Highly pathogenic avian influenza has been confirmed in a large commercial dairy in central Michigan, following cattle from an affected premises in Texas. The cattle left Texas on March 7 and did not appear ill. The first animals to be ill were on March 20th, and the initial screening diagnosis was on the 26th. Michigan’s state veterinarian, Dr. The commercial milk supply remains safe due to federal animal health requirements and pasteurization. The virus’s genome sequence is being monitored to determine if the threat to mammals has increased. The affected premises voluntarily stopped the movement of all animals. The Idaho State Department of Agriculture confirmed highly pathogenic avian influenza in a dairy cattle operation, and the affected facility also imported cattle from another state with cases of HPAI. Operations are encouraged to implement enhanced biosecurity measures and closely monitor herds.
The highly pathogenic avian influenza (HPAI) virus outbreak began in 2022, with H5N1 being the primary strain. The virus has been identified in wild birds in every US state and has also affected domestic birds and other wild mammals, such as red foxes and skunks. Cases of affected ruminants were only recently reported, and are thought to be the first US detections of HPAI in domestic ruminants. On March 20, the Minnesota Board of Animal Health reported that a juvenile goat, which lived on a farm with a HPAI-positive poultry flock, had tested positive for the same virus, specifically the H5N1 strain. The investigation began when the owner of the farm notified the Board of Animal Health of unusual deaths of newly-kidded goats on the property. State veterinarian Dr. Brian Hoefs said the diagnosis was significant because it highlights the possibility of the virus infecting other animals on farms with multiple species.
The Texas Department of Agriculture was looking to identify a mystery illness affecting dairy cattle in the state. On March 25, the Texas Agriculture Commissioner confirmed the disease was caused by a strain of HPAI. The US Department of Agriculture (USDA) announced it was “investigating an illness among primarily older dairy cows in Texas, Kansas, and New Mexico”, with samples collected for further testing from two farms in Texas and two in Kansas.
Both the USDA and veterinarians agree that the virus has likely been introduced on US dairy farms by wild birds. Dr. Alex Hamberg, Bureau Director of the Pennsylvania Department of Agriculture, revealed during an update for Pennsylvania dairy farmers on Wednesday, March 27, that the sequencing of the samples collected from Texas and Kansas farms matched the avian influenza that is circulating in the Central and Western Flyways or Pacific Flyways. He said that the most likely way that this virus is introduced is through wild birds, specifically waterfowl, which carry the biggest risk of transmitting the virus.
There is no evidence at this point to support transmission amongst dairy cattle. Genetically, this virus does not carry indicators that it would transmit easily to humans. It is likely that cattle are dead-end hosts, meaning that when a pathogen enters a dead-end host, its ability to spread beyond that animal is relatively low. USDA also confirmed that testing by the National Veterinary Services Laboratories found that the virus hadn’t evolved to be more transmissible to humans, meaning that the current risk to the public remains low.
Dairy cows and milk production are affected by the virus, with reduced feed intake, reduced rumen motility, and reduced bulk tank milk. About 10% of cows become more severely ill, and some will dry off very quickly or produce thicker colostrum-like milk. While there have been reports of some cows culled early due to not returning to production, most of these cows can return to production.
As for whether asymptomatic cattle could harbor the virus, Dr. Hamberg said that from testing done so far, the answer to this is negative.
The US Department of Agriculture (USDA) has stated that there is no concern about the safety of commercial milk supplies due to the HPAI outbreak. Milk from impacted animals is being diverted or destroyed, and pasteurization inactivates the virus, ensuring that only pasteurized milk can enter interstate commerce. Dr. Alex Hamberg explained that the abnormal milk coming out of affected cows is decreasing, making it unlikely to make it into the bulk tank. Pasteurization also inactivates the virus, so there is no risk for consumers.
A major impact on milk supply and dairy prices is not expected since the outbreak has affected only a small number of farms. Farm owners and workers are encouraged to stay vigilant and monitor their herds for any symptoms and contact their veterinarian if signs of illness are detected. Supportive care for animals that have contracted the disease is recommended, including isolation, reducing sources of stress, monitoring feed and water intake, and ensuring they are not dehydrated.
To manage bird populations, farmers should address the three reasons why birds come to farms: food, shelter, and water. This can be done by removing natural food sources, blocking bird access to cattle feed, removing bird feeders near the property, ensuring proper disposal of waste that can draw in birds of prey, limiting vehicle access to areas close to a water source, reducing access to areas for perching, eliminating areas with standing water, fencing cattle away from ponds, and limiting the use of unfiltered surface water for cattle.
Implementing biosecurity measures is now more important than ever, with farmer workers told to use boot covers, keep logs of who enters and exits the property, and disinfect footwear between farms. If visiting areas with a lot of waterfowl feces, consider a car wash or disinfecting clothing and boots before moving on to another farm.
There are no movement controls associated with cattle coming out of Texas and USDA is not supporting movement controls. However, veterinarians are asking for reports of suspect cases and are still developing the response protocol for this specific incident. As the investigation continues and authorities look at multiple factors that likely caused the outbreak, there is no firm timeline on when the investigation will reach a conclusion. Key takeaways so far include that the virus affects older, mid-lactation cows who tend to recover in 10 to 14 days, pasteurization inactivates the virus, and dairy cows appear to be dead-end hosts, meaning that transmission doesn’t occur beyond them, either cow to cow or cow to human.
