Screening programme for avian influenza in Denmark
Screening of poultry in 2002
The first screening programme for avian influenza in Denmark was carried out in the autumn of 2002, and was performed on samples taken in connection with the epidemiological investigations of the Newcastle disease outbreaks. The screening included samples from backyard flocks and wild birds. The backyard flocks were examined both serologically and by virology. Blood samples from 53 backyard flocks that had been sampled in August 2002 were tested and none were positive. In addition, 102 backyard flocks were examined virologically in August 2002, and the virus isolation performed did not show any presence of virus in the samples.
Screening of wild birds in 2002
The screening of the wild birds included 1730 fresh droppings collected from wild birds (cormorants, geese, seagulls, jackdaws, rooks and crows) near the four primary outbreaks of Newcastle disease and 240 cloacal swabs from hunted game birds (mallards and pheasants). The bird droppings were sampled in September and October 2002, whereas the cloacal swabs were sampled in December 2002. The samples were pooled in pools of five samples and tested virologically. Avian influenza virus could be isolated from three of the 394 pools, and the avian influenza virus subtypes found were H2N3 (mallard) and H16N3 (seagull and cormorant).
Screening of poultry in 2003 - 2005
The screening programme for avian influenza in poultry was considerably more comprehensive in 2003, where the screening program was expanded to include samples from the major poultry types in Denmark, i.e. fattening turkey, chicken breeders, broilers, layers and ducks (table 1).
The screening programme in poultry was only slightly revised in 2004, where the two changes were that only free ranging broilers were sampled and ducks were examined serologically.
The screening programme in poultry was also only slightly revised in 2005, where the main change was that all holdings with free range laying hens were examined. All test results from the screening program for avian influenza in poultry were negative (table 1).
Table 1: Number of samples examined in the screening programmes for avian influenza in poultry in 2003, 2004 and 2005. All samples were examined serologically for subtypes H5 and H7, except for ducks in 2003 that were examined virologically.
| Type of poultry |
2003
No. of samples |
2003
No. of positive |
2004
No. of samples |
2004
No. of positive |
2005
No. of samples |
2005
No. of positive |
| Fattening turkey |
120 |
0 |
320 |
0 |
300 |
0 |
| Chicken breeders |
690 |
0 |
480 |
0 |
440 |
0 |
| Broilers |
578 |
0 |
60 |
0 |
50 |
0 |
| Layers |
40 |
0 |
550 |
0 |
1858 |
0 |
|
Ducks |
330 |
3 |
540 |
0 |
806 |
0 |
Screening of wild birds in 2003
The screening programme for avian influenza in wild birds was also more comprehensive in 2003, with both a wider temporary and geographic covering. Bird droppings were sampled in both spring/summer (March to June) and autumn/winter (September to December), and were sampled from 20 locations. The bird droppings were collected from cormorant, lapwing, Bewick's swan, mallard, widgeon, teal and six different geese species. The samples were pooled in pools of five samples and tested virologically (by both virus isolation and RT-PCR). Avian influenza virus was detected by RT-PCR in 34 of 579 pools and could be isolated in 15 pools (table 2). The avian influenza virus was mainly found in the duck species in the autumn months. Neither H5 nor H7 subtypes of avian influenza virus could be isolated, but low pathogenic H5 and H7 subtypes were detected with RT-PCR (table 2). The following avian influenza virus subtypes were isolated in the 15 pools: H1N1, H3N2, H3N6, H3N8, H4N6, H6N5, H6N8 and H10N7.
Screening of wild birds in 2004
The screening programme for avian influenza in wild birds was slightly revised in 2004, where the bird dropping was sampled in September to December from 16 locations. The bird droppings were only collected from mallard, widgeon, teal and pintail. The samples were pooled in pools of five samples and tested by both virus isolation and RT-PCR. Avian influenza virus was detected by RT-PCR in 131 of 696 pools and 65 individual samples and could be isolated in 14 samples (table 2). Low pathogenic avian influenza virus subtype H5N2 was isolated from two pools, and low pathogenic avian influenza virus subtype H5 could be detected with RT-PCR in 13 pools. The H7 subtype was neither isolated nor was it detected with RT-PCR. The following avian influenza virus subtypes were isolated in the 15 pools: H2N3, H3N2, H3N8, H5N2 (low pathogenic), H6N2, H8N1 and H8N4.
Screening of wild birds in 2005
In the screening programme for avian influenza in wild birds was slightly revised in 2005, where the bird droppings were sampled in August to December from two locations. The bird droppings were collected from mallard, teal, widgeon, goose and pheasant. The samples were pooled in pools of five samples and tested by RT-PCR. Avian influenza virus was detected by RT-PCR in 140 of 558 pools and could be isolated in 16 samples (table 2). Low pathogenic avian influenza virus subtype H5 or H7 were isolated from three pools, and low pathogenic avian influenza virus subtype H5 or H7 could be detected with RT-PCR in 27 pools. All the H5 and H7 positive findings were from mallards. The following avian influenza virus subtypes hwere isolated in the 16 pools: H1N1, H1N9, H3N8, H4N6, H5Nx (low pathogenic), H7N5 (low pathogenic), H7Nx (low pathogenic), H9N1 and H11N9.
Table 2: Results of the screening programmes for avian influenza in wild bird. Five samples were pooled and examined virologically.
| Year |
2002 |
2003 |
2004 |
2005 |
|
Number of pools
(Number of samples) |
394
(1,970) |
579
(2,895) |
761
(3,545) |
558
(2,790) |
|
AIV isolation (No. of pools)
- LPAI subtype H5 or H7 |
3
0 |
15
0 |
14
2 |
16
3 |
|
AIV detection by RT-PCR (No. of pools)
- LPAI subtype H5 or H7 |
-
- |
34
6 |
131
13 |
140
27 |
LPAI H5N7 detected in a holding with mallard ducks in 2003
In addition to the results from the screening programme, LPAI was detected on 4 September 2003 in a holding with mallard ducks, which was examined due to elevated mortality. The presence of LPAI subtype H5N7 was detected by virus isolation during the laboratory diagnostic examination of the holding. There were 11,000 mallard ducks on the holding, which were raised for restocking for hunting purpose. The elevated mortality was noted on 25 August 2003. The infected flock was further examined by virus isolation and serology. The Danish Veterinary and Food Administration decided for precautionary reasons to cull and destroy the affected flock. All free ranging poultry flocks within a radius of 10 km from the infected holding were clinically examined and serologically tested. Furthermore, all contact flocks were traced and clinically inspected and examined by virus isolation and serology. All tests were negative for avian influenza virus and none of the inspected animals showed any signs of disease. This and other evidence supports the assumption that the clinical signs found in the flock of mallards was not caused by the LPAI virus strain. Isolation of the H5N7 strain is considered to be a coincidental event.
Contact
Animal Health Division - 1kontor@fvst.dk