Livestock Drugs and Disease: The Fatal Combination behind Breeding Failure in Endangered Bearded Vultures

Blanco, Guillermo; Lemus, Jesús A.

The presence of West Nile virus is not likely to be associated with nestling disease or mortality because the lack of lesions in target tissues and viral antigen particles in the immunohistochemistry study. Fatal septicaemia caused by Streptococcus suis, one of the most important swine pathogens worldwide [49] , in combination with septicaemia from Streptococcus pneumoniae and infection by chicken infectious bronchitis virus were found in a single embryo. This concentration of livestock pathogens has not been reported before and, to our knowledge, this is the first report of the three pathogens causing disease in a wild bird. Other pathogens recorded in embryos and nestlings, including Salmonella serotypes and phages typical of livestock [50] , and enterotoxigenic Escherichia coli O86 causing septicaemia, were potentially transmitted by consumption of carcasses of infected poultry and other livestock [22, 27, 28] . In addition, we found that the IBD virus infected most individuals alone or together with other pathogens also potentially acquired from livestock carrion. This virus causes a highly contagious immunosuppressive bursal disease in poultry [51] and may be transmitted to wildlife in contact with poultry waste or by ingestion of carcasses [22, 52] . Nestlings are especially susceptible to IBD because of the primary role of bursa of Fabricius in immune function development at this age. In fact, immunosuppression due to IBD was indicated by the inflammation, necrosis and loss of lymphocytes in the bursa of Fabricius together with the presence of viral antigens recorded by means of immunocytochemical procedures. The potential impact of highly pathogenic and contagious poultry viruses has been previously recognized as a threat to wildlife health due to the increasing contact of wildlife with livestock operations in general, and poultry farms and their residues in particular, in natural areas worldwide [52] [53] [54] [55] . However, damage from IBD virus on the bursa of Fabricius represents, to our knowledge, the first evidence of clinical disease compatible with death caused by this poultry virus in wildlife. The presence of IBD has been not previously recorded in embryos of wild birds, probably because vertical transmission has been ruled out in poultry and, as consequence, it has probably not been evaluated in other species until now. This striking and concerning result could be related to the longer egg development and incubation periods of bearded vultures compared with poultry, and/or due to contrasting environmental conditions during incubation between bearded vultures and poultry. Thus, embryo infection with IBD may occurs via the female or during incubation as a consequence of egg contact between the egg and poultry remains in the nests of bearded vultures, which requires more research.