The Mystery of Bat Antiviral Immunity

Bats are most commonly known as creatures of the night; but few know their full potential as a reservoir of deadly viruses. In a recent seminar at Macquarie University; Doctor Michelle Baker of the Australian Animal Health Lab, Geelong, Victoria;explains how the unique Bat immune system responds to a host of deadly viruses they appear to happily coexist with. The Australian Animal Health Lab is a CSIRO funded, state of the art facility aimed at protecting Australia’s livestock, aquaculture and the public’s health from range of infectious diseases. Research on Bats tends to focus on immunology, genomics, pathogen discovery, the movements and transfer of virulence and potential vaccination remedies1. Doctor Baker’s work centres on the species of Megachiroptera (Megabats); Pteropus alecto or the Black Flying Fox [below – Figure 1].

Black_Flying_Fox_(Pteropus_alecto)

Figure 1: Pteropus alecto taken from  http://en.wikipedia.org/wiki/Black_flying_fox

Bat Facts

Bats are the second most abundant and species rich of the mammalian group, yet they remain one of the least studied groups1. Bats are interesting creatures due to a number of reasons; they are the only mammal with powered flight, are long lived in relation to body size (up to 40 years), show low incidences of tumours and have long history associated with some of the globes most deadly viruses1. Studies have shown that over 100 viruses are associated with Bats. The top 5 most deadly viruses carried by Bats include: Rabies, Ebola, SARS, Hendra and the Marburg viruses2. Remarkably Bats show no symptoms of illness even whilst being associated with multiple viruses at one time; it is only the rabies virus that on occasion negatively impacts the Bats health2.

Bat Immunology

The study of Bats as virus reservoirs and their unique immunity to the diseases they carry is quite a young area of study, only truly taking flight in 2008. One of the key studies within this field was the Bat Genome Project which sequenced the genomes of two bat species: Pteropus alecto (The Black Flying Fox) and Myotis davidii (David’s Myotis) and thereby set the foundation for all future studies on Bat immunology3. One of the most significant discoveries to come from this project was the identification of changes in innate immunes genes involved in interferon production; or simply how the Bat’s immune system works.

Interferons (IFN) are proteins created and released by a hosts (in this case, a Bat) cells in response to the threat of pathogen such as a virus. IFN’s are a potent first line of defence against viral infection, keeping a virus in an ‘antiviral state’ as well as stopping the virus from spreading2,4. Studies have focused on two key interferons: alpha (α) and beta (β) in which Bats have the fewest IFNα loci in comparison to a number other mammals. Bat immunology presents us with another interesting fact; IFNα is invariably expressed within the Bat’s immune system and isn’t induced following stimulation (e.g. experimental infection)4. What makes this situation more extraordinary is the fact that IFNα is in fact toxic at high levels4. It is this rapid control of viral replication that potentially holds the key for a Bats ability to coexist with these deadly viruses4. This would mean that Bats are constantly primed for viral defence, a defence that would presumably be at a high cost towards the host; surprising given the long lifespan of these unique mammals.

The study of Bat immunology is still in its infancy; the continuation of studies such as these has huge implications to our understanding of viral responses and the mechanics of viral spill overs, which not only have huge economic implications but the safety of human life.

Bat References

  1. Baker ML, Schountz T, Wang L–F. 2013. Antiviral Immune Responses of Bats:  A Review. Zoonoses and Public Health, 60:1, 104-116.
  2. Bean, A.G.D., Baker, M.L., Stewart, C.R., Cowled, C. Deffrasnes, C., Wang, L-F. & Lowenthal, J.W. 2013. Studying immunity to zoonotic diseases in the natural host – keeping it real. Nature Reviews Immunology, 13(12): 851-861.
  3. Zhang, G., Cowled, C., Shi, Z., Huang, Z., Bishop-Lilly, K.A., Fang, X., Wynne, J.W., Xiong, Z., Baker, M.L., Zhao, W., Tachedjian, M., Zhu, Y., Zhou, P., Jiang, X., Ng, J., Yang, L., Wu, L., Xiao, J., Feng, Y., Chen, Y., Sun, X., Zhang, Y., Marsh, G.A., Crameri, G., Broder, C.C., Frey, K.G., Wang, L.F. & Wang, J. 2013. Comparative Analysis of Bat Genomes Provides Insight into the Evolution of Flight and Immunity. Science, 339(6118): 456-460.
  4. Zhou, P., Cowled, C., Wynne, J., Ng, J., Wang, L. & Baker, M.L. 2013. Type I interferon in bats: Is it special? Cytokine, 63(3): 313-314.

 

 

 

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