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Reconstruction
of
the
Schmallenberg
virus
epidemic
in
Belgium:
Complementary
use
of
disease
surveillance
approaches
Antoine
Poskin
a,b
,
Léonard
Théron
c
,
Jean-Baptiste
Hanon
a
,
Claude
Saegerman
d
,
Muriel
Vervaeke
e
,
Yves
Van
der
Stede
a
,
Brigitte
Cay
b
,
Nick
De
Regge
b,
*
a
CODA-CERVA,
Coordination
of
Veterinary
Diagnostics
Epidemiology
and
Risk
Analysis,
Groeselenberg
99,
B-1180
Brussels,
Belgium
b
CODA-CERVA,
Operational
Directorate
Viral
Diseases,
Groeselenberg
99,
B-1180
Brussels,
Belgium
c
Faculty
of
Veterinary
Medicine,
University
of
Liège,
Clinic
Department
of
Production
Animals
(DCP),
Boulevard
de
Colonster,
20,
B42,
Quartier
Vallée
2,
Avenue
de
Cureghem
7A,
B-4000
Liège,
Belgium
d
Faculty
of
Veterinary
Medicine,
University
of
Liège,
Research
Unit
of
Epidemiology
and
Risk
Analysis
Applied
to
Veterinary
Sciences
(UREAR),
Boulevard
de
Colonster,
20,
B42,
Quartier
Vallée
2,
Avenue
de
Cureghem
7A,
B-4000
Liège,
Belgium
e
Agentschap
Natuur
en
Bos,
Koning
Albert
II-laan
20
bus
8,
B-1000
Brussels,
Belgium
A
R
T
I
C
L
E
I
N
F
O
Article
history:
Received
12
May
2015
Received
in
revised
form
19
November
2015
Accepted
27
November
2015
Keywords:
Schmallenberg
virus
Belgium
Surveillance
Epidemic
Recommandation
Perspectives
A
B
S
T
R
A
C
T
Schmallenberg
virus
(SBV)
emerged
across
Europe
in
2011
and
Belgium
was
among
the
first
countries
affected.
In
this
study,
published
findings
are
combined
with
new
data
from
veterinary
surveillance
networks
and
the
Belgian
reference
laboratory
for
SBV
at
the
Veterinary
and
Agrochemical
Research
centre
(CODA-CERVA)
to
reconstruct
the
epidemic
in
Belgium.
First
retrospective
cases
of
SBV
were
reported
by
veterinarians
that
observed
decreased
milk
yield
and
fever
in
dairy
cattle
in
May
2011.
The
number
of
SBV
suspicions
subsequently
increased
in
adult
cattle
in
August
2011.
That
month,
first
SBV
positive
pools
of
Culicoides
were
detected
and
extensive
virus
circulation
occurred
in
Belgium
during
late
summer
and
autumn
2011.
As
a
consequence,
most
pregnant
ruminants
were
infected
and
their
fetuses
exposed
to
the
virus.
This
resulted
in
an
outbreak
of
abortions,
still-births
and
malformed
new-borns
observed
between
January
and
April
2012.
The
number
of
cases
drastically
diminished
in
2012–2013,
although
multiple
lines
of
evidence
obtained
from
cross-sectional
serological
surveys,
analyses
on
aborted
foetuses,
sentinel
herd
surveillance
and
surveillance
of
SBV
in
vectors
prove
that
SBV
was
still
circulating
in
Belgium
at
that
time.
Virus
circulation
was
then
probably
strongly
reduced
in
2013–2014,
while
increasing
evidence
indicates
its
recirculation
in
2014–2015
in
Belgium.
Based
on
the
experience
gathered
with
the
closely
related
Akabane
virus,
recurrent
outbreaks
of
congenital
events
can
be
expected
for
a
long
period.
Vaccination
of
seronegative
animals
before
the
first
mating
could
be
used
to
prevent
the
deleterious
effects
of
SBV.
During
this
epidemic,
different
surveillance
approaches
including
syndromic
surveillance,
sentinel
herd
surveillance,
cross-sectional
seroprevalence
studies
and
pathogen
surveillance
in
vectors
have
proven
their
utility
and
should
be
considered
to
continue
in
the
future.
ã
2015
Elsevier
B.V.
All
rights
reserved.
1.
Introduction
During
summer
2011,
several
dairy
cattle
herds
in
Germany
presented
high
fever,
decreased
milk
yield
and
severe
diarrhea
from
unknown
origin.
In
September
2011,
blood
samples
were
collected
from
cattle
showing
these
symptoms
in
Schmallenberg,
a
small
city
located
in
Western
Germany
nearby
the
Dutch
and
Belgian
borders.
Metagenomic
analysis
identified
a
virus
that
was
probably
responsible
for
this
unspecific
syndrome
and
the
newly
emerged
virus
was
named
Schmallenberg
virus
(SBV)
(Hoffmann
et
al.,
2012).
Starting
from
November
2011,
a
wide
outbreak
of
aborted,
stillborn
and
malformed
new-borns
due
to
transplacental
infection
with
SBV
was
observed
in
cattle,
sheep
and
goat
(Garigliany
et
al.,
2012b).
The
teratogenic
effects
due
to
SBV
are
mostly
reported
to
affect
the
musculoskeletal
system:
arthrogryposis,
hydranencephly,
brachygnathia,
scoliosis,
kyphosis
or
lordosis
were
malformations
frequently
reported
during
the
epidemic
(Herder
et
al.,
2012).
Also
morphologically
normal
SBV
infected
animals
were
born
present-
ing
central
nervous
system
alterations,
mostly
porencephaly
and
*
Corresponding
author.
Tel.:
+32
2
379
05
80.
E-mail
address:
nick.deregge@coda-cerva.be
(N.
De
Regge).
http://dx.doi.org/10.1016/j.vetmic.2015.11.036
0378-1135/ã
2015
Elsevier
B.V.
All
rights
reserved.
Veterinary
Microbiology
183
(2016)
50–61
Contents
lists
available
at
ScienceDirect
Veterinary
Microbiology
journa
l
homepage:
www.e
lsevier.com/loca
te/vetmic
hydranencephaly
(Hahn
et
al.,
2013).
Lesions
due
to
SBV
in
peripheral
organs
were
only
demonstrated
in
muscle
and
consisted
in
myofibrillar
hypoplasia
(Seehusen
et
al.,
2014).
It
remains
unclear
if
the
muscular
alterations
are
the
consequence
of
primary
myositis
or
due
to
the
central
nervous
loss
inducing
denervation
and
alteration
of
muscle
development
(Herder
et
al.,
2012).
Sequencing
analysis
classified
SBV
in
the
family
Bunyaviridae,
genus
Orthobunyavirus
(Hoffmann
et
al.,
2012).
Orthobunyaviruses
are
enveloped
RNA
viruses
with
a
negative
sense,
single-stranded
genome.
The
genome
is
divided
in
3
segments
named
after
their
size
small
(S,
1
kb),
medium
(M,
4.5
kb)
and
large
(L,
6.9
kb)
respectively
(Elliott
and
Blakqori,
2011).
The
S-segment
encodes
a
non-structural
protein
(NSs)
and
the
nucleocapsid
protein
(N)
that
together
with
the
viral
RNA
forms
the
ribonucleoprotein
complex
(Elliott
and
Blakqori,
2011;
Yanase
et
al.,
2012).
The
M-segment
encodes
a
non-structural
protein
(NSm)
and
a
polyprotein
precursor
that
is
cleaved
in
2
glycoproteins
forming
the
basis
of
the
virus
envelope
(Gn
and
Gc)
(Doceul
et
al.,
2013).
Finally,
the
L-
segment
encodes
a
RNA-dependent
RNA
polymerase,
also
called
the
L-protein
(Elliott
and
Blakqori,
2011).
SBV
is
a
member
of
the
Simbu
serogroup
to
which
Aino
virus
(AINO),
Akabane
virus
(AKAV),
Douglas
virus
(DOUV),
Oropouche
virus
(ORO),
Sathuperi
virus
(SATV)
and
Shamonda
virus
(SHAV)
belong
(Hoffmann
et
al.,
2012).
