A recent ProMed posting (Saturday, May 4 2013 Volume 2013 : Number 216) provides an update on the outbreak in China of the H7N9 strain of avian influenza, which as of May 1 has resulted in 127 confirmed human cases, of which 26 (20.5%) have been fatal. While the virus does not appear to have caused significant human-human transmission, the route of exposure from an animal source to humans is only now beginning to be understood. In a number of cases , there is no history of recent contact with birds or other animals. According to the ProMed posting, an official with the Chinese CDC has indicated that chicken feather plucking machines are suspected of spreading the virus through the air. Feather plucking machines (see picture below) can create aerosols of small feather particles as well as droplets of blood and other secretions. Such small particles are capable of being transporters of flu viruses, and the Chinese CDC official has been quoted as saying “If there is a virus, it can be easily inhaled this way…This is what we suspect to be a major environmental exposure that causes human infections.” (see the original story here).
Of course, it is not clear what evidence has been collected to support the theory implicating the feather plucking machines. Ideally one would like to see evidence that the virus is present in aerosols created by the machine, that the size of the particles with virus are small enough to remain airborne for significant amounts of time, and that such airborne virus is still viable (as opposed to being present but damaged during transport and not able to be infectious). It would also seem logical that workers close to such machines would be at increased risk of infection, and that a study of such workers would reveal increased rates of infection. At present it seems that such evidence has not yet been documented. Maybe the feather plucking machines are spreading H7N9, but maybe not.
This turn of events reveals once again how little we know about zoonotic (animal to human) transmission of influenza viruses such as avian flu or swine flu. Of course we are still learning how human influenza itself passes from person to person, and the debate continues about the relative importance of human flu transmission over distances in the air as very small particles versus direct contact with secretions or spread by droplets from a sneeze or cough that only travel several feet. Yet we know even less about how animal flu viruses move around environments where often there are dusts (such as in a barn) or other unusual types of aerosols (such as with feather plucking machines) that potentially can carry viruses for extended distances.
While this recent disturbing outbreak of avian influenza reinforces the need to consider new approaches to vaccination and diagnosis, it should also spur research into the ways that these viruses spread and persist in the environment. Adequate prevention needs to include smart environmental management of infection risk, and answering questions such as “how long can the virus survive in the air?”. “When is it necessary to wear a mask to protect oneself?” And “how can environments be decontaminated in the midst of an outbreak”. Answering such questions will require sampling environments and high risk populations such as workers for evidence of the avian influenza virus, and developing an understanding of how the virus can and cannot travel and persist outside of an animal or human. Without such knowledge, we may miss important opportunities for prevention, and risk either scaring the public unnecessarily, or reassuring them inappropriately.