One Health Rapid Response: PCR testing of milk samples from the UC Davis dairy herd showed no evidence of infection with H5N1 influenza

In late April, a significant increase of influenza A RNA was observed in samples collected from the UC Davis wastewater treatment plant. The increase was not explained by known clinical cases at Student Health or Occupational Health on campus. Out of an abundance of caution, the Yolo County Public Health Officer, Dr. Aimee Sisson, recommended testing of the dairy herd on campus for avian influenza, instigating a One Health early warning alert investigation. Thankfully, none of the UC Davis dairy cattle had shown any clinical signs of influenza infection, nor had cats on the dairy site.

The avian influenza concern stemmed from detections of H5N1 influenza A in dairy cows in nine other states, with high viral loads found in the raw milk of infected cows and indirect evidence that infected dairy cows might remain asymptomatic. As of May 24,, there have been only 3 reported human cases of H5N1 influenza, with no evidence of subsequent transmission between humans. However, due to the potential public health risk, it is important to continue to monitor for the presence of the virus in wastewater, livestock, other animals, and people.

In addition to milk samples from the dairy herd, additional wastewater samples were collected and processed from throughout the time period where the influenza A wastewater spike was observed. Wastewater monitoring for influenza A and other pathogens at UC Davis is led by Associate Professor Heather Bischel through Healthy Central Valley Together, a collaborative public health project that uses wastewater monitoring to inform community prevalence of disease in Merced, Stanislaus, and Yolo counties.

No avian influenza was detected in any of the dairy or wastewater samples, suggesting that the most likely source of the spike was probably subclinical human cases of influenza A on campus. H5N1 avian influenza is a subtype of influenza A, which also includes the more common seasonal influenza viruses.  The wastewater plant processes material from the entire UC Davis campus, so it is difficult to pinpoint the specific source of a particular virus.

UC Davis continues to use a vigilant One Health approach to monitor for any increases in clinical cases of influenza A, as well as to monitor campus wastewater for a number of other viruses of potential public health concern, including avian influenza.