Avian influenza: 2 waves, different routes and changing dynamics

While it was still assumed in June 2022 that the outbreaks would follow the pattern observed so far and that there would be no or only a few cases in the warmer summer months, it soon became apparent that this would not be the case. Although no new outbreaks occurred between 9 June and 13 July, 3 turkey farms in Utah were affected in the second half of July. This was followed by a period of almost a month without any new cases before a new wave of massive outbreaks began on 22 August.

A more detailed analysis of the timeline shows that, strictly speaking, these were 2 separate waves also showed different spatial patterns. The last case of the epidemic was documented on 28 December, but new outbreaks had already occurred in January 2023, so it can be assumed that the epidemic will continue in the following months.

It is obvious that the outbreaks in the first half-year of 2022 were triggered by infected migratory birds using the Atlantic route and the Mississippi route. The wave in the second half-year was also triggered by migratory birds which, this time, used the Pacific and Rocky Mountain routes, as well as the Mississippi route. However, since the wild birds frequented the flight routes less in the summer months than in winter, it can be assumed that the avian influenza virus, which had become endemic, also triggered infections in poultry farms. This would explain the large number of cases and high animal losses in the summer months.

High regional concentration

Of the 306 avian influenza outbreaks in 2022, 188 occurred in the first half-year and 118 in the second half-year. Figure 1 shows that in both half-year periods, Minnesota and South Dakota had the highest number of cases, but there are significant differences in the following rankings.

While Pennsylvania ranked 3rd in the first half-year, followed by Iowa and Indiana, Utah and California ranked 3rd and 4th in the second half-year. Taking animal losses as a criterion, we can easily see that there were different spatial patterns in the 2 half-years. This reflects the large differences in the stock sizes of laying hens and other poultry species.

Table 1 lists the 10 states with the highest animal losses in each of the 2 half-year periods and for 2022 as a whole. In the first half-year, a loss of 40.1 million animals was documented. They either died from infection of the virus, or were culled. That matched the animal loss of 40.1 million in the 2015 epidemic. Two northern Midwestern states ranked as number 1 and number 2, followed by Pennsylvania on the east coast. Of the western states, only Utah was represented among the top 10 states.

In the second half-year, the spatial pattern changed significantly. Ohio was in 1st place, followed by Colorado. In addition to 4 states from the northern Midwest, 3 states from the western United States now showed up, 2 of them on the Pacific coast. Apparently, the infections were caused by migratory birds that used the Pacific flight route.

For the year as a whole, Iowa ranked 1st by a wide margin, followed by Nebraska, Colorado and Pennsylvania. The composition of the 10 states with the highest animal losses reflects the different patterns in the 2 half-year periods and reveals that infections from migratory birds occurred on all 3 flight corridors, and that the virus which had become endemic apparently also caused infections in the second half-year.

Laying hens and turkeys

As with the epidemic of 2015, laying hen and turkey farms were particularly affected in 2022. Of the 57.6 million birds that died from the infection or were culled, laying hens and turkeys accounted for 54 million or 93.7%. Of these, 44.3 million were laying hens and 9.7 million were turkeys. Table 2 shows the distribution over the 2 half-year periods.

While broiler losses were high in the first half-year due to infections by wild birds using the Atlantic route, losses in the second half-year were comparatively insignificant. Laying hens and turkeys accounted for 92.3% of the losses in the first half-year and 97.2% in the second half-year.

It is worth noting that farms with more than 5 million places were not affected in the second half-year. This is probably due to the fact that after the events of the first half-year, farm managers improved the biosecurity of their farms and, possibly, if they were affected again, they may not have been fully restocked when the epidemic flared up again.

Impacts on production and retail prices

Animal losses had a significant impact on egg and turkey meat production. Assuming that 306 million laying hens were housed in commercial farms with more than 30,000 places at the beginning of 2022, the outbreaks reduced the total inventory by 44.3 million, or 14.5%.

Individual states were affected differently. Nebraska lost a good half of its inventory, Iowa over a third, Ohio 14%. The impacts in Colorado were particularly serious. In the first half-year, 68.6% of its laying hens were lost. No exact percentage can be given for the second half-year. For reasons of data protection, it is not known to what extent farms had already been restocked and if they were affected again. The loss of another 2.7 million hens led to a further reduction in egg production and supply shortages in December 2022 and January 2023.

