Gulls have a world#x2010;wide distribution but are more common in temperate regions. The numbers of several species have increased enormously in recent decades, but for some populations this growth has now ceased or even reversed. The population growth followed cessation of prior persecution, and has substantially depended upon increased availability of food resulting directly or indirectly from human activities. Gulls and humans often share the same habitats and increasing numbers of gulls occupy urban areas so that there are chances for fecal contamination. These are greatest through water supplies. Pathogens carried by gulls are chiefly enteric microorganisms originating from anthropogenic sources such as landfills and untreated sewage. The greatest threats to public health arise when gulls feed at such sites and then visit reservoirs of potable water. Gulls may disseminate several bacteria notably Campylobacter which is probably endemic to birds, and Salmonella, but are not reported to be involved in spread of enteric protozoa, nor of major metazoan endoparasites. Visitors to gull nesting areas may be exposed to tick#x2010;borne pathogens and fungal spores.
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