In the summer of 2002, a Newcastle Disease-epidemic occurred in Denmark. At that time, the disease had not been diagnosed in Denmark since February 1998. A total of 135 outbreaks were registered during the epidemic. Four primary outbreaks and 131 secondary outbreaks were identified. Most outbreaks were found in the central and southern parts of Jutland, but a single outbreak occurred on the Island of Sejerø in the county of West Zealand (figure 5). The majority of outbreaks (126) were observed in backyard flocks. Only 9 commercial flocks were infected. All infected commercial flocks were layers or pullets, whereas no broiler holdings became infected.
The first outbreak was confirmed by virus isolation and ICPI-determination on 26 July 2002, and the last outbreak was confirmed on 28 August 2002. However, eradication of infected flocks, establishment of protection and surveillance zones and restrictions on poultry movements were initiated for precautionary reasons already on 16 July, ie. 10 days before the first virological confirmation was obtained. The preliminary diagnosis was based on clinical signs and serological reactions. Positive serology could be used as an indicator of ND infection, because Denmark at that time applied a non-vaccination policy for ND. All poultry on holdings on which the disease was diagnosed have been killed and destroyed.
In the majority of the outbreaks, no obvious clinical symptoms were observed. Among all 135 outbreaks only poultry in 13 outbreaks revealed clinical symptoms such as ataxia, torticollis and drop in egg production. Seven of these were outbreaks in commercial flocks. The pathological lesions were also limited as was the spread by any other means than movement of already infected pullets.
As a consequence of the very slow in-vitro growth of the virus involved, the diagnostic methods were primarily based on serology in order to ensure a rapid eradication of the outbreaks. Avian paramyxovirus-1 (APMV-1) was isolated from three flocks of commercial poultry, but not from any of the backyard flocks. The two isolates tested both belonged to antigenic group C1 viruses.
Based on the epidemiological investigations, one of the primary outbreaks was linked to all of the 131 secondary outbreaks. This was due to the involvement of two poultry dealers, and the infection was spread among backyard flocks by trade of infected pullets. Thereby, this primary outbreak and the related contacts comprised one large epidemiological cluster of infected flocks.
The epidemiological investigations did not succeed in identifying a common source of infection with regards to the four primary outbreaks in commercial flocks. These were all situated less than 2 km from the coastline. The waterfowl populations in the vicinity of these holdings were investigated in an attempt to locate the potential source of infection, but the results were inconclusive.
Following preliminary cleaning and disinfection of the affected premises, a serological screening of the more than 600 flocks in the vicinity of the outbreaks was carried out. A limited prevalence of low serological titres was found in 39 of these flocks, and no virus could be isolated.
During the progress of the eradication process, six regionalisations of Denmark were carried out in order to successively re-open the export of live poultry and hatching eggs from ND-free regions of Denmark. All restrictions were lifted by 1 January 2003, and Denmark regained its ND-free status according to the Office International des Epizooties (OIE) standards by 1 March 2003.
In July 2004, the Danish Ministry of Food, Agriculture and Fisheries decided to change the control strategy for Newcastle Disease from a non-vaccination strategy to a vaccination strategy, which was implemented in autumn 2004. The change of control strategy is based on a risk analysis, which was performed because the Danish poultry industry wished to change the control strategy after the outbreaks of Newcastle Disease in Denmark in 2002.
Newcastle disease outbreaks in Denmark in 2002 (final report)
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