ResearchersarescramblingtostudytheevolutionandspreadofthenovelH1N1strainofswineinfluenzawhoseleaptohumanswasofficiallyconfirmedlastweek.Thepossibleimminentonsetofaswine-flupandemicisalsotestinginternationalpreparednessplansputintoplacetodealwithsomethingelse:themuch-fearedH5N1avianfluvirusthathasspreadacrossAsia,EuropeandAfricasince2003.Thegeneticmake-upofthisswinefluvirusisunlikeanythatresearchershaveseen.ItisanH1N1strainthatcombinesatripleassort-mentfirstidentifiedin1998—includinghuman,swineandavianinfluenza—withtwonewpigH3N2virusgenesfromEurasia,themselvesofrecenthumanorigin.“Ithasbeenmixingallovertheplace,andsothegeneticsarequitecomplicated,”saysJohnMcCauley,avirologistattheUKMedicalResearchCouncil’sNationalInstituteforMedi-calResearchinLondon.“Wherethehellitgotallthesegenesfromwedon’tknow,”saysRobertWebster,afluvirologistatStJudeChildren’sResearchHospitalinMemphis,Tennessee.“Butthisisarealsuper-mixed-upvirus.”AsNaturewenttopress,morethan150peo-plewerethoughttohavediedfromthevirusinMexico,withsome1,600casessuspectedthere.Atleast87caseshavebeenconfirmedinothercountries,includingtheUnitedStates,Canada,NewZealand,theUnitedKingdom,SpainandIsrael.On27April,theWorldHealthOrganization(WHO)raiseditspandemicthreatfromphase3—anewfluvirusinfectinghumansbutwithlim-itedhuman-to-humanspread—tophase4,withcommunityoutbreaksthatmark“asignificantupwardsshiftintheriskforapandemic”.Thescalerunsto6:afull-blownpandemic.“Thescarythingisthatthisvirusseemsenormouslytransmissible,”saysWebster.InNewYork,forinstance,atleast28studentsataschoolinQueenshavecomedownwithit.TheUSCentersforDiseaseControlandPrevention(CDC)andtheWHOaretryingtonaildownhowmanyofthereporteddeathsinMexicoareduetoswinefluandhowmanyareduetoothercauses.“Thespectrumofill-nessisstillamatterofdoubtandconjecture,”saysDavidOzonoff,anepidemiologistattheBostonUniversitySchoolofPublicHealthinMassachusetts.Forinstance,rumour