemic, as almost half (23/51) of the seropositive animals were 1 or 2 years old.     

Schmallenberg Virus in Belgium: Estimation of Impact in Cattle and Sheep Herds

Schmallenberg virus (SBV) emerged during summer 2011. SBV induced an unspecific syndrome in cattle and congenital signs (abortions, stillbirths and malformations) in domestic ruminants. To study the impact of SBV in Belgium, a phone survey was conducted upon September 2012. Hereto two groups of cattle farmers (A and B) and two groups of sheep farmers (C and D) were randomly selected. Farms from groups A (n = 53) and C (n = 42) received SBV‐positive result at RT‐PCR in the Belgian National Reference Laboratory (NRL). Farms from groups B (n = 29) and D (n = 44) never sent suspected samples to NRL for SBV analysis but were however presumed seropositive for SBV after the survey. Questionnaires related to reproduction parameters and clinical signs observed in newborn and adult animals were designed and addressed to farmers. As calculated on a basis of farmers’ observations, 4% of calves in group A and 0.5% in group B were reported aborted, stillborn or deformed due to SBV in 2011–2012. The impact as observed by sheep farmers was substantially higher with 19% of lambs in group C and 11% in group D that were reported aborted, stillborn or deformed due to SBV in 2011–2012. Interestingly, abortions or stillbirths were not clear consequences of SBV outbreak in cattle farms, and the birth of a deformed animal was an essential condition to suspect SBV presence in cattle and sheep farms. This study contributes to a better knowledge of the impact of the SBV epidemic. The results suggest that SBV impacted Belgian herds mostly by the birth of deformed calves, stillborn lambs and deformed lambs. This work also demonstrates that the birth of a deformed calf or lamb was a trigger for the farmer to suspect the presence of SBV and send samples to NRL for further analyses.     

Exposure of Wildlife to the Schmallenberg Virus in France (2011–2014): Higher,Faster, Stronger (than Bluetongue)!

The Schmallenberg virus (SBV) has recently emerged in Europe, causing losses to the domestic livestock. A retrospective analysis of serodata was conducted in France for estimating seroprevalence of SBV among six wildlife species from 2011–2012 to 2013–2014, that is during the three vector seasons after the emergence of the SBV in France. Our objective was to quantify the exposure of wildlife to SBV and the potential protective effect of elevation such as previously observed for bluetongue. We also compared the spatiotemporal trends between domestic and wild animals at the level of the departments. We tested 2050 sera using competitive ELISA tests. Individual and population risk factors were further tested using general linear models among 1934 individuals. All populations but one exhibited positive results, seroprevalence up to 30% being observed for all species. The average seroprevalence did not differ between species but ranged from 0 to 90% according to the area and period, due to the dynamic pattern of infection. Seroprevalence was on average higher in the lowlands compared to areas located up to 800 m. Nevertheless, seroprevalence above 50% occurred in areas located up to 1500 m. Thus, contrary to what had been observed for bluetongue during the late 2000s in the same areas, SBV could spread to high altitudes and infect all the studied species. The spatial spread of SBV in wildlife did not fully match with SBV outbreaks reported in the domestic livestock. The mismatch was most obvious in mountainous areas where outbreaks in wildlife occurred on average one year after the peak of congenital cases in livestock. These results suggest a much larger spread and vector capacity for SBV than for bluetongue virus in natural areas. Potential consequences for wildlife dynamics are discussed.     

Schmallenberg Virus beyond Latitude 65°N

Extensive and rapid spread of Schmallenberg virus (SBV) in Sweden was detected by consecutive serological bulk milk surveys conducted before and after the vector season of 2012. Whereas <0.2% of cattle herds tested positive in a first survey in spring 2012, SBV‐specific antibodies were detected in almost 75% of 723 bulk milk samples randomly collected all over the country 6 months later, beyond the 65th northern latitude, and with an observed spatial distribution suggesting multiple introductions of the virus. Circulation of virus was later confirmed by the detection of SBV in malformed lambs and calves starting from November 2012 and January 2013, respectively. These observations suggest SBV circulation starting from July 2012, with a peak in transmission between August and October. A local heterogeneity of within‐herd seroprevalence was found, indicating that SBV‐naïve animals remain also in highly infected areas enabling the re‐emergence of the infection in the coming vector season.     

