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.
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