BYLENAH.SUNINeJIDoPADReKINo,MexICoTheboycamehomefromschoolweak-enedbyfever,hisearsburninghot.overthenextfewdays,the7-year-oldgotsicker—vomitingandcomplainingofabdom-inalpain,hismotherrecalled.Then,thetelltaleredspotsappearedonhishands.ButnoneofthedoctorsinthisruralcommunityalongMexico’sPacificcoastrecognizedthewarningsignforoneofthemostlethalinfectiousdiseasesintheAmericas—RockyMountainspottedfever.Aweeklater,theboywasdead.Thefollowingyear,in2020,thediseasekilleda5-year-oldboyinanearbyhouse.Thenlastoctober,afewblocksaway,another7-year-oldsuccumbedtothesamescourge.Thedisease,spreadthroughthebiteofaninfectedtickthatlivesprimarilyondogs,israre,butitsincid...