PHOTO: USGS
similar situation had existed during the epidemic of 2015, when the same two large farms were also affected. The de- tailed analysis APHIS has announced for 2023 will perhaps clarify why the highly pathogenic virus could break out again despite the experience gained in 2015. Notably, the number of affected layer flocks in Iowa in 2022 was about half what it had been in 2015, when a much larger number of small farms had been affected. Improved biosecurity may have played a role here. A consideration of the situation regarding the infect- ed turkey flocks also has to take into account that the herds kept were significantly smaller on average and were mostly owned by farmers, while the large laying hen farms belonged to agro-industrial companies. A comparison of the distribution of cases and animal losses reveals that farms with herd sizes of between 10,000 and 50,000 turkeys were particularly affected. They accounted for 73.3% of the outbreaks and 55.2% of the losses. There were only a few large turkey farms (>100,000 places), however, they contributed a large share to the total losses. Broiler farms had significantly larger flocks than turkey farms. This explains the high average size of 168,300 animals per infected farm. One farm with 570,000 broiler places ac- counted for 24.2% of animal losses, and six farms with herd sizes of between 100,000 and 500,000 broilers for 61.5%.
The spatial pattern In 2015, 227 avian influenza outbreaks occurred in just nine states. Minnesota with 109 and Iowa with 71 outbreaks alone accounted for 79.3% of the total. In addition, apart from a few minor cases in other poultry species, turkeys and laying hens were affected in particular, which is directly explained by the importance of the two states in turkey growing and egg pro- duction. The 2022 epidemic exhibited 186 outbreaks in 20 states, including 59 in Minnesota, 36 in South Dakota, 17 in Pennsylvania, and 15 in Iowa (Tables 1 and 2). Overall, there was a significantly different spatial pattern in 2022 compared
Table 1 – A comparison of the chronology of the Avian Influenza outbreaks in 2015 and 2022.
Calendar week 6 ->10 11 ->12 13->14 15->16 17->18 19->20 21->22 23->24 25->26 Total
2015 5 5 6
31 73 57 28 20 2
227 Source: Böckmann 2021 and APHIS 2022
2022 13 14 55 45 39 12 5 3 0
186
to 2015. In addition to states in the northern Midwest, states in the Northeast, the Mid-Atlantic and in the western United States were also affected. This was a completely different dis- tribution pattern than in 2015 because in 2022 states from the Rocky Mountains to the Atlantic were affected which indi- cates different routes of infection (Figure 1). In his detailed analysis of the spatial diffusion of the virus, Böckmann (2021) stated that the primary infections were, in all probability, due to virus transmission from infected wild birds. The further spread then was a result of other transmis- sion routes, i.e. shared use of equipment, stocking and depop- ulation crews, supply of feed and disposal of fallen animals by trucks entering the farm premises. In summary, two clusters emerged. A Mid-Atlantic cluster affecting turkey, layer, broiler and duck farms, and a second cluster in the Midwest where mainly layer and turkey farms were infected. This second cluster is very similar to that of 2015 (Böckmann 2021).
Summary and outlook In his final assessment of the 2015 epidemic, Böckmann reached the conclusion that the underestimated epidemic risk among farmers, limited resource availability (capital, technical equipment) and the state authorities’ lack of experi- ence with large outbreaks had made the devastating epidem- ic possible in the first place. When the virus penetrated the densely populated areas of laying hens and turkeys it was al- ready too late to take countermeasures. The epidemic could perhaps have been contained if the disease pressure in wild bird stocks, known from an extensive monitoring pro- gramme, had prompted the veterinary authorities to warn farmers even more urgently about the risk of a virus introduc- tion and push for measures to increase biosecurity on the farms. It would also have been important to track infection routes after the first outbreaks. The ex-post analysis of the 2015 epidemic carried out by APHIS in 2016 clearly showed
▶ POULTRY WORLD | No. 6, 2022 13
Figure 1. AI out- breaks in North America in 2022 according to USGS; status at 26 June 2022.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36
