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Third Human Case of Dairy-Herd Associated H5N1 Emerges

06/07/2024

 

As a result of an ongoing program of surveillance, authorities in Michigan identified a third in a series of cases of H5N1 infection in dairy-herd workers.  The patient demonstrated conjunctivitis but unlike the two previous cases, mild respiratory symptoms were apparent. The patient received antiviral treatment and was isolated at home.  Household contacts have not developed symptoms and are being monitored for H5N1 virus.

 

Notwithstanding this case, the Centers for Disease Control justifiably claim that at present there is a low risk to the general public. There is no evidence of human-to-human transmission that would be a cause for concern.  In the first two cases, investigations determined that the virus isolated was identical to H5N1 virus in milk and from nasal swabs of affected dairy cows.  Recent studies have confirmed that conjunctival and bovine udder tissues have sialic acid receptors for both mammalian and avian influenza viruses.  Dr. Amesh Adalja of John Hopkins Center for Health Security stated, “This case underscores the risk that is particular to dairy farm workers.”

 

Michigan health officials will collaborate with the Centers for Disease Control and Prevention to implement a widespread surveillance program to determine the prevalence rate of virus among workers and to establish whether asymptomatic humans can transmit virus.  Serologic studies will be performed to determine the extent of possible previous exposure given that molecular genetic evidence indicates that bovine influenza-H5N1 has been present in herds since December 2023. The overriding concern is that widespread distribution of H5N1 influenza virus among dairy herds could result in a mutation, facilitating transmission to human contacts and the development of person-to-person contagion.

 

In a comment by a ProMED moderator, it was stated, “It should be a surprise that its taking this long to even start to get more expansive testing programs up and running in addition to testing those workers of dairy farms and their contacts.  We should be testing beef cattle and feed-lot workers to fully understand if this is a risk confined to dairy cattle and dairy farm personnel or if it is far more widespread in cattle populations and those humans in contact with cattle.  It would also be interesting to understand what if any protective equipment that workers were offered and were actually using”.

 

The moderator also questioned the practicality of using PPE under hot and humid conditions and the efficacy of respirators.  Experience has shown that N95 masks deform and lose efficacy when saturated.  The epidemiology of bovine influenza H5N1 and the protection provided by PPE are important questions given that the USDA is to subsidize measures to prevent bovine influenza-H5N1 as part of an $820 million emergency allocation from the Community Credit Corporation. These funds must be judiciously expended with appropriate controls and not simply be regarded as “throwing money at a problem” in response to political pressure.

The response of the USDA to the prevention of bovine influenza-H5N1 and determining the epidemiology of the infection contrasts with the reaction to the epornitic responsible for the culling of close to 90 million commercial poultry over three years. To their credit APHIS established diagnostic protocols in conjunction with state departments of agriculture and through bitter experience has improved the logistics of depopulation and payment of indemnity. In effect this reactive approach is the extent of the response by the Agency. APHIS has been less than effective in conducting epidemiologic studies and providing relevant science-based advice on prevention other than distributing posters on ho-hum general biosecurity. Poultry producers were never given financial support to design or to implement biosecurity procedures or to provide workers with PPE. The Agency has also slow-walked evaluation of the tactical application of preventive vaccination in high-risk areas and for turkeys and egg production complexes creating the risk of emergence of potentially zoonotic strains of H5N1 avian influenza. It appears that APHIS is following Napoleon in the satire Animal Farm with “four legs good, two legs bad”.