Lelystad, April 2015: According to a recently published study (in Dutch) by the University of Wageningen, wild ducks are are identified as a high risk factor for the introduction of Low Pathogen Avian Influenza viruses in free-range laying hens.

Through a case-control study investigated presumed risk factors for introduction of low-pathogenic avian influenza (LPAI) virus in poultry laying farms free range. Under a LPAI virus was defined in this study: an avian influenza virus of each subtype (H1 H16 tm), with the exception of the highly pathogenic avian influenza (HPAI) viruses.

In order to determine the potential risk factors for infection with LPAI virus, forty Dutch free range poultry farms where the introduction of Low Pathogen Avian Influenza virus has been confirmed in the past (cases) were compared with 81 free range poultry farms where no introduction has taken place (controls). Questions about the presence of potential risk factors through surveys submitted to the poultry farmers.

The analysis of the various factors shows that the risk of introduction of LPAI virus on free range laying farms 3.3 (95% CI: 1.2-9.7) times higher as mallards has identified by the farmer entering the free range area at least once a week, in comparison to free-range laying farms where wild ducks have been identified by the farmer once a month or less.

It seems logical that the regular presence of wild ducks in the free-range increases the risk exposure of the chickens LPAI virus since wild waterfowl are the natural reservoir of avian influenza viruses.

The study also revealed that the risk factor for free range layer farms located on clay is 5.8 (95% CI: 2.2-15.1) times have higher risk of introduction of LPAI virus then free range layer farms on sandy soil or a soil other than clay. The soil on which the free range farm is situated is probably an indirect risk factor (association and not causation): especially in case the farm is located near the coast or close to rivers.