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Descriptive Epidemiology of HPAI H5N1 in the Baltic Sea Region in 2006. Preben Willeberg DVM, PhD, Dr. Vet. Sc., Dr. Vet. Sc.h.c., Dipl. ECVPH CVO, Professor. World-wide occurrence of HPAI H5N1. AI-infected tufted duck. Chronology of HPAI H5N1- events in or near Denmark in 2006.
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Descriptive Epidemiology of HPAI H5N1 in the Baltic Sea Region in 2006 Preben Willeberg DVM, PhD, Dr. Vet. Sc., Dr. Vet. Sc.h.c., Dipl. ECVPH CVO, Professor
Chronology of HPAI H5N1- events in or near Denmark in 2006 • 15 February – wild bird case in Rügen • Early March – w.b.cases in Sweden • 12 March – first w.b.case in Denmark • 2 May – 43rd w.b. case in Denmark • 18 May – positive back-yard poultry flock • 24 May – positive magpie on AI premise
Predicted risk areas (March 2006) poultry density & wild water fowl locations
Location of wild birds tested for HPAI January through May 2006
Diagnostic methods Routine test: RT-PCR for influenza A and specific H5 subtype RT-PCR: specific H7 subtype Pos influenza A – negative H5 Sequencing of PCR-product – HP or LP Positive subtype H5 Positive subtype H7 Pos influenza A - negative H7 Pos influenza A - negative H5 RT-PCR for nucleoprotein Influenza A confirmation + Inoculation in embryonated eggs
Table 1 Location of cases of HPAI H5N1 in wild birds in 2006 County Number of AI pos. No. of birds tested Prop. mortality rates Nordjylland 0 74 - Viborg 0 21 - Århus 0 52 - Ringkøbing 0 25 - Vejle 0 46 - Ribe 0 47 - Storstrøm 8 93 9% Fyn 27 141 19% Frederiksborg 4 58 7% Sønderjylland 3 170 2% Vestsjælland 1 67 2% Roskilde 0 21 - Københavns/Frb. kommune 0 57 - Bornholm 1 97 1% Unknown 0 151 - Total 44 1120 (626) 4% (7%) Location by county of AI tested dead wild birds in 2006
Zones established as of 7 April 2006 Red: Protection zones Blue: Surveillance zones
Additional testing • 1112 samples of bird dropping have been analysed by PCR • These samples were collected ultimo February to ultimo April 2006. • All samples have given negative test results, except one pool with samples from five herring gulls (Larus argentatus), which were HP H5N1-pos.
The first outbreak of HPAI H5N1 in Denmark • Confirmed: 18 May 2006 • Location: Near the town of Kerteminde on the island of Funen. • Affected population: A backyard poultry holding with 102 animals (51 chickens, 41 ducks, 5 geese, 3 guinea fowls and 2 peacocks) of which 47 had died. • Source of infection: Contact with wild birds.
Species North Germany Sweden Number of cases Proportion Number of cases Number of tested birds Proportional mortality rate 138 6 58 Swans 10% 3 74 4% 48 230 21% 35 0 85 - 9 1 60 Crows 2 0 21 Total 222 58 528 Occurrence of HPAI in Northern Germany and Sweden by species 10% 62% Birds of prey 23 Ducks 15 7% Other water fowl - 16% 2% Gulls and terns 4% - 1% 11% 100%
Wild birds tested in other member states around the Baltic Sea (February – May 2006) H5N1-positive H5N1-negative Estonia 0 151 Finland 0 440 Latvia 0 139 Lithuania 0 574 Poland 70 (3.5%)* 1904 * 67 were swans
Discussion • Why did it last 4 weeks for the infection to reach the 40 km from Rügen to the Danish coast? • AI “frontier” through Europe/Denmark – did the infection stop /die out – or did the birds just fly somewhere else – and what about the indigenous birds? • First cases of documented spread from poultry to wild birds and of “healthy carriers” in Europe? • Species differences among wild birds in risk of transmission – which birds to monitor?
Possibilities of a “die-out” of the (local) epidemic ? • Low AI-specific mortality, which was only detected due to (unusually?) high unspecific mortality (cold winter) – so AI epidemic was never severe (after Rügen) • Possible reasons for low AI-specific mortality: • Low field diagnostic sensitivity – with PCR not likely? • Low case fatality – not likely with HPAI H5N1 – species differences? • Low incidence of AI infection in regional wild birds – species differences? Reason for few situations of poultry becoming affected? • Low prevalence of AI infections – self-cure? Immunity? Species differences? • Lower no. of cases and % HPAI of dead birds by month and sub-region – migration of birds would presumably not change % of HPAI among dead birds (unless all infected birds migrated) • “Frontier” without other sub-regions on the migration route becoming affected (Norway, Finland) • Could a “die-out” in late spring explain the absence of infection in the fall migration (so far)? • What are the reasons for a “die-out”?
Decision to raise risk level from low to medium --------------------------------------------------------------------------------------- Cases --------------------------- ---------------------------------------------------------- No. tested All neg. < X YES YES Surveillance of relevant wild ---------------------------------------------------------- bird populations during the > X NO YES relevant period --------------------------------------------------------------------------------------------- X: for design prevalence = 5% with 95% confidence: X = 60 for design prevalence = 5% with 99% confidence: X = 90 for design prevalence = 1% with 95% confidence: X = 300 for design prevalence = 1% with 99% confidence: X = 460