Dr. Peter Petermann for WAI
Netherlands: No Evidence that Wild Birds are spreading Avian Influenza ! (PDF)
After a series of outbreaks of highly pathogenic avian Influenza H5N8 (HPAI H5N8) in poultry holdings in the Netherlands (1), the Dutch authorities have recently reported two H5N8-HPAI-positive samples supposedly from feces of two wild ducks, widgeons (Anas penelope) (2). This has been regarded as evidence, that wild birds are responsible for the introduction of H5N8-HPAI from East Asia and for their further spread through western Europe (2, 3).
However, these two samples obviously do not constitute a proof for the wild-bird hypothesis.
The Dutch authorities have so far (Dec. 4th 2014) failed to publish a comprehensive report about the circumstances of the sampling of duck feces. It thus remains mysterious how they can be sure that the samples are really from two different birds. As in former outbreaks in several European countries, there is an irritating lack of transparency in the epidemiological investigations (see as an outstanding example 4).
What is known so far must raise doubts on the suggested interpretation:
First, these H5N8-positive samples were taken considerable time AFTER the outbreaks were detected (Dec. 1st). Accepting a reasonable incubation time, the wild ducks would have been infected only after the first outbreak was reported (Nov. 18th 2014). In more than 1.500 wild bird samples taken BEFORE the poultry outbreaks in the Netherlands, no HPAI was detected (2). Unknown sample numbers were analysed in neighbouring countries, with just one H5N8-positive sample in Germany, found likewise only AFTER the detection of an outbreak in poultry in the same province (according to different sources it was either an unidentified duck, 5, or a Common Teal, Anas crecca, 6).
Second, the samples were taken in the region of outbreaks in chicken farms (affected farms are between 11 and 25 km to the south and west of the sample site at Kamerik, Utrecht; 1). It is an obvious possibility that the infection of wild birds may have been caused in some way by the outbreaks in poultry farms.
Third, Widgeons use to graze on farmland, where they may have come into contact with poultry manure used as fertilizer. As long as no report on the sample protocol und laboratory tests is available it can't even be ruled out that the samples of duck feces may have been contaminated in situ by poultry manure containing virus, in which case the ducks may not even have been infected.
Fourth, in South Korea considerable numbers of wild ducks have died during the outbreaks in poultry farms (7, 8). Though the virus has apparently not changed genetically, there is no sign of raised wild bird mortality in Europa so far. This is obvious evidence against a widespread circulation of HPAI among wild ducks, which would be necessary to explain the serie of wide-spaced outbreaks in poultry holding. However, if the outbreaks can not be contained soon, the probability of a spread to wild birds will undoubtedly increase.
Fifth, as the source of the virus introduction into the poultry holdings is obviously not yet known, it seems reasonable to assume, that an as yet unknown common source may be responsible for both the poultry outbreaks and the infection of wild ducks.
There are several ways the HPAI-virus could spread from farm to farm, ways that would not be detectable in retrospective epidemiological investigations. Just as one example, road transport of asymptomatically infected birds could spread virus by scattering contaminated feathers along the road. Ducks are notorious for not showing symptoms when infected with HPAI. It should be kept in mind, that outbreaks in duck holdings may pass unnoticed, sometimes for many weeks (as in Germany in 2007; 10).
However, it can not be expected that the way the virus has spread can ever be reconstructed in detail. With luck, genetic analyses of the virus gene sequences may at least give some hints about the way the outbreaks are connected. Unfortunately, European virus gene sequences are now "published" on the GISAID data base (9), which is not open to the interested public (despite claims to the contrary)*.
* We have since been informed by staff members of GISAID that this important database of gene sequences and other information concerning influenza maintains its access open for everybody. We apologize for any misinterpretation! Everyone interested in the transparency of GISAID is kindly requested to look the details up in the GISAID database access agreement (http://platform.gisaid.org/epi3/app_entities/entities/downloads/epifludb_daa.pdf).
Dr. P.Petermann (15.12.2014)
6) http://www.fli.bund.de/fileadmin/dam_uploads/Publikationen/Risikobewertungen/HAPI_H5_Risikobewertung_ 20141125.pdf
7) http://www.wildlifedisease.org/wda/Portals/0/Education/Scientific Task Force on Avian Influenza and Wild Birds H5N8 HPAI 28 Jan....pdf
10) FLI (17.12.2007, 12.00 Uhr): Epidemiologisches Bulletin Nr. 10/2007. Lagebericht zur Aviären Influenza.- 13 S. (apparently no longer posted on the internet-site of FLI: http://www.fli.bund.de/)