By Dr. Simon M. Shane

The number of cases of H5N2 low pathogenicity strain avian influenza in two adjacent counties in Minnesota has reached eight in five weeks.  There appears to be an attitude of complacency given that the isolates involved are characterized as low-pathogenic strains.  It is axiomatic that given sufficient time and a susceptible population of commercial poultry, mutation to produce a highly pathogenic strain is inevitable.  This is especially the case when virus can be disseminated by deficiencies in biosecurity.  The shift from LPAI to HPAI has been demonstrated successively in outbreaks in Pennsylvania (1983), Mexico (1994), Italy (1997), Chile (2002) and Indiana (2016).

The significant questions relating to the current cluster of cases should be addressed by aggressive and diligent epidemiologic evaluation.  These include:

• Are the H5N2 isolates homologous?
• From a molecular standpoint with respect to basic amino acids at the HA cleavage point, how likely is it that the H5N2 strain may become highly pathogenic?
• What is the source of infection? If free-living birds, what species are involved, how long do they shed AI virus and the prevalence rate in these populations?
• What is the connection among the affected farms in Kandiyohi and Stearns County? Commonality of ownership? Integrator? Service companies? Feed supplier?
• Are any of the risk factors identified following the 2015 epornitic still present and contributing to infection? These include dead-bird and garbage collection?  Unrestricted access to farms?  Deficiencies in personal decontamination?
• Are feed delivery vehicles and drivers subject to acceptable decontamination given that older flocks require more frequent deliveries increasing the probability of introduction of infection?
• What is the role of multi-age placement? Three of the eight farms identified to date have two-age flocks common in Minnesota.
• What are the risks of applying a “controlled slaughter and marketing” program with either an H5 or H7 low-pathogenicity infection? While it is generally accepted that turkeys will cease shedding within three weeks of infection, can quarantine be maintained during the viremic stage of infection especially with multi-age placement?
• If other farms within the infected zone are free of infection, factors which contributed to introduction of virus onto affected farms should be evaluated. If farms which are in close proximity become infected, how is the virus transmitted? Air movement. Feed delivery? Service personnel? State and Federal employees? Farm families? Farmworkers?

Now is the time for epidemiologic evaluation.  It is possible that an understanding of how the infection was introduced to farms in the two counties and how it has spread, presuming that each case is independent will be of help in advising the turkey industry in Minnesota to avoid a recurrence of 2015.

Minnesota has an established policy of controlled slaughter and marketing of flocks seasonally infected with diverse strains of other than H5 and H7 AI serotypes. This approach is justified from a practical and financial perspective. Between 1978 and 2000 there were over 108 introductions of LPAI reported in Minnesota turkey flocks. Although 20 cases involved either H5 or H7 LPAI strains, there were no instances of mutation to HPAI, attributed to depletion of affected flocks at the time of scheduled slaughter. Most of the affected farms were allowed outside access or were supplied with contaminated surface water.

Outbreaks of LPAI in Minnesota turkeys included 178 farms in 1995 infected with H9N2, presumably derived from migratory waterfowl. Subsequent to adoption of confined rearing by Minnesota growers in 2000, only 28 flocks were infected with LPAI up until the 2015 HPAI outbreak. This event disclosed deficiencies in biosecurity which would logically, cast doubt on the policy of controlled slaughter and marketing given extensive dissemination of infection.

There is a precedent for depletion of turkey flocks infected with LPAI. During the spring and summer of 2002, 4.7 million commercial turkeys in 210 flocks in Virginia, West Virginia and North Carolina were depopulated after contracting H7N2 virus, possibly from live bird markets.

Given the cost and consequences of the HPAI epornitic of 2015, a more aggressive approach to detection and control of LPAI is required to protect the domestic U.S. poultry industry and to maintain critical export markets, irrespective of the OIE principle of regionalization.

Dr. Simon Shane, FRCVS, BVSc, Ph.D., MBL, dip ACPV, is the publisher of EGG-NEWS and CHICK-NEWS.