The sharp reduction in laying hen inventory affected retail prices for both shell eggs and egg products. According to the Egg Industry Center, the average price for grade L (large) shell eggs increased from US$ 1.32 per dozen in January to US$ 3.88 per dozen in November 2022. In California, prices were even as high as US$ 6.72 per dozen.

The significantly higher price there is a consequence of Proposition 12 which prohibits the sale of eggs produced in farms with conventional cages. Affected farms with alternative housing systems reduced the available egg supply considerably, so that higher prices could be enforced in retail.

The loss of 9.7 million fattening turkeys also led to a significant increase in retail meat prices. Due to high animal losses in Minnesota and South Dakota, leading processors in the Midwest were forced to cut production by 20-30%. The price of turkey breast increased from an average of US$ 4.40 per kg in 2020 to over US$ 14 in the fourth quarter of 2022.

Summary and outlook

When considering the 2022 epidemic in context, it becomes obvious that, in contrast to 2015, not only the Mississippi flight route of migratory birds led to primary outbreaks, but that infections also occurred along the Atlantic and Pacific flight routes, which caused several epi-centres of outbreaks (Figure 8). While there were no more outbreaks in the early summer months of 2015, a new wave of outbreaks occurred in 2022 from mid-July onwards.

A closer analysis of the spatio-temporal development reveals 2 separate waves of outbreaks. While in the first half-year of 2022 the outbreaks were probably mainly infections triggered by migratory birds which mostly affected farms in the northern Midwest and the mid-Atlantic, states in the western United States and again in the Midwest were affected in the second half-year.

Here it became clear that the familiar spatial pattern of avian influenza epidemics had changed. The avian influenza virus had obviously become endemic, occurring in native wild birds and triggering infections on commercial poultry farms. This explains why, in 2022, outbreaks were detected in commercial poultry farms in 27 states and a new record was reached with 57.6 million animals killed or culled.

Although estimates have not yet been released by the US Department of Agriculture, it is reasonable to assume that the financial loss will be between US$ 4 billion and US$ 5 billion, assuming a loss of around US$ 3 billion in 2015.

In his detailed analysis of the epidemic in 2015, Böckmann (2021) already pointed out that, in addition to the financial losses, the large number of outbreaks led to psychological stress for poultry farmers, especially turkey farmers. Renewed outbreaks in 2022 are likely to have resulted in similar problems, especially in Minnesota and South Dakota.

Since the financial losses of farmers and companies are compensated for by payments from the federal government, the direct losses caused by an epidemic are small. However, financial losses resulting from the vacancy after a ban on restocking, as well as losses of compound feed mills, processing plants, transport companies or veterinary practices are not reimbursed.

The changed temporal and spatial pattern of the avian influenza outbreaks in 2022 and the occurrence of the virus in domestic wild birds have rekindled the discussion about preventive vaccination of poultry stocks and a change in housing systems (Brockötter, 2022).

In view of the fact that the virus has become endemic, the predominant method of keeping turkeys in open barns represents an unacceptable risk. Given the high infection pressure, this also applies for laying hens in closed facilities. A change in the attitude of the poultry industry will be necessary to prevent further epidemics of the magnitude seen in 2015 and 2022. In addition, it will be necessary to increase the monitoring of wild birds, both migratory and resident.

Quite clearly, despite the experience gained from the 2015 epidemic, it was not possible to educate poultry farmers adequately in how to improve the biosecurity of their farms, because there is almost no other way to explain the large number of outbreaks on turkey farms, even taking into account the susceptibility of turkeys. In large laying hen farms with several million birds, the management were obviously also unable to prevent the virus from penetrating the farm buildings.

One way to prevent or at least limit devastating epidemics in future would be the vaccination of flocks. This is endorsed by major egg producers, as the author’s interviews with representatives of the 2 leading US egg companies in the summer of 2022 showed. However, most poultry meat slaughterhouses and processors continue to reject compulsory vaccination because they fear that this would severely limit their export opportunities or could lead to the loss of important markets. Whether a compromise is possible here, is still completely open.

References are available on request.