ESTIMATION OF NUMBERS OF MALARIA CLONES IN BLOOD-SAMPLES

Methods are derived for estimating the mean number of clones of the ha ploid malaria parasite Plasmodium falciparum from samples of blood of infected hosts which have been tested for the presence of alleles at m arker loci. For example, at a locus with three alleles the sample migh t contain only A(1), or A(1) and A(2), or A(1), A(2) and A(3), with mu ltiple allele classes being more common at high infection rates. Assum ing either a Poisson or negative binomial distribution of numbers of i nfections per host, formulae are derived for the frequency of differen t classes of blood samples, and maximum likelihood methods are used to estimate the mean number of clones and allele frequencies. Two data s ets, each on two loci, are analysed. One data set was from the same lo cality in Tanzania from which oocysts of the parasite in mosquito vect ors were tested for clonality (i.e. diploid unions of gametes from the same clone) using genetic markers. Good agreement was obtained betwee n the observed clonality in oocysts and that expected from the number of infections per host (mean approximately three).