On June 9, the USDA issued a report that summarizes the findings from field epidemiological investigations of disease spread between premises for 15 dairy herds and eight poultry flocks confirmed with HPAI genotype B3.13 in Michigan.
The following information is pulled from the USDA’s 2024 Highly Pathogenic Avian Influenza (H5N1) - Michigan Dairy Herd and Poultry Flock Summary (see Michigan Dairy Herd and Poultry Flock Summary).
The information offers potential insights for how the dairy and poultry industries in states beyond Michigan likely have been impacted, as well.
A ‘Eurasian Lineage Goose’
Whole genome sequencing (WGS) of viruses from the dairy and poultry premises identified Eurasian lineage goose/Guangdong clade 2.3.4.4b, genotype B3.13 on the Michigan farms and suggests likely indirect transfer of virus from the dairy premises to the poultry premises.
USDA reports that interstate animal movement initially introduced the HPAI genotype B3.13 virus from Texas into a Michigan dairy. However, USDA says the continued disease transmission within Michigan has been determined to be multifactorial.
Transmission between farms is likely due to indirect epidemiological links related to normal business operations such as numerous people, vehicles, and other conveyances frequently moving on and off the affected dairy premises, with many of these indirect links shared between premises.
Importantly, USDA says, disease spread due to independent introduction of the virus onto dairy or poultry premises from migratory waterfowl is not supported based on both genomic and epidemiological data analysis.
Key findings identified to date and potential risk factors for local transmission in Michigan specifically, include:
Shared personnel between premises
o 20% of affected dairies’ employees and 7% of dairies’ employees family members work on other dairy premises
o 7% of affected dairies’ employees also work on poultry premises; 13% of affected dairies’ employees have family members who work on poultry premises
o 31% of dairies have employees who own livestock or poultry at their personal residence
Shared vehicles between premises
o 62% of affected dairy premises use shared vehicles to transport cattle, with only 12% of premises cleaning vehicles before use
Frequent visitors on/off premises
o 100% of affected dairy premises have regular visits by veterinarians, nutritionist/feed consultant, and/or contract haulers (e.g., cattle or manure); the majority of these visitors have direct contact with cattle
o 40% of affected dairy premises have regular visits for deadstock removal, with 20% having direct contact with cattle. Furthermore:
-53% of affected dairies utilized the same deadstock removal company and 40% had animals removed from the premises by that company within 30 days prior to clinical onset
o Milk haulers visit dairy premises, on average, 34 times within a 30-day time period. Furthermore:
-93.3% of affected dairy premises are part of the same milk co-op with at least one other affected dairy premises within the state (i.e., only one of the affected dairy herds is part of a milk co-op that none of the other 14 affected dairy herds belong to)
Disease Spread Between Dairy and Poultry Premises
Apart from the potential for resident wild birds or peri-domestic species to move and transmit the virus, the only other potential transmission routes found from dairy herds to the poultry flocks were through shared employment, housing, or movement of employees.
Approximately 22 employees of three poultry flocks worked weekend shifts at two different dairy premises. Shared housing between dairy and poultry workers was identified between three poultry premises and two dairy premises. It is also possible that dairy employees have social contact with poultry premises employees, USDA reports.
In Summary
The investigations discussed in this report, including the respective WGS information, indicate that HPAI H5N1 genotype B3.13 was introduced into Michigan through animal movement from Texas and subsequently spread within the state between dairy premises with spillover into poultry premises through multiple possible routes.
Factors that appear to be of greater risk for introduction into a dairy premises may be mitigated through enhanced biosecurity, increased animal testing, and potentially through within-state animal movement restrictions if they can be implemented without impacting animal welfare.
USDA says the willingness of Michigan producers to participate in these investigations has greatly increased the body of knowledge of HPAI H5N1 B3.13 detections in Michigan and throughout the nation; this report could not have been completed without them.
For more information on the H5N1 issue:
H5N1 Virus Found in Beef for First Time, FSIS Says
FDA Says New Round of Tests Prove the U.S. Milk Supply is Safe From H5N1 Virus
