SHIC/AASV Webinar Addresses H5N1 Influenza Risk to US Swine

The Swine Health Information Center, in collaboration with the American Association of Swine Veterinarians, hosted a webinar on H5N1 influenza risk to US swine on November 20, 2024. The goal of the webinar was to provide current information on H5N1 in livestock including updates on the H5N1 outbreak in dairy cattle, the first detection of H5N1 in a pig on a small backyard farm in Oregon, research on H5N1 in swine, and a literature review covering gaps in knowledge for H5N1. Additionally, an update on the use of aspirin in livestock was presented. The webinar can be accessed here. 

Fred Gingrich, II, DVM, executive director of the American Association of Bovine Practitioners, shared information on the H5N1 outbreak in dairy cattle first identified in a Texas dairy herd exhibiting unusual clinical signs of illness. On March 25, 2024, USDA officially announced the first isolation of influenza A H5N1 in milk from an affected cow. The initial introduction of H5N1 into dairy cattle was likely from wild birds, potentially as early as December 2023. But since that time, the source of virus transmission among dairy herds is thought to be from infected cattle.  

Dr. Gingrich stated that clinical signs of virus infection and impact on lactating dairy cows are different from infection in poultry and wild birds. In dairy cattle, there is low morbidity of 20% – 30% with a low mortality of 2% – 5% reported. He noted that there is no need for depopulation as cattle recover from the infection. H5N1 affects mostly lactating dairy cows, and clinical signs include decreased appetite and rumination, tacky manure, decreased milk production, and milk turning abnormally thick and yellow. Herd-level production losses can average 20% and the long-term impact on herds is yet unknown.   

Recent research into the dairy outbreak has shown that bulk milk tank samples can have PCR positive test results 10 to 14 days before peak clinical signs are observed. This offers an opportunity for increased surveillance for early detection and can facilitate implementation of biosecurity measures for preventing transmission. Biosecurity remains a challenge due to the segmented dairy industry structure and specialized production sectors. Transportation of adult and young stock cattle occurs daily, sometimes over long distances. Continued development of biosecurity to decrease disease transmission is critically important. Moving forward, Dr. Gingrich said safe movement will be more manageable than stopping movement in the event of an outbreak. Other needed methods for disease control include the development of safe and effective vaccines.  

Dr. Gingrich also noted that the dairy industry has worked closely with FDA and USDA to ensure food safety for consumption of products. FDA has performed testing on bulk tank samples of raw milk to confirm that pasteurized milk is safe to consume while unpasteurized milk carries a significant risk for pathogens.  In addition, USDA has confirmed the safety of eating properly handled and cooked beef. Dr. Gingrich noted that the USDA plan for national bulk tank surveillance is critically important, and that this surveillance effort continues to inform efforts for effective disease prevention and control in the US dairy industry. 

Ryan Scholz, DVM, MPH, State Veterinarian of Oregon, provided an overview of the first detection of H5N1 in a pig co-housed with poultry on a small backyard farm. The call to the Oregon Department of Agriculture on October 22, 2024, was initiated due to sick and dying birds observed on the farm. Birds on the farm included ducks, geese, peafowl, and chickens. There were three kunekune pigs housed with sheep and goats and two teacup pigs housed with chickens. A USDA technician was sent to the farm to sample affected birds. The kunekune pigs were sampled because they had direct contact with dead waterfowl on the farm but none of the pigs showed any clinical signs of illness. Samples were submitted to the Oregon Veterinary Diagnostic Lab for testing. After the initial detection of H5N1 in birds and one pig, all poultry were depopulated, and the decision was made to euthanize all of the pigs for a comprehensive diagnostic case evaluation. Samples from one kunekune pig were PCR positive including nasal and tracheal swabs, brain tissue, heart, and lymph nodes, and one teacup mini pig had PCR positive samples of tracheal tissue and tracheal swab. Virus sequencing from poultry sampled on the farm confirmed detection of the D1.2 genotype of H5N1.