Drawing the line – they shall not pass?

The Wallace Line It has been known for over 100 years that a major biogeographic barrier exists between the Australo-Papuan and Wallacean region on the one hand, and southeast Asia on the other, with different groups of both terrestrial vertebrates and invertebrates occurring on either side of the “Wallace Line“. It has even been suggested that this boundary has protected Australia from the recent H5N1 avian influenza epidemic. Of the major groups of terrestrial mammals, only rodents and bats extend across this region from southeast Asia into Australia. There are 13 species of Old World fruit bat that occur only to the west of Wallace’s Line and 67 species that are confined to the east, while 20 species have wide distributions throughout the region and occur on both sides of the line.

The aim of a new paper in PLOS ONE is to investigate the occurrence of henipaviruses in fruit bat populations in the regions of northeast Australia (Queensland), New Guinea (Papua New Guinea) and Wallacea (Indonesia and East Timor) by testing the hypothesis that Nipah virus is restricted in distribution to west of Wallace’s Line. Fruit bats were sampled from northeast Australia, Papua New Guinea, East Timor and Indonesia, and tested for the presence of anti-Hendra virus (HeV) and anti-Nipah virus (NiV) antibodies. PCR tests were also conducted to determine the presence of henipavirus RNA.

The authors found that fruit bats from regions on both sides of the line tested positive for Nipah virus and other related henipaviruses. Only certain species of fruit bats carried Nipah virus but even in their absence, other bat species could still carry these related viruses. Henipaviruses were also detected in some species not previously known to carry these viruses. Based on these results, the authors conclude that Wallace’s line is not a restricting factor for the transmission of Nipah virus.

 

The Distribution of Henipaviruses in Southeast Asia and Australasia: Is Wallace’s Line a Barrier to Nipah Virus? (2013) PLoS ONE 8(4): e61316. doi:10.1371/journal.pone.0061316
Nipah virus (NiV) (Genus Henipavirus) is a recently emerged zoonotic virus that causes severe disease in humans and has been found in bats of the genus Pteropus. Whilst NiV has not been detected in Australia, evidence for NiV-infection has been found in pteropid bats in some of Australia’s closest neighbours. The aim of this study was to determine the occurrence of henipaviruses in fruit bat (Family Pteropodidae) populations to the north of Australia. In particular we tested the hypothesis that Nipah virus is restricted to west of Wallace’s Line. Fruit bats from Australia, Papua New Guinea, East Timor and Indonesia were tested for the presence of antibodies to Hendra virus (HeV) and Nipah virus, and tested for the presence of HeV, NiV or henipavirus RNA by PCR. Evidence was found for the presence of Nipah virus in both Pteropus vampyrus and Rousettus amplexicaudatus populations from East Timor. Serology and PCR also suggested the presence of a henipavirus that was neither HeV nor NiV in Pteropus alecto and Acerodon celebensis. The results demonstrate the presence of NiV in the fruit bat populations on the eastern side of Wallace’s Line and within 500 km of Australia. They indicate the presence of non-NiV, non-HeV henipaviruses in fruit bat populations of Sulawesi and Sumba and possibly in Papua New Guinea. It appears that NiV is present where P. vampyrus occurs, such as in the fruit bat populations of Timor, but where this bat species is absent other henipaviruses may be present, as on Sulawesi and Sumba. Evidence was obtained for the presence henipaviruses in the non-Pteropid species R. amplexicaudatus and in A. celebensis. The findings of this work fill some gaps in knowledge in geographical and species distribution of henipaviruses in Australasia which will contribute to planning of risk management and surveillance activities.

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