Resurgence of Schmallenberg virus in Belgium after 3 years of epidemiological silence Delooz Laurent1,2, Saegerman Claude2, Quinet Christian1, Petitjean Thierry1, De Regge Nick3, Cay Brigitte3
(1) Association Régionale de Santé et d’Identification Animales - ASBL, Département Santé Animale, B-5590 Ciney, Belgium
(2) Research Unit of Epidemiology and Risk Analysis applied to veterinary science (UREAR-ULg), Fundamental and Applied Research for Animals & Health (FARAH) Center, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium
(3) Veterinary and Agrochemical Research Centre (CODA-CERVA), Brussels, Belgium Keywords: Schmallenberg virus, SBV, Resurgence, Abortion, Cattle, Congenital, Malformations, Belgium.
Abstract
In spring 2016, three years after the last reported outbreak of Schmallenberg virus (SBV) in Belgium, an abortion was notified in a two year old Holstein heifer that previously had not been vaccinated against SBV. The autopsy of the eight-month-old malformed foetus revealed hydrocephalus, torticollis and arthrogryposis. Foetal brain tissue and blood were found to be SBV-positive by RT-PCR and ELISA test, respectively. Evidencing the circulation of SBV in Belgium in the autumn 2015 is important in order to anticipate future outbreaks and advise veterinarians about the risks associated with calving, as more bovine foetuses might have been infected.
SIR, - Schmallenberg virus (SBV) was discovered in November 2011 by the Friedrich Loeffler Institute (FLI, Germany) following the metagenomic analysis of a pool of blood samples from bovines originating from a farm in the town of Schmallenberg, Nordrhein Westphalia, Germany (Hoffmann et al., 2012). These analyses were carried out following the report by breeders and veterinarians from this region of a drop in milk production associated with hyperthermia, diarrhoea and abortions in cattle since August 2011 (Hoffmann et al., 2012). In January 2012, the virus was detected by RT-PCR conducted at the Belgian National Reference Laboratory (NRL) in Brussels on a large number of malformed bovine aborted foetuses originating from different regions in Belgium (Martinelle et al., 2012). The 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
emergence of this virus in Europe has caused a wave of abortions in cattle in 2012. It was estimated that 8.5% (95% CI: 7.7 to 9.4) of aborted foetuses presented lesions of the central nervous system and/or the musculoskeletal system (ARSIA, 2013) which were consistent with SBV infection (Herder et al., 2012). However, only a third of these suspected cases were found to be SBV-positive by RT-PCR. This could be explained by the fact that (i) these lesions are not specific to SBV infection, or (ii) the virus was no longer present in the foetus at the time of sampling due to the delay between infection and abortion (de Regge et al., 2013).
The last case of SBV infection in Belgium was confirmed by PCR on aborted foetal tissues on the 26th March 2013.
In 2014 and 2015, the rate of congenital abnormalities had remained low (1.7%; 95% CI: 1.4-1.9) and stable. While each reported abortion case was systematically screened for SBV infection by RT-PCR, no more cases of the disease were detected during this period. This may suggest that a large proportion of the Belgian cattle population had been previously exposed to SBV, and developed immunity against the virus (Méroc and collaborators in 2013).
On the 4th April 2016, 1105 days after the last reported case, a two-year old Holstein cow aborted in Lavaux Saint-Anne, province of Namur, Belgium. The eight-month-old malformed foetus was autopsied at the Regional Association for Animal Registration and Health (ARSIA). The cow was not vaccinated against SBV. The foetus presented with hydrocephalus, torticollis and arthrogryposis. Brain and blood were sampled and analysed by SBV-specific RT-PCR and ELISA tests, respectively. The RT-PCR performed at the Belgian NRL revealed the presence of viral RNA of SBV in the brain sample. In addition, the ELISA antibody test performed at ARSIA on maternal and foetal sera showed that the cow and its foetus were seropositive for SBV. Based on the date of abortion and the age of the aborted foetus, we estimated that the conception occurred in August 2015. Gross lesions of the foetus suggested that the infection occurred between the 60th and 100th day of pregnancy (Martinelle
et al., 2012). The cow had thus probably been infected in October or November 2015. The
virus circulated during this period, which is known to be the period of activity of the vector. This was further confirmed by the detection of SBV-specific antibodies in another cow and its new-born calf on the 11th April 2016. These animals were sampled before colostrum intake, and had not been vaccinated against SBV. The farm from which they originated was used as a sentinel to monitor the circulation of various pathogens, and was located 50 kilometres away from the farm where the abortion case described in this paper took place. Evidencing the circulation of SBV during the autumn 2015 in Belgium is important in order to anticipate 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68
future outbreaks and advise veterinarians about the risks associated with calving, as more bovine foetuses may have been infected during this period. These results confirm the
resurgence of the virus in Belgium (figure 1) as also observed in Germany in 2014 (Wernike
et al. 2015).
Insert Figure 1. Acknowledgements
We thank Wayne Anderson and Guillaume Fournie for the reading of this note. Figure caption
Figure 1: Geographical location of the two bovine herds found to be infected by SBV in 2016 Legend: The area represents the southern part of the Belgium subdivided in five different provinces. The two infected herds are located in the province of Namur.
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