A recent study led by researchers at Cornell University investigated the effects of an H5N1 avian influenza outbreak on a dairy herd in Ohio comprising approximately 3,900 cows. The findings revealed a significant decline in milk production among clinically affected cows, lasting up to 60 days, and extensive asymptomatic infections among other cows. The team published their findings as a preprint study in Nature Portfolio.
Outbreak Initiation and Clinical Observations
The outbreak was traced back to the introduction of apparently healthy lactating cows from Texas into the Ohio herd. Approximately two weeks post-introduction, the first signs of illness were observed. Notably, decreased rumination and a decline in milk production were detected approximately five days before clinical diagnosis.
Production Impact and Economic Losses
Clinical disease manifested in about 20% of the cows, each experiencing an average milk loss of approximately 900 kg over the subsequent 60 days. This translated to an estimated economic loss of $950 per clinically affected cow. Considering factors such as mortality and herd removal, the total estimated cost of the outbreak amounted to $737,500 during the observation period.
Risk Factors and Transmission Dynamics
The study identified higher risks in multiparous cows compared to those lactating for the first time, suggesting a potential link between cumulative exposure to the milking process and the risk of clinical disease. Seroprevalence findings indicated that nearly 90% of the 637 animals present during the clinical phase tested positive, highlighting high transmission efficacy. Notably, antibodies were detected in 17 of 42 dry-phase cows, indicating that nonlactating cows can also serve as virus reservoirs.
Implications and Recommendations
The study underscores the need for heightened biosecurity measures in dairy operations, especially when introducing new animals. Given the potential for extensive asymptomatic infections and significant economic losses, proactive monitoring and preventive strategies are crucial to mitigate the impact of such outbreaks.