Contradictory
results
have
been
published
on
the
origin
of
SBV.
First
sequencing
analysis
conducted
by
Hoffmann
et
al.
(2012)
identified
a
high
degree
of
homology
between
SBV
and
SHAV
S-
segment,
AINO
M-segment
and
AKAV
L-
segment.
Another
study
suggests
that
SBV
is
a
reassortant
between
SATV
M-segment
and
SHAV
S
and
L-segments
(Yanase
et
al.,
2012),
while
a
third
study
suggested
that
SBV
belongs
to
the
species
SATV
and
is
likely
to
be
the
ancestor
of
SHAV
(Goller
et
al.,
2012).
AKAV
is
probably
the
most
studied
virus
within
the
Simbu
serogroup.
Since
its
first
isolation
in
1958,
evidence
of
virus
presence
was
reported
in
four
continents:
Asia,
Oceania,
Europe
(Cyprus)
and
East-Africa
(Sellers
and
Herniman,
1981;
Al-Busaidy
et
al.,
1987;
Kono
et
al.,
2008).
The
last
known
emergence
of
the
more
restricted
SATV
and
SHAV
took
place
in
Japan
back
in
1999
and
2002,
respectively
(Yanase
et
al.,
2004,
2005).
SBV
was
therefore
the
first
Orthobunyavirus
of
veterinary
importance
to
emerge
in
continental
Europe
(Saeed
et
al.,
2001).
After
the
first
identification
in
Germany
in
August
2011,
SBV
spread
rapidly
and
widely
over
a
large
part
of
Europe.
SBV
infection
was
confirmed
in
at
least
one
herd
in
Belgium,
Denmark,
England,
France,
Italy,
Luxembourg,
the
Netherlands,
Poland,
Sweden,
Spain
and
Switzerland
by
August
2012
(EFSA,
2013).
The
Culicoides,
also
known
as
biting
midges,
are
small
hematophagous
insects
belonging
to
the
order
Diptera,
family
Ceratopogonidae
(Mellor
et
al.,
2000).
Culicoides
can
be
transmitted
over
long
distance
by
wind
(Hendrickx
et
al.,
2008)
what
most
probably
explains
the
virus
expansion
from
its
place
of
emergence
which
precise
location
remains
currently
unknown.
Much
indirect
evidence
supports
the
role
of
the
Culicoides
in
this
wide
expansion.
SBV
RNA
was
found
in
field-caught
Culicoides
in
many
countries
(EFSA,
2014).
In
this
context,
Culicoides
obsoletus,
Culicoides
scoticus,
Culicoides
chiopte-
rus
and
Culicoides
dewulfi
midges
have
been
proposed
to
be
putative
vectors
while
the
role
of
Culicoides
pulicaris,
Culicoides-
nubeculosus,
Culicoides
punctatus
and
Culicoides
imicola
remains
to
be
clarified
(De
Regge
et
al.,
2012;
Rasmussen
et
al.,
2012;
Elbers
et
al.,
2013a,b;
Goffredo
et
al.,
2013;
Larska
et
al.,
2013;
Balenghien
et
al.,
2014;
De
Regge
et
al.,
2014,
2015).
Different
seroprevalence
studies
carried
out
in
Europe
show
that
Belgium
was
one
of
the
first
and
most
SBV
affected
countries
(Elbers
et
al.,
2012;
EFSA,
2013;
Gache
et
al.,
2013;
Helmer
et
al.,
2013;
Méroc
et
al.,
2013a,b;
Veldhuis
et
al.,
2013;
Astorga
et
al.,
2014;
Méroc
et
al.,
2014;
Veldhuis
et
al.,
2014).
The
goal
of
this
manuscript
is
to
reconstruct
the
SBV
outbreak
in
Belgium
using
information
gathered
via
different
monitoring
approaches
that
were
simultaneously
conducted.
Published
findings
will
be
combined
with
unpublished
data.
Perspectives
for
future
SBV
circulation
will
be
discussed
and
recommendations
for
different
surveillance
strategies
and
preventive
measures
will
be
addressed.
2.
Material
and
methods
2.1.
Syndromic
surveillance
The
‘Veterinary
technical
Network:
Milk
Objective’
(RTVOL)
is
an
organization
hosted
by
the
Professional
Union
of
Veterinarians
(UPV)
in
southern
Belgium.
It
was
founded
in
2007
in
order
to
increase
communication
among
veterinarians
dedicated
to
milk
production
and
udder
health.
It
consists
of
a
free
mailing
list,
a
social
network
group
and
two
annual
forums.
Membership
is
voluntary,
but
controlled
through
verification
of
the
professional
status
of
the
participants.
The
members
are
mostly
field
practitioners,
but
the
network
also
includes
regional
lab
veter-
inarians,
specialists
working
at
the
veterinary
faculty,
and
technical
veterinarians
working
in
the
pharmaceutical
industry.
Sending
messages
and
questions
via
the
mailing
list
is
free,
and
can
be
commented
by
all
members
on
a
voluntary
basis.
The
coordinator,
originating
from
the
veterinary
faculty
of
Liège,
keeps
track
of
the
exchanges
in
order
to
keep
in
touch
with
the
needs
and
aspirations
of
field
practitioners,
leading
to
educational
and
scientific
proposals.
Between
260
and
430
emails
are
exchanged
each
year
with
a
seasonal
peak
between
January
and
May.
2.2.
Diagnostic
surveillance
at
the
Belgian
reference
laboratory
CODA-CERVA
is
the
Belgian
reference
laboratory
responsible
for
SBV
diagnosis
since
the
first
suspected
cases
in
fetuses
and
neonates
appeared
from
mid-December
2011
in
Belgium.
Follow-
ing
the
case
definition
of
EFSA
(2013)
this
means
fetuses
and
neonates
with
congenital
anomalies
classified
as
arthrogryposis
hydranencephaly
syndrome
(AHS)
(stillbirth,
premature
birth,
mummified
fetuses,
arthrogryposis,
hydranencephaly,
ataxia,
paralysis,
muscle
atrophy,
joint
malformations,
torticollis,
kypho-
sis,
scoliosis,
behavioral
abnormalities
and
blindness).
Although
SBV
has
never
been
declared
as
a
notifiable
disease,
samples
were
sent
to
us
in
the
context
of
an
existing
mandatory
notification
of
all
aborted
fetuses
in
cattle
(abortion
protocol).
All
samples
were
analysed
in
rRT-PCR
following
methods
described
in
De
Regge
et
al.
(2013).
Since
June
2012,
CODA-CERVA
also
regularly
received
serum
that
was
tested
for
the
presence
of
SBV
specific
antibodies
via
a
virus
neutralization
test
(VNT).
Details
on
this
test
can
be
found
in
De
Regge
et
al.
(2013).
Most
samples
originated
from
adult
cattle
present
in
artificial
insemination
centres
in
order
to
follow-up
their
status,
or
from
cattle
meant
to
be
exported.
Adult
animals
that
are
found
positive
in
VNT
(or
ELISA,
IFAT
or
PCR)
are
considered
as
confirmed
cases
(EFSA,
2013).
2.3.
Cross-sectional
seroprevalence
studies
Three
large
scale
cross-sectional
seroprevalence
studies
for
SBV
at
the
Belgian
level
have
been
supervised
by
CODA-CERVA:
two
after
the
first
vector
season
(end
2011-beginning
2012)
and
one
after
the
second
vector
season
(beginning
2013).
In
2011–2012,
11.635
cattle
sera
from
422
herds
stratified
by
province
and
following
the
average
age
distribution
of
Belgian
cattle
herds
(max.
40
samples
per
farm:
10
animals
of
6–12
months
of
age;
10
animals
of
12–24
months
of
age;
and
20
animals
>24
months
of
age)
were
tested.
Furthermore
1.082
sheep
sera
and
142
goat
sera
of
animals
A.
Poskin
et
al.
/
Veterinary
Microbiology
183
(2016)
50–61
51
>1
year
from
respectively
83
sheep
and
8
goat
herds
were
tested.
