H7N1 in Asymptomatic Domestic and Wild Waterfowl in Denmark
Recombinomics Commentary 21:49
April 29, 2008
The disease was detected a routine, annual check carried out by Danish veterinary authorities. The infected birds showed no outward clinical symptoms of the H7N1 flu virus, but laboratory tests revealed the birds had the disease, the spokesperson said. In all, 300 geese and 250 ducks at the farm will be killed, as well as around 1500 wild mallard.
The above comments describe the detection of H7N1 in asymptomatic waterfowl in Denmark (see satellite map) as described in the OIE report. This outbreak increases the number of recent H7 infections in the region. Last year England reported an H7N2 outbreak, which followed an H7N3 outbreak a year earlier. The largest outbreak was H7N7 in the Netherlands in 2003. All of these earlier outbreaks were associated with human infections. In 2003 there was one fatality and approximately 80 cullers were positive and had symptoms, which were primarily ocular. However, H7 antibody tests indicated the number of infected contacts was greater than 1000.
This high frequency of human infections has raised concerns that the number of undetected humans infected with H7 may be high. H7N2 patients were identified in the eastern United States, and H7N3 positive workers were identified during the 2004 H7N3 outbreak in British Columbia.
The current H7N1 outbreak in Denmark raises concerns of asymptomatic human infections in contact with the infected birds.
The release of sequence data from a New York resident infected with H7N2 in 2003 has raised additional concerns. The isolate had 3 avian genes (H7, N2, and NP), but it also had at least 4 human flu genes (PB1, PA, MP, NS – the PB2 sequence wasn’t released). The presence of the human genes in the avian H7N2 isolate supports a co-infection involving an avian H7N2 and a human H3N2 in 2003, based on the relatedness of the human genes to other human isolates. However, since the patient had no history of contact with birds, he may have been infected by another human infected with the H7N2 reassortant.
Mouse and ferret studies of the isolate created respiratory disease and the H7N2 levels in the nasal passages were higher than animals infected with human H3N2 raising additional concerns of efficient human to human transmission.
Since the patient recovered, the presence of an H7N2 recombinant raises concerns of additional undetected human cases. Similarly, the presents of an avian H and N raises concerns of additional human gene flu genes in birds which could then reassort or recombine with avian genes, including H5N1. H7 has been reported in other mammals, including seals and horses, raising concerns of additional genetic exchanges between avian and mammalian flu genes.
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