Is all Zika dan­ger­ous? Asia out­breaks prompt ques­tion

Kuwait Times - - HEALTH & SCIENCE -

Zika’s ram­page last year in Brazil caused an ex­plo­sion of in­fec­tions and in­flicted a crip­pling neu­ro­log­i­cal de­fect on thou­sands of ba­bies - an ef­fect never seen in a mos­quito-borne virus.

It also pre­sented a mys­tery: why had a virus that had been lit­tle more than a foot­note in the an­nals of in­fec­tious dis­eases taken such a dev­as­tat­ing turn in the Amer­i­cas? How had Africa and Asia, where Zika had qui­etly cir­cu­lated for decades, es­caped with no re­ports of ma­jor out­breaks or se­ri­ous com­pli­ca­tions?

Sci­en­tists ini­tially the­o­rized that Zika’s long ten­ure in Africa and Asia may have con­ferred wide­spread im­mu­nity. Or, per­haps older strains were less vir­u­lent than the one linked in Brazil to more than 2,100 cases of mi­cro­cephaly, a birth de­fect char­ac­ter­ized by ar­rested brain de­vel­op­ment. Now, amid out­breaks in Sin­ga­pore, Thai­land, Viet­nam and other parts of South­east Asia, a much graver ex­pla­na­tion is tak­ing shape: per­haps the men­ace has been there all along but neu­ro­log­i­cal com­pli­ca­tions sim­ply es­caped of­fi­cial no­tice.

The ques­tion is driv­ing sev­eral re­search teams, ac­cord­ing to lead­ing in­fec­tious dis­ease ex­perts and pub­lic health of­fi­cials. The an­swer is im­me­di­ately im­por­tant for Asia, the re­gion most af­fected by Zika af­ter the Amer­i­cas. Thai­land has been hardest hit with more than 680 re­ported Zika in­fec­tions this year, fol­lowed by Sin­ga­pore with more than 450 and Viet­nam with as many as 60. Much of the pop­u­la­tion lives in the so-called “dengue belt,” where mos­quito-borne dis­eases are preva­lent. And vul­ner­a­ble coun­tries - in­clud­ing Viet­nam, the Philip­pines, Pak­istan and Bangladesh - are ill­pre­pared to han­dle an out­break with any se­ri­ous con­se­quences, ex­perts said.

Lack­ing ev­i­dence of vary­ing de­grees of vir­u­lence, pub­lic health of­fi­cials have warned Asia lead­ers to pre­pare for the worst. The sci­en­tific com­mu­nity is fol­low­ing sim­i­lar as­sump­tions. “Zika is Zika un­til proven other­wise. We as­sume that all Zikas are equally dan­ger­ous,” said Dr. Derek Gath­erer, a bio­med­i­cal ex­pert at Lan­caster Univer­sity in Bri­tain.

Which Zika dan­ger­ous?

The World Health Or­ga­ni­za­tion rec­og­nizes two ma­jor lin­eages of Zika. The first orig­i­nated in Africa, where it was dis­cov­ered in 1947 and has not been iden­ti­fied out­side that con­ti­nent. The Asian lin­eage in­cludes strains that have been re­ported in Asia, the Western Pa­cific, Cabo Verde and, no­tably, the Amer­i­cas, in­clud­ing Brazil.

The Asian lin­eage was first iso­lated in the 1960s in mos­qui­toes in Malaysia. But some stud­ies sug­gest the virus has been in­fect­ing peo­ple there since the 1950s. In the late 1970s, seven cases of hu­man in­fec­tion in In­done­sia were re­ported. The first record of a wide­spread out­break was in 2007 on Mi­crone­sia’s Is­land of Yap.

Ex­perts be­gan to sus­pect a link to birth de­fects dur­ing a 2013 out­break in French Poly­ne­sia when doc­tors re­ported eight cases of mi­cro­cephaly and 11 other cases of fe­tal mal­for­ma­tion.

In 2015, it hit Brazil, caus­ing spikes in an ar­ray of neu­ro­log­i­cal birth de­fects now called con­gen­i­tal Zika virus syn­drome, as well as Guil­lain-Barre syn­drome, a neu­ro­log­i­cal dis­or­der that can lead to tem­po­rary paral­y­sis. Viruses mu­tate rapidly, which can lead to strains that are more con­ta­gious and more vir­u­lent. Many re­searchers the­o­rized early on that the dev­as­ta­tion in Brazil was caused by an Asian strain that had mu­tated dra­mat­i­cally.