All
tests
were
done
with
the
commercial
ID
Screen
SBV
indirect
ELISA
kit
(IDVet,
Montpellier,
France).
In
2013,
the
same
kit
was
used
to
test
the
presence
of
SBV
specific
antibodies
in
7.130
serum
samples
from
188
cattle
herds,
again
stratified
by
province
and
following
the
average
age
distribution
as
described
above.
Details
can
be
found
in
Méroc
et
al.
(2013a,b,
2014).
No
further
cross-
sectional
seroprevalence
studies
were
performed
in
2014
or
2015.
2.4.
Surveillance
in
Culicoides
vectors
Two
large
scale
SBV
monitoring
studies
in
Culicoides
have
been
performed
in
vectors
collected
between
July
and
November
2011
and
between
May
and
November
2012,
respectively.
Culicoides
were
collected
with
Onderstepoort
Veterinary
Institute
(OVI)
traps
installed
at
different
locations
(16
in
2011
and
12
in
2012)
in
Belgium
covering
4
different
regions
(Antwerp,
Liège,
Gembloux
and
Libramont).
All
were
placed
in
the
near
vicinity
of
livestock
and
the
traps
were
operated
one
night
weekly
or
biweekly
depending
on
the
month.
All
Culicoides
were
morphologically
identified
till
at
least
subgenus
level.
A
total
of
7.305
female
midges
divided
over
480
pools
and
18.820
females
divided
over
973
pools
were
tested
in
rRT-PCR
in
2011
and
2012,
respectively.
More
details
can
be
found
in
De
Regge
et
al.
(2014,
2015).
No
monitoring
in
Culicoides
was
performed
in
2013,
2014
and
2015.
2.5.
Surveillance
in
wildlife
31
serum
samples
originating
from
wild
boar
shot
in
Flanders
(Belgium)
during
fall
and
winter
2012–2013
were
tested
in
VNT
to
check
for
the
presence
of
SBV
specific
antibodies.
Details
on
the
VNT
test
can
be
found
in
Poskin
et
al.
(2014a)
.
2.6.
Sentinel
herd
surveillance
To
our
knowledge,
the
only
sentinel
sheep
herd
that
has
been
closely
monitored
during
the
SBV
epidemic
in
Belgium
belongs
to
the
University
of
Namur.
The
flock
consists
out
of
400
ewes
and
about
20
rams.
They
were
sampled
monthly
or
bimonthly
during
2011
and
2012
(Claine
et
al.,
2013a,b).
2.7.
Statistical
analyses
Differences
between
the
ratios
of
SBV
confirmed
malformed
animals
by
rRT-PCR
to
the
number
of
suspected
cases
in
lambs
and
calves
submitted
to
the
reference
laboratory
between
different
seasons
of
the
epidemic
were
assessed
with
two-sided
Fischer
exact
tests.
Statistical
analysis
was
performed
using
SPSS
Statistics
V22.0
(IBM)
software
and
P
values
<
0.05
were
considered
to
be
significant.
3.
Results
The
following
paragraphs
summarize
findings
of
the
SBV
epidemic
in
Belgium
during
2011-2015.
This
time
span
was
divided
in
four
time
periods
(seasons
1–4)
ranging
each
from
May
till
April
of
the
next
year.
This
coincides
with
the
beginning
of
the
Culicoides
vector
season
and
the
end
of
the
peak
period
of
SBV
associated
congenital
malformations
induced
by
infection
during
that
vector
season
(Fig.
1).
Fig.
1.
Fifteen
key
observations
summarizing
the
SBV
epidemic
in
Belgium.
The
review
was
structured
in
four
seasons
of
one
year
each
(from
May
to
April
onwards).
The
beginning
of
this
season
corresponds
to
the
beginning
of
the
vector
period
and
the
end
with
the
drop
of
the
peak
of
congenital
malformations
induced
by
infections
during
that
vector
season.
The
observations
are
classified
according
to
the
surveillance
method
that
contributed
to
the
understanding
of
the
epidemic:
syndromic
surveillance,
vector
surveillance,
cross-sectional
seroprevalence
studies
and
sentinel
herd
surveillance.
Abbreviations
used
in
the
figure
are
rRT-PCR,
real-time
reverse
transcriptase
polymerase
chain
reaction;
SBV,
Schmallenberg
virus;
VNT,
virus
neutralization
test.
52
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50–61
3.1.
May
2011–April
2012:
emergence
of
SBV
in
Belgium
3.1.1.
Clinical
suspicions
of
SBV
Three
veterinarians
of
a
veterinary
surveillance
network
for
dairy
production
called
“Réseau
Technique
Vétérinaire
Objectif
Lait”
(RTVOL)
reported
cases
of
milk
drop
syndrome
of
unknown
origin
that
started
mid-May
2011.
Intriguingly,
the
symptoms
were
simultaneously
observed
at
three
different
places
in
the
Walloon
region
of
Belgium:
Somzée,
Julémont
and
Fléron
(Fig.
2).
The
symptoms
reported
by
the
veterinarians
consisted
of
high-
hyperthermia,
generally
above
40.5
C
and
up
to
41.3
C,
and
a
drop
of
milk
production,
without
any
other
remarkable
symptom.
Treatments
with
non-steroidal
anti-inflammatory
drugs
and
antibiotics
remained
without
satisfactory
results
and
subsequent
diagnostic
investigations
were
unsuccessfully
oriented
to
ehrlichi-
osis
and
heat-stress.
Retrospectively,
the
syndrome
observed
by
the
veterinarians
probably
represents
the
first
cases
of
SBV
in
Belgium,
even
though
this
could
not
be
strictly
confirmed
because
blood
samples
were
no
longer
available
(Théron,
unpublished
data).
The
emergence
of
SBV
in
Belgium
at
that
time
is
further
supported
by
putative
SBV
cases
reported
by
a
cattle
farmer
in
May
2011
and
a
veterinarian
in
July
2011,
as
revealed
in
retrospective
studies
(Martinelle
et
al.,
2014;
Poskin
et
al.,
2015a,b).
One
should
however
be
careful
to
attribute
these
symptoms
solely
to
SBV
without
a
confirmed
diagnosis
and
also
other
causes
inducing
high
temperature
and
drop
of
milk
production
should
be
considered.
The
number
of
notifications
of
milk
drop
syndrome
and
diarrhea
from
unknown
origin
increased
in
August
and
September
2011
at
the
Belgian
regional
Animal
Health
Care
centres
(ARSIA
and
DGZ)
(De
Regge
et
al.,
2012).
Based
on
the
birth
of
malformed
lambs
and
calves,
most
SBV
suspicions
were
afterwards
reported
between
January
and
February
2012
by
sheep
famers
and
between
March
and
April
2012
by
cattle
farmers
(Poskin
et
al.,
2015a).
3.1.2.
rRT-PCR
confirmation
of
SBV
circulation
in
livestock
in
2011–
2012
The
earliest
detection
of
SBV
in
Belgium
via
real-time
polymerase
chain
reaction
(rRT-PCR)
in
animal
hosts
was
done
on
samples
from
adult
cattle
showing
fever
and
milk-drop
syndrome
in
September
and
October
2011
and
in
3
sheep
belonging
to
a
sentinel
herd
surveillance
of
the
University
of
Namur
on
September
6th,
2011
(ProMED-Mail,
20120117.1012402;
Claine
et
al.,
2013b).
The
first
PCR
detection
of
SBV
in
a
lamb
born
with
signs
of
malformations
due
to
SBV
was
reported
later
on
December
23th,
2011
(ProMED-Mail,
20111223.3665).
During
the
first
season
of
the
epidemic,
after
optimization
of
the
diagnostic
technique
(De
Regge
et
al.,
2013),
CODA-CERVA
received,
from
November
2011
onwards,
1282
suspected
samples
from
aborted
cattle
for
SBV
analysis
of
which
353
were
positive.
In
sheep,
499
samples
from
SBV
suspected
aborted
lambs
were
submitted
of
which
267
were
positive
(Fig.
3).
