Malaria infection begins when an infected female Anopheles mosquito bites a person, injecting Plasmodium parasites, in the form of sporozoites, into the ...SkiptomaincontentHomeMalaria&vaccinesMalariaparasitelifecycleMalariaparasitelifecycleManyfactorsmakemalariavaccinedevelopmentchallenging.ThemalariaparasitedevelopsbothinhumansandinthefemaleAnophelesmosquitoes.Thesizeandgeneticcomplexityoftheparasitemeanthateachinfectionpresentsthousandsofantigens(proteins)tothehumanimmunesystem.Theparasitealsochangesthroughseverallifestagesevenwhileinthehumanhost,presentingdifferentantigensatdifferentstagesofitslifecycle.Understandingwhichofthesecanbeausefultargetforvaccinedevelopmenthasbeencomplicated.Inaddition,theparasitehasdevelopedaseriesofstrategiesthatallowittoconfuse,hide,andmisdirectthehumanimmunesystem. Malariainfectionbeginswhenaninfectedfemale Anopheles mosquitobitesaperson,injecting Plasmodium parasites,intheformofsporozoites,intothebloodstream. Thesporozoitespassquicklyintothehumanliver. Thesporozoitesmultiplyasexuallyinthelivercellsoverthenext7to10days,causingnosymptoms. Inananimalmodel,theparasites,intheformofmerozoites,arereleasedfromthelivercellsinvesicles,journeythroughtheheart,andarriveinthelungs,wheretheysettlewithinlungcapillaries.Thevesicleseventuallydisintegrate,freeingthemerozoitestoenterthebloodphaseoftheirdevelopment.* Inthebloodstream,themerozoitesinvaderedbloodcells(erythrocytes)andmultiplyagainuntilthecellsburst.Thentheyinvademoreerythrocytes.Thiscycleisrepeated,causingfevereachtimeparasitesbreakfreeandinvadebloodcells. Someoftheinfectedbloodcellsleavethecycleofasexualmultiplication.Insteadofreplicating,themerozoitesinthesecellsdevelopintosexualformsoftheparasite,calledgametocytes,thatcirculateinthebloodstream. Whenamosquitobitesaninfectedhuman,itingeststhegametocytes,whichdevelopfurtherintomaturesexcellscalledgametes. Thefertilizedfemalegametesdevelopintoactivelymovingookinetesthatburrowthroughthemosquito'smidgutwallandformoocystsontheexteriorsurfac