INTRODUCTION
• Swans and geese occur in larger numbers near more people than ever before, in Sweden as well as in Western Europe.
• Increasing populations sometimes lead to problems and conflicts. On agricultural land geese and swans can cause costly damage to growing crops. Intense grazing by these birds may also affect natural vegetation, sometimes leading to conflict with conservation and biodiversity goals.
• Geese and swans are obligate herbivores, consuming leaves, stems, seeds and root parts of terrestrial and aquatic plants.
• Grazing on growing crops may cause conflicts of interest also when geese and swans congregate in large numbers in wetlands adjacent to cropland.
• Geese and swans provide a multitude of ecosystem services, for example viewing, hunting, meat, and eco-tourism revenues.
GEESE AND SWANS AS VECTORS OF DISEASE
• A large number of disease agents has been recorded in geese and swans, viz. viruses, bacteria and unicellular parasites.
• Some of these have the capacity to infect other bird species and mammals.
• Geese and swans are highly mobile and often occur close to humans and in our agricultural landscape. As a consequence, they are sometimes suspected of transmitting disease to livestock and humans.
DISEASE TRANSMISSION TO LIVESTOCK AND HUMANS
• A recent review of the scientific literature demonstrates that geese and swans very rarely constitute a health hazard to humans, but slightly more often to livestock, especially poultry.
• Under some circumstances geese and swans may play a role as disease agents of the following diseases to livestock or humans: avian influenza, campylobacter, salmonella (mainly poultry) and bacteria carrying resistance towards antibiotics. However, in all cases other agents are more important for transmission than are geese and swans.
• There is no scientific evidence that geese and swans may act as transmitters of Newcastle virus, West Nile virus, botulism, psittacosis, or borrelia to livestock or humans.
• In the case of some disease agents, for example E. coli and cryptosporidia, it is still not known if geese and swans may transmit disease to livestock or humans.
• Climate change and a growing understanding of variation in occurrence and pathogenicity of different disease agents highlight a need for continued monitoring as well as a preparedness to re-evaluate their significance.
• There are no known disease transmission concerns related to livestock grazing alongside geese and swans, neither in pastures nor in shore meadows of wetlands.
• Despite the general conclusion that very small disease transmission risks are associated with geese and swans, it is prudent to adopt precautionary measures; e.g. to supply grazing livestock with water from wells, and to keep poultry separated from wild birds. From a human perspective, fencing can keep geese and swans from entering beaches, and where swimmers and birds use the same water, proper sanitation facilities and showers should be provided.