Transcription and Copy Number Variation of Plasmodium falciparum var2csa among Nonpregnant Malaria Patients in Thailand

Placental malaria is an important cause of fetomaternal morbidity and mortality among pregnant women infected with Plasmodium falciparum. The pathogenesis involves the binding of VAR2CSA on the surface of infected erythrocytes to chondroitin sulfate proteoglycans on syncytiotrophoblasts in the intervillous space of the placenta. Anti-VAR2CSA antibodies confer protection from adverse pregnancy outcomes in falciparum malaria; therefore, VAR2CSA is a strong vaccine candidate against placental malaria. To date, little is known about transcription of var2csa among isolates from male and nonpregnant patients in low transmission areas. In this study, transcription and copy number variation of var2csa were analyzed in 55 P. falciparum isolates from nonpregnant women, men and children with symptomatic malaria in five endemic provinces of Thailand. Reverse transcription polymerase chain reaction (PCR) detected var2csa transcripts in 43 (78.2%) blood samples. Multiple copies of var2csa were identified in 16 of 55 (29.1%) isolates by quantitative real-time PCR. Copy number variation of var2csa was not associated with the patients' sex, age group, ethnicity, parasite genotypes, parasite density, and geographic origins. These data suggest that P. falciparum carrying multicopy var2csa had a wide geographic distribution in Thailand with a prevalence rate comparable to those observed in high transmission areas of Africa. The high prevalence of isolates from male and nonpregnant patients with var2csa transcription suggests that the transcription of this gene occurs naturally during blood stage infection. Whether VAR2CSA is expressed and immunogenic among nonpregnant falciparum malaria patients requires further study.