Yawancin ƙwayoyin cuta suna shiga cikin huhu ta hanyar ƙananan burin kwayoyin da ke zaune a cikin makogwaro ko hanci. Rabin mutanen da ke da al'ada suna da waɗannan ƙananan burin a lokacin barci. Yayin da makogwaro koyaushe yana ƙunshe da ƙwayoyin cuta, waɗanda ke iya kamuwa da cuta suna zaune a can ne kawai a wasu lokuta kuma a ƙarƙashin wasu yanayi. Ƙananan nau'in ƙwayoyin cuta irin su Mycobacterium tuberculosis da Legionella pneumophila sun isa huhu ta hanyar gurɓataccen iska mai gurɓata. Kwayoyin cuta kuma suna iya yaduwa ta hanyar jini. Da zarar a cikin huhu, ƙwayoyin cuta na iya mamaye sararin samaniya tsakanin ƙwayoyin cuta da tsakanin alveoli, inda macrophages da neutrophils (ƙwayoyin farin jini masu karewa) ke ƙoƙarin kashe ƙwayoyin cuta. Neutrophils kuma suna sakin cytokines, suna haifar da kunnawa gaba ɗaya na tsarin rigakafi. Wannan yana haifar da zazzabi, da gajiya na yau da kullun. Abin da ke faruwa a cikin ƙwayoyin cuta
macrophages da neutrophils (farin ƙwayoyin jini masu kariya) suna ƙoƙarin kashe ƙwayoyin cuta