A Messy Story - The Monster at Our Door: The Global Threat of Avian Flu - page 26

ménage à trois that had generated the 1997 killer. The internal proteins in H5N1 were virtually identical
with those from H9N2. 99
With this double recognition that H9N2 was a precursor of H5N1 reassortment, as well as a human
invader in its own right, the story was getting surprisingly messy. Nonlinear complexity now governed the
plot. As some theorists had already recognized, the “interactive dynamics” between multiple, coevolving
subtypes might “introduce complexities and substantial mathematical challenges” that would make mod-
eling or predicting viral evolution extraordinarily difficult, if not impossible. 100 To gain a better under-
standing of what was actually happening, the University of Hong Kong research team headed by Guan,
Peiris, and Shortridge decided to explore the viral underworld of Guangdong in unprecedented detail.
They wanted to find out how many subtypes and strains were circulating in the avian population and,
most importantly, how they were interacting with one another. For a year, starting in July 2000, research-
ers carefully isolated viruses from ducks in the live-poultry markets of the Guangdong city of Shantou.
The results of their study, published in the summer of 2003, fundamentally revised the standard picture of
influenza evolution.
First of all, they discovered extraordinary and unexpected genetic diversity: almost 500 distinct strains
of influenza, including fifty-three different iterations of the H9 subtype. “The diversity of genotypes, gene
constellations, and host receptor specificities,” they warned, “will provide these viruses and their progeny
with options of hosts.” Second, they established that reassortment was a more common event than previ-
ously imagined. Gene segments were vigorously being traded throughout the diverse network of influen-
zas. Previously, “influenza gene flow was usually considered to occur from aquatic birds to other anim-
als.” Now they found ample evidence that viruses were evolving from ducks to poultry and back again:
“i.e., there is a two-way transmission between terrestrial and aquatic.” “The species barriers between the
birds have become much more permeable than previously anticipated. Increasing the heterogeneity of in-
fluenza viruses in these hosts results in an enlarged and dynamic influenza gene pool in continuous flux
rather than one that is limited to aquatic birds and therefore in evolutionary stasis.” 101 Or, as American

virologist Richard Webby pithily put it, “we have a bucket of evolution going on.” 102
The bottom-line of the Shantou report was that several subtypes of influenza were traveling on the
path toward pandemic potential. The industrialization of south China, perhaps, had altered crucial para-
meters in an already very complex ecological system, exponentially expanding the surface area of contact
between avian and nonavian influenzas. As the rate of interspecies transmission of influenza accelerated,
so too did the evolution of protopandemic strains. The Hong Kong research team had discovered, in other
words, that contemporary influenza, like a postmodern novel, has no single narrative, but rather disparate
storylines racing one another to dictate a bloody conclusion. “The H5N1 virus was in the process of ad-
apting from aquatic to land-based poultry from the duck via the partially aquatic goose to the chicken,”
while the H9N2 (and probably H6N1) were “adapting through a mechanism that took them to the quail
and probably other minor land-based poultry such as the pheasant.” Alternately, “aquatic migratory or
domestic birds could introduce a 'genetically adaptable' virus directly into land-based poultry. The intens-
ification of the poultry industry through large-scale commercial operations in East Asia (and elsewhere)
could facilitate this.” 103
Each of the aspirant subtypes had different assets. If H5N1 was an assassin of unparalleled lethality,
the fact that H9N1 strains—according to the Hong Kong team—were “not highly pathogenic for poultry
. . . makes them more, rather than less, likely to be of pandemic relevance.” A milder chicken virus was
more likely to survive detection and extermination and thus have time to continue to reassort until it found
the optimal gene constellation for rapid infection of human populations. 104 In 2003 the Hong Kong re-
searchers would find further evidence to corroborate the pandemic potential of H9N2 in a study of viruses
in the live-poultry markets of their own city. 105