Abstract Book of EAVLD2012 - eavld congress 2012

S1 - K - 01
THE EMERGENCE OF SCHMALLENBERG VIRUS – HOW TO RESPOND TO NEW EPIZOOTICS IN
EUROPE
Wim H. M. van der Poel
Central Veterinary Institute of Wageningen University and Research Centre, Lelystad, The Netherlands, Tel. +31320238383, email:
wim.vanderpoel@wur.nl
Schmallenberg virus, epizootic, sheep, cattle, goat
The emergence of Schmallenberg virus
Schmallenberg virus was discovered in November 2011,
and named after the village in Germany where it was
first detected in blood samples from a dairy herd (1).
The provisionally named “Schmallenberg virus” is an
enveloped, negative-sense, segmented, single-stranded
RNA virus. It belongs to the Bunyaviridae family, within
the Orthobunyavirus genus. Schmallenberg virus is
related to the Simbu serogroup viruses, which also
includes ruminant viruses like Shamonda, Akabane,
Sathuperi, Douglas and Aino virus. Based on what is
already known about the genetically related Simbu
serogroup viruses, Schmallenberg virus affects domestic
ruminants. At its first occurrence in dairy cattle in both
Germany and The Netherlands Schmallenberg virus
infections presented with fever and reduced milk yield, in
the Netherlands also severe diarrhoea (2). In early
December 2011, congenital malformations were reported
in new-born lambs in the Netherlands, and
Schmallenberg virus was detected in and isolated from
the brain tissue. Thereafter the virus was also detected
in malformed calves and goat kids. Gross pathology in
malformed animals and stillbirths (calves, lambs, kids)
included arthrogryposis, hydrocephaly, brachygnathia
inferior, ankylosis, torticollis, scoliosis, hydranencephaly,
hypoplasia of the central nervous system, porencephaly
and subcutaneous oedema (3). The symptoms can be
summarised as arthrogryposis and hydranencephaly
syndrome (AHS). The spatial and temporal distribution
suggests that the disease is first transmitted by insect
vectors, in particular culicoides spp and then vertically in
utero. The detection of SBV in midges (culicoides spp) in
several countries supports this assumption.
The emergence of Schmallenberg virus in Europe
resulted in a rapid increase of malformations in new
borne lambs and later on calves. In spring 2012 the
numbers of cases started to decrease, first in sheep and
then in cattle. By May 2012 Schmallenberg virus had
affected farms in at least 8 countries in Western Europe,
and although the epidemic curve seemed to come to an
end by May 2012 a further spread over Europe still is
likely (4). Schmallenberg virus clearly causes severe
disease in ruminants and as a result economic losses
which may be enhanced by trade restrictions. As the
family of Bunyaviridae contains several important
zoonoses, studies were performed to elucidate its
zoonotic potential. In a rapid risk assessment in Dec
2011 it was concluded that human infections were
unlikely but could not be excluded. Therefore both in the
Netherlands and Germany serosurveys in the human
population were performed. In the Netherlands 301
persons exposed to SBV, farmers and veterinarians,
were tested and in North Rhine-Westphalia 60 cattle and
sheep farmers were tested. None of the tested
individuals showed antibody to SBV and it was concluded
that there is no evidence for zoonotic infection (5).
How to respond to new epizootics in Europe
The “Schmallenberg virus experience” again has shown
that the introduction of a completely new virus on the
continent can encompass an important threat to animal
health and public health. Moreover, continued changes in
human and animal demography, coupled with
environmental changes and changes within a virus itself
make it likely that the trend for increased viral disease
emergence will continue.
Strategies to improve veterinary and public health
protection with regard to emerging pathogens have
focused towards improved surveillance. Improved
detection of viruses in reservoirs, early disease outbreak
detection, or broadly based research to clarify important
factors that favour (re-)emergence. In order to recognize
and combat viral diseases, it is pivotal to understand the
epidemiology of these infections. We need to know the
pathogen, its vertebrate hosts and the methods of
transmission between these hosts. This should be
coupled with knowledge of spatio-temporal disease
patterns together with changes over time. Together,
these can be used to build a picture of the dynamic
processes involved in virus transmission that can be
used to account for observed disease patterns and
ultimately to forecast spread and establishment into new
areas.
Longitudinal veterinary surveillance should include food
producing animals as well as wildlife and also insect
vectors should be considered. A main goal of infectious
disease surveillance is the early detection of new
emerging pathogens. For this we will primarily be
dependant of clinicians and laboratories testing field
samples from potential reservoirs. Case reports will have
to be generated and combined to early detect new
emerging pathogens. Electronic systems, preferably
web-based, could be very helpful to achieve this. In
addition, improved detection may also be achieved
through use of syndromic approaches. Syndromic
surveillance, which collects non-specific syndromes
before diagnosis, has great advantages in promoting the
early detection of new emerging diseases before disease
confirmation. By combining syndromic surveillance with
case report surveillance in online reporting systems, a
sensitive early detection system for new emerging
diseases could be build.
Novel molecular methods, for example DNA microarrays
and whole genome approaches offer unprecedented
opportunities for rapid detection but these require
significant optimisation and validation before they can be
deployed broadly. Also due to costs limitations, the rapid
detection of a new virus will only be feasible by
employing the different molecular techniques, including
microarray, (RT)-PCR and whole genome sequencing, in
a sensible combination. By applying molecular
approaches, positive detections of a lot of different
pathogens in a lot of different samples have been
performed. However, it is much more difficult to proof
causation. The agent should be present at high
concentrations and seroconversion should be
demonstrated. Confidence in a causal relationship
between a candidate pathogen and a disease is
enhanced by fulfilment of Kochs’ Postulates (i.e.
demonstration of the presence of an agent in all cases of
a disease and not in the absence of disease, replication
of disease following ex vivo cultivation and introduction
into a naïve host); however, this will not always be
feasible. Apart from the fact that this can be extremely
time-consuming, some viruses cannot be cultured and
experimental infection can be extremely difficult.
Prompt detection and instigation of control measures
such as vaccination are crucial to prevent spread. Cloned