That the­ory re­lies, among other things, on the ab­sence of Zika-re­lated mi­cro­cephaly in Asia. So when Zika broke out in parts of Asia ear­lier this year, re­searchers were on the look­out. If re­searchers were to con­nect a case of mi­cro­cephaly to an older Asian strain - and not one that boomeranged back from Brazil-it would de­bunk the early the­ory. It would mean Zika “did not mu­tate into a mi­cro­cephaly-caus­ing vari­ant as it crossed the Pa­cific,” Gath­erer said.

At least three mi­cro­cephaly cases have been iden­ti­fied in Asia, but the ver­dict is still out. For two mi­cro­cephaly cases in Thai­land, pub­lic health of­fi­cials could not de­ter­mine whether the moth­ers had an older Asian strain of Zika or a newer one that re­turned from the Amer­i­cas, said Dr Boris Pavlin, WHO’s act­ing Zika in­ci­dent man­ager at a re­cent brief­ing.

In Viet­nam, where there have been no re­ports of im­ported Zika in­fec­tion, of­fi­cials are in­ves­ti­gat­ing a third case of mi­cro­cephaly. If it is linked to Zika, Pavlin said it would sug­gest the older strains there could cause mi­cro­cephaly and, per­haps, Guil­lain-Barre. In Malaysia, where at least six cases of Zika in­fec­tion have been re­ported, au­thor­i­ties have iden­ti­fied both an older South­east Asian strain and one sim­i­lar to the strain in the Amer­i­cas, sug­gest­ing the pos­si­bil­ity that strains from both re­gions could be cir­cu­lat­ing in some coun­tries.

The hunt is on in Africa as well. In GuineaBis­sau, five mi­cro­cephaly cases are un­der in­ves­ti­ga­tion to de­ter­mine whether the African lin­eage of Zika can cause mi­cro­cephaly. It is a top re­search pri­or­ity at WHO, said Dr Peter Salama, ex­ec­u­tive di­rec­tor of the agency’s health emer­gen­cies pro­gram, in a press brief­ing Tues­day.

“That is a crit­i­cal ques­tion be­cause it has real pub­lic health im­pli­ca­tion for African or Asian coun­tries that al­ready have Zika virus trans­mis­sion,” Salama said. “We are all fol­low­ing this ex­tremely closely.”

Sci­en­tists also are try­ing to learn whether peo­ple in places where Zika is en­demic are pro­tected by “herd im­mu­nity.” The phe­nom­e­non lim­its the spread of virus when enough of a pop­u­la­tion is in­oc­u­lated against in­fec­tion through vac­ci­na­tion, prior ex­po­sure or both. Ex­perts be­lieve Zika moved ex­plo­sively in the Amer­i­cas be­cause there was no prior ex­po­sure. It’s not clear how widely Zika has cir­cu­lated in Africa and Asia, whether there could be pock­ets of nat­u­ral im­mu­nity - and, im­por­tantly, whether im­mu­nity to one strain would con­fer im­mu­nity to an­other.

One re­cent re­view of stud­ies sug­gests 15 to 40 per­cent of the pop­u­la­tion in some African and Asian coun­tries may have been pre­vi­ously in­fected with Zika, said Alessan­dro Ve­spig­nani, a pro­fes­sor of health sci­ences at North­east­ern Univer­sity in Bos­ton.

That’s far be­low the 80 per­cent pop­u­la­tion im­mu­nity one mos­quito borne virus ex­pert es­ti­mated in the jour­nal Sci­ence would be nec­es­sary to block Zika. Re­searchers also be­lieve it’s pos­si­ble that mi­cro­cephaly went un­de­tected in parts of Asia and Africa where birth de­fects weren’t well tracked.

That too, is un­der in­ves­ti­ga­tion, said Dr David Hey­mann, Chair of the WHO Emer­gency Com­mit­tee, at a press brief­ing last week. “Now,” he said, “coun­tries are be­gin­ning to look back into their records to see on their reg­istries what the lev­els of mi­cro­cephaly have been.” — Reuters

SAL­VADOR, Brazil: This file photo taken on Jan­uary 28, 2016 shows phys­i­cal ther­a­pist Isana San­tana treat­ing Ruan Hen­tique dos San­tos, suf­fer­ing from mi­cro­cephalia caught through an Aedes Ae­gypti mos­quito bite, at Obras So­cias irma dulce hos­pi­tal. — AFP

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