Abstract Book of EAVLD2012 - eavld congress 2012

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LOW PATHOGENIC AVIAN INFLUENZA VIRUS INFECTIONS ON POULTRY FARMS IN THE
NETHERLANDS
Sylvia Pritz-verschuren 1 , Jeanet van der Goot 1 , Johan Bongers 1 , Guus Koch 1
1
Central Veterinary Institute of Wageningen UR,Lelystad,The Netherlands
Avian Influenza Virus, low pathogenic, poultry
Introduction
Outbreaks of highly pathogenic avian influenza (HPAI) have a
devastating economic impact on the poultry industry and also
causes social distress. In countries free of HPAI, epidemics start
after introduction of low pathogenic AI virus which may evolves to
HPAI viruses. Early detection of AI infection is crucial for the
control of outbreaks. Infections of LPAI viruses in laying birds is
subclinical or causes mild symptoms such as a drop in egg
production.
Early detection of AI virus infection is crucial to prevent HPAI
outbreaks. Therefore, in the Netherlands LPAI infections are
detected by early warning and compulsory serological monitoring
programmes of all poultry farms.
In the period of 2006-2011, an increase in the number of LPAI
virus infections in poultry was observed. A number of possible
causes is discussed.
Materials & methods
Serological samples were screened in an competitive NP
antibody ELISA and the positive samples were confirmed and
typed by hemagglutination inhibition and neuraminidase inhibition
test.
For detection of the virus an in house developed PCR with the M-
gene as target is used. Positive samples were tested in an H5
and H7 specific PCR described by the community EU reference
lab (AHVLA, Weybridge). H5 and H7 negative samples were
subtyped using a generic, hemagglutinin and neuraminidasespecific
RT-PCR (1) followed by sequencing the PCR product.
Results
The number LPAI introductions either detected by PCR and/or
antibodies increased in the period 2006-2011, especially since
2009 (Table 1). Although there is a marked increase in the
number of detections, the period is too short to speak about a
tendency.
Table 1. Number of poultry farms where LPAI viruses and/or
antibodies were detected in period 2006-2011
Year
Number of LPAI Number of primary
detected farms infections
2006 4 2
2007 13 8
2008 10 9
2009 11 10
2010 20 18
2011 33 23
Total 91 70
A number of possible causes for the increase of LPAI detections
are:
More intensive search for LPAI viruses and introduction of the
early warning.
The early warning program was started in 2008/2009. However
most farms (57/70) are detected by serological monitoring which
was in place since 2004. So, this can’t be an explanation for the
increase.
Higher sensitivity of the serological test used for the monitoring.
Sera are tested in an ELISA by the Dutch Animal Health Service
(AHS). In January 2009 the AHS has changed to another test.
However, the validation tests revealed no differences in
sensitivity between the old and new test.
of the Erasmus Medical Centre in Rotterdam there is no
sufficient evidence to assume such an increased prevalence of
LPAI viruses in wild birds.
An increase of the number wild birds in the Netherlands.
Reports of Dutch Bird research group (SOVON) shows that the
number of wild birds was more or less constant in the period
2004-2009. Thus this also can’t explain the increase of the
number of detection.
More contact between poultry and wild birds due to the increased
number of outdoor-layer farms.
Data of the Product Boards for Livestock, Meat and Eggs (PVE)
shows that the total number of outdoor-layer farms was lower in
2008 and 2009 than in the years before and gradually increased
again in 2010 and 2011.
Different subtypes are found on the poultry farms (Table 2). In
poultry H5, H7 and H8 viruses and/or antibodies are the most
common in the period 2006-2011. For serology the
neuraminidase inhibition test is used for typing, however the test
is not suitable to test large numbers of sera samples and
therefore the neuraminidase type is not yet determined for most
farms, because 57/70 farms were detected in the serological
monitoring programme. Therefore the most common N-type is
not known.
Table 2. Avian Influenza virus subtypes detected in poultry farms
in the Netherlands in period 2006-2011
HA N1 N2 N3 N4 N5 N6 N7 N8 N9 N?* Totaal
H1 2 1 3 6
H2 2 1 3
H3 2 2
H4
H5 1 10 11
H6 1 1 3 5
H7 1 1 2 4 4 12
H8 3 9 12
H9 3 1 4
H10 2 1 3
H11
H12 1 1
H13
H14 1 1
H16
H?* 1 13 14
Totaal 4 5 3 5 2 6 49 74
* Typing of the haemagglutinine and/or neuraminidase was not
possible.
Discussion & conclusions
Every year in the Netherlands more infections with LPAI viruses
are detected in poultry farms . Up to now we did not identify an
obvious explanation for the increase of LPAI virus introduction in
poultry. However, different subtypes are found. The most
common H-types are H5, H7 and H8.
References
1. Gall,A, Hoffmann, B, Harder, Timm, Grund, C, Ehricht, R, Beer, M
(2009). Rapid an Highly Sensitive Neuramidase Subtyping of Avian
Influenza Viruses by Use of a Diagnostic DNA Microarray. J. of Clin.
Microbiol., 47, 2985-2988
A increased prevalence of LPAI viruses in wild birds.
The prevalence varies per season, year, wild bird and location,
but from a wild bird surveillance studies performed by the group