The
high
number
of
rRT-PCR
analyses
made
at
CODA-CERVA
at
the
beginning
of
2012
reflects
the
high
number
of
abortions,
still-births
and
malformed
new-borns
that
Belgian
farms
encountered
due
to
SBV
at
that
time
(Poskin
et
al.,
2015a).
The
observation
of
numerous
SBV
cases
at
the
beginning
of
2012
is
also
supported
by
different
studies
reporting
SBV
detection
from
January
2012
onwards.
SBV
RNA
was
identified
in
10
lambs
at
the
University
of
Namur
in
January
2012
(Kirschvink
et
al.,
2012).
In
the
same
period,
SBV
presence
was
confirmed
in
a
Fig.
2.
Important
locations
for
the
reconstruction
of
the
SBV
epidemic
in
Belgium.
Provinces
in
Flanders
(North
of
Belgium)
are
indicated
in
light-gray,
provinces
in
Wallonia
(South
of
Belgium)
are
white.
Cities
that
are
relevant
for
the
purpose
of
this
review
are
indicated
by
dots
in
open
circles.
The
superposed
dark
gray
zone
over
Wallonia
represents
the
approximate
location
of
the
Ardennes,
an
upland
region
largely
covered
with
dense
forest.
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50–61
53
calf
born
at
term
with
porencephaly
in
Hamois-en-Condroz
(Fig.
2),
and
identified
via
rRT-PCR
and
next-generation
sequencing
in
brain
tissue
from
two
aborted
lambs
born
on
January
13th
and
18th,
2012
(Garigliany
et
al.,
2012a;
Rosseel
et
al.,
2012).
At
the
University
of
Liège
(Fig.
2),
15
calves
that
were
deformed
or
died
without
obvious
reason
were
received
during
January
to
March
2012,
and
all
scored
positive
in
rRT-PCR
for
SBV
(Bayrou
et
al.,
2014).
3.1.3.
Seroprevalence
in
Belgium
in
2011–2012
A
limited
number
of
sera
from
adult
cattle
collected
in
spring
2010
(n
=
71)
and
during
the
first
quarter
of
2011
(n
=
40)
were
negative
for
SBV
antibodies
(Garigliany
et
al.,
2012c).
A
retrospec-
tive
study
analysing
the
sera
from
a
sentinel
sheep
flock
of
about
400
ewes
and
20
rams
that
belongs
to
the
University
of
Namur
(Fig.
2)
revealed
that
a
first
seroconversion
occurred
in
September
2011
and
that
the
seroprevalence
increased
strongly
thereafter
resulting
in
a
seroprevalence
of
99%
(n
=
422)
in
January
2012
(Claine
et
al.,
2013a,b).
Three
large-scale
cross-sectional
seroprevalence
studies
were
conducted
in
Belgian
farms
at
the
end
of
the
first
vector
season.
The
first
study
was
carried
out
on
422
cattle
farms
between
January
2nd,
2012
and
March
7th,
2012.
By
that
time
the
between-herd
seroprevalence
had
already
reached
99.8%
and
the
within-herd
seroprevalence
was
86.3%
(Méroc
et
al.,
2013a).
The
second
study
was
conducted
on
83
sheep
flocks
and
8
goat
farms
that
were
sampled
between
November
4th,
2011
and
April
4th,
2012.
A
between-herd
seroprevalence
of
98%
and
a
within-herd
seroprev-
alence
of
85.1%
were
found
in
sheep.
In
goat,
the
within-herd
seroprevalence
was
40.7%
(Méroc
et
al.,
2014).
In
a
third
study,
cattle
sera
were
collected
in
209
farms
from
the
Walloon
region
between
February
13th,
2012
and
April
22nd,
2012.
A
seropreva-
lence
of
90.8%
was
found
(Garigliany
et
al.,
2012c).
Interestingly,
different
seroprevalence
studies
indicated
a
lower
SBV
circulation
among
both
cattle
and
sheep
during
the
first
season
of
the
epidemic
in
the
Ardennes.
This
is
an
upland
region
in
the
south
of
Belgium
(Fig.
2),
largely
covered
with
dense
forest
neighboring
pastures.
It
usually
has
a
prolonged
winter
and
temperature
is
lower
compared
to
the
rest
of
the
country
(Méroc
et
al.,
2013a,
2014),
suggesting
that
factors
like
altitude,
tempera-
ture,
rainfall,
host-availability
and
landscape
related
parameters
has
an
impact
as
has
been
suggested
before
for
BTV
transmission
(Pioz
et
al.,
2012;
Faes
et
al.,
2013).
Taken
together,
seroprevalence
studies
support
a
massive
virus
expansion
in
Belgium
between
the
end
of
the
summer
2011
and
the
beginning
of
2012.
This
demonstrates
the
remarkable
expansion
capacity
of
SBV.
The
high
seroprevalence
observed
after
the
2011–2012
season
suggested
that
a
comparable
circula-
tion
and
spread
would
be
impossible
the
following
years.
3.1.4.
SBV
impact
in
wildlife
and
other
species
SBV
infection
is
not
restricted
to
domestic
livestock.
Also
wildlife
was
shown
to
be
affected.
First
seroconversions
were
observed
during
autumn
2011
in
Belgium.
The
seroprevalence
was
evaluated
in
deer
shot
during
the
hunting
seasons
of
2010
and
2011
in
the
different
provinces
of
the
Walloon
Region
(Fig.
2).
All
sera
collected
in
2010
were
seronegative
while
seroprevalence
was
47%
in
red
deer
(54/116)
Fig.
3.
Number
of
SBV
suspected
samples
from
aborted
fetuses
of
cattle
and
sheep
monthly
submitted
to
CODA-
CERVA
for
rRT-PCR
diagnosis
between
November
2011
and
April
2015
in
(a)
cattle
(n
=
2419)
and
(b)
sheep
(n
=
535).
54
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183
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50–61
and
48%
in
roe
deer
(52/109)
in
sera
collected
in
winter
2011
(Linden
et
al.,
2012).
Desmecht
et
al.
(2013)
studied
the
seroprevalence
in
wild
boars
from
Walloon
region.
Wild
boars
were
seronegative
in
fall
2010
but
reached
seroprevalence
of
27%
in
2011.
This
decreased
to
11%
in
2012.
At
CODA-
CERVA,
31
serum
samples
originating
from
wild
boar
shot
in
Flanders
region
(Fig.
2)
during
fall
and
winter
2012-2013
were
tested
in
VNT.
This
revealed
a
low
seroprevalence
of
4%.
The
role
of
dogs,
poultry
and
domestic
pigs
as
potential
hosts
for
SBV
was
assessed
in
Belgium
but
these
showed
to
play
only
a
minor
role
in
SBV
epidemiology
since
only
low
seroconversion
was
observed
in
few
individuals
and
no
viraemia
has
been
reported
so
far
(Garigliany
et
al.,
2013;
EFSA,
2014;
Poskin
et
al.,
2014a).
These
studies
show
that
deer
and
wild
boars
became
infected
with
SBV
and
therefore
could
act
as
a
potential
reservoir
that
helps
the
virus
in
its
massive
expansion.
The
exact
role
of
these
species
remains
however
to
be
clearly
determined.
3.1.5.
SBV
in
Belgian
Culicoides
in
2011–2012
Besides
monitoring
in
host
species,
SBV
has
also
been
monitored
in
its
Culicoides
vector.
The
Culicoides
were
collected
throughout
2011
with
‘Onderstepoort
Veterinary
Institute’
(OVI)
traps
located
in
the
regions
of
Antwerp,
Liege,
Gembloux
and
Libramont
(Fig.
2).
A
total
of
7305
Culicoides
were
pooled
and
tested
for
SBV
presence
in
Culicoides’
heads
via
rRT-PCR
(De
Regge
et
al.,
2015).
The
absence
of
SBV
in
Culicoides,
collected
before
August
2011,
supports
the
indications
described
above
and
confirms
that
only
limited
virus
circulation
occurred
during
early
summer
2011.
SBV
positive
pools
containing
midges
collected
between
August
10th,
2011
and
October
28th,
2011
were
found
confirming
SBV
circulation
at
that
time.
