▁disease ▁might ▁die ▁from ▁another . ▁Multiple ▁simultane ous ▁in fe ctions ▁( e . g ., ▁small po x ▁and ▁ty ph us ▁at ▁the ▁same ▁time ) ▁or ▁in ▁close ▁succession ▁( e . g ., ▁small po x ▁in ▁an ▁individual ▁who ▁was ▁still ▁weak ▁from ▁a ▁recent ▁bout ▁of ▁ty ph us ) ▁are ▁more ▁dead ly ▁than ▁just ▁the ▁sum ▁of ▁the ▁individual ▁dise ases . ▁In ▁this ▁scenario , ▁death ▁rates ▁can ▁also ▁be ▁elev ated ▁by ▁combinations ▁of ▁new ▁and ▁familiar ▁dise ases : ▁small po x ▁in ▁combination ▁with ▁American ▁stra ins ▁of ▁y aws , ▁for ▁example . ▁ ▁Other ▁contrib uting ▁factors : ▁ ▁Native ▁American ▁medical ▁treat ments ▁such ▁as ▁swe at ▁bath s ▁and ▁cold ▁water ▁imm ersion ▁( p ract iced ▁in ▁some ▁areas ) ▁weak ened ▁some ▁patients ▁and ▁probably ▁increased ▁mort ality ▁rates . ▁ ▁Europe ans ▁brought ▁many ▁dise ases ▁with ▁them ▁because ▁they ▁had ▁many ▁more ▁domestic ated ▁animals ▁than ▁the ▁Native ▁Americans . ▁Dom estic ation ▁usually ▁means ▁close ▁and ▁frequent ▁contact ▁between ▁animals ▁and ▁people , ▁which ▁allows ▁dise ases ▁of ▁domestic ▁animals ▁to ▁migr ate ▁into ▁the ▁human ▁population ▁when ▁the ▁necessary ▁mut ations ▁occur . ▁ ▁The ▁E uras ian ▁land mass ▁extends ▁many ▁thousands ▁of ▁miles ▁along ▁an ▁east - west ▁axis . ▁Cl imate ▁zones ▁also ▁extend ▁for ▁thousands ▁of ▁miles , ▁which ▁facil itated ▁the ▁spread ▁of ▁agricult ure , ▁domestic ation ▁of ▁animals , ▁and ▁the ▁dise ases