The Fly­ing Virus Lab­o­ra­tory

Fruit bats carry more deadly viruses than all of those stored in the world’s high se­cu­rity lab­o­ra­to­ries put to­gether. But why do other an­i­mals and hu­mans die when the hosts them­selves re­main healthy? Could the key to fight­ing deadly dis­eases be found in t

World of Knowledge (Australia) - - Contents -

How do fruit bats defy the world’s most deadly dis­eases?

The stum­ble seemed so in­con­se­quen­tial that Sonja Metesch* will only re­mem­ber it sev­eral weeks later. Dur­ing a tour of a cave in the mid­dle of the Ugan­dan rain­for­est, the 40-year-old Dutch woman loses her foot­ing and in­jures her hand sup­port­ing her­self on some rocks. Just a scratch, she thinks, as she re­joins the group. It’s a mis­take that will prove fa­tal.


Back in the Nether­lands, Metesch de­vel­ops a rag­ing fever. Then things spi­ral out of con­trol – fast. She is rushed to hospi­tal suf­fer­ing from mul­ti­ple or­gan fail­ure and, just days later, dies. Metesch has fallen vic­tim to the Mar­burg virus, a dis­ease trans­mit­ted by wild an­i­mals – even though she never came into di­rect con­tact with one. How could that have hap­pened? The virus must have en­tered her body when she cut her hand on the rocks. The open wound must have come into con­tact with some fae­ces in the bat-in­fested cave. Fruit bat fae­ces to be pre­cise. Drop­pings from a species that car­ries more viruses in­side its body than all of those stored in the world’s high se­cu­rity lab­o­ra­to­ries.

So do fruit bats re­ally pose such a risk to hu­mans or was the Dutch woman’s case an ex­tremely un­lucky one-off? Hu­mans have been afraid of bats for cen­turies. In re­cent times, this fear has soared as sci­en­tists have proved that the an­i­mals carry viruses that cause deadly epi­demics like Ebola – even though it is very rare for them to trans­mit the virus di­rectly to hu­mans. “It only hap­pens if you are bitten or eat the meat of an in­fected fruit bat,” ex­plains Tony Schountz from Colorado State Uni­ver­sity. Or – as in Metesch’s case – when an open wound comes into con­tact with the an­i­mal’s saliva, blood or ex­cre­ment. Which begs the ques­tion: if fruit bats carry deadly pathogens like the Ebola and Mar­burg viruses, why do they never fall ill them­selves? Re­searchers have now dis­cov­ered that while other an­i­mals and peo­ple die from these viruses, fruit bats won’t suf­fer so much as a fever. On the con­trary, their life­span is ten times that of other sim­i­lar-sized mam­mals and they al­most never de­velop can­cer.

So does the key to heal­ing also lie in­side the fruit bats’ deadly cargo? Re­searchers are con­vinced it does and are now try­ing to un­cover the se­cret of the fruit bat im­mune sys­tem. They hope that we may soon be able to thank fruit bats for im­prov­ing our health – and even our life ex­pectan­cies.


For that to be­come a re­al­ity, sci­en­tists first need to un­der­stand how fruit bats can live seem­ingly healthy lives un­harmed by the pathogens lurk­ing in their cells. The virologist Linfa Wang from DukeNUS Med­i­cal School in Sin­ga­pore has re­searched just that. He spent al­most two decades in Aus­tralia study­ing fruit bats and how they trans­mit the deadly Hen­dra virus to horses. Wang dis­cov­ered that, un­like other mam­mals, the fruit bats could con­trol the virus. They dis­played nei­ther a fever nor a raised level of white blood cells in their blood. But how did their im­mune sys­tems some­how ren­der the virus harm­less?

Sci­en­tists be­lieve the an­swer lies in the an­i­mals’ fast me­tab­o­lism. To help them fly, fruit bats re­quire up to 20% more calo­ries than a non-fly­ing mam­mal. This speedy me­tab­o­lism raises the level of free rad­i­cals in their blood, which have the po­ten­tial to dam­age their DNA. To pre­vent this from hap­pen­ing, a bat’s im­mune sys­tem is con­stantly in over­drive. It cleans up the danger­ous mol­e­cules – in­clud­ing po­ten­tially deadly viruses. Since their im­mune sys­tem func­tions so well, the an­i­mals don’t get sick. The virus mul­ti­plies in their bod­ies and they pass it onto their off­spring – but they never de­velop symp­toms.

Con­trary to pop­u­lar per­cep­tion, few viruses kill hu­mans. Hu­mans ac­tu­ally kill them­selves, be­cause of ex­ces­sive IN­FLAM­MA­TION. LINFA WANG, VIROLOGIST DUKE-NUS MED­I­CAL SCHOOL

Un­for­tu­nately, how­ever, this is by no means the case for hu­mans. In the event of a sim­i­lar vi­ral in­va­sion, our im­mune sys­tem would re­act by ex­hibit­ing an ex­tremely pow­er­ful in­flam­ma­tory re­sponse. Wang ex­plains: “Con­trary to pop­u­lar per­cep­tion, few viruses kill hu­mans. Hu­mans ac­tu­ally kill them­selves be­cause of the ex­ces­sive in­flam­ma­tion.” In other words, un­like fruit bats, which have a con­stantly ac­ti­vated im­mune fire­wall, our op­er­at­ing sys­tem ends in a short cir­cuit – and it col­lapses.


Sci­en­tists are now try­ing to iden­tify the pro­teins that fruit bats use to con­trol in­flam­ma­tion and pre­vent tu­mours form­ing. These pro­teins – or mod­i­fi­ca­tions thereof – could then be used to treat con­di­tions char­ac­terised by life-lim­it­ing in­flam­ma­tion such as arthri­tis, rheuma­tism and heart dis­ease. The find­ings could also con­trib­ute to a cure for deadly viruses like SARS and Ebola. Many hu­man lives could be saved. Zo­ol­o­gist Emma Teeling from the Uni­ver­sity of Dublin is con­vinced: “It’s only a mat­ter of time un­til we will be able to un­lock this se­cret once and for all. Mother Na­ture has the an­swer.”

Erad­i­cat­ing fruit bats for fear of con­ta­gion could have cat­a­strophic con­se­quences, says Linfa Wang. Stud­ies have shown that culling pop­u­la­tions can ac­tu­ally in­crease the risk of an epi­demic – mov­ing or de­stroy­ing colonies in­creases stress lev­els in the bats, which raises their vi­ral load and the risk of spillover. The con­tam­i­na­tion of vast ar­eas from in­jured and dead bats also raises the risk of the virus spread­ing. This in turn raises the risk of other an­i­mals be­ing in­fected.

More­over, bats are cru­cial to the planet’s ecological balance be­cause they eat in­sects that dam­age crops. In fact, a colony of bats can end a pest out­break in a sin­gle night, not thanks to the viruses they carry but sim­ply by de­ploy­ing their ex­cel­lent hunt­ing in­stinct.

Fruit bats live up to ten times longer than other sim­i­lar-sized mam­mals – and they al­most never get can­cer. EMMA TEELING, ZO­OL­O­GIST, UNI­VER­SITY OF DUBLIN

TOP SE­CU­RITY These re­searchers are test­ing fruit bats for the Ebola virus. The an­i­mals are eaten in Africa and were the likely cause of the epi­demic.

WHAT MAKES THE EN­EMY TICK? Cana­dian re­searchers in pro­tec­tive suits ex­per­i­ment with the Ebola virus in a high­se­cu­rity lab­o­ra­tory.

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