Frequency of MSP1 block 2 alleles in Rondônia field isolates. A: RO33 was the most prevalent followed by the K1 allele. The RO33 allele was more prevalent in symptomatic infections while K1 alleles were dominant in asymptomatic samples (Chi-square method, p < 0.03 and p < 0.009, respectively). B: K1A and MAD20A were the most frequent K1 and MAD20 type sequences for both groups. Note that the sum of values is higher than 100% since a number of isolates presented more than one genotype at this locus.