Infectious Diseases 2024

In early April 2024, the Michigan Department of Agriculture and Rural Development (MDARD) invited a USDA Epidemiological Strike Team into Michigan to investigate the links between HPAI affected dairy premises and evidence of spillover into poultry premises. A new report summarizes the findings from field epidemiological investigations of disease spread between premises for 15 dairy herds and 8 poultry flocks confirmed with HPAI genotype B3.13 in Michigan.
After interstate animal movement initially introduced the HPAI genotype B3.13 virus into a Michigan dairy, continued disease transmission within the state is 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, 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 include: 
• Shared personnel between premises 
-20% of affected dairies’ employees and 7% of dairies’ employees family members work on other dairy premises
- 7% of affected dairies’ employees also work on poultry premises; 13% of affected dairies’ employees have family members who work on poultry premises 
-31% of dairies have employees who own livestock or poultry at their personal residence 
• Shared vehicles between premises
-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
- 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
- 40% of affected dairy premises have regular visits for deadstock removal, with 20% having direct contact with cattle 
         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       
         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)
Based on the epidemiological findings, the majority of links between affected dairy premises, and between dairy and poultry premises, are indirect from shared people, vehicles, and equipment. As such, HPAI disease spread between dairy and poultry premises can be mitigated by identifying potential interconnections between operations (people, conveyances, etc.) and increasing biosecurity practices on all premises and associated animal businesses (e.g., milk haulers, deadstock/contract haulers and other shared vehicles/trailers between premises, livestock markets).