Bird flu in dairy cattle: Unknowns

Researchers still aren’t sure how bird flu spreads within dairy herds
calendar icon 29 October 2024
clock icon 4 minute read

Research has demonstrated that highly pathogenic avian influenza (HPAI) strains can infect dairy cows and that although the genotype B3.13 virus is found mostly in the udder and milk, it can also be found in the urine and neuronal tissue. One study showed that calves get infected and shed the virus nasally, but didn’t infect sentinel cows. The very rapid spread of the disease within a herd suggests an alternative form of dissemination, which has yet to be identified, said Kay Russo, DVM, RSM Consulting, Colorado, during the Second International Avian Influenza Summit held at the University of Arkansas.

At the same conference, Juan Piñeiro, DVM, MS, PhD, assistant professor and dairy extension specialist, Texas A&M AgriLife Research and Extension, noted that the outbreak of HPAI H5N1 in dairy cattle led to a 10-11% decrease in milk production and dry matter intake, although those numbers varied depending on the herd. Within a month after the outbreak began (February 2023) lactating cows had decreased rumination and had thicker mammary glands.

Piñeiro noted that the outbreak followed a sequential pattern, starting with individual cows, then spreading to pens, dairies, and eventually counties and states. Data from three different dairy farms in Texas showed that the virus moved quickly through the herds. On Day 1 of the discovery of the suspected disease on the farms, approximately 40 cases a day were reported until Day 6, when the suspect cases rose to over 60 a day and by Day 9 around 150 daily suspect cases were reported. Starting on Day 10 the number of suspect cases began to go down. In these three dairy farms, 1865 suspect cases were reported over a 14-day period, affecting 23,000 cows.

A closer look at these same three dairy herds revealed that cows in their third lactation (older cows) were by far the most affected, with 1,000 cases reported. Cows in their first or second lactations had around 400 cases, Piñeiro said.

Insufficient workforce, lack of funding, and miscommunication were among the many challenges the dairy sector faced in the early days of the outbreak. Plus, the absence of a system to quickly investigate and respond to new diseases resulted in the spread of the disease, Piñeiro concluded.

Veterinarians challenged

Russo, a certified veterinarian in dairy cattle and poultry, highlighted the challenges faced by veterinarians and animal caregivers, including job losses and increased workload. There were also reports that some milk producers tried to conceal the virus from authorities. This was extraordinarily stressful for the veterinarians who were trying to do what’s best for the cows, the dairy industry, and the consumers.

Even though the mode of transmission within a dairy herd is not yet understood, calves do get fed waste milk and get infected. About 30% of a dairy herd is replaced with heifers each ear, which is why the virus quickly spread to 14 states, she explained.

Russo mentioned several actions that are needed to control this outbreak and prevent the next one:

  • Conduct more epidemiological investigations to better understand how the virus is spreading within and between herds.
  • Implement routine bulk tank testing for H5N1 at processing plants to identify infected dairies.
  • Wastewater monitoring is needed to detect the virus.
  • Explore vaccination strategies for non-lactating animals (e.g., heifers, dry cows) to reduce viral cycling within herds.
  • Develop safe protocols for managing H5N1-positive waste milk to prevent further environmental contamination.
  • Increase transparency and timely sharing of virus sequence data and metadata with researchers to support a better understanding of virus evolution and spread.
  • Improve access and monitoring of at-risk populations, such as workers, to better understand the human health impacts.

“The goal is to get a handle on this virus and avoid going into another pandemic, which nobody wants. At the end of the day, this isn't the dairy industry's fault that it was introduced. It's not the poultry industry's fault it was introduced. It’s about how we act and what we do as a country, as scientists, as regulators, today and tomorrow that will define the sustainability of our industries, and I think we can do better, and we need to do better,” Russo concluded.

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