Medical Microbiology

&Plasmodiummalariae:quartanmalaria(malariaquartana),

&Plasmodiumfalciparum:malignanttertianmalaria(malariatropica).

ThesePlasmodiumspeciescanbeidentifiedanddifferentiatedfromeach

otherbylightmicroscopyinstainedbloodsmearsduringtheerythrocytic

phaseoftheinfectioninhumans(Fig.9. 18 ,p. 52 4).Areducedapicalcomplex

andothercharacteristicsofapicomplexanprotozoaarerecognizableinvar-

iousstagesoftheorganism(sporozoite,merozoite,ookinete)ontheelectron

microscopiclevel(seeToxoplasma,p.509).

Lifecycle.Thelifecycleofmalariaplasmodiaincludesphasesofasexualmul-

tiplicationinthehumanhostandsexualreproductionandformationofspor-

ozoitesinthevector,afemaleAnophelesmosquito(Fig.9. 17 ).Thedevelop-

mentalcyclewithinthehumanhostisasfollows:

&Infection and exoerythrocyticdevelopment. Humans are infected

throughthebiteofaninfectedfemaleAnophelesmosquitothatinoculates

spindleshapedsporozoites(seebelow)intothebloodstreamordeepcorium.

Onlyasmallnumberofsporozoitesareneededtocauseaninfectioninhu-

mans(about 10 P.falciparum).Withinabout 15 – 45 minutesofinoculation,

thesporozoitesofallPlasmodiumspeciesreachtheliverinthebloodstream

andinfecthepatocytes,inwhichasexualmultiplicationtakesplace.Inthis

process,thesporozoitedevelopsintoamultinuclear,large(30– 70 lm)

schizont(meront)describedasatissueschizont.Followingcytoplasmicdivi-

Plasmodium 521

DistributionofMalaria

Areas with limited infection risk

Areas with high infection risk

Malaria-free areas

Fig.9. 16 Status: 1 999.(From:InternationalTravelandHealth,Geneva.World

HealthOrganization,2000.)

9

Kayser, Medical Microbiology © 2005 Thieme