It is evident that a proportion of workers depopulating flocks diagnosed with H5N1 or in close contact with herds excreting the virus in milk are susceptible to infection   Approximately fifty cases of clinical H5N1 have been documented without contagion although structured sampling for virus and antibody response has yet to be conducted.

Notwithstanding the limited zoonotic ability of H5N1 at present, a leading specialist in the molecular biology of influenza viruses is concerned over emergence of infection in both marine and terrestrial mammals. Dr. Richard Webby, the Director of the World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds at St. Jude Children’s Research Hospital expresses a conservative view on the potential for extensive infection of humans based on current studies of viruses isolated from dairy cattle and poultry flocks.  He stated, “From where we are now to a pandemic virus, reassortment alone is not going to get us there.”  He added, “ It is going to take reassortment followed by some critical mutations necessary for the virus to spread efficiently among humans.  The specific changes in the genome that would facilitate person-to-person spread (contagion) have not been detected in any of the genetic sequences of isolates from human cases.  In the event that mutations do occur in the future to increase the ability of the virus to infect the lower respiratory tract, or to result in contagion, the situation will obviously change.

It is considered essential that all people coming into contact with live poultry at farm and processing level should be vaccinated against the seasonal influenza viruses.  This would reduce the probability of a reassortment event leading to a novel potentially zoonotic strain.  Reassortment was in all probability the origin of the 1918 worldwide pandemic with catastrophic mortality. The 2009 H1N1 swine flu event was responsible for both clinical cases and a limited number of fatalities compared to the post-World War I outbreak.

Until H5N1 vaccines are deployed among farm workers in the U.S., sensible precautions including the effective use of PPE should be followed.