HPAI in cattle: What's next? Highly pathogenic avian influenza has moved into mammals, posing new challenges

Several speakers at the Second International Avian Influenza Summit held at the University of Arkansas addressed the recent spillover of highly pathogenic avian influenza (HPAI) into dairy cattle in the United States.

Dr. Erica Spackman, US National Poultry Research Center, USDA Agricultural Research Service, noted that HPAI outbreaks are now global and affecting species not traditionally associated with HPAI, such as dairy cows.

Almost all HPAI cases are from the H5N1 Gs/GD (Goose/Guandong/1996) lineage with clade 2.3.4.4 behaving in ways never seen before. This virus has become endemic in numerous wild bird species, particularly dabbling ducks and has the potential to adapt to new hosts.

These ducks are a reservoir for different genes that can reassort with highly pathogenic viruses and have low barrier to transmission among different species. This virus has caused great losses in the US poultry industry since 2022 and is still ongoing.

Historically, low pathogenic AI (LPAI) was transmitted from ducks to chickens and turkeys, becoming highly pathogenic and then transmitting back to ducks. Ducks are now virus factories, spreading HPAI not just LPAI.

LPAI, and now HPAI, can spread from wild birds to humans, pigs, dogs, horses, sea lions and other mammalian species. It has now infected dairy cows and these could evolve into a sustained reservoir for the virus, which calls for new control measures, Spackman concluded.

Juan Piñeiro, DVM, MS, PhD, assistant professor and dairy extension specialist, Texas A&M AgriLife Research and Extension, said that the outbreak of HPAI H5N1 in dairy cattle started in the Texas panhandle in February 2023 and has now spread to 14 states, affecting over 319 dairy herds (and counting). The outbreak caused a 10-11% decrease in milk production and dry matter intake. There was significant variation in how different dairies were affected, with some experiencing only a 4% decrease in milk production and others up to 20%, with some cows experiencing up to an 80% loss.

The disease was initially misdiagnosed but later confirmed as HPAI H5N1 clade B3.13. On March 25, 2023, USDA confirmed HPAI in samples from Kansas and Texas. Interstate movement restrictions were implemented for lactating cows, requiring negative test results for at least 30 cows before moving dairy herds. By the time of the USDA no-movement order was issued, infected cattle had moved across the country; in August 2023 there were 197 cases in 14 states.

Precision dairy technologies like wearable collars which measure rumination, activity, and feeding time, alerted producers that something was wrong. Initial investigations focused on mycotoxins, due to the high number of cases.

Collaboration with the Texas Animal Health Commission and the USDA highlighted the spread and impact of the outbreak. The diagnostic process was lengthy, requiring elimination of differential diagnoses and confirmatory tests from national laboratories.

The outbreak followed a sequential pattern, starting with individual cows, then spreading to pens, dairies, and eventually counties and states. The absence of a system to quickly investigate and respond to new diseases was identified as a key challenge.

The FDA and USDA provided evidence that commercial milk supplies remain safe due to pasteurization and separation of sick cows from the milk supply. Studies show that pasteurization effectively inactivates HPAI, alleviating public concerns about food safety.

Piñeiro emphasized the importance of improving timely communication and collaborative efforts from different agencies to stop the spread of this or other emerging diseases. While there is an official system in place to deal with foot and mouth disease, no system really exists for other infectious diseases.

Piñeiro concluded by highlighting the need for development of vaccines for dairy cattle to address HPAI. Vaccination is critical in preventing similar outbreaks in the future.

Dr. Kay Russo, DVM, MAHM, DACPV, RSM Consulting, Colorado, is a practicing veterinarian in dairy cattle and poultry. She was involved in the initial efforts to diagnose the mystery disease in dairy cattle in Texas in early 2023. There were many challenges in diagnosing and managing the outbreak. The suggestion to consider HPAI as a possible cause was initially met with skepticism.

"There were just all sorts of rumors swirling about what this disease could be." Dairy veterinarians in Texas had gone through a litany of tests which came up negative on all the usual diseases. Currently working as a poultry veterinarian, Russo was aware of the damage HPAI has done over the last two years in the US. "Since this strain moved into a lot of mammalian species... with the respiratory involvement, the digestive involvement...we ought to consider influenza."

A Texas dairy veterinarian mentioned that all the birds on the farm were dead. That raised alarms with Russo. She asked the dairy to collect dead birds and submit them for influenza testing. Those samples came up positive for HPAI. But it took a lot of convincing to get dairy samples tested for HPAI.

Typically, about 30% of a dairy herd is replaced with heifers each year. Calves get fed waste milk and get infected. The USDA stop-movement order did not include replacement heifers. There is no clear playbook for handling the HPAI virus on dairy farms or potential for depopulation, which is the typical response on poultry farms.

Russo emphasized the importance of a cross-species approach to manage the virus and the need for better testing and reporting. The focus on lactating cows ignores the spread of the disease by calves. Wastewater monitoring is needed to detect the virus, along with better surveillance in general.

She concluded by emphasizing the need for a coordinated response to avoid another pandemic and the importance of public health measures in general.

Dr. Michelle Kromm, DVM, MPH, MAM, Diplomate ACPV, Food Forward LLC, noted that HPAI virus clade B3.13 presents unique challenges for all animal agriculture, including the need for a consistent national strategy, better science generation, and the exploration of vaccine programs to break transmission cycles.

The occurrence of genotype B3.13 HPAI in dairy cattle requires a reevaluation of traditional disease response strategies. Challenges include a lack of consensus by the poultry and dairy industries on the aim of the response programs, which is eradication in poultry but not in dairy cattle.

Additional resources are needed to minimize long-term impacts on human health, food security, and economic sustainability. Field-level data informing science-based policies is critical; policies must be based on good science to mitigate risks. Vaccine programs are needed for at-risk animal populations, including humans, to break transmission cycles.

Kromm's conclusion reflects the comments of other speakers at this conference: HPAI in dairy cattle is a game-changer for animal agriculture and even poses the risk of causing a human pandemic.