2. Intestinal microbiota in wild birds

The majority of information regarding enteropathogens in wild birds has been ascertained by applying traditional microbiological techniques [10–12]. Research on the fecal flora of wild birds in a few well-studied species has focused on the prevalence of enteropathogenic bacteria that are most likely zoonotic. Representative species that are often found in diseased wild birds include Salmonella enterica serotypes Typhimurium and Enteritidis, Escherichia coli, Campylobacter jejuni, Pseudomonas aeruginosa, Pasteurella multocida, Clostridium botulinum, and Listeria monocytogenes. The carrier birds are often diverse species, including house sparrows, brown-headed cowbirds, white-throated sparrows, tufted ducks, crows, pheasants, pigeons, hook-bills, finches, free-living flamingos, quails, pheasants, red grouse, and waterfowl [1, 6, 8].

Many classical methods such as microscopy, culture, or serology have been used to detect and isolate pathogenic protozoa or fungi from excreta of migratory birds. Candida albicans and Candida tropicalis, which can become pathogenic in immunocompromised individuals, have been isolated from excreta of migratory gulls and geese [13]. Toxoplasma gondii has been isolated from many migratory species including ducks and raptors. Eimeria spp., which cause severe intestinal coccidiosis, are distributed by geese and diving ducks. These infections are mainly caused by oral ingestion of oocysts excreted from feces. The oocysts of Cryptosporidium baileyi, an intracellular enteric coccidian parasite that can cause gastrointestinal and respiratory tract disorders in birds, have been found in excreta of migratory gulls and Canada geese. Thus, waterfowls can disseminate intestinal protozoan parasites in the environment [4].

Representative virus species that often cause fecal-oral disease transmission in wild birds include Influenza A virus (found in species of ducks, geese, gulls, terns, shearwaters, guillemots, shorebirds, and passerines), Newcastle disease virus (found in many species of free-living birds), anatid herpesvirus 1 (found in many species of anseriform such as ducks, geese, and swans), and aviadenovirus (found in migratory anseriform species) [6, 8].

As vectors of enteropathogens, wild birds have been associated with global outbreaks of water-borne and food-borne diseases. For example, outbreaks of infectious diseases have been attributed to fecal water supply contamination by wild birds [14]. Birds were strongly suspected as a source of enteropathogens for livestock when infected birds were found foraging on the livestock feed, and domestic cats have been known to contract enteropathogens by feeding on infected dead birds [15]. The incidence of infectious diseases in humans has also been linked to the handling of dead wild birds [16].
