Medical Microbiology

DevelopmentintheMosquito(SexualDevelopmentandSporogony)

ThisdevelopmentalstageisshownindetailinFig.9. 17 bandwillonlybedescribed

brieflyhere.Inthemosquitomidgut,eachmicrogamontdevelopsinto(inmost

cases)eightuninucleate,flagellatemicrogametesandthemacrogamontistrans-

formedintoamacrogamete!fusionofamicrogameteandmacrogameteto

formamotilezygote(ookinete)!theookinetesoccupythespacebetween

theepitheliallayerandbasalmembraneofthemidgut!morphologicaltransfor-

mationintooocysts(40– 60 lm)!inoocystnuclearproliferationandproduction

ofthousandsofsporozoites!sporozoitesemergeintothehemolymphand

migratethroughthebodycavitytothesalivaryglands,fromwheretheycanbe

transmittedtoanewhost.Thedurationofthecycleinthemosquitodepends

ontheplasmodialspeciesandtheambienttemperature;at 20 – 288 C,ittakeseight

to 14 days.

Clinicalmanifestations

&Incubationperiods.Theclinicalmanifestationsofmalariaarecausedby

theasexualerythrocyticstagesoftheplasmodiaandthereforecommence

shortlyafterparasitemiaattheearliest.Theincubationperiodsvary,depend-

ingonthePlasmodiumspeciesinvolved,fromsevento 35 daysafterinfection.

Theseperiodscan,however,beextendedbyweeksorevenmonths,particu-

larlyiftheinfectionissuppressedbyprophylacticmedication.

&Clinicalmanifestations.Theclinicalmanifestationsofmalariadependon

anumberofdifferentfactors,aboveallthePlasmodiumspeciesandimmune

statusofthepatient.ThePlasmodiumspecieswiththemostpronounced

pathogenicityisPlasmodiumfalciparum,whichcauses“malignanttertian

malaria”(malariatropica),whereastheotherPlasmodiumspeciescause

milderforms(“benignmalaria”).Childrenandnonimmuneadultsfrom

nonmalariousareas(e.g.,EuropeanandUStourists),aswellaschildrenin

endemicregionsagedsixmonthstothreeyears,aremostsusceptibleto

infection.

&Onsetsymptoms.Malariabeginswithnonspecificinitialsymptomsthat

lastseveraldays,includingforinstanceheadache,paininlimbs,generalfa-

tigue,chills,andoccasionallynauseaaswellasintermittentfever,eithercon-

tinuousoratirregularintervals.Thesesymptomscaneasilybemistakenfor

signsofinfluenza!

&Febrilepatterns.Severaldaystoaweekafteronsetofparasitemia,the

schizogoniccyclesynchronizes:ininfectionswithP.vivax,P.ovale,andP.fal-

ciparum,acycleiscompletedwithin 48 hours,ininfectionswithP.malariae

within 72 hours.Boutsoffeveroccuratthesameintervals,i.e.,onday 1 ,then

48 hourslateronday 3 (hence“malariatertiana”)oronday 1 andthenagain

after 72 hoursonday 4 (hence“malariaquartana”).Itisimportanttonote

526 9 Protozoa

9

Kayser, Medical Microbiology © 2005 Thieme