Abstract Book of EAVLD2012 - eavld congress 2012

S1 - O - 03
INTRODUCTION RATE OF A LOW PATHOGENIC AVIAN INFLUENZA VIRUS INFECTION IN
DIFFERENT DUTCH POULTRY SECTORS
Jose Gonzales 1 , Guus Koch 1 , Ruth Bouwstra 1 , Armin Elbers 1 , J.J. de Wit 2 , Arjan Stegeman 3
1 Central Veterinary Institute, of Wageningen University and Research Centre (CVI-Lelystad), Lelystad, The Netherlands
2 Animal Health Service, Deventer, The Netherlands
3 Utrecht University, Faculty of Veterinary Medicine, Department of Farm Animal Health, Utrecht, The Netherlands
Avian Influenza, low pathogenic, introduction rate
Introduction
Low Pathogenic Avian Influenza (LPAI) viruses of the H5 and H7
subtype have the potential to evolute to Highly Pathogenic Avian
Influenza (HPAI) viruses in poultry and therefore infections with
these subtypes are notifiable . Consequently, member states of
the European Union have implemented surveillance programmes
(1). In the Netherlands a syndromic surveillance and serological
monitoring programme is in place. In the monitoring programme,
all poultry farms are tested 1-4 times a year. Frequency differs
between the different poultry types and housing systems (indoor
and outdoor layer chickens, broilers, ducks, turkeys, etc) based
on the supposed differences in the risk of introduction of LPAI
infections. However, quantitative information regarding the
possible differences in risk between these poultry types is sparse.
In this study the rate of introduction of LPAI in different poultry
types was quantified. .
Materials & methods
Data from the Dutch LPAI surveillance programme(2007–2010)
were analysed using a generalised linear mixed and spatial
model. All poultry farms should be tested at least once a year. In
addition, outdoor-layer farms are tested 3 to 4 times per year.
Farms were identified by their unique farm number (UBN) and
poultry sector (duck-breeders, duck-meat (meat production),
turkeys, broilers, indoor-layers, outdoor- layers, pullets and
breeders). Based on the sampling frequency (time interval
between samplings), the time at risk of exposure to a LPAI
infection (“time at risk”) was calculated per poultry sector. For
poultry sectors sampled once a year or once per production
cycle, the age of the birds, at the moment of sampling, was taken
as the time at risk. For poultry sectors sampled more than once
per production cycle, the average sampling interval was taken as
the time at risk. Positive cases were defined as: 1) farms with at
least one seropositive animal – to any LPAI strain – in both, the
screening test (IDEXX FLockCheck AI MultiS-Screen or agar gel
precipitation, which is only used for broilers) and the confirmatory
test (Hemagglutination Inhibition test) or 2) three or more
positives in the screening test. Furthermore, only primary cases
were included.
Results
The results are summarised in Table 1. Almost all seropositive
results appeared to be single introductions. Results showed that
outdoor-layer farms had a 11, turkey 8, duck-breeder 23 and
meat-duck 13 times higher rate of introduction of LPAI than
indoor-layer farms.
Table 2. Relative risk (RR), with accompanying lower (LCI) and
upper (UCI) 95% confidence intervals, of introduction of a LPAIv
infection on poultry farms. Indoor - layers were considered as the
reference category.
Poultry Type
RR
Mean LCI UCL
breeders 0.3 0.0 2.4
pullets 0.7 0.1 5.7
layers indoor 1.0
layers outdoor 11.0 4.9 24.8
turkeys 7.6 2.0 29.0
duck meat 12.8 1.6 102.7
duck breeders 23.0 6.2 85.7
Discussion & conclusion
Our analysis shows that outdoor-layer farms, duck (breeders and
meat) farms and turkey farms have a significantly higher risk of
introduction of a LPAI infection compared to indoor-layer farms.
Breeder ducks have the highest risk. This could be related to 1)
their higher susceptibility to infection with LPAI of wild bird origin
(ducks, geese, swans) than chickens, 2) their long production
cycle (time of exposure), and 3) their higher exposure to LPAI
from a contaminated environment and/or contact with wild
waterfowl. The latter could also be the reason for the higher risk
observed in outdoor-layer than indoor-layer farms.
In the Netherlands, turkeys are raised indoors and despite the
small population of turkey farms, we observed a higher risk of
introduction of a LPAI infection on turkeys than indoor-layers.
This higher risk might be partly associated with the apparent
higher susceptibility of turkeys to LPAI infections than chickens
(2). We also observed a significant higher risk of introduction in
meat-duck farms. This was surprising because this poultry type is
kept indoors and has a short production cycle (6 weeks). The
above mentioned higher susceptibility of ducks than chickens
could be one reason for the observed higher risk. Differences in
the rate of introduction of LPAI could be used to (re)design a
targeted risk-based surveillance programme.
References
1.European Commission, 2007. Commission Decision 2007/268/EC of 13
April 2007 on the implementation of surveillance programmes for avian
influenza in poultry and wild birds to be carried out in the Member States
and amending Decision 2004/450/EC. OJEU ;L 115:3.5.2007, p.2003.
2. Tumpey, T, M, Kapczynski, D, R, Swayne, D,E 2004. Comparative
susceptibility of chickens and turkeys to avian influenza A H7N2 virus
infection and protective efficacy of a commercial avian influenza H7N2
virus vaccine. Avian Diseases 48:167-176.