A large Virginia turkey flock testing positive for antibodies to the H5N1 sub-type of avian influenza (AI) sent shudders down the Shenandoah Valley even though birds showed no signs of disease and indications were of previous exposure only to a low-pathogenic form of the virus.

Antibodies were identified in July 2007 during routine pre-slaughter testing of the 54,000 flock with birds showing no signs of illness prior to testing. The flock will be culled and composted on site instead of being slaughtered for market. United States federal and state policies dictate unequivocal eradication of H5 and H7 viruses because the low pathogenic form can mutate into a highly pathogenic form of AI during the course of an outbreak. This happened in 2004 in the Canadian province of British Columbia during an outbreak of H7N3.

There is a history of AI in turkey flocks in the US state of Virginia. A low pathogenic form of the H7N2 sub-type affected around 200 farms (mostly turkeys) in 2002 leading to the destruction of 4.7 million birds and costing the poultry industry US$130 million.

Turkeys as targets for these potentially lethal H5 and H7 AI viruses comes as no surprise. Recent (2006-2007) outbreaks across Europe in France, the United Kingdom and most recently the Czech Republic have featured turkeys. Turkeys are one of the first types of poultry to succumb to AI.


During the French outbreak of H5N1 HPAI (highly pathogenic avian influenza) in February 2006, the national reference laboratory for AI in Italy told New Scientist magazine in London, “You can infect turkeys by stepping into relatively small amounts of contaminated bird faeces and tracking it into the barn.” Bales of straw contaminated by infected wild waterfowl and brought inside for bedding were considered the most likely source of H5N1 that ‘wiped out’ 11,000 turkeys on a farm in the Ain region of south-east France.

Appearance of H5N1 in US poultry flocks should come as no surprise either. In 2006, USDA expanded its AI testing programme for wild birds beyond Alaska. Subsequently, wild waterfowl such as green-winged teal found in Delaware and mallard ducks in Illinois and Michigan have tested positive or were presumed positive for the mild North American strain of H5N1.

The USDA fact sheet on low-pathogenic H5N1 shows the virus was detected in otherwise healthy wild birds as long ago as 1975. Antibodies to the same low pathogenic North American H5N1 strain were also found in samples of turkeys in Michigan back in 2002 but the virus could not be isolated.