#19,147
Last August, in Preprint: Surveillance on California Dairy Farms Reveals Multiple Sources of H5N1 Transmission, we looked at the testing of air, wastewater, and milk samples from 5 California farms/milking parlors, which found evidence of extensive environmental (air, water & milking equipment) contamination with H5N1.Key findings included:
- detection of infectious H5N1 virus in milking parlor air and farm wastewater evidence of airborne transmission from exhaled cow breath
- H5N1 infection without mastitis symptoms, suggesting subclinical milk producing cows may be going undetected
- the detection of an N189D HA mutation (which may affect the receptor binding domain) in at least one air sample
This week PLoS Biology has published a revised and extended (now 14 farm) study by these same authors which (again) reports multiple plausible H5N1 transmission routes on dairy farms; including milk contact, aerosols in parlors, and contaminated wastewater.
- and heterogeneous patterns of viral infection across individual udder quarters that call into question the assumed `primary role' played by milking equipment
The published version provides additional evidence for infectious H5N1 detection in both air and wastewater (not just viral RNA detection), along with a much larger sampling size.
Due to its length, I've only posted the link, abstract, and some excerpts from the conclusion. Follow the link to read it in its entirety. I'll have a brief postscript after you return.
RESEARCH ARTICLE
Surveillance on California dairy farms reveals multiple possible sources of H5N1 influenza virus transmission
A. J. Campbell1 , Meredith Shephard1☯, Abigail P. Paulos2☯, Matthew D. Pauly1 , Michelle N. Vu1 , Chloe Stenkamp-Strahm3 , Kaitlyn Bushfield1 , Betsy Hunter-Binns4 , Orlando Sablon2 , Emily E. Bendall5 , William J. Fitzimmons5 , Kayla Brizuela1 , Grace E. Quirk1 , Nirmal Kumar1 , Brian McCluskey3 , Nishit Shetty6 , Linsey C. Marr7 , Jenna J. Guthmiller8 , Jefferson J. S. Santos9 , Scott E. Hensley9 , Edith S. Marshall10, Kevin Abernathy4 , Adam S. Lauring5 , Blaine T. Melody11, Marlene K. Wolfe2 , Jason Lombard3 *, Seema S. Lakdawala
Abstract
Transmission routes of highly pathogenic H5N1 between cows or to humans remain unclear due to limited data from affected dairy farms. We performed air, farm wastewater, and milk sampling on 14 H5N1-positive dairy farms across two different California regions.
Infectious virus was detected in the air in milking parlors and in wastewater streams, while viral RNA was found in exhaled breath of cows. Sequence analysis of infectious H5N1 virus from air and wastewater samples on one farm revealed viral variants relevant for potential human susceptibility. Longitudinal analysis of milk from the individual quarters of cows revealed a high prevalence of subclinical H5N1-positive cows.
Additionally, a heterogeneous distribution of infected quarters that maintained a consistent pattern over time was observed, inconsistent with shared milking equipment serving as the sole transmission mode. The presence of subclinically infected cows was further supported by detection of antibodies in the milk of animals that exhibited no clinical signs during the H5N1 outbreak on one farm. Our data highlight additional sources and potential modes of H5N1 transmission on dairy farms.
(SNIP)
Discussion
Elucidating the routes of transmission of H5N1 between cows is critical to defining successful mitigation strategies. In this study, we successfully detected H5N1 in the air and in reclaimed farm wastewater on separate dairy farms on multiple days. This included infectious air samples from three different milking parlors and viral RNA from the exhaled breath of rows of cows on two distinct farms. Additionally, we detected viral RNA in farm wastewater at multiple sites on various farms and infectious virus at two different sites on the same farm.
Together, these results highlight the extensive environmental contamination of H5N1 on affected dairy farms and identify additional sources of viral exposure for cows, peridomestic wildlife, and humans.
Dairy parlors, which are often enclosed spaces and where aerosolization of milk occurs, pose the greatest threat from inhalation of the virus to dairy farm workers compared to the open-air housing pens.
(SNIP)
Taken together, our data confirm the presence of infectious H5N1 virus in the air and reclaimed farm wastewater sites. In addition, we observed high viral loads and H5 antibodies in the milk of cows, including those without clinical signs, and heterogenous patterns of H5N1 positivity by quarter, suggesting that multiple modes of H5N1 transmission likely exist on farms.
These transmission routes could include contaminated milking equipment from an infected cow, aerosols generated within the milking parlor, and/or contact of teats with contaminated water used to clean housing pens.
Multiple mitigation strategies should therefore be implemented to reduce the risk of H5N1 spread within a herd and to humans. Respiratory and ocular personal protective equipment (PPE) for farm workers to prevent deposition of virus-laden aerosols on these sites, especially in the milking parlor. Disinfection of milking equipment between milking of each cow, such as with consistent use of backflush system, could also reduce spread of H5N1 between cows. Treatment of milk from sick cows to inactivate H5N1 prior to disposal as well as treatment of waste streams prior to their use in fields or on farms should also be considered. Finally, identification of infected cows, regardless of clinical signs, for isolation will help reduce the transmission of H5N1 on farms.
This paper calls for a number of actions to reduce the spread of H5N1 on dairy farms, including:
- Respiratory & ocular personal protective equipment (PPE) for farm workers
- Treating waste milk before disposal
- Treating manure/wastewater/waste streams
- Isolating infected cows, including subclinical cases
