Colorado currently has the highest number of reported cases of highly pathogenic avian influenza (HPAI) in dairy herds in the United States, with 47 confirmed detections. Since April 2022, there have also been 33 poultry flocks affected by the virus, resulting in the loss of more than 6.3 million domestic poultry in the state.

In an effort to curb further spread of the HPAI virus and implement additional control measures to protect the dairy and poultry industries and public health in the state, the Colorado Department of Agriculture announced it is implementing mandatory statewide surveillance for all Colorado Department of Public Health and Environment (CDPHE) licensed commercial cow dairies. The action, which makes it the first state to do mandatory testing, will help identify any additional infected dairies with the virus with the goal of preventing further spread of the disease, according to the agency. The order for statewide mandatory bulk-tank HPAI testing by the Commissioner of Agriculture was issued July 22, 2024.

“We have been navigating this challenging, novel outbreak of HPAI in dairy operations for nearly three months in Colorado and have not been able to curb the spread of disease at this point,” said Dr. Maggie Baldwin, Colorado state veterinarian. “We have seen devastating impacts of this disease not only to our dairy industry, but our poultry industry as well. With the strong support of the dairy and poultry industries, we feel that this is the best next step in order to protect these vital industries in our state.”

Colorado is now experiencing spillover of the dairy H5N1 strain, genotype B 3.13, into commercial poultry facilities. Colorado has had two spillover events, confirmed through genomic sequencing, and one presumptive spillover event from dairy operations into commercial poultry operations that have resulted in the death and depopulation of more than 3.2 million domestic chickens during the month of July. 

The statewide surveillance will take place under the joint supervision of CDA and CDPHE with support from USDA and will remain until further notice by the Commissioner of Agriculture or State Veterinarian. Dairy producers will receive further guidance directly on the implementation of this order to meet the testing requirements.

During this time, all Colorado CDPHE licensed dairy cow facilities with lactating dairy cattle that produce products for human consumption will be required to submit weekly samples for testing. These samples will be collected by CDPHE-certified collection samplers and tested by the Colorado State University Veterinary Diagnostic Laboratory. Dairies currently under order of quarantine or order for testing are subject to those specific orders. This does not include raw milk facilities.

“We appreciate the ongoing cooperation and partnership with both the poultry and dairy industries,” said Colorado Commissioner of Agriculture Kate Greenberg. “Mandatory surveillance of highly pathogenic avian influenza across all of Colorado’s Grade A commercial dairies is a critical next step to tamping down the virus and protecting the food system. Ongoing cooperation is key to supporting workers’ health and safety, protecting animal health and welfare, and minimizing the spread of the virus.”

More human cases confirmed

The CDC confirmed two more human cases have occurred, bringing the total to eight human cases. The virus was contracted by workers helping depopulate poultry.

In good news, the CDC said the virus’ sequence has maintained primarily avian genetic characteristics and lacks changes that would make the virus better adapted to infect or spread among humans. The agency also noted that the sequence in one of the infected farm workers is related to the first human case in Michigan. The findings, the agency said, are “reassuring” as it shows the virus does not have changes associated with antiviral resistance.