Serosurvey of Schmallenberg Virus Infection in the Highest Goat‐Specialized Region of France

The monitoring of both the spread and clinical impact of Schmallenberg virus (SBV) infection within its full host range is important for the control of the epidemic and potential new outbreaks. In France, a national surveillance plan based on voluntary notifications of congenital malformations in newborn ruminants revealed that goats were the less affected host species. However, seroprevalence studies only targeted sheep and cattle, preventing accurate estimations of the real impact of SBV infection in goats. Here, a serological survey was conducted in the highest goat‐specialized region of France between June 2012 and January 2013. A total of 1490 goat sera from 50 herds were analysed by ELISA. The between‐herd and within‐herd prevalences were estimated at 62% and 13.1%, respectively. Seroprevalence was not uniformly distributed throughout the territory and markedly differed between intensive and extensive herds. The low within‐herd seroprevalence demonstrates that a large fraction of the French goat population remains susceptible to SBV infection.     

Herd‐Level Risk Factors for the Seropositivity to Mycoplasma hyopneumoniae and the Occurrence of Enzootic Pneumonia Among Fattening Pigs in Areas of Endemic Infection and High Pig Density

The aim of the present study was to identify potential risk factors for the occurrence of enzootic pneumonia (EP) in herds situated in a region of high pig density, where a majority of herds is endemically infected with Mycoplasma hyopneumoniae. Between 2006 and 2010, overall 100 herds were enrolled in a case–control study. Data were collected through personal interview with the farmers, clinical examination of pigs and their environments, and serological testing for M. hyopneumoniae, swine influenza virus and porcine reproductive and respiratory syndrome virus. There were 40 case herds (coughing index high, seroprevalence high) with a mean coughing index of 4.3 and a seroprevalence of 86.6%. There were two control groups. Control group I consisted of 25 herds (coughing index low, seroprevalence low) with mean values of 0.7 and 11.2%, and 35 herds were allocated to control group II (coughing index low, seroprevalence high) where the mean coughing index was 0.9 and seroprevalence 86.3%. Case herds and control II herds had an increased age of piglets at weaning compared to control I herds. Any contact between fattening pigs of different age during restocking of compartments increased the risk for the occurrence of EP in a herd. Finally, farms that use living animals for the exposure to gilts during the acclimatization and farms that had increased number of weaned piglets per sow and year were less likely to test positive for M. hyopneumoniae and less likely to develop clinical symptoms of EP in fattening pigs.     

Schmallenberg virus in Culicoides Latreille (Diptera: Ceratopogonidae) populations in France during 2011‐2012 outbreak

Following the emergence of the Schmallenberg virus (SBV) in 2011 in Germany and its rapid spread in Europe, Culicoides (Diptera: Ceratopogonidae) collected through the French surveillance network were analysed in order to record the presence of virus genome into species diversity collected, to assess the minimum infectious rates (MIR) and the virus circulation dynamics in Culicoides populations. Two vector activity periods were selected (2011, August to October, 53 sites and 2012, June to October, 35 sites) corresponding to 704 night collections. A total of 29,285 individual midges covering at least 50 species were tested either in pools of maximum 50 females or individually (for Culicoides obsoletus /Culicoides scoticus ) using real‐time RT‐PCR. Nine species were found SBV positive (C. obsoletus , C. scoticus , Culicoides chiopterus , Culicoides dewulfi , Culicoides imicola , Culicoides pulicaris , Culicoides newsteadi , Culicoides lupicaris and Culicoides nubeculosus ) with overall MIR ranging from 0.2% to 4.2%. While the Culicoides nubeculosus laboratory strain is generally considered to have only low vector competence for viruses, interestingly, field‐caught C. nubeculosus specimens were found positive twice for SBV. The first SBV‐positive pool was recorded in August 2011 in north‐eastern France, dating the virus circulation in France 5 months earlier than the first recorded congenital malformations and 2 months earlier than the former recorded date based on retrospective serological data. The MIR were maximum in October 2011, and in July 2012 according to dates of virus arrival in the studied areas. Moreover, our study also showed that virus circulation could be locally intense with infection rate (IR) reaching up to 16% for C. obsoletus /C. scoticus in July 2012 in one site of western France. This retrospective study demonstrates the importance of large‐scale analysis to describe the spatio‐temporal dynamics of virus circulation.     

