Serological evidence of a pararubulavirus and a betacoronavirus in the geographically isolated Christmas Island flying-fox (Pteropus natalis)

Abstract

Due to their geographical isolation and small populations, insular bats may not be able to maintain acute immunizing viruses that rely on a large population for viral maintenance. Instead, endemic transmission may rely on viruses establishing persistent infections within hosts or inducing only short-lived neutralizing immunity. Therefore, studies on insular populations are valuable for developing broader understanding of viral maintenance in bats. The Christmas Island flying-fox (CIFF; Pteropus natalis) is endemic on Christmas Island, a remote Australian territory, and is an ideal model species to understand viral maintenance in small, geographically isolated bat populations. Serum or plasma (n = 190), oral swabs (n = 199), faeces (n = 31), urine (n = 32) and urine swabs (n = 25) were collected from 228 CIFFs. Samples were tested using multiplex serological and molecular assays, and attempts at virus isolation to determine the presence of paramyxoviruses, betacoronaviruses and Australian bat lyssavirus. Analysis of serological data provides evidence that the species is maintaining a pararubulavirus and a betacoronavirus. There was little serological evidence supporting the presence of active circulation of the other viruses assessed in the present study. No viral nucleic acid was detected and no viruses were isolated. Age-seropositivity results support the hypothesis that geographically isolated bat populations can maintain some paramyxoviruses and coronaviruses. Further studies are required to elucidate infection dynamics and characterize viruses in the CIFF. Lastly, apparent absence of some pathogens could have implications for the conservation of the CIFF if a novel disease were introduced into the population through human carriage or an invasive species. Adopting increased biosecurity protocols for ships porting on Christmas Island and for researchers and bat carers working with flying-foxes are recommended to decrease the risk of pathogen introduction and contribute to the health and conservation of the species.

Keywords: Pteropodidae; bat; betacoronavirus; insular populations; pararubulavirus; viral maintenance.

FIGURE 1

Map indicating Christmas Island flying‐fox (Pteropus natalis) capture locations. Inset shows location of Christmas Island relative to mainland Australia and the nearby island of Java, Indonesia

FIGURE 2

Histogram of data overlaid with density of the fitted one‐component shifted‐Gompertz model for bound antibodies to (a) Cedar virus, (b) Hendra virus, (c) Menangle virus, (d) Nipah virus, (e) Tioman virus, (f) severe acute respiratory syndrome coronavirus, (g) Middle East respiratory syndrome coronavirus and (h) Australian bat lyssavirus using a multiplex microsphere‐based immunoassay. Samples were considered cross‐reactive if they exceeded both the median florescence intensity (MFI) threshold of 1000 (lnMFI value of 6.9; solid red line) and the threshold (dotted red line) established by the shifted‐Gompertz upper percentile

FIGURE 3

Histogram of data overlaid with density of the fitted one‐component shifted‐Gompertz model for detection of viral nucleic acid to (a) Cedar virus, (b) Hendra virus, (c) henipaviruses, (d) Nipah virus, (e) Menangle virus and (f) Tioman virus using the multiplex X‐TAG assay. Samples were considered cross‐reactive if they exceeded both the median florescence intensity (MFI) threshold of 1000 (lnMFI value of 6.9; solid red line) and the threshold (dotted red line) established by the shifted‐Gompertz model upper percentile. No samples were above the established thresholds