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Epidemiologic Evaluation of Bovine Influenza Apparently Obstructed by States


From a statement issued by Dr. Nirav Shah, Principal Deputy Director of the Center for Disease Control and Prevention (CDC), there is unanimity between his agency and USDA but state agricultural departments and individual dairy operations are obstructing investigations relating to the prevalence of infection in herds and workers.


With an emerging infection such as bovine influenza-H5N1 it is critical to determine as rapidly as possible the prevalence rate and geographic extent of the infection.  Both field and molecular data must be obtained and analyzed to ascertain the rate of spread and modes of infection in order to implement counter measures. Epidemiologic data can be used to predict the progress of the disease in cattle and genomic evaluation can assess the risk of extension to the human population.


The CDC, with their focus on human health, is obviously concerned over the possible incidence rate of H5N1 infection among workers and should be allowed to conduct surveys.  Texas Agriculture Commissioner Sid Miller stated, “They don’t need to do that, it’s overreach.”  With respect to Commissioner Miller, he is in no position to comment on the epidemiologic realities of emerging disease and apparently is oblivious to the potential of extension to humans, although only one diagnosed case has been documented.  Anecdotal reports by veterinarians visiting affected dairy herds suggest that individual workers demonstrated influenza-like symptoms including conjunctivitis.  Colorado with only one case is following 70 workers to establish infection and possible transmission to contacts.  Based on data from the CDC only 220 farm workers have been monitored for symptoms suggesting that only 150 workers have been evaluated among eight states where outbreaks have occurred.  Texas with the most cases among dairy farms reported has only tested 20 workers with clinical signs and the results of diagnostic procedures have not been released. PCR assay results are available within 24 hours!


It is now five weeks since the index case of bovine influenza was diagnosed. Preliminary studies on the sequencing of isolates of H5N1 belatedly released by USDA-APHIS suggest that the disease has been present in dairy herds since late December 2023.  To date there has been no structured evaluation of H5N1 prevalence among dairy herds on a national basis and the appropriate epidemiologic surveys on workers have not been conducted. This is despite the presence of RNA consistent with H5 influenza virus in both milk and wastewater especially in areas where outbreaks in dairy herds have occurred.


The World Health Organization has designated H5N1 avian influenza virus as a potential pandemic strain.  The Agency has urged surveillance including documentation of outbreaks in avian and now mammalian species and the WHO maintains a database of outbreaks and the library of genomic sequences. 


The parochial but understandable concern of state departments of agriculture as expressed in their desire to protect the milk industry is self-evident.  This standpoint obviously conflicts with the greater need to understand the epidemiology of bovine influenza-H5N1 and to develop a national program to limit infection.  Of greater concern is the possible extension of a mutant virus to workers and then to the general population.  The distribution of PPE is perhaps an initial step in preventing infection but will be difficult to implement given the underlying deficiencies in structural and operational biosecurity in comparison to egg-production complexes. Practical and cultural issues exist with the deployment and use of PPE that requires availability and acceptance.  We need to know the numbers of workers that may have been infected from an affected herd, the duration of the clinical phase and of viral shedding.  Surveillance based on molecular epidemiology including gene sequencing will be critical to timeously detect mutations that may contribute to infection of humans and person-to- person spread. It is understood that up to $98 million will be distributed by the USDA to provide 3,500 dairy farms with up to $28,000 to “contain the spread of the virus between animals and humans and for testing milk and animals for the virus” This commentator suggests that grants should be conditional on cooperation with federal agencies with respect to herd and worker surveillance.


We are not China.  We should not suppress necessary epidemiologic investigations or the data collected.  Bovine influenza-H5N1 and its avian counterpart will not simply go away, irrespective of the intensity of hope, denial and prayer. Fortunately it appears that the risk of contracting H5N1 from direct contact with cattle is minimal but this assumption is based on the current circulating virus and inadequate surveillance.  Pasteurization obviously destroys the virus that is secreted into milk from infected mammary tissue. A mutation in the viral genome could profoundly alter present circumstances and could result in widespread infection as with “swine flu”.  Dr. Shah notes, “We have all seen how a virus can spread around the globe before public health is even had a chance to gets shoes on, that’s a risk and one we have to be mindful of.” It is not what we know that has the potential to hurt the industry and population—but what we do not know.


The dairy industry, state agriculture organizations, and federal agencies including USDA-APHIS and the CDC should cooperate according to a coordinated and agreed plan to determine the extent of bovine infection following “One Health” principles.  Currently the risk of mutation to a strain capable of infecting humans is very low based on accumulated knowledge. We are however in a situation of confronting a condition with a low probability of an adverse outcome for humans but with an extreme potential for morbidity and mortality and devastation of the Nation’s economy in a worst case scenario.  Let us learn from our unfortunate experience with COVID from 2019 onwards and not underrate the significance of the infection at a stage when practical control is still possible.