Novel Plasmodium falciparum clones and rising clone multiplicities are associated with the increase in malaria morbidity in Ghanaian children during the transition into the high transmission season

A survey of Plasmodium falciparum infection and clone multiplicity in Ghana ian children was carried out to study the effect of the onset of the malari a transmission season on disease incidence. Fortnightly blood samples were collected from 40 children living in the rural town of Dodowa, between Febr uary and August 1998. P. falciparum parasite densities were calculated and PCR genotyping was carried out using the polymorphic MSP-1 and MSP-2 genes as target loci for the estimation of the number of parasite clones in each sample. The average clone number was estimated using maximum likelihood tec hniques and the minimum number of clones per patient was analysed for the e ffects of age, sex, season, minimum number of clones per child, level of pa rasitaemia and parasite genotype. The statistical analysis indicated that t he more clones a child carried, the more likely they were to have a clinica l malaria episode. This was true after adjusting for age and season effects and for the measured circulating parasitaemia. The probability of clinical disease also increased if the MSP-1 MAD 20 and the MSP-2 FC 27 alleles wer e pre-sent. This longitudinal analysis thus indicates that the probability of a Ghanaian child having a symptomatic malaria episode is positively asso ciated with both increasing numbers and novel types of P. falciparum clones .