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Bovine Influenza in Central Valley, CA. Associated with Elevated Cow Mortality

10/21/2024

Unlike cases of bovine influenza in Texas, Colorado and eleven other states, mortality among affected herds in the Central Valley of California has assumed concerning proportions.  To date, over 120 herds have been diagnosed with H5N1 B3.13 strain with some operations recording 15-20 percent mortality compared to less than five percent in other states collectively recording 210 cases to date. Although ambient heat has been implicated as a stress factor contributing to mortality, it is noted that temperatures in the Central Valley frequently exceed 100F without resulting in an appreciable elevation in losses.

 

Rendering companies are overwhelmed and carcasses have been stacked in the open in areas close to herds adding to the risk of contamination of soil followed by dispersal by wind, carrion birds or mammalian vermin.

 

It is of extreme urgency that the whole genome sequence of isolates associated with high mortality in cows should be analyzed to determine if there has been a shift in pathogenicity to animals and humans due to mutation.

 

It is noted that eleven dairy herd workers have been diagnosed with H5N1v influenza.  Epidemiologic studies should be conducted to determine risk factors other than those that are currently recognized and to determine whether appropriate PPE was issued and used by those who were infected.  Surveillance to ascertain whether domestic contacts of those affected yielded H5N1v virus on PCR appears necessary to determine whether the virus has become contagious among humans.  It is also necessary to conduct serologic surveys on workers and their immediate contacts for individuals known to have been infected based on clinical symptoms or PCR assay as compared to those who were unaffected. On Tuesday 20th October health officials in Washington state reported five workers with conjunctivitis and respiratory symptoms associated with the affected farm in Franklin County. Whether these individuals were infected as part of their routine flock duties or were part of a depopulation team has not been announced but it is anticipated that information will be made available to the WHO after samples have been collected and expeditiously analyzed. 

 

In the interim, it is presumed that the California Department of Food and Agriculture is actively following a program of surveillance in order that affected herds can be quarantined as far as possible.  It is hoped that epidemiologic studies in progress will identify risk factors and vehicles of transmission.

 

The occurrence of cases of H5N1v infection in farm workers in contact with dairy herds and infected egg-production flocks requires more follow up. Assay for H5N1 antibody among potentially exposed but unaffected individuals will be required. Determining how and when individuals were infected, duration of shedding virus from the respiratory tract requires structured investigation both at the field and molecular levels.

 

Despite the USDA/CDC contention that H5N1 strain B3.13 responsible for bovine influenza does not represent a risk for human population in affected areas, more transparency by public agencies would be reassuring.