MicrobiologyBytes

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.

twitter.com/search/%23microtwjc

Read:

Bats host major mammalian paramyxoviruses. (2012) Nature Communications 3, Article number: 796 doi:10.1038/ncomms1796
The large virus family Paramyxoviridae includes some of the most significant human and livestock viruses, such as measles-, distemper-, mumps-, parainfluenza-, Newcastle disease-, respiratory syncytial virus and metapneumoviruses. Here we identify an estimated 66 new paramyxoviruses in a worldwide sample of 119 bat and rodent species (9,278 individuals). Major discoveries include evidence of an origin of Hendra- and Nipah virus in Africa, identification of a bat virus conspecific with the human mumps virus, detection of close relatives of respiratory syncytial virus, mouse pneumonia- and canine distemper virus in bats, as well as direct evidence of Sendai virus in rodents. Phylogenetic reconstruction of host associations suggests a predominance of host switches from bats to other mammals and birds. Hypothesis tests in a maximum likelihood framework permit the phylogenetic placement of bats as tentative hosts at ancestral nodes to both the major Paramyxoviridae subfamilies (Paramyxovirinae and Pneumovirinae). Future attempts to predict the emergence of novel paramyxoviruses in humans and livestock will have to rely fundamentally on these data.

Questions:
Why look for viruses? What about bacteria or parasites?
Why bats? What other kinds of species would you look at? Or are bats special?
Are their sample sizes enough to capture true diversity of bats/rodents?
Why did they specifically look for paramyxoviruses? Why not utilize deep sequencing approaches?
What does having a viral sequence tell us? Of most of these viruses they never actually found the virus, only sequences. What problems are associated with this?
Does their data really back up the title of the paper? To show that a species is the reservoir host, what kind of evidence do you need?
What’s the deal their phylogenetic methods?
What would you do next with this data? Should we kill all the bats?

The fungi are angry. First it was the frogs, then it was the bats. Are humans next?

Fungal Disease and the Developing Story of Bat White-nose Syndrome. (2012) PLoS Pathog 8(7): e1002779. doi:10.1371/journal.ppat.1002779
Two recently emerged cutaneous fungal diseases of wildlife, bat white-nose syndrome (WNS) and amphibian chytridiomycosis, have devastated affected populations. Fungal diseases are gaining recognition as significant causes of morbidity and mortality to plants, animals, and humans, yet fewer than 10% of fungal species are known. Furthermore, limited antifungal therapeutic drugs are available, antifungal therapeutics often have associated toxicity, and there are no approved antifungal vaccines. The unexpected emergence of WNS, the rapidity with which it has spread, and its unprecedented severity demonstrate both the impacts of novel fungal disease upon naïve host populations and challenges to effective management of such diseases.

Rapid evolution of RNA viruses is intimately linked to their success in overcoming the defenses of their hosts. Several studies have shown that rates of viral evolution can vary dramatically among distantly related viral families. Variability in the speed of evolution among closely related viruses has received less attention, but could be an important determinant of the geographic or host species origins of viral emergence if certain species or regions promote especially rapid evolution.

A new paper uses a dataset of rabies virus sequences collected from bat species throughout the Americas to test the role of inter-specific differences in reservoir host biology on the tempo of viral evolution. This shows the annual rate of molecular evolution to be a malleable trait of viruses that is accelerated in subtropical and tropical bats compared to temperate species. The association between geography and the speed of evolution appears to reflect differences in the seasonality of rabies virus transmission in different climatic zones.

These results illustrate that the viral mechanisms commonly invoked to explain heterogeneous rates of evolution among viral families may be insufficient to explain evolution in multi-host viruses and indicate a role for host biology in shaping the speed of viral evolution.

Rates of Viral Evolution Are Linked to Host Geography in Bat Rabies. (2012) PLoS Pathog 8(5):e1002720. doi:10.1371/journal.ppat.1002720
Rates of evolution span orders of magnitude among RNA viruses with important implications for viral transmission and emergence. Although the tempo of viral evolution is often ascribed to viral features such as mutation rates and transmission mode, these factors alone cannot explain variation among closely related viruses, where host biology might operate more strongly on viral evolution. Here, we analyzed sequence data from hundreds of rabies viruses collected from bats throughout the Americas to describe dramatic variation in the speed of rabies virus evolution when circulating in ecologically distinct reservoir species. Integration of ecological and genetic data through a comparative Bayesian analysis revealed that viral evolutionary rates were labile following historical jumps between bat species and nearly four times faster in tropical and subtropical bats compared to temperate species. The association between geography and viral evolution could not be explained by host metabolism, phylogeny or variable selection pressures, and instead appeared to be a consequence of reduced seasonality in bat activity and virus transmission associated with climate. Our results demonstrate a key role for host ecology in shaping the tempo of evolution in multi-host viruses and highlight the power of comparative phylogenetic methods to identify the host and environmental features that influence transmission dynamics.