In addition to vehicle traffic and visitors, such as nutritionists, feed delivery and contract haulers, USDA’s Animal and Plant Health Inspection Service investigators found that 22 employees of three poultry flocks worked weekend shifts at two different dairy premises. Shared worker housing was identified between three poultry premises and two dairy premises. Photo by AgriStaff USA, LLC

LANSING — USDA’s Animal and Plant Health Inspection Service (APHIS) has released the findings of its investigation into how highly pathogenic avian influenza (HPAI) was introduced and, more importantly, spread among 25 Michigan dairy herds and eight poultry flocks since March 29 — when it was first confirmed in a Montcalm County dairy herd.

Dubbed the 2024 Highly Pathogenic Avian Influenza (H5N1) — Michigan Dairy Herd and Poultry Flock Summary, the report summarizes the findings from a USDA Epidemiological Strike Team investigation of disease spread between premises for 15 dairy herds and eight poultry flocks confirmed with HPAI genotype B3.13 in the state.

Whole genome sequencing (WGS) analysis suggests an initial single spillover event of the virus from wild birds to dairy cattle, most likely occurred in the Texas panhandle in December 2023, with onward spread of the virus to now 12 other states.

According to APHIS, Michigan’s first affected dairy was infected by the importation of lactating dairy cows from an affected herd in Texas, which was undetected at the time of movement, based on movement information and WGS before spreading to other Michigan dairy herds and poultry flocks.

On April 2, HPAI was confirmed on an Ionia County commercial poultry operation with the same B3.13 genotype as the first Michigan dairy herd, with directional movement of the virus from the dairy premises to the poultry premises, APHIS reported.

“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,” the report stated.

“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,” APHIS continued.

As part of its epidemiological investigation, APHIS conducted WGS analysis and follow-up field epidemiology investigations with producers, herd veterinarians on affected dairy premises and associated animal businesses — including deadstock haulers, milk haulers and feed deliveries — to identify epidemiological links between affected dairy and poultry premises.

A subset of affected dairy and poultry premises also agreed to additional on-farm sampling of wild birds and peri-domestic species (rodents and other wildlife such as rabbits and skunks) by USDA Wildlife Services personnel to rule out possible wildlife transmission.

“Despite no genomic evidence that migratory birds are spreading HPAI genotype B3.13 within Michigan, the potential for resident wild birds or peri-domestic species to move and transmit the virus between dairy herds cannot be ruled out, especially for dairy premises located in close proximity,” APHIS reported.

“All dairy herds reported wild bird, wild animal, or rodent presence on farms, with these species always having access to cattle feed. HPAI H5N1 genotype B3.13 detections in pigeons, a starling, cats, racoons, opossums, and foxes have occurred on 5 affected dairy premises and 1 affected poultry premises that participated in on-farm sampling. Still, it was a small number of individual animals and species that were detected from the large number of samples collected.”

So how did it spread?

Apart from the potential for resident wild birds or peri-domestic species to move and transmit the virus, APHIS reported that the only other potential transmission routes found from dairy herds to the poultry flocks were through shared employment, housing, or movement of employees.

Investigators found that approximately 22 employees of three poultry flocks worked weekend shifts at two different dairy premises. Shared housing between dairy and poultry workers was also identified between three poultry premises and two dairy premises, with APHIS noting that dairy and poultry employees have social contact too.

APHIS investigators determined the 15 dairy herds and eight poultry flocks that were part of its investigation had about 1,000 cattle and 84,000 birds onsite. The range of distances between dairy premises was 1 to 93 miles; between dairy and poultry premises was 1 to 93 miles; and between poultry premises was 0.7 to 68 miles.

According to APHIS, key findings identified to date and potential risk factors for local transmission included:

• Shared personnel between premises

20% of affected dairies’ employees and 7% of dairies’ employees family members work on other dairy premises;

• 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); most 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

— Milk haulers visit dairy premises, on average, 34 times within a 30-day 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)

Recommendations to mitigate disease spread APHIS said the “intensive, integrated, and specialized nature of the dairy industry results in biosecurity risks that are not completely avoidable, but these risks can be mitigated.”

While the USDA Federal Ordering requiring premovement testing for interstate movement of lactating dairy cattle greatly reduces transmission risks, APHIS said nine of the 15 affected Michigan dairy herds were closed herds and did not bring any new cattle into the herd, meaning live cattle movement restrictions would not have prevented disease in those herds.

“Movement restrictions on cattle in some Michigan-affected herds may result in serious animal welfare issues since these specialized operations do not have the facilities to manage all classes of dairy cattle and rely on an integrated network of operations to raise and manage the different classes of cattle,” AHIS wrote.

“However, testing before moving cattle would help limit premises-to-premises transmission from cattle movement within the state and may identify additionally affected herds.”

APHIS also recommended implementing biosecurity practices outlined in the Secure Milk Supply’s “Enhanced Biosecurity Plan” which emphasizes not moving cattle if possible, restricting visitors’ access to the premises and cleaning and disinfecting vehicles and equipment moved on/off the farm.

“Factors that appear to be of greater risk for introduction into 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,” APHIS concluded.

Source: Farm News Media,

Michigan Farm News



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