In
Liège,
half
of
the
pools
containing
midges
collected
in
October
2011
were
found
positive,
leading
to
a
minimum
infectious
rate
(MIR)
in
C.
obsoletus
complex
of
3.1%.
Similarly,
a
MIR
of
3.6%
in
C.
obsoletus
s.s.
midges
was
found
in
Antwerp
in
September
2011
(De
Regge
et
al.,
2015).
In
contrast,
only
one
positive
pool
containing
midges
collected
on
October
11th,
2011
was
found
in
Gembloux
and
no
positive
pools
were
found
in
Libramont
(De
Regge
et
al.,
2015).
The
absence
of
positive
Culicoides
at
Libramont,
which
is
located
in
the
south
of
the
country
(Fig.
2),
correlates
with
the
lower
virus
circulation
in
the
Ardennes
during
the
season
2011–2012
as
observed
in
cross-sectional
seroprevalence
studies
(Méroc
et
al.,
2013a,
2014).
3.2.
May
2012–April
2013:
second
SBV
season
3.2.1.
Recirculation
of
SBV
in
Belgium
in
2012–2013
Considering
the
seroprevalence
measured
after
the
first
vector
season,
it
was
expected
that
recirculation
of
SBV
would
preferen-
tially
be
observed
in
the
Ardennes
area
(Fig.
2)
where
seropreva-
lence
was
lower.
The
first
evidence
for
recirculation
was
found
in
the
sentinel
sheep
herd
of
the
University
of
Namur.
Fifty
lambs
were
monitored
between
April
and
October
2012
and
blood
was
collected
twice
a
month.
Three
animals
were
found
SBV
positive
by
rRT-PCR
on
July
27th,
2012.
Most
rRT-PCR
positive
results
were
observed
between
August
8th
and
October
3rd,
2012
and
all
lambs
monitored
during
the
study
had
been
infected
before
October
17th,
2012
(Claine
et
al.,
2013a).
At
CODA-CERVA,
the
first
SBV
positive
sample
from
an
aborted
animal
for
the
second
season
of
the
epidemic
was
received
only
on
November
13th,
2012.
The
sample
originated
from
a
sheep
farm
located
in
the
very
South
of
the
country,
in
the
city
of
Chassepierre
(Fig.
2).
While
this
herd
had
been
spared
from
SBV
during
the
first
season
of
the
epidemic,
it
went
through
a
severe
SBV
episode
of
congenital
malformations
that
lasted
3
weeks.
The
farmer
reported
120
gestations
meaning
that
223
lambs
were
expected
that
year
taking
1.86
expected
lambs
per
gestation
(Saegerman
et
al.,
2014).
In
total,
7%
of
still-births
lambs
(15/223)
plus
7%
of
deformed
lambs
(15/223)
were
reported
(Poskin
et
al.,
unpublished
data).
0
20
40
60
80
100
120
140
160
180
200
220
Nb of
VNT/month
Month of analysis
Positive
Negative
Fig.
4.
Number
of
bovine
serum
samples
analysed
each
month
between
November
2011
and
April
2015
for
the
presence
of
SBV-specific
antibodies
with
virus
neutralization
test
(VNT)
(n
=
1101).
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183
(2016)
50–61
55
After
these
first
cases
in
Chassepierre,
831
and
only
24
SBV
suspected
samples
from
aborted
cattle
and
lambs,
respectively,
were
received
for
rRT-PCR
analysis
at
CODA-CERVA,
of
which
114
and
2
scored
positive.
The
ratio
of
confirmed
cases
in
the
second
season
was
significantly
lower
than
during
the
first
season
of
the
epidemic
and
this
for
both
calves
(27.5%
vs
13.7%;
P
<
0.0001)
and
lambs
(53.5%
vs
8.3%;
P
<
0.0001).
Most
of
these
positive
SBV
samples
were
received
between
January
and
March
2013
(Fig.
3).
In
Liege,
(Fig.
2)
only
a
limited
number
of
12
calves
highly
suspected
of
SBV
infection
were
presented
between
January
and
February
2013,
and
3
were
found
SBV
positive
in
rRT-PCR
(Bayrou
et
al.,
2013).
The
decrease
in
the
number
of
SBV
suspected
malformed
animals
reported
to
the
authorities
in
2012–2013
(from
1282
to
831
in
cattle
and
from
499
to
24
in
sheep)
and
in
the
ratio
of
confirmed
cases
(see
above)
indicates
a
more
limited
virus
circulation
compared
to
the
first
season.
It
must
however
be
emphasized
that
SBV
has
never
been
a
notifiable
disease
in
Belgium
and
that
no
compensation
has
been
given
to
the
farmers
for
SBV
positive
malformed
lambs
or
calves.
It
is
hypothesized
that
farmers
and
veterinarians
did
not
send
all
SBV
suspected
cases
for
diagnostic
identification.
Although
reporting
of
aborted
calves
and
lambs
is
mandatory
in
Belgium
and
SBV
is
routinely
investigated
as
a
potential
cause
for
the
abortion,
it
is
estimated
that
less
than
1
out
of
30
aborted
animals
is
reported
(Delooz
et
al.,
2011).
Consequently,
the
real
number
of
SBV
cases
observed
during
the
second
season
of
epidemic
was
probably
underestimated.
3.2.2.
Seroprevalence
in
Belgium
in
2012–2013
Since
only
a
limited
number
of
samples
from
SBV
suspected
malformed
animals
were
received
for
analysis
in
rRT-PCR,
seroprevalence
studies
were
a
better
tool
to
evaluate
virus
circulation
in
2012–2013.
First
VNT
were
conducted
at
CODA-CERVA
from
June
2012
onwards.
The
vast
majority
of
the
samples
received
at
that
time
were
positive
(Fig.
4)
and
most
probably
represent
antibody
persistence
due
to
infection
during
the
first
season
of
the
epidemic
(Elbers
et
al.,
2014).
Evidence
of
renewed
virus
circulation
was
found
in
the
sheep
flock
belonging
to
the
University
of
Namur
(Fig.
2).
Seroconversion
of
naive
ewes
occurred
starting
from
July
2012
(Claine
et
al.,
2013a)
and
the
VNT
values
measured
in
previously
immunized
ewes
increased
between
February
2012
and
February
2013
suggesting
a
“booster
effect”
due
to
reinfection
during
the
second
season
of
SBV
circulation
(Claine
et
al.,
2013c).
More
conclusive
results
were
obtained
via
a
nation-wide
follow-
up
cross-sectional
serological
survey
in
188
Belgian
herds
between
January
and
February
2013.
The
between-herd
seroprevalence
was
estimated
to
be
100%
in
the
entire
cattle
population,
while
the
mean
within-herd
seroprevalence
was
65.7%
indicating
a
substan-
tial
decrease
compared
to
2011–2012
(Méroc
et
al.,
2013b).
This
decrease
was
merely
due
to
the
fact
that
a
low
seroprevalence
of
only
20,6%
was
found
in
calves
of
6–12
months
old.
The
positive
results
in
animals
born
after
the
first
season
of
the
epidemic
indicate
a
re-circulation
of
SBV
during
the
second
season
of
the
epidemic,
but
to
a
lower
extent
than
the
circulation
that
occurred
during
2011
(Méroc
et
al.,
2013a,
2013b).
It
can
however
not
be
excluded
that
the
antibodies
detected
in
a
part
of
these
seropositive
animals
in
this
age
category
originate
from
an
infection
in
utero
or
represent
remaining
maternal
antibodies
that
have
been
passed
from
the
cow
to
its
calve
via
colostrum
(Méroc
et
al.,
2013b),
certainly
since
maternal
SBV
specific
antibodies
have
been
shown
to
persist
for
up
to
6
months
(Elbers
et
al.,
2014).
In
conclusion,
the
seroprevalence
studies
support
the
occur-
rence
of
a
new
virus
circulation
in
2012–2013
and
they
further
confirm
that
animals
infected
under
natural
conditions
remain
protected
over
a
long
period
of
time.
