CIRCUMSPOROZOITE GENOTYPING OF GLOBAL ISOLATES OF PLASMODIUM-VIVAX FROM DRIED BLOOD SPECIMENS

The prevalence and global distribution of two circumsporozoite (CS) genotypes of Plasmodium vivax (VK210 and VK247) were determined by genetic analysis of isolates from 234 malaria-infected patients. Whole blood specimens were collected on filter paper from patients infected with malaria in Thailand, Mexico, Papua New Guinea, Peru, Afghanistan (Pakistan), India, and western Africa and from 50 asymptomatic smear-negative controls. Following extraction of DNA from the filter paper samples, the CS gene was amplified by the polymerase chain reaction and genotyped by using oligoprobes specific for the VK210 and VK247 repeat epitopes. The sensitivity of genotyping from a single blood dot was 95.2%. The VK247 CS genotype was identified in the blood of patients from all seven study areas and was the predominant form present in samples from Thailand (83%) and Papua New Guinea (90%). In contrast, VK247 DNA was present in only 9% of isolates from Mexico. Individuals infected with both genotypes simultaneously were identified in all study areas except Mexico and were particularly common in Thailand (58%) and Papua New Guinea (60%). These findings indicate that the VK247 genotype of P. vivax is widely distributed but that its prevalence varies geographically. In addition, we conclude that use of samples of whole blood on filter paper is a practical and sensitive method for determining the genotypes of large numbers of malaria isolates collected in field settings.