, ▁gas , ▁and ▁ab dom inal ▁pain ▁in ▁some ▁people . ▁If ▁un tre ated , ▁in fection ▁can ▁be ▁chron ic . ▁In ▁children , ▁chron ic ▁Gi ard ia ▁in fection ▁can ▁cause ▁st un ting ▁( st unted ▁growth ) ▁and ▁lower ed ▁intelligence , ▁In fection ▁with ▁Gi ard ia ▁is ▁now ▁univers ally ▁recognized ▁as ▁a ▁disease , ▁and ▁treated ▁by ▁phys icians ▁with ▁anti - proto zo al ▁dru gs . ▁Since ▁ 2 0 0 2 , ▁Gi ard ia ▁cases ▁must ▁be ▁reported ▁to ▁the ▁Center ▁for ▁D ise ase ▁Control , ▁according ▁to ▁the ▁CD C ' s ▁Report able ▁D ise ase ▁Sp readsheet . ▁The ▁United ▁States ▁National ▁Instit utes ▁of ▁Health ▁ ▁Gast ro int est inal ▁Par as ites ▁Lab ▁studies ▁Gi ard ia ▁almost ▁exclus ively . ▁ ▁However , ▁Gi ard ia ▁experienced ▁an ▁extra ordin arily ▁long ▁term ▁of ▁emer gence , ▁from ▁its ▁discovery ▁in ▁ 1 6 8 1 , ▁until ▁the ▁ 1 9 7 0 s ▁when ▁it ▁was ▁fully ▁accepted ▁that ▁in fection ▁with ▁Gi ard ia ▁was ▁a ▁treat able ▁cause ▁of ▁chron ic ▁di arr he a : ▁ ▁Some ▁of ▁the ▁first ▁evidence ▁in ▁modern ▁times ▁of ▁Gi ard ia ' s ▁path ogen icity ▁came ▁during ▁World ▁War ▁II ▁when ▁soldiers ▁were ▁treated ▁for ▁mal aria ▁with ▁the ▁ant ip ro to zo al ▁Qu in ac r ine , ▁and ▁their ▁di arr he a ▁disappeared