A recent publication* from Taiwan confirmed that concentrations of migratory birds on wetlands excrete avian influenza virus that can be detected by air sampling. In the study, 357 ambient air samples were collected seasonally between October 2017 and December 2019 and were analyzed using rtPCR assay.
Strain H7 was detected in 12 percent of the air samples, H5 in 8 percent and H9 in 10 percent. The frequency of isolation was related to low temperature and the concentration of birds including common teal, spot-billed ducks, Eurasian widgeons, spoonbills and cormorants.
The authors proposed that air sampling could be a predictive technique for outbreaks of avian influenza.
Apparently, this publication was the first to demonstrate airborne avian influenza in the vicinity of wild birds. The observation lends support to a frequently expressed opinion in EGG-NEWS that HPAI can be spread by the aerogenous route over distances of up to a mile depending on wind direction, cloud cover, ambient temperature and humidity. Avian influenza virus shed by migratory birds is obviously deposited on soil and vegetation and in theory can be aerosolized on dust and be transmitted by wind currents. Houses with negative-ventilation contain flocks that are vulnerable to infection by the aerogenous route given the large volume of air extracted by fans.
The implications from the observations in Taiwan are self-evident. Even with extreme structural and operational biosecurity, complexes cannot be absolutely protected from introduction of HPAI virus.
Given the recent series of outbreaks involving depopulation of 12 million hens and a history of seasonal waves of infection on a regional basis since 2021 and the evident futility in attempting eradication, protection in the intermediate and long term will have to incorporate vaccination as an adjunct to biosecurity.
The previously stated maxim, Avian influenza is the Newcastle disease of the 2020’s suggests the approach to control going forward. Newcastle disease was as commercially significant and as catastrophic in the 1960s and 1970s as avian influenza at the present time. It is questioned as to how long APHIS can pursue a program of “whack-a-mole” control without accepting the necessity for vaccination on a regional basis for turkeys and egg production flocks.
The needs and concerns of the broiler industry over exports are justifiable considerations. Given that HPAI is now worldwide in distribution and with more nations adopting vaccination as a preventive measure and with the recent endorsement by the WOAH, serious consideration should be accorded to establishing immune populations in high-risk states. To their credit, APHIS is initiating field trials on vaccination but this should not be regarded as a delaying tactic. Costs to the public sector for indemnity and control and to consumers who will pay more for eggs are also financial considerations in developing a national strategy to suppress HPAI with no prospect of long-term eradication.
*Zhang, J. L. et al. (2022).Airborne avian influenza virus in ambient air in the winter habitats of migratory birds. Environ. Sci. Technol. 56:15365-15376.