Schmallenberg virus detection in Culicoides biting midges in Spain: First laboratory evidence for highly efficient infection of Culicoides of the Obsoletus complex and Culicoides imicola

Since Schmallenberg disease was discovered in 2011, the disease rapidly spread across Europe. Culicoides biting midges have been implicated as putative Schmallenberg vectors in Europe. The detection of Schmallenberg virus (SBV) in field collected Culicoides was evaluated through retrospective (2011–2012) collections and captures performed in 2013. This study represents the first detection of SBV in field collected Culicoides in Spain. Infectious midges were detected at the foothills of Pyrenees, Aramunt, in the summer 2012. All the specimens infected with Schmallenberg were of the species Culicoides obsoletus s.s. confirming its putative vector status in Spain. Experimental infection on field collected Culicoides provided evidence of atypical high efficiency for SBV vector infection and transmission potential in local populations of Culicoides imicola and in Culicoides of the Obsoletus complex. However, captured individuals of C. imicola were more susceptible to SBV infection than C. obsoletus s.l. (p  < .001), with an infection ratio of 0.94 and 0.63, respectively. In contrast, a Culicoides nubeculosus colony appeared to be refractory to SBV infection.     

Serological Study of Exposure to Selected Arthropod‐Borne Pathogens in European Bison (Bison bonasus) in Poland

Bison bonasus is an indigenous species of Central and Eastern Europe with the largest wild population inhabiting Białowieża Primeval Forest; however, free‐living and captive European bison are reared in many countries around the world. Despite that the European bison was rescued from the extinction after the First World War, it remains as endangered species. Changing environment as well as human activity may have contributed to the observed increase of the risk of the emergence and re‐emergence of pathogens. The aim of the survey was to establish the distribution of four pathogens transmitted by arthropods including three arboviruses [Bluetongue disease virus (BTV), Epizootic haemorrhagic disease virus (EHDV) and Schmallenberg virus (SBV)] and a bacteria (Francisella tularensis) in the main populations of European bison in Poland. A total of 251 European bison originating from eight main populations were included in the study and sampled between February 2011 and December 2014. Serum samples originated from chemically immobilized, eliminated or dead by natural causes animals. Additionally, 65 cervids from Białowieża Forest were tested to compare the seroprevalences of other ruminants inhabiting the same environment. The antibodies to SBV and BTV were found in 76.1% and 24.7% of European bison, respectively. In autumn 2012, simultaneous emergence of SBV and BTV in European bison was observed; however, while SBV has spread in all populations scattered around the country, BTV infections were observed only in the north‐eastern part of Poland, where BTV cases have been previously reported in domestic ruminants. European bison age was found to be the only significant risk factor for SBV and BTV seroprevalences; however, this association was connected to the animal size, rather than to the length of exposure. None of the animals tested positive for antibodies against EHDV or F. tularensis. SBV exposure rate of cervids was much lower (35.4%) than in European bison, while BTV seroprevalence was comparable in both groups.     

Serological Screening Suggests Presence of Schmallenberg Virus in Cattle,Sheep and Goat in the Zambezia Province,Mozambique

Schmallenberg virus (SBV) is a novel Orthobunyavirus within the family Bunyaviridae belonging to the Simbu serogroup. Schmallenberg virus infects ruminants and has since its discovery in the autumn 2011 been detected/spread to large parts of Europe. Most bunyaviruses are arboviruses, and SBV has been detected in biting midges in different European countries, suggesting that they may play a role in the transmission of the virus. It is not known how SBV was introduced to Europe and if SBV is present in countries outside of Europe. Thus, in this study, we conducted a serological screening for SBV antibodies in cattle (no. 79), sheep (no. 145) and goat (no. 141) in the Zambezia Province in Mozambique during September 2013. The results show a high percentage of antibody‐positive animals. All farms tested had seropositive animals; cattle displayed the highest prevalence with 100% positive animals. Sheep and goat also displayed high number of positive animals with a 43–97% and 72–100% within‐herd seroprevalence, respectively. This initial serological screening suggests that SBV is present on the African continent. However, cross‐reactivity with other members of the Simbu serogroup cannot be ruled out, and further studies are needed to identify and characterize the virus responsible for the antibody‐positive results.     

