Abstract
Isolated islands provide valuable opportunities to study the persistence of viruses in wildlife populations, including population size thresholds such as the critical community size. The straw-coloured fruit bat, Eidolon helvum, has been identified as a reservoir for henipaviruses (serological evidence) and Lagos bat virus (LBV; virus isolation and serological evidence) in continental Africa. Here, we sampled from a remote population of E. helvum annobonensis fruit bats on Annobón island in the Gulf of Guinea to investigate whether antibodies to these viruses also exist in this isolated subspecies. Henipavirus serological analyses (Luminex multiplexed binding and inhibition assays, virus neutralisation tests and western blots) and lyssavirus serological analyses (LBV: modified Fluorescent Antibody Virus Neutralisation test, LBV and Mokola virus: lentivirus pseudovirus neutralisation assay) were undertaken on 73 and 70 samples respectively. Given the isolation of fruit bats on Annobón and their lack of connectivity with other populations, it was expected that the population size on the island would be too small to allow persistence of viruses that are thought to cause acute and immunising infections. However, the presence of antibodies against henipaviruses was detected using the Luminex binding assay and confirmed using alternative assays. Neutralising antibodies to LBV were detected in one bat using both assays. We demonstrate clear evidence for exposure of multiple individuals to henipaviruses in this remote population of E. helvum annobonensis fruit bats on Annobón island. The situation is less clear for LBV. Seroprevalences to henipaviruses and LBV in Annobón are notably different to those in E. helvum in continental locations studied using the same sampling techniques and assays. Whilst cross-sectional serological studies in wildlife populations cannot provide details on viral dynamics within populations, valuable information on the presence or absence of viruses may be obtained and utilised for informing future studies.
Highlights
Reservoir host population size and density play a critical role in the ability of a species to maintain viruses that cause acute or immunising infections, reflected through epidemiological principles such as the critical community size (CCS) and the effective reproductive number (Reff)
Consistent with previous studies in Ghana [18] and in continental Africa, Luminex binding median fluorescence intensities (MFI) were higher against NiV than HeV in all samples above background levels
We interpret this as a greater cross-reactivity between African henipaviruses and NiV, than with HeV
Summary
Reservoir host population size and density play a critical role in the ability of a species to maintain viruses that cause acute or immunising infections, reflected through epidemiological principles such as the critical community size (CCS) and the effective reproductive number (Reff). Pathogens causing acute immunising infections require large host population sizes to maintain an adequate supply of susceptible individuals to maintain transmission [3], unless birth rates are very high. Important in shaping pathogen transmission dynamics is host population density, via its effect on Reff: the expected number of secondary infections that arise from each primary infection in a partially immune population [2]. Together, these factors mean that host species which exist in large population sizes and in high densities are capable of acting as reservoirs for a greater number of viruses than smaller, low density populations [4,5]
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