3.2.3.
SBV
in
Belgian
Culicoides
in
2012–2013
A
study
whereby
SBV
was
monitored
in
Culicoides
collected
in
2012
with
12
OVI
traps
located
in
Antwerp,
Liege,
Gembloux
and
Libramont
(Fig.
2)
allowed
to
study
whether
the
lower
virus
circulation
observed
in
seroprevalence
studies
was
correlated
with
a
lower
circulation
of
SBV
in
the
Culicoides
population.
Culicoides
were
collected
between
May
2012
and
November
2012
and
analysed
for
SBV
RNA
presence
with
rRT-PCR.
Positive
pools
were
found
in
all
studied
regions,
but
remarkably
only
in
the
month
of
August.
The
MIR
of
0.4%,
0.3%
and
0.2%
in
Antwerp,
Gembloux
and
Liege,
respectively,
in
the
subgenus
Avaritia
were
clearly
lower
than
those
observed
the
previous
year
(De
Regge
et
al.,
2012,
2014).
In
contrast,
the
MIR
was
2.86%
and
3.26%
in
the
subgenera
Avaritia
and
Culicoides,
respectively,
in
the
South
of
the
country
in
Libramont
(De
Regge
et
al.,
2014).
These
results
correlate
with
the
increase
of
seroprevalence
observed
in
the
Ardennes
after
the
first
episode
of
2011-2012
(Méroc
et
al.,
2013b)
and
with
the
outbreak
observed
in
Chassepierre
in
2012-2013.
These
results
show
that
virus
surveillance
in
vectors
is
an
interesting
and
powerful
tool
to
study
the
SBV
epidemic
and
was
complementary
to
seroprevalence
and
virus
detection
studies
in
host.
The
fact
that
SBV
infected
Culicoides
were
only
found
in
August
indicate
however
that
this
surveillance
has
to
be
performed
continuously.
3.3.
May
2013–April
2014:
third
season
of
the
epidemic
In
2013–2014,
less
effort
was
done
to
follow
the
SBV
situation
in
Belgium.
No
seroprevalence
studies
were
carried
out
and
the
presence
of
SBV
in
Culicoides
was
no
longer
monitored.
Only
a
low
number
of
SBV
suspected
samples
from
aborted
animals
(161
cattle
samples
and
2
sheep
samples)
were
received
at
CODA-CERVA
for
SBV
rRT-PCR
analysis,
and
all
samples
were
found
negative
(Fig.
3).
This
indicates
a
significant
decrease
in
the
ratio
of
confirmed
cases
in
aborted
calves
compared
to
2012–2013
(13.7%
vs
0%:
P
<
0.0001),
while
this
cannot
be
concluded
for
lambs
due
to
the
limited
amount
of
submitted
samples
(8.3%
vs
0%:
P
=
1).
Similarly,
few
sera
were
received
for
VNT,
and
only
a
low
number
(52
out
of
230
samples
analysed
in
cattle
and
1
out
of
3
in
sheep)
was
positive
(Fig.
4).
These
elements
support
the
hypothesis
that
the
number
of
cases
was
drastically
reduced
compared
to
the
two
previous
seasons
due
to
a
lower
virus
circulation
in
2013–
2014.
Again,
since
no
clear
incentive
was
present
for
the
farmers
to
send
in
suspected
samples,
it
can
be
strongly
suspected
that
not
all
SBV
suspected
samples
were
submitted
to
the
authorities,
potentially
leading
to
an
underestimation
of
SBV
circulation
and
its
impact.
3.4.
May
2014–April
2015:
fourth
season
of
epidemic
As
in
2013–2014,
no
specific
SBV
surveillance
was
put
in
place
in
2014–2015.
Interestingly,
Germany
and
the
Netherlands
reported
renewed
SBV
circulation
(ProMED-Mail,
20141121.2978286).
Given
the
presumed
low
virus
circulation
in
Belgium
in
2013-2014
and
the
associated
increase
of
the
number
of
susceptible
seronegative
livestock,
it
was
expected
that
SBV
circulation
would
then
also
have
occurred
in
Belgium.
However,
no
SBV
PCR
positive
results
in
tissues
from
suspected
aborted
animals
(n
=
145
in
cattle
and
10
in
sheep)
have
been
found
for
the
4th
season
of
epidemic
at
CODA-
CERVA.
A
substantial
increase
of
the
number
of
VNT
positive
samples
was
even
though
observed
in
January
2015
(55
positive
samples
out
of
66
analyses)
(Fig.
4).
Although
this
increase
is
suggestive
of
a
virus
circulation
in
Belgium
at
the
end
of
summer
and
in
autumn
2014,
it
cannot
be
excluded
that
these
positive
samples
are
the
consequence
of
infections
that
occurred
between
2011
and
2013
knowing
that
SBV
antibodies
produced
after
natural
56
A.
Poskin
et
al.
/
Veterinary
Microbiology
183
(2016)
50–61
infection
are
known
to
persist
for
long
times
in
both
cattle
and
sheep
(Elbers
et
al.,
2014;
Poskin
et
al.,
2015b).
4.
Discussion
4.1.
Time
of
SBV
introduction
in
Belgium
Based
on
all
available
data,
the
detection
of
SBV
by
rRT-PCR
in
a
pool
of
Culicoides
collected
at
August
10th
2011
is
the
first
confirmed
detection
of
SBV
in
Belgium.
SBV
presence
was
later
on
confirmed
by
its
detection
in
blood
samples
from
adult
cattle
and
sheep
collected
in
September
and
October
and
the
massive
seroconversion
of
cattle,
sheep
and
wildlife
around
that
time.
This
indicates
that
that
the
first
extensive
circulation
of
SBV
occurred
during
late
summer
and
early
autumn
of
2011.
It
was
only
some
months
later
that
we
were
confronted
with
abortion
storms
of
malformed
fetuses
which
peaked
between
December
2011-
January
2012
for
sheep
and
between
March-May
2012
for
cattle.
The
latter
indicates
that
only
infection
of
pregnant
animals
during
the
first
third
of
gestation
eventually
leads
to
congenital
confirmations.
Otherwise
it
could
be
expected
that
we
would
have
been
confronted
with
malformed
fetuses
earlier
after
virus
circulation
(from
pregnant
animals
that
were
in
a
later
phase
of
gestation
at
the
moment
of
infection).
This
seems
to
be
in
line
with
observations
done
for
the
related
AKAV
(Parsonson
et
al.,1988)
and
with
the
fact
that
SBV
seems
to
colonize
the
placenta
of
sheep
when
experimentally
infected
during
the
first
2
months
of
gestation
(Martinelle
et
al.,
2015).
Most
probably,
the
virus
had
been
introduced
in
Belgium
earlier
in
2011
and
was
circulating
at
low
levels
as
suggested
by
reports
of
SBV
related
symptoms
in
adult
cattle
by
syndromic
surveillance
networks
from
May
2011
onwards.
This
low
level
of
circulation
has
however
not
been
detected
in
retrospective
monitoring
studies
in
vectors
and
seroprevalence
studies,
most
probably
due
to
the
limited
amount
of
samples
that
were
collected
and
tested
before
the
summer
of
2011
(De
Regge
et
al.,
2015;
Garigliany
et
al.,
2012c).
4.2.
Overwintering
process
of
SBV
in
Belgium
The
recovery
of
viraemic
sheep
in
Germany
during
winter
2011–2012
evidenced
the
persistence
of
SBV
during
the
winter
season
(Wernike
et
al.,
2013b).
Also
the
increase
in
seroprevalence
observed
in
Belgium
between
February
and
April
2012
suggested
SBV
circulation
during
winter
(Garigliany
et
al.,
2012c).
The
actual
mechanism
by
which
SBV
persists
during
winter
stays
however
poorly
understood.
Wilson
et
al.
(2008)
proposed
four
potential
overwintering
strategies
for
BTV,
and
all
seem
transposable
to
SBV.
A
first
option
is
that
SBV
overwinters
in
adult
midges
that
survive
during
winter.
