The Need for Better Quality Data to Understand Avian Influenza in Wild Birds
23 Nov, 2006 05:11 pm
Since H5N1 highly pathogenic avian influenza was first isolated from poultry in China in 1996, this disease has been shown to be spread by infected poultry, the trade of wild birds and recently, short distances through wild birds. In last week?s BioScience journal (06 Nov 2006), four avian ecologists published an article showing how simple, but detailed ecological and ornithological data, collected in a standardised way, at wild bird outbreaks can significantly improve our ability to understand the ecology of this disease in wild bird populations.
These reports often do not include highly relevant information on the outbreaks such as: species identity, when the samples were collected, how the individuals were caught, details on the location of where they were collected, the number of wild birds that were found in the area that were not infected with the disease and the actual number of birds that were tested. This type of information is essential to understanding how the disease may be transmitted locally or regionally, to detect changes in disease virulence, to assess the health of infected individuals, as well as to identify species that are resistant to avian influenza and could be asymptomatic carriers of the disease.
The article begins with examples illustrating the importance of correctly identifying the species. Last spring an infected dead swan, was found in Scotland, UK. For several days this whooper swan (C. cygnus) was mis-identified as a mute swan (Cygnus olor). Mute swans are resident (non-migratory) species and this implied that the birds had contracted the virus in Scotland and led to the activation of outbreak contingency plans involving a prohibition of poultry movements and searches for infected poultry Scotland. However whooper swans are migratory and spend part of the winter in northern Germany (where there had been several wild bird outbreaks earlier that month). Thus it was much more likely that the bird had drifted into the UK and that Scotland was free of the disease.
Inadequate identification of species is not only a problem in the UK. In Germany the official national reference laboratory only identified 15% of the 167 wild birds that were found dead and infected with the disease in 2006. Most of the birds were identified only as “wild duck”, “swan” or even “wild bird” even though there were several different species with very different habitat use or migration patterns. If this is the standard in European countries where there is a large number of ornithologists, species identification is likely to be a much greater problem in developing countries.
The most significant wild bird outbreak occurred in the summer of 2005 at Qinghai Lake, western China, where several thousand water birds were found dead and some tested positive for H5N1. Virologists and veterinarians visited the site but failed to record or report the number of birds and species that were in the area but not infected by the disease. It was particularly important to determine which species were present and might have carried the disease to the lake because this outbreak occurred in a remote region and wild birds were thought to have carried the disease to the lake. Initial scientific studies on the outbreak suggested the viral strain was from poultry in southern China, but this was refuted by Chinese officials, who favoured an official report that bar-headed geese Anser indicus (the species that died in the greatest numbers) may have carried the virus to the region. However this is unlikely because this goose species migrates to the region in March several weeks before the first H5N1 outbreak. This type of important ornithological information can provide insight into the likelihood of different sources of infection. Another important piece of information that was only reported a year later by an independent journalist, was the fact that there was a bar-headed geese captive breeding facility at Qinghai Lake as well as domestic poultry near the lake. Bar-headed geese are bred in other regions of northern and western China and released into the wild where there have been wild bird infections, and it is possible that the disease was introduced into wild populations through the release of birds set free from these captive breeding facilities.
The scale and rapid spread of H5N1 has caught national governments by surprise. Over the last two years it has become evident that, ecologists and ornithologists must play a greater role in H5N1 research, monitoring, and management, as members of response teams, research advisors, and journal referees. More generally, the growth in international trade and human travel has lead to an increase in the number of infectious disease. The design of effective mitigation strategies that will reduce the human and socioeconomic impacts of these new diseases requires a greater commitment from the global community towards more effective collaboration across a wider range of disciplines.
Yasue, Mai and Feare, Chris J. Virology Journal 2006,
3:96 doi:10.1186/1743-422X-3-96. Published 17 November 2006