Coxiella burnetii Infections in Small Ruminants and Humans in Switzerland

The recent Q fever epidemic in the Netherlands raised concerns about the potential risk of outbreaks in other European countries. In Switzerland, the prevalence of Q fever in animals and humans has not been studied in recent years. In this study, we describe the current situation with respect to Coxiella (C.) burnetii infections in small ruminants and humans in Switzerland, as a basis for future epidemiological investigations and public health risk assessments. Specific objectives of this cross‐sectional study were to (i) estimate the seroprevalence of C. burnetii in sheep and goats, (ii) quantify the amount of bacteria shed during abortion and (iii) analyse temporal trends in human C. burnetii infections. The seroprevalence of C. burnetii in small ruminants was determined by commercial ELISA from a representative sample of 100 sheep flocks and 72 goat herds. Herd‐level seroprevalence was 5.0% (95% CI: 1.6–11.3) for sheep and 11.1% (95% CI: 4.9–20.7) for goats. Animal‐level seroprevalence was 1.8% (95% CI: 0.8–3.4) for sheep and 3.4% (95% CI: 1.7–6) for goats. The quantification of C. burnetii in 97 ovine and caprine abortion samples by real‐time PCR indicated shedding of >10⁴ bacteria/g in 13.4% of all samples tested. To our knowledge, this is the first study reporting C. burnetii quantities in a large number of small ruminant abortion samples. Annual human Q fever serology data were provided by five major Swiss laboratories. Overall, seroprevalence in humans ranged between 1.7% and 3.5% from 2007 to 2011, and no temporal trends were observed. Interestingly, the two laboratories with significantly higher seroprevalences are located in the regions with the largest goat populations as well as, for one laboratory, with the highest livestock density in Switzerland. However, a direct link between animal and human infection data could not be established in this study.     

Rift Valley Fever in Kruger National Park: Do Buffalo Play a Role in the Inter‐Epidemic Circulation of Virus?

Rift Valley fever (RVF) is a zoonotic mosquito‐borne virus disease of livestock and wild ruminants that has been identified as a risk for international spread. Typically, the disease occurs in geographically limited outbreaks associated with high rainfall events and can cause massive losses of livestock. It is unclear how RVF virus persists during inter‐epidemic periods but cryptic cycling of the virus in wildlife populations may play a role. We investigated the role that free‐living African buffalo (Syncerus caffer caffer) might play in inter‐epidemic circulation of the virus and looked for geographic, age and sex patterns of Rift Valley fever virus (RVFV) infection in African buffalo. Buffalo serum samples were collected (n = 1615) in Kruger National Park (KNP), South Africa, during a period of 1996–2007 and tested for antibodies to RVF. We found that older animals were more likely to be seropositive for anti‐RVFV antibody than younger animals, but sex was not correlated with the likelihood of being anti‐RVFV antibody positive. We also found geographic variation within KNP; herds in the south were more likely to have acquired anti‐RVFV antibody than herds farther north – which could be driven by host or vector ecology. In all years of the study between 1996 and 2007, we found young buffalo (under 2 years of age) that were seropositive for anti‐RVFV antibody, with prevalence ranging between 0 and 27% each year, indicating probable circulation. In addition, we also conducted a 4‐year longitudinal study on 227 initially RVFV seronegative buffalo to look for evidence of seroconversion outside known RVF outbreaks within our study period (2008–2012). In the longitudinal study, we found five individuals that seroconverted from anti‐RVFV antibody negative to anti‐RVFV antibody positive, outside of any detected outbreak. Overall, our results provide evidence of long‐term undetected circulation of RVFV in the buffalo population.     

