Yes indeed very interesting. The mention of birds being the source of contamination is important and maybe more widespread than reported.I was presented with a problem many years back of maggots dropping into the work and packing area of one of the factories my company owned.Major hassle with this one as the factory made fancy undergarments for the high end of the market! One maggot in a pair of knickers and the papers would have a field day. [I was Company Engineer,but all sorts of problems came my way
]
So to the birds.The problem was caused by seagulls which came to roost on the nice warm roof at night but which inconveniently died from a strain of botulism and fell into the roof valleys,became infested with flies whose larvae wriggled into the roof space.Yuk. So off forfi and team go to find solution.Nearest feeding place to said factory [as we thought]was a landfill or open bloody tip some 5 miles distant.This seemed a long way for the birds to travel for a place to roost and a post-mortem on a few samples did not show up the botulism we had earlier found.After a period of observation we noticed that
our gulls were not coming form the direction of the obvious feeding sites and we traced them to a fish handling unit nearby which had broken its permissions and had fish offal in open containers.End of our problem.
Point is that landfill sites attract large flocks of gulls and that these birds pick up so many diseases to list here.Not their fault of course.Since then the better run land-fill sites cover the trash with top-soil on a constant basis and no more gulls. I guess that was one of my first introductions to the importance of understanding ecology.