This
has
recently
been
suggested
as
the
most
probable
overwintering
mechanism
of
BTV
in
California
(Mayo
et
al.,
2014)
and
could
be
applicable
to
SBV
and
Belgian
Culicoides
.
In
Belgium,
it
is
known
that
adult
midges
are
able
to
accomplish
their
life-cycle
and
overwinter
inside
cowsheds
and
low
numbers
of
Culicoides
have
been
caught
outdoors
all
along
the
winter
(Losson
et
al.,
2007;
Zimmer
et
al.,
2010;
De
Regge
et
al.,
2015).
Since
it
has
been
shown
that
only
a
very
low
dose
is
necessary
to
induce
an
SBV
infection,
this
low
number
of
persisting
Culicoides
could
be
enough
to
perpetuate
the
infection
(Wernike
et
al.,
2012;
Poskin
et
al.,
2014b).
A
second
potential
mechanism
is
transovarial
transmission
of
SBV
from
the
midge
to
its
eggs.
Such
transovarial
virus
transmis-
sion
has
however
never
been
shown
in
Culicoides
for
other
viruses,
including
the
closely
related
AKAV
(Mellor
et
al.,
2000;
Kono
et
al.,
2008).
The
recent
detection
of
SBV
RNA
in
nulliparous
midges
seems
to
support
the
hypothesis
of
transovarial
transmission,
but
this
should
be
further
examined
since
age
grading
was
solely
done
on
pigmentation
of
the
abdomen
(Larska
et
al.,
2013).
Furthermore
SBV
RNA
detection
in
midges
is
not
sufficient
to
prove
the
transmission
of
viable
virus
(Mellor
et
al.,
2000;
Mellor,
2000)
and
in
the
same
context,
no
SBV
was
detected
in
a
limited
set
of
nulliparous
midges
collected
in
Belgium
(De
Regge
et
al.,
2014).
Thirdly,
also
the
persistence
of
SBV
within
ruminant
hosts
during
the
winter
should
be
considered
as
an
option.
SBV
RNA
was
indeed
detected
in
lymph
nodes
at
44
days
post-infection
despite
rapid
seroconversion
(Wernike
et
al.,
2013c).
It
remains
however
to
be
determined
whether
infectious
virus
is
still
present
in
the
lymph
nodes
and
how
the
virus
could
be
transmitted
to
a
Culicoides
and
perpetuate
the
SBV
life-cycle.
Also
the
potential
role
of
wildlife
as
a
natural
reservoir
should
be
further
evaluated
since
some
species
were
associated
with
lower
seroprevalence
rates
during
winter
2011–2012
in
which
virus
could
have
persisted
(Claine
et
al.,
2013a).
A
fourth
overwintering
strategy
could
be
the
transplacental
transmission
of
SBV
from
the
dam
to
the
fetus
and
its
persistence
until
birth.
SBV
RNA
persistence
was
proven
at
birth
of
one
lamb
in
Germany
(Wernike
et
al.,
2014).
It
was
however
unclear
if
the
virus
remained
infectious
in
the
newborn
lamb.
Since
supporting
but
inconclusive
evidence
can
be
found
for
all
options,
it
remains
difficult
to
clearly
pinpoint
the
overwintering
option
(s)
used
by
SBV
and
this
should
be
further
examined
in
the
future.
4.3.
Perspectives
on
SBV
circulation
A
large
part
of
the
domestic
ruminant
livestock
has
been
renewed
since
2013
due
to
normal
farmer’s
managing
practices.
Although
the
seroprevalence
in
livestock
is
currently
unknown,
it
is
to
be
expected
that
young
animals
are
seronegative
due
to
the
low
virus
presence
since
2013,
the
limited
lifespan
of
passive
immunity
(6
months
in
calves
and
3–4
months
in
lambs)
and
the
fact
that
vaccines
are
currently
not
used
in
Belgium
(Claine
et
al.,
2014;
Elbers
et
al.,
2014).
Together
with
the
indications
that
SBV
is
still
present
in
surrounding
countries,
this
causes
growing
concerns
for
occurrence
of
a
new
episode
of
congenital
malfor-
mations
in
the
coming
months
or
years.
If
observations
from
AKAV,
a
Culicoides
borne
Orthobunyavirus
causing
congenital
malformations,
are
extrapolated
to
SBV,
it
is
to
be
expected
that
SBV
will
remain
endemic
in
Belgium
for
a
long
period
of
time
with
recurrent
outbreaks
of
congenital
malforma-
tions
every
5
or
6
years,
the
time
needed
for
the
immunity
to
decrease
in
livestock
(Kono
et
al.,
2008;
CFSPH,
2009).
Considering
the
wide
expansion
shown
for
AKAV
since
its
first
emergence
in
Japan
(Kono
et
al.,
2008),
further
spread
of
SBV
can
also
be
expected.
It
is
interesting
to
notice
that
AKAV
genetically
evolved
since
its
first
identification.
In
this
respect,
the
first
emergence
of
the
Iriki
strain
took
probably
place
in
1984
in
calves,
25
years
after
the
first
AKAV
isolation
(Miyazato
et
al.,
1989;
Kono
et
al.,
2008).
The
Iriki
strain
affects
bovines
by
an
encephalomyelitis
in
cattle
and
young
calves,
clinical
symptoms
that
had
never
been
observed
with
the
common
strains
of
AKAV
(Kono
et
al.,
2008;
Oem
et
al.,
2012;
Kamata
et
al.,
2009).
Since
SBV
has
a
similar
potential
for
genetic
variability
(Coupeau
et
al.,
2013;
Fischer
et
al.,
2013;
Hulst
et
al.,
2013),
new
strains
of
SBV
could
emerge
in
the
future
and
should
be
monitored.
It
further
seems
advisable
that
SBV
remains
included
in
the
differential
diagnosis
of
outbreak
of
malformations
and
pathologies
from
unknown
origin.
4.4.
Prevention
of
clinical
or
financial
impact
of
SBV
recirculation
Vaccination
seems
an
efficient
way
to
prevent
SBV
infection
and
its
deleterious
effects.
First
vaccines
were
successfully
developed
A.
Poskin
et
al.
/
Veterinary
Microbiology
183
(2016)
50–61
57
shortly
after
SBV
emergence
(Wernike
et
al.,
2013a;
Hechinger
et
al.,
2014;
Kraatz
et
al.,
2015)
and
different
efficient
commercial
vaccines
are
available
on
the
market
(Hamers
et
al.,
2013;
Moulin
et
al.,
2013).
Information
on
their
long
term
efficacy
is
however
missing.
Vaccination
seems
most
useful
when
applied
to
seronegative
animals
during
a
season
with
SBV
circulation
and
before
mating.
The
latter
implies
an
intensive
surveillance
during
the
vector
season
in
order
to
intervene
from
the
moment
SBV
is
detected.
Another
option
would
be
to
protect
livestock
from
Culicoides
.
Several
approaches
like
extra
hygenic
measure,
insecticide
treat-
ments
or
specific
managing
practice
of
herds
have
been
tested
in
this
respect
(Zimmer
et
al.,
2008a,b;
Calvete
et
al.,
2010;
Papadopoulos
et
al.,
2009;
Weiher
et
al.,
2014),
but
all
led
to
disappointing
or
contradictory
results.
4.5.
Future
monitoring
and
surveillance
of
SBV
and
new
emerging
diseases
In
order
to
have
an
efficient
monitoring
and
surveillance
strategy
for
SBV
and
other
(new)
emerging
diseases
it
is
clear
that
such
a
system
must
consist
of
a
combination
of
passive
and
active
surveillance
components.
Very
often,
the
purpose
of
the
surveil-
lance
as
a
whole
(fit
for
purpose)
will
influence
the
final
choice
of
these
components.
4.5.1.
Passive
surveillance
components
Passive
surveillance
components
can
be
installed
in
a
‘space-
and
timeliness’
way
with
the
aim
to
provide
as
soon
as
possible
real
time
information
about
SBV
(re)-introduction
and/or
spread
of
the
infection.
