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. 2007 Mar;13(3):404-11.
doi: 10.3201/eid1303.061130.

Surveillance of influenza A virus in migratory waterfowl in northern Europe

Anders Wallensten  1 , Vincent J Munster, Neus Latorre-Margalef, Mia Brytting, Johan Elmberg, Ron A M Fouchier, Thord Fransson, Paul D Haemig, Malin Karlsson, Ake Lundkvist, Albert D M E Osterhaus, Martin Stervander, Jonas Waldenström, Olsen Björn
Affiliations

Surveillance of influenza A virus in migratory waterfowl in northern Europe

Anders Wallensten et al. Emerg Infect Dis. 2007 Mar.

Abstract

We conducted large-scale, systematic sampling of influenza type A virus in migratory waterfowl (mostly mallards [Anas platyrhynchos]) at Ottenby Bird Observatory, southeast Sweden. As with previous studies, we found a higher prevalence in fall than spring, and among juveniles compared with adults. However, in contrast to other studies, we found that prevalence in spring was sometimes high (mean 4.0%, highest 9.5%). This finding raises the possibility that ducks are capable of perpetuating influenza A virus of different subtypes and subtype combinations throughout the year and from 1 year to the next. Isolation of the H5 and H7 subtypes was common, which suggests risk for transmission to sensitive domestic animals such as poultry. We argue that wild bird screening can function as a sentinel system, and we give an example of how it could have been used to forecast a remote and deadly outbreak of influenza A in poultry.

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Figures

Figure 1
Figure 1
Female mallards banded in Sweden south of 57°30′N (indicated by a solid line in the inserted figures) in Oct–Dec (A) and May–Sep (B) and recovered in winter (Nov–Feb, n = 255 and n = 98) and summer (May–Aug, n = 135 and n = 53). Black dots represent summer recoveries; gray squares represent winter recoveries. Symbols on inset maps represent calculated mean positions and the location of Ottenby Bird Observatory.
Figure 2
Figure 2
Seasonal variation in the number of sampled mallards (black bars) and common shelducks (open bars). Data from 2002–2005 have been pooled.
Figure 3
Figure 3
Seasonal influenza A virus prevalence in mallards (n = 4,106) in the 4 study years. Data from months represented by ≤5 samples are not included.
Figure 4
Figure 4
Monthly average influenza A virus prevalence in mallards (n = 4,106), 2002–2005, with bars indicating the standard error. Data from months represented by ≤5 samples are not included.
Figure 5
Figure 5
Mean influenza A virus prevalence in the 4 age classes. Birds that we were unable to age correctly were denoted as unaged. Bars indicate standard error.
Figure 6
Figure 6
Occurrences of the most common influenza A virus subtype combinations (≥5 isolates) in mallards over time.
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