▁Pet ten ko fer ▁considered ▁his ▁experience ▁proof ▁that ▁V ib rio ▁ch ol era e ▁was ▁har ml ess , ▁as ▁he ▁did ▁not ▁develop ▁ch ol era ▁from ▁cons uming ▁the ▁culture . ▁ ▁Between ▁ 1 8 4 9 ▁when ▁P ouch et ▁discovered ▁V ib rio ▁ch ol era e ▁and ▁ 1 8 9 1 , ▁over ▁a ▁million ▁people ▁died ▁in ▁ch ol era ▁ep ide m ics ▁in ▁Europe ▁and ▁Russia . ▁ ▁In ▁ 1 9 9 5 , ▁research ers ▁published ▁a ▁study ▁in ▁Science ▁explaining ▁why ▁some ▁persons ▁are ▁able ▁to ▁be ▁inf ected ▁with ▁ch ol era ▁without ▁sympt oms , ▁possibly ▁explaining ▁why ▁Pet ten ko fer ▁did ▁not ▁get ▁sick . ▁ ▁The ▁study ▁showed ▁that ▁a ▁series ▁of ▁gen etic ▁mut ations ▁in ▁some ▁people ▁provide ▁resistance ▁to ▁ch ol era ▁to x in ; ▁but ▁these ▁mut ations ▁come ▁at ▁a ▁price . ▁If ▁too ▁many ▁of ▁them ▁occur ▁in ▁a ▁person , ▁they ▁will ▁develop ▁c yst ic ▁fib ros is , ▁an ▁in cur able ▁and ▁often ▁fatal ▁gen etic ▁dis order . ▁▁ 2 0 th - century ▁discover ies ▁ ▁Gi ard ia ▁l amb lia ▁( 1 6 8 1 - 1 9 7 5 ) ▁ ▁Gi ard ias is ▁is ▁a ▁disease ▁caused ▁by ▁in fection ▁with ▁the ▁proto zo an ▁Gi ard ia ▁l amb lia . ▁ ▁In fection ▁with ▁Gi ard ia ▁can ▁produce ▁di arr he a