Pandora’s Pond

Aquaculture

Prior to Graeme Laver and Robert Webster’s landmark experimental work proving the avian origin of human influenza—Webster’s self-described “barnyard theory”¹²⁵¹ —any links between bird flu and human flu were scoffed at, Laver remembers, as “scornful remarks about ‘Webster and his obsession with chicken influenza.’”¹²⁵² No one is scoffing anymore. Analyzing the genome of H5N1, scientists now suspect that the 1997 outbreak arose when an H5 goose virus combined with an N1 duck virus with quail acting as the mixing vessel (another species “raised under battery conditions”¹²⁵³ ). The virus then jumped from quail to chickens and then from chickens to humans.¹²⁵⁴

In 2001, in what seems to be a separate emergence, that same H5 goose virus combined with an N1 duck virus in a duck, then jumped to chickens directly, bypassing the quail.¹²⁵⁵ In both cases, the H5 virus first isolated from a farmed domestic goose population in Guangdong province was found,¹²⁵⁶ surprisingly, to be already partially adapted to mammals.¹²⁵⁷ Scientists speculate that this could have been a result of the virus acclimating to a pig, especially, perhaps, given Asia’s unique fish-farming technique.¹²⁵⁸

Pig-hen-fish aquaculture involves perching battery cages of chickens directly over feeding troughs in pig pens which in turn are positioned above fish ponds. The pigs eat the bird droppings and then defecate into the ponds. Depending on the species of fish, the pig excrement is then eaten directly by the fish¹²⁵⁹ or acts as fertilizer for aquatic plant fish food.¹²⁶⁰ The pond water can then be piped back up for pig and chicken drinking water.¹²⁶¹ The efficiency of integrated aquaculture in terms of reduced feed and waste disposal costs is considered key to the economics of chicken farming in some areas in Asia,¹²⁶² and, as such, led to increasing support from international aid agencies.¹²⁶³ “The result,” wrote experts from the German Institute for Virology in the science journal Nature, “may well be creation of a considerable potential human health hazard….”¹²⁶⁴

In parts of Asia, human feces are also added to the ponds for additional enrichment.¹²⁶⁵ For pathogens spread via a fecal-oral route, this aquaculture system is a dream come true. These fully integrated systems are blamed for the high incidence of an emerging strain¹²⁶⁶ of cholera in shrimp farmed in the Calcutta region of India.¹²⁶⁷ According to aquaculture experts, rampant disease on Asian aquaculture farms is considered the primary constraint to the industry’s growth. They write in a 2005 review that “the aquaculture industry has been overwhelmed with its share of diseases and problems caused by viruses, bacteria, fungi, parasites, and other undiagnosed and emerging pathogens.”¹²⁶⁸ Concludes an earlier review, “Although the recycling of excrements in integrated agriculture-aquaculture farming systems offers many advantages, the spread of diseases to man via aquatic organisms multiplying in excreta-laden water needs special attention.”¹²⁶⁹ Much of that attention has focused on influenza.¹²⁷⁰

“The ducks, the ducks, the ducks are the key to the whole damned thing,” Webster once exclaimed to a Newsday reporter.¹²⁷¹ Due to the growing industrialization and pollution of migratory aquatic flyways, wild ducks are landing in increasing numbers on these farmed fish ponds.¹²⁷² The influenza virus found naturally and harmlessly in ducks’ intestines are excreted in the water. The chickens may drink the virus-laden water. The pigs then eat the virus-laden chicken feces. The ducks then drink the pond water contaminated by the virus-laden pig excrement and the cycle can continue. The pond water ends up a “complete soup” of viruses, admits the head of the Hong Kong environmental think tank Civic Exchange.¹²⁷³ Dead ducks or chickens may also be fed to pigs, providing another potential route of infection. This risky practice is not limited to Asia. In the H5N2 outbreak in the United States in the 1980s, pigs raised under chicken houses in Pennsylvania and fed dead birds came down with the infection as well.¹²⁷⁴

Integrating pigs and aquaculture affords this waterborne duck virus a rather unique opportunity to cycle through a mammalian species, accumulating mutations that may better enable it to adapt to mammalian physiology. Migratory ducks could then theoretically fly the mutant virus thousands of miles to distribute it to other ponds, pigs, and ducks across the continent. Although there is concern that the virus could infiltrate the abdominal fluid or even the muscle meat of the farmed fish,¹²⁷⁵ the aquatic animals are largely thought to be innocent bystanders.¹²⁷⁶ Without the Trojan duck vectors, fish farming wouldn’t pose a pandemic threat. Likewise, without the pigs, the fish farms would be no riskier than the thousands of Canadian lakes where ducks congregate and discharge virus into the water every summer. Any spoonful of lake water from this “veritable witches’ brew of avian influenza” (as Webster puts it) may contain virus, but as long as it stays between ducks, as it has for millions of years up until domestication, it poses no pandemic threat.¹²⁷⁷

The aquaculture industry disagrees that its practices are potentially hazardous.¹²⁷⁸ Indeed, one review noted that “enormous differences of opinion exist between epidemiologists and aquaculturists.”¹²⁷⁹ Fish farming advocates argue that integrated aquaculture is “uncommon.”¹²⁸⁰ One aquaculture professor estimates that, at most, only 20% of pigs in China are involved in aquaculture production.¹²⁸¹ However, 20% is 100 million pigs, plenty of fodder for viruses to potentially extract adaptive pearls from swine.¹²⁸² An industry insider admitted that aquaculturists have too often adopted a “bury-your-head-in-the-sand” attitude when it comes to human disease threats.¹²⁸³ While fish farmers continue to downplay the risks, medical historians speculate that integrated aquaculture may have played a role in the increasing threat of pandemic influenza.¹²⁸⁴ “As these agricultural practices increase,” wrote one commentator in the journal Science, “so does the likelihood that new potentially lethal influenza viruses will increase at the same time.”¹²⁸⁵