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Flight may mean fight against viruses

04 January 2013

The evolution of flight in bats such as the black flying fox, Pteropus alecto, may have contributed to the development of a highly effective immune system
Photo: Susanne Wilson/CSIRO AAHL

How do bats carry some of the world's most lethal viruses such as Ebola and SARS without being infected themselves? This intriguing question could now be explained in a study led by the Duke-NUS Graduate Medical School (Duke-NUS) in Singapore. The recent report published in the journal Science found that the evolution of flight in bats may have contributed to the development of a highly effective immune system.

Professor Wang Linfa, Director of the Programme in Emerging Infectious Diseases at Duke-NUS, headed the work, with an international team of researchers from Australia, China, Denmark, Singapore and the US. They used a state-of-the-art whole-genome sequencing technique to analyse the genomes of two distantly related bat species, the fruit bat Pteropus alecto (black flying fox) and the insect-eating bat Myotis davidii (David's mouse-eared bat), which are endemic in different geographical regions.

Bats are the only mammals capable of true flight; others such as flying squirrels can only glide. Studies have shown that the flying ability is likely linked to the bats' high metabolic rates. As raised metabolism also increases the amount of free radicals in living cells that damage DNA, the bats must have evolved genetic variants to solve this undesired side-effect of flying.

The researchers concluded that the same genes in bats that minimise DNA damage may also boost their immunity against viruses. This could explain why bats are natural hosts to many viruses such as Hendra, Nipah and Ebola, yet hardly get infected. In sharp contrast, humans or other animals are severely affected by diseases caused by these viruses.

In addition, a group of genes responsible for inflammation, the body's response to pathogen invasion, are found to be absent in bats. This may have implication for the creatures' strong immunity.

Prof Wang, an expert in bat-borne viruses, noted that this first in-depth research of bat genomes provided important genomics insights into the biology of bats. Bats have unusually long life despite their small size and high metabolic rate. The study implies that the mechanisms for the evolution of flight and viral immunity in bats may also be potentially associated with their life expectancy, which calls for further investigation.

Prof Wang hopes that the work will shed light on the treatment, prevention, and control of emerging infectious diseases. "Our findings highlight the potential of using bats as a model system to study infection control, tumour biology, and the mechanisms of ageing," he said. He plans to tap Duke-NUS' experience in human infectious disease research for viral diseases such as dengue and influenza.