Parasite genotyping by a polymerase chain reaction was used to distinguish recrudescent from newly acquired Plasmodium falciparum
infections in 50 of 160 Nigerian children taking part in a
chloroquine efficacy study in Ibadan, Nigeria. A finger prick blood sample was taken from each child before and
after treatment to identify recrudescent parasites. By investigating allelic variation in three polymorphic
antigen loci,
merozoite surface protein-1 (MSP-1), MSP-2, and
glutamate-rich
protein (GLURP), we determined parasite diversity in the population and in the infected host.
DNA from pretreatment and post-treatment samples from 47 of the 50 patients who failed
therapy was successfully amplified by the PCR. The
MSP-1, MSP-2, and GLURP genotypes in all samples showed extensive diversity, indicating polyclonal
infections. The average number of clones per
infection in pre-treatment sample was 2.5 with
MSP-1, 4.9 with MSP-2, and 2 with GLURP. The extent of multiplicity decreased significantly (P = 0.016) in posttreatment samples. Multiplicity of
infection and initial parasite density were not age dependent. Comparison of the variant alleles in pretreatment and post-treatment samples of each patient indicates that 26 of the 47 children had genuinely recrudescent disease. Conversely, post-treatment samples from five children showed completely new genotypes, indicating either a previously sequestered population of parasites or a newly acquired
infection. Overall, this study has shown the diversity and complexity of P. falciparum population in Ibadan, Nigeria. The study has also shown the dynamics of P. falciparum
infections in this population before and after
chloroquine treatment in an area of high
malaria transmission.