Avian Flu Diary: Bats, Viruses, And Their Immune Response

Common pipistrelle (Pipistrellus pipistrellus) – Credit Wikipedia

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For virologists and chiroptologists, an enduring mystery has been how bats are able to carry – without apparent ill effect – viruses that are normally deadly to most other mammals.

Long known for carrying rabies, over the past two decades we’ve discovered that bats can also harbor viruses such as Ebola, Marburg, Nipah, Hendra, and a variety of coronaviruses (including SARS).

This week, in an article that appears in the Journal Science, we learn that some of the evolutionary changes that enable the bat to be the only mammal that can fly, may also help them to carry deadly viruses.

First a link to the Abstract (the whole paper is behind a pay wall), then excerpts from a Reuter’s news article that help flesh out the findings.

Published Online December 20 2012
< Science Express Index

Science DOI: 10.1126/science.1230835

Report

Comparative Analysis of Bat Genomes Provides Insight into the Evolution of Flight and Immunity

Guojie Zhang, Christopher Cowled, Zhengli Shi, Zhiyong Huang, Kimberly A. Bishop-Lilly, Xiaodong Fang, James W. Wynne, Zhiqiang Xiong, Michelle L. Baker, Wei Zhao, Mary Tachedjian, Yabing Zhu, Peng Zhou, Xuanting Jiang, Justin Ng, Lan Yang, Lijun Wu, Jin Xiao, Yue Feng, Yuanxin Chen, Xiaoqing Sun, Yong Zhang, Glenn A. Marsh, Gary Crameri, Christopher C. Broder, Kenneth G. Frey, Lin-Fa Wang, Jun Wang

Abstract

Bats are the only mammals capable of sustained flight and are notorious reservoir hosts for some of the world’s most highly pathogenic viruses, including Nipah, Hendra, Ebola, and severe acute respiratory syndrome (SARS). To identify genetic changes associated with the development of bat-specific traits, we performed whole-genome sequencing and comparative analyses of two distantly related bat species, fruit bat Pteropus alecto and insectivorous Myotis davidii.

We discovered an unexpected concentration of positively selected genes in the DNA damage checkpoint and nuclear factor–κB pathways that may be related to the origin of flight, as well as expansion and contraction of important gene families. Comparison of bat genomes with other mammalian species has provided new insights into bat biology and evolution.

Admittedly, there is not much specificity in this abstract.

Luckily, Tan Ee Lyn - Asia Health correspondent for Reuters – has an interview with the lead author -Professor Lin-Fa Wang, who reveals that some genetic changes necessary for flight may also help to moderate dangerous out-of-control immune responses known as Cytokine Storms.

Cytokines are a category of signaling molecules – proteins – that are released by immune cells that have encountered a pathogen, and are designed to alert and activate other immune cells to join in the fight against the invading pathogen.

Although poorly understood, the theory behind a `cytokine storm’ is this signaling process spirals out of control, resulting in an overwhelming immune response that can potentially kill the host.

According to Professor Lin-Fa Wang, this built-in suppression of the inflammatory (cytokine) response may be behind the bat’s unusual longevity (20 to 40 years), and their ability to `handle’ infection by normally deadly viruses.

Long-lived bats offer clues on diseases, aging

December 21, 2012 12:52 PM

HONG KONG: The bat, a reservoir for viruses like Ebola, SARS and Nipah, has for decades stumped scientists trying to figure out how it is immune to many deadly bugs but a recent study into its genes may finally shed some light, scientists said on Friday.Studying the DNA of two distant bat species,...

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In another article, this time in The Asian Scientist, the author talks about practical applications of this research, and is quoted as saying, “Our findings highlight the potential of using bats as a model system to study infection control, tumor biology, and the mechanisms of aging,”

Bats’ Immunity Against Deadly Viruses Linked To Their Ability To Fly

AsianScientist (Dec. 21, 2012) – An international team led by an infectious disease expert, Professor Lin-Fa Wang, at the Duke-NUS Graduate Medical School (Duke-NUS) in Singapore has found that the evolution of flight in bats may have contributed to the development of a highly effective immune system, allowing bats to harbor some of the world’s deadliest viruses such as Ebola and SARS.

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Both news articles are worth reading in their entirety.

For more on cytokine storms, and how they may affect pandemic influenza mortality, you may wish to revisit some of these earlier blogs.