Asynchronous seasonal dynamics of nycteribiid bat flies and Bartonella spp. in Australian flying foxes (Pteropus spp.)

Abstract

Bat flies are ubiquitous ectoparasites of bats, recognised as potential vectors for viral and bacterial transmission between individual bats within a roost. Despite this, little is known about the seasonal dynamics of bat flies. Here, we present the results of a longitudinal study that compares seasonal prevalence and host risk factors for bat fly (Diptera: Nycteribiidae) parasitism with that of Bartonella and Borrelia spp. detected in Pteropus alecto and P. poliocephalus in eastern Australia. Methods. Flying foxes were sampled at nine different roosts in south-east Queensland and northern New South Wales between February 2018 and September 2022 using mist nets. Host and ectoparasite data were recorded, and bat fly specimens were collected for identification. Blood samples collected from the flying foxes were screened for the presence of Bartonella and Borrelia DNA using polymerase chain reaction (PCR). Results. Ectoparasite data were recorded from 2235 flying foxes and 840 had blood samples screened for Bartonella and Borrelia DNA. Cyclopodia albertisii was the predominate nycteribiid species identified, with few detections of C. australis. Nycteribiid prevalence had a consistent annual cycle (ranging from 8.6% to 100%) that depended on local climatic factors, increasing with increased temperature and humidity during summer and decreasing in winter. Bartonella spp. prevalence exhibited less variation seasonally (ranging from 50% to 100%) with a peak in winter that was driven by host age, with juvenile bats having a reduced probability of infection compared with subadults and adults. Borrelia spp. were rare and showed no clear seasonality. Conclusions. This study reports the longitudinal occurrence of the blood-borne bacteria Bartonella spp. and their likely ectoparasite vectors in Australian flying foxes. The findings contribute to knowledge of nycteribiid ecology critical for understanding their vector potential within flying fox roosts and provide direction for future research into nycteribiid-mediated transmission dynamics.