Avian mycobacteriosis in free-living raptors in Majorca Island,Spain

Avian mycobacteriosis is a chronic, infectious disease caused by different species of mycobacteria, usually belonging to the Mycobacterium avium complex. From 2004 to 2007, 589 raptors brought dead or sick to a wildlife rehabilitation centre in Majorca (Balearic Islands, Spain) were necropsied. The birds belonged to 12 different species, chiefly common kestrel (Falco tinnunculus) (n=297), scops owl (Otus scops) (n=109), barn owl (Tyto alba) (n=75), long-eared owl (Asio otus) (n=58), peregrine falcon (Falco peregrinus) (n=27), and booted eagle (Hieraaetus pennatus) (n=13). Gross lesions compatible with mycobacteriosis were observed in 14 birds (2.4%) found in several locations in Majorca. They were 12 kestrels (prevalence in this species, 4.0%), one long-eared owl (1.7%) and one scops owl (0.9%), all the birds presenting white–yellowish nodules from pinpoint size to 1 cm in diameter in diverse organs, mainly in the liver, spleen and intestine. Affected organs were subjected to bacteriology and molecular identification by polymerase chain reaction and, in all cases, infection with M. avium subspecies avium was confirmed. The observed prevalences are similar to those previously observed in Holland, although the actual prevalence detected in this study is likely to be higher than reported because only birds with gross lesions were subjected to culture. Further molecular characterization with a set of six mycobacterial interspersed repetitive unit–variable number tandem repeat loci was used to sub-type the isolates in order to show the existence of possible epidemiological links. Six different genotypes were found, which points to infection from multiple foci. No temporal or geographical aggregation of the cases was observed to be associated with the presence of positive birds or with the different variable number tandem repeat allelic profiles. The most feasible origin might be water or food sources, although the reservoir of mycobacteria remains unknown.