Significant re‐emergence and recirculation of Schmallenberg virus in previously exposed dairy herds in Ireland in 2016

Schmallenberg virus (SBV) circulation was investigated in 25 previously exposed dairy herds in Ireland in 2016. A population of 1,550 spring‐2014‐born animals, which had been monitored for SBV infection in 2014 and 2015 as part of a previous SBV surveillance study, were resampled for evidence of SBV infection during 2016. A total of 366 blood samples were collected in the 25 study herds (15 samples per herd) between 3 March 2017 and 10 March 2017 (before the 2017 vector‐active season) and analysed for SBV antibodies using a competitive ELISA kit (IDVet). A total of 256 animals tested seropositive, an AP of 69.9% (95% CI: 65.1–74.4) and TP of 77.7% (95% CI: 72.3%–82.8%) when correcting for imperfect test characteristics. These results demonstrate that a new epidemic of SBV circulation occurred in these previously exposed herds in Ireland in 2016.     

Prevalence of Classical Swine Fever Virus in Domestic Pigs in South Korea: 1999–2011

The major policy for eradication of classical swine fever (CSF) in South Korea has focused on the implementation of compulsory vaccination of the susceptible pig population. A vaccine strain of CSF virus, the LOM strain, is used to maintain high herd seroconversion, a practice complementary to the ‘stamping‐out policy’ and restriction of animal movement during disease outbreaks. To survey for the prevalence of CSF in domestic pigs in South Korea over the past 13 years (1999–2011), we tested 4 193 782 and 1 162 645 samples for antibodies and antigens, respectively. Whereas seropositivity for CSF antibodies has been maintained at over 95% in the mainland, in Jeju Island, where no‐vaccination has been administered since 1999, seroprevalence has been below 1% during the last 3 years of study (2009‐2011). The highest number of outbreaks in South Korea occurred in 2002 and 2003; since then, outbreaks have decreased each year, with the last CSF outbreak recorded in 2009. No outbreaks have occurred during the past 3 years, and a high level of herd immunity has been maintained in the mainland pig population for 8 years; therefore, South Korea could now switch to a no‐vaccination policy throughout the country. However, the constant threat of the re‐emergence of the disease in the susceptible pig population should be the main consideration in planning and carrying out the last phase of the CSF eradication process.     

Likely Introduction Date of Schmallenberg Virus into France According to Monthly Serological Surveys in Cattle

To estimate the date of introduction of Schmallenberg virus (SBV) into France, the prevalence of antibodies against the virus was determined monthly in cattle from two northern departments from August 2011 to April 2012. Seropositive cattle were detected from October 2011 in both departments with a prevalence of 55.6% in the westernmost department (Meurthe‐et‐Moselle) and of 12.7% in the easternmost department (Manche). Schmallenberg virus seroprevalence then increased rapidly to high levels.     

Factors affecting Porcine Reproductive and Respiratory Syndrome virus time‐to‐stability in breeding herds in the Midwestern United States

The time needed to wean porcine reproductive and respiratory syndrome (PRRS) virus negative pigs consistently from a breeding herd after an outbreak is referred to as time‐to‐stability (TTS). TTS is an important measure to plan herd closure as well as to manage economic expectations. Weekly PRRS incidence data from 82 sow farms in six production systems located in the Midwestern United States were used for the analysis. The objective of this study was to evaluate the effect of recorded predictors on TTS in participant sow farms. The median TTS was 41.0 weeks (1st quartile 31.0 weeks–3rd quartile 55.0 weeks). In the final multivariable mixed‐effects Cox model, farms that experienced winter (hazard ratio (HR) 2.18, 95% confidence interval (CI) 1.28–3.70) and autumn (HR 1.91, 95% CI 1.16–3.13) PRRS outbreaks achieved stability sooner than farms that experienced PRRS outbreaks during summer. No statistically significant difference (p = 0.76) was observed between the TTS of farms that had a PRRS outbreak during spring and summer (HR 1.09, 95% CI 0.62–1.91). Additionally, farms that had a PRRS outbreak associated with a 1‐7‐4 restriction fragment length polymorphism (RFLP) cut pattern took significantly longer to achieve stability (HR 0.44, 95% CI 0.27–0.72) compared to farms which had a non‐1‐7‐4 PRRS outbreak. Finally, farms that had a previous PRRS outbreak within a year achieved stability sooner (HR 2.18, 95% CI 1.23–3.86) than farms that did not have a previous PRRS outbreak within a year. This study provides information that may result useful for planning herd closure and managing expectations about the time needed to wean PRRS virus negative pigs in breading herds according to the season of the year when the outbreak occurred and the RFLP cut pattern associated with the outbreak virus.