If
early
detection
of
SBV
is
a
choice
for
veterinary
authorities,
passive
surveillance
components
such
as
syndromic
surveillance
and/or
clinical
detection
may
be
a
proper
and
cheap
choice
for
surveillance.
Syndromic
surveillance
(the
use
of
real-time
collected
data
with
relation
to
animal
health
in
general)
and
clinical
notifications
can
be
carried
out
by
veterinary
and
farmer
(organization)
networks.
Therefore
farmers
and
veterinarians
should
be
encouraged
to
notify
all
cases
of
syndromes
that
remain
undiagnosed
in
order
to
allow
detection
of
spatial
or
timely
clusters.
Sometimes,
syndromic
surveillance
and
notification
represents
an
extra,
time
consuming
task
for
the
veterinarian
and
therefore
it
should
be
more
valorized,
encouraged
and
supported
by
the
veterinary
authorities.
This
is
particularly
the
case
for
new
emerging
diseases,
such
as
SBV
in
Belgium,
that
are
not
notifiable.
Due
to
the
highly
suspected
underreporting
of
SBV
at
Belgium
level,
it
could
be
an
interesting
opportunity
to
make
new
emerging
diseases
like
SBV
notifiable
diseases
in
order
to
get
a
better
follow-up
of
the
epidemic.
In
Belgium
there
is
a
mandatory
notification
of
all
aborted
fetuses
in
cattle
with
laboratory
analysis
of
samples
sent
towards
accredited
laboratories.
This
abortion
protocol
can
be
considered
as
an
early
warning
syndromic
surveillance
component.
This
system
allowed
a
continual
follow-up
and
a
large
scale
evaluation
of
SBV
impact
with
rRT-PCR
and
VNT.
Combined
with
technologies
like
next-generation
sequencing,
it
is
a
powerful
mechanism
for
surveillance
of
new
emerging
diseases
that
induce
abortions
(Rosseel
et
al.,
2012)
and
provides
valuable
material
for
scientific
studies
dealing
with
new
emerging
diseases.
However,
this
protocol
is
not
always
followed
by
the
farmers
(Delooz
et
al.,
2011),
even
if
it
is
financially
supported
by
the
animal
health
authorities,
because
of
the
potential
impact
that
the
detection
of
a
contagious
disease
could
have
on
their
economic
activities
due
to
animal
movement
restriction
or
sanitary
euthanasia.
Consequent-
ly,
it
might
be
an
interesting
exercise
to
see
if
the
system
could
not
be
adjusted
to
a
less
constraining
protocol
that
would
encourage
farmers
to
participate.
4.5.2.
Active
surveillance
components
Besides
the
passive
surveillance
components,
active
surveil-
lance
such
as
a
sentinel
surveillance
system
may
also
be
useful
to
detect
new
emerging
diseases
in
an
early
phase.
To
achieve
an
early
detection
of
a
new
disease
in
a
‘space
and
timeliness’
way,
a
good
sentinel
system
must
be
adequately
sensitive.
This
can
be
achieved
by
applying
a
proper
sample
size
and
an
acceptable
and
realistic
design
(sero)-prevalence
to
calculate
this
sample
size.
A
sentinel
herd
surveillance
helped
to
understand
the
time-
course
of
the
epidemic
and
proved
to
be
an
efficient
mean
for
identification
of
SBV
recirculation
in
Belgium.
Furthermore,
it
provided
valuable
samples
used
to
increase
our
fundamental
knowledge
on
SBV
and
allowed
to
study
antibody
persistence
into
domestic
livestock
under
natural
conditions.
Close
follow-up
of
sentinel
herd
surveillance
is
however
time
consuming
and
in
the
absence
of
apparent
clinical
disease
and/or
delayed
immune
reaction,
samples
need
to
be
stored
and
might
only
become
useful
months
or
years
later.
Besides
the
sampling
of
animals
in
different
sentinel
herds
there
is
also
the
possibility
to
define
different
locations
with
traps
to
collect
the
Culicoides/vectors
once
the
vector
season
starts
(vector
sentinel
system).
Detection
of
SBV
in
vectors
has
proven
to
be
an
excellent
technique
for
early
detection
of
SBV
recirculation.
The
short
time
period
in
which
SBV
could
be
detected
in
2012
shows
however
that
it
has
to
be
performed
on
a
continuous
basis.
This
makes
pathogen
monitoring
in
vectors
a
labor
intensive
and
expensive
surveillance
tool.
New
techniques
including
mass
spectrometry
and
rRT-PCR-based
techniques
will
contribute
to
make
large-scale
pathogen
surveillance
studies
in
vectors
more
easy
and
less
expensive
(Cêtre-Sossah
et
al.,
2004;
Mathieu
et
al.,
2011,
2012;
Kaufmann
et
al.,
2012a,b).
Since
global
warming
and
the
increasing
international
transport
affects
the
distribution
of
Culicoides
in
Europe
(Purse
et
al.,
2005)
and
increases
the
risk
for
introduction
of
vector
borne
diseases,
it
seems
advisable
to
keep
the
expertise
for
vector
collection
and
identification
in
place.
Cross-sectional
studies
are
preferred
and
very
useful
to
estimate
in
global
way
if
a
new
emerging
disease
such
as
SBV
circulated
or
re-
circulated
again
during
a
season.
Cross-sectional
studies
helped
to
understand
to
which
extent
the
virus
had
spread
among
the
livestock
population
and
to
predict
the
potential
impact
of
future
reemergences.
It
may
be
helpful
to
evaluate
the
necessity
for
intervention
strategies
such
as
vaccination
in
case
of
recirculation.
If
done
on
a
broad
scale,
it
allows
determining
regions
that
can
be
particularly
susceptible
to
virus
circulation
or
reemergence
during
a
specific
time
period
in
the
year.
The
cross-
sectional
studies
executed
for
SBV
were
shown
to
be
useful
and
cost
effective
(Méroc
et
al.,
2013a,
2014).
The
downside
of
such
cross-sectional
seroprevalence
studies
is
that
they
cannot
be
used
to
detect
the
emergence
in
real-time
or
early
during
an
epidemic
and
that
they
do
not
allow
immediate
actions
in
contrast
to
sentinel
and/or
clinical
surveillance.
In
case
sound
knowledge
is
gathered
about
the
risk
factors
for
a
certain
emerging
disease
it
might
be
worthwhile
to
limit
the
surveillance
resources
to
only
these
time
periods
or
places
where
it
makes
more
sense
to
detect
the
disease
with
sufficient
sensitivity
(=target
surveillance
strategy).
Indeed,
Poskin
et
al.
(2015a,b)
showed
that
SBV
was
more
frequently
confirmed
with
rRT-PCR
in
bigger
herds
compared
to
smaller
herds.
A
sentinel
system
for
SBV
could
therefore
preferentially
and
consequently
be
implemented
in
large
farms.
4.5.3.
Recommendations
Different
surveillance
approaches,
including
syndromic
sur-
veillance,
abortion
surveillance,
sentinel
herd
and
Culicoides
surveillance
as
well
as
cross-sectional
epidemiological
studies
have
all
proven
their
utility
and
complementarity
to
understand
58
A.
Poskin
et
al.
/
Veterinary
Microbiology
183
(2016)
50–61
the
SBV
epidemic.
This
helped
scientists,
veterinary
authorities
and
decision
makers
to
increase
the
knowledge
on
the
virus
and
should
be
considered
to
continue
in
the
future.
The
choice
and/or
the
combination
of
different
surveillance
components
will
mainly
be
influenced
by
the
epidemiological
situation
and/or
the
aim
of
the
surveillance
strategy.
This
choice
can
be
to
detect
as
fast
as
possible
the
disease
in
order
to
avoid
a
big
epidemic
(reduce
transmission),
to
provide
proper
intervention
strategies
if
needed
(vaccination)
and/or
to
reduce
as
much
as
possible
the
economic
impact
and
consequences.
If
the
latter
is
judged
to
be
rather
low
it
might
be
enough
to
install
surveillance
systems
which
only
allow
a
follow
up
or
monitoring
(cross
sectional
studies).
Conflict
of
interest
The
authors
declare
no
conflict
of
interest.
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