Novel microfilariae detected in Galápagos passerines

Emerging parasites pose a serious risk to the health and survival of wild animal populations, particularly on islands where species often lack prior exposure and evolved defenses. We present the first report of a novel microfilaria infection found in blood from six species of Galápagos passerines in the coastal zone of Santa Cruz Island. Across 13 months, spanning two wet seasons and one dry season, 294 individuals were sampled and evaluated for microfilarial presence through microscopy and/or polymerase chain reaction. We barcoded the mitochondrial Cytochrome c oxidase I (COI) gene to tentatively place this microfilaria in the genus Eufilaria. We found host species level variation in infection, with certain species, like the vegetarian finch (Platyspiza crassirostris) and the common cactus finch (G eospiza . scandens) having very high prevalence, while others, like the Galápagos mockingbird (Mimus parvulus) and small tree finch (Camarhynchus parvulus) showing significantly lower prevalence. We investigated leukocyte counts, H/L ratios and body condition to evaluate the potential effects of infection on birds and found no relationship between infection status and these health indices. We also tested to see if seasonality could predict the infection trends found in our data and found a relationship with monthly rainfall, where more rain predicts higher microfilarial prevalence. Although we cannot confirm exactly when this parasite established in the Galápagos, our study highlights the importance of continued disease surveillance in endemic systems and underscores the need for species-level COI barcodes to improve microfilaria identification and phylogenetics.