Living in the city: effects of urbanisation on house sparrow digestive yeasts

Resumen del trabajo presentado a la 12th Conference of the European Wildlife Disease Association (EWDA), celebrada en Berlin (Alemania) del 26 al 31 de agosto de 2016.
The bouse sparrow (Passer domesticus) is one of the most widely distributed urban birds and has successfully expanded its range to all continents. Recent population declines of this and other garden bird species in central and Northern Europe have raised concern and are considered due to several factors, including pathogens such as the protozoan parasite Trichomonas gallinae. To study the presence of this potential pathogen in Spanish sparrow populations we sampled 76 house sparrows in three areas with different degrees of urbanisation and during both wintering and the reproductive season. Swab samples from the oropharynx and oesopbagus were cultured in trichomonas culture medium enriched with 10% foetal calf serum and tested by direct microscopic observation and PCR for presence of T. gallinae. None of the sparrows was colonised by T. gallinae but two yeasts were detected, Macrorhabdus ornitogaster and Candida sp. in 29% and 23.7% of the cultures, respectively. Candida albicans was identified in most cases by culture in Sabouraud dextrose agar and biochemical tests while Macrorhabdus ornitogaster has characteristic microscopic features. Macrorhabdus ornitogaster was found more frequently in juvenile sparrows (38.89 %, 7 of 18) than adults (25.7 %, 15 of 58; GzLM, p = 0.049, β = -1,304, SE = 0.663). Macrorhabdus prevalence also increases as degree of urbanisation raises (GzLM, p = 0.018, β = 0.906, SE = 0.383). A co-infection effect with Candida sp.has been observed (GzLM, p = 0.034, β = 0.043, SE = 0.383). M. ornithogaster is an ascomycetes yeast tbat is present at tbe junction of the proventriculos and gizzard of wild and domestic birds. It has been described in numerous captive and wild birds, but to our knowledge not previously in house sparrows. Although the sparrows were apparently healthy and M ornithogaster is potentially a commensal, in some passerine, gallinaceous and psittacine species it has been identified as a significant pathogen. The degree of M ornithogaster carriage in sparrows may be affected by environmental conditions and they may act as reservoirs for other more susceptible species. Urban birds have to cope with many stressors that could affect the presence of this commensal yeast. Finally, under stressful conditions fitness of infected individuals could be comprornised and lead to clinical infections.