Abstract Book of EAVLD2012 - eavld congress 2012

S3 - O - 10
DIAGNOSTIC ASPECTS OF SUID HERPESVIRUS 1 INFECTION IN WILD BOAR
Adolf Steinrigl, Sandra Revilla-Fernández, Eveline Wodak, Zoltán Bagó, Friedrich Schmoll
AGES Institute for Veterinary Disease Control, Mödling, Austria
SuHV-1, wild boar, prevalence, molecular characterization
Introduction
Many infectious diseases that are strictly controlled in livestock
may remain unnoticed in wild animals, posing the risk of entering
domestic animal populations with potentially devastating
consequences. Suid herpesvirus 1 (SuHV-1), the causative agent
of Aujeszky’s disease (AD), was eradicated from domestic pig
populations in many European countries, including Austria. At the
same time, SuHV-1 infection is common in European wild boar,
as shown by a number of studies, reporting detection of SuHV-1
DNA or antibodies in wild boar (1). An additional indicator of
SuHV-1 presence in wild boar are occasional cases of AD in
hunting dogs, usually in close connection to hunting events (2).
Recently, we reported about the first detection of SuHV-1 in
Austrian wild boar and the molecular characterization of SuHV-1
field isolates from wild boar and hunting dogs (3).
In the course of the Wild Animal Survey 2011, a nationwide study
that was partly financed by the Austrian Federal Ministry of
Health, additional sera and tissue samples from Austrian wild
boar were collected and analysed, with the aim to provide a
representative estimate of the prevalence of both, SuHV-1 DNA
and antibodies, in Austrian wild boar. This work shows the results
of this survey and reflects our experiences with detection and
molecular characterization of SuHV-1 in wild boar.
Materials & methods
Wild boar tissues and sera were sampled according to a survey
design that was based on recent wild boar hunting bag statistics.
Anti-SuHV-1 gB ELISA, real-time PCR (qPCR), amplification and
sequencing of the SuHV-1 glycoprotein C coding region,
phylogenetic analysis and virus isolation were performed as
described previously (3).
Results
From April 2011 to January 2012, tissues from 298 wild boars
were sampled, corresponding to 78% of the scheduled sample
size for the whole country. Wild boar sera of sufficient amount
and quality were available from 259 animals. Results of
serological and virological screening are shown in Table 1. All
qPCR positive wild boars were adult females at 2-4 years of age.
One of them was also serologically positive, while the other two
animals were seronegative.
Table 1: Results of serological (ELISA) and virological (qPCR)
screening of Austrian wild boars
Samples Samples Prevalence
tested positive
ELISA 259 59 22.8%
qPCR 298 3 1.0%
Virus was successfully isolated from one of the qPCR-positive,
yet seronegative, wild boars: tissue homogenate from a qPCRpositive
tonsil was inoculated onto PK15 cells, resulting in
massive cytopathic effect within 24 hours post inoculation. An
attempt to isolate virus from the other two qPCR positive animals
was unsuccessful. Phylogenetic analysis of SuHV-1 gC
sequences amplified from the three qPCR positive wild boars
sampled in 2011 showed that all three animals hosted virus that
was identical in gC sequence and belonged to one of the
previously described lineages of SuHV-1 (3), which are currently
present in Austria (Figure 1).
Figure 1: Neighbour Joining tree, based on a 639 bp alignment of
the SuHV-1 partial gC coding region. Sequences were amplified
from wild boars (WB), hunting dogs (HD) and from a domestic pig
(DP). Year of isolation is in brackets. Numbers along the
branches indicate the percentage of 1000 bootstrap replicates.
Discussion & conclusions
The presented study confirms the presence of SuHV-1 in
Austrian wild boar. SuHV-1 seroprevalence detected during the
Wild Animal Survey 2011 was lower than that previously
described (3), which is probably due to the more representative
sampling strategy applied for the current study. In contrast to the
high numbers of wild boars with detectable SuHV-1 antibodies,
SuHV-1 DNA was detected by qPCR in only a few animals.
Furthermore, Cq-values of qPCR-positive tissue pools or
individual organs were relatively high (30 - 38 Cq), indicating a
low viral load in these tissues. This is also supported by our
previous observation of weak immunohistochemistry signals in
qPCR positive tissues (3) and by the fact that virus isolation was
positive in a single case only. In summary, our results indicate
that most SuHV-1 infected wild boars harbour virus in a latent
form, whereas only a small proportion of infected wild boars is
actually shedding virus and may infect other susceptible animals.
This is also the most likely explanation for the relatively rare
cases of AD in hunting dogs, despite rising numbers of wild boars
in many European countries and the frequent involvement of
hunting dogs in wild boar hunting. Despite the fact that only few
potentially virus shedding wild boars were found in this study,
direct contact between wild boars and domestic pigs could result
in SuHV-1 transmission. Feeding of wild boar intestines to
domestic animals, especially pigs, dogs and cats, is another
reasonable possibility of transmission and must be strictly
discouraged.
Acknowledgements
This study was financially supported in part by the Austrian
Federal Ministry of Health. The excellent technical assistance of
the laboratory staff of the Departments for Molecular Biology,
Virology and Electron Microscopy, and Pathology is
acknowledged.
References
1. Müller T, Hahn EC, Tottewitz F, Kramer M, Klupp BG, Mettenleiter TC,
Freuling C (2011). Pseudorabies virus in wild swine: a global perspective.
Arch. Virol., 156, 1691-705.
2. Cay AB, Letellier C (2009). Isolation of Aujeszky’s disease virus from
two hunting dogs in Belgium after hunting wild boar. Vlaams
Diergeneeskundig Tijdschrift, 78, 194-195.
3. Steinrigl A, Revilla-Fernández S, Kolodziejek J, Wodak E, Bagó Z,
Nowotny N, Schmoll F, Köfer J (2011). Detection and molecular
characterization of Suid herpesvirus type 1 in Austrian wild boar and
hunting dogs. Vet Microbiol., Dec 30. [Epub ahead of print]