Preliminary epidemiology report: Avian Influenza outbreak in Suffolk
Following a report of suspected avian notifiable disease in turkeys in
Suffolk on 11 November 2007, highly pathogenic (HP) H5N1 avian influenza (AI) infection was confirmed on 12 November, 2007.
-The infected premises (IP) comprised 5,000 growing turkeys, kept in 5 groups of 1,000, 1,118 ducks and 410 geese maintained under a free range system. Samples collected at slaughter for laboratory examination revealed that two groups of turkeys had a significant prevalence of infection (>50%), a further group had a maximum prevalence of 5%. No evidence of infection was found in the geese, but infection was detected in the ducks for which the maximum prevalence was 2%. The findings suggest that there had been an initial focal introduction of virus into one of the groups of turkeys, rather than a widespread exposure of all poultry on the site.
-Epidemiological investigations of the IP resulted in the identification of five dangerous contact (DC) premises as a result of them being tended by the same stockmen who employed poor biosecurity measures. Only turkeys were kept on four of these DC premises, ducks, geese and turkeys were kept on the other DC premises. Samples were taken for laboratory examination from the birds culled at the DC premises. Infection was detected in one group of turkeys on one of these premises, which became designated as IP2. The maximum prevalence of infection in this group was 10%. This was consistent with infection having been transmitted from IP1.
-Genetic analyses of the virus isolates from the turkeys on the two IPs and the ducks on IP1 indicated that the birds were infected from a single source.
The current isolate has the closest genetic identity to an isolate from wild birds in the Czech Republic detected in mid-2007. The current isolate is phylogenetically distinct from the previous isolate of H5N1 in 2007 obtained from the Holton outbreak.
– Two important and epidemiologically significant findings are evident from the investigations to date. These are:
-The poor biosecurity measures employed by the stockmen, which in this case were peripatetic and therefore cared for more than one unit of poultry which resulted in the transmission of infection in the area
-The siting of a free range poultry unit (IP1), which is likely to attract wild birds because of feed availability, in an area already unavoidably occupied by populations of wild bird species, notably migratory waterfowl, but also „bridge‰ species (such as gulls) which are capable of becoming infected by HP H5N1 and transmitting the virus from primarily infected wild birds to commercial poultry.
– The poultry on the premises which supplied the birds to IP1 and IP2 were sampled and tested with negative results. All of the birds were hatched in Great Britain.
– The surveillance of poultry in the PZ and SZ has not revealed any further infected flocks indicating that infection has been confined to the two IPs.
-The results of the epidemiological investigations to date provide no
evidence that infection was introduced via imported poultry or poultry products or any activities associated with such importations.
– IP1 was located in an area where wild birds were relatively common and as notably near to an ornamental lake which supports some 1000 waterfowl. H5N1 infection has not been detected in wild birds nor have any incidents of high mortality been observed in the area. An enhanced surveillance programme has been initiated. At the present time wild birds, most likely migratory species from central Europe, cannot be ruled out as the source of infection. Epidemiological investigations are continuing and the results will be provided in further reports.
The full report is available at: http://www.defra.gov.uk/animalh/diseases/notifiable/disease/ai/pdf/ai-prelim-epireport071129.pdf