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University of Liege - Faculty of Veterinary Medicine
Department of Infectious and Parasitic Diseases,
Fundamental and Applied Research on Animal and Health (FARAH)
Research Unit of Epidemiology and Risk Analysis Applied to Veterinary Sciences (UREAR-ULg)
Epidemiology of Schmallenberg virus in Belgium
and study of its pathogenesis in sheep
Epidémiologie du virus Schmallenberg en Belgique
et étude de sa pathogenèse chez le mouton
Antoine Poskin
THESE PRESENTEE EN VUE DE L’OBTENTION DU GRADE DE DOCTEUR EN SCIENCES
VETERINAIRES - ORIENTATION MEDECINE VETERINAIRE
Academic Year 2015–2016

University of Liege - Faculty of Veterinary Medicine
Department of Infectious and Parasitic Diseases,
Fundamental and Applied Research on Animal and Health (FARAH)
Research Unit of Epidemiology and Risk Analysis Applied to Veterinary Sciences (UREAR-ULg)
Veterinary and Agrochemical Research Centre (CODA-CERVA)
Operational Directorate Viral Diseases
Enzootic and (re)Emerging Diseases (ENZOREM)
Epidemiology of Schmallenberg virus in
Belgium and study of its pathogenesis in sheep
Antoine Poskin
Promoter:
Prof. Dr. Claude Saegerman
University of Liege - Faculty of Veterinary Medicine
Department of Infectious and Parasitic Diseases
Fundamental and Applied Research on Animal and Health (FARAH)
Research Unit of Epidemiology and Risk Analysis Applied to Veterinary Sciences (UREAR-ULg)
Co-promoter:
Ir. Brigitte Cay
Enzootic and (re)Emerging Diseases (ENZOREM)
Operational Directorate Viral Diseases
Veterinary and Agrochemical Research Centre (CODA-CERVA)

I would like to dedicate this manuscript to my lovely Emeline…

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ABSTRACT
During summer 2011, cattle presented severe hyperthermia combined with dropped
milk yield and diarrhoea from unknown origin. In October 2011, blood was collected from
cattle presenting these clinical signs in Schmallenberg, a small city in West Germany. A new
Orthobunyavirus, responsible for these unspecific clinical signs was identified and named
Schmallenberg virus (SBV). Upon November 2011, an epizootic outbreak of abortion,
stillbirths and malformed new-born was observed in bovine, ovine and caprine herds in
Europe due to transplacental transmission of SBV to the foetus. The SBV vectors are small
hematophagous midges of the gender Culicoides.
This work contributed to estimate the impact of the SBV epidemic in Belgium (Study
1). On the basis of farmer’s observations, between 0.5% and 4% of calves were aborted,
stillborn or malformed due to SBV in 2011-2012. Abortions and stillbirths were not clear
consequences of the SBV outbreak in cattle. In sheep, between 11% and 19% of lambs were
aborted, stillborn or malformed due to SBV in 2011-2012. Deformed animal was the most
important finding of SBV outbreak at herd level and an essential condition for the farmer to
send suspected samples to the National Reference Laboratory (NRL) for SBV analysis. The
results gathered from the study indicate that SBV surveillance and monitoring should be
implemented by SBV RNA detection with rRT-PCR in organs collected from stillborn and
deformed calves and lambs born in big herds.
The high impact of SBV highlighted in the Study 1 was putatively explained by
unknown host supporting the SBV activity. In this respect, the role of pigs had never been
evaluated. This was essential considering the suggested role of the domestic pigs in the life-
cycle of the SBV-closely related Akabane virus (AKAV) (Huang et al., 2003). The absence of
RNAemia after experimental infection of piglets with SBV realized in the Study 2 of the

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thesis suggests the absence of obvious role of domestic pigs in SBV life-cycle. The absence of
RNAemia is indeed a strong indication that further spread of SBV from the pigs to the
Culicoides during a blood meal of the vector is not likely to occur, therefore making
impossible an SBV transmission. The limited and temporary seroconversion observed after
SBV inoculation in only half of the inoculated piglets and the absence of seroconversion
reported in a limited number of field collected samples support this consideration.
To prevent SBV progression, it was crucial to further study the pathogenesis of SBV.
The Study 1 proved that the most important clinical impact of SBV was the consequence of
the malformed new-born; hereto it was particularly crucial to improve the knowledge on the
development of the SBV-related teratogenic effects. In this respect, experimental infection of
pregnant sheep with SBV constituted an appropriate research approach. An experimental
model was therefore essential to standardize. This thesis contributed to the standardization of
in vivo experiments (in collaboration with another working group) by determining the
minimum infectious dose of an SBV infectious inoculum. This reference infectious serum
must contain approximately 20 TCID50 to induce a homogeneous effective infection in sheep.
This dose is rather low and could be inoculated by a single Culicoides under natural
conditions. Beyond this minimum infectious dose, no dose dependent effect was observed in
productively inoculated ewes, either in the duration of the RNAemia, the quantity of SBV
RNA detected by rRT–PCR in the blood, or in the number of SBV RNA copies present in the
organs collected at necropsy.
The experimental model developed (partly) in the Study 3 was used to inoculate
pregnant ewes at day 45 and 60 of gestation, and increase the knowledge on SBV
transplacental transmission. The inoculation induced the persistence of SBV RNA in placental
organs until birth. Schmallenberg virus RNA was recovered from the organs collected at birth
from the lambs of both groups. However, the chance to obtain SBV RNA positive placental