Transcription of var genes other than var2csa in Plasmodium falciparum parasites infecting Mozambican pregnant women

BACKGROUND: Increased susceptibility to Plasmodium falciparum infection during pregnancy has been attributed to the accumulation of infected erythrocytes in the placenta. This phenomenon is mediated by a var gene coding for VAR2CSA, which adheres to chondroitin sulphate A. However, the contribution of parasites transcribing other var genes to maternal infections has not been well characterized.

METHODS: Transcription of var2csa and var groups A, B, and C was measured by real-time polymerase chain reaction in 30 placental and 21 peripheral P. falciparum isolates from pregnant women and in 42 isolates from nonpregnant adults and children. Associations of infections with non-var2csa isolates with maternal parasitemia and immune responses were assessed.

RESULTS: Placental parasites showed the highest levels of var2csa. ABC var genes were transcribed by 20 (67%) of 30 placental isolates and were associated with higher parasitemia compared with infections by parasites only transcribing var2csa (P = .004). Peripheral isolates from pregnant women transcribed ABC var genes at levels similar to those of parasites infecting nonpregnant adults with clinical malaria (P[varA] = .420, P[varB] = .808, and P[varC] = .619).

CONCLUSIONS: Transcripts of var2csa are abundant in pregnancy-associated P. falciparum infections; however, ABC var types are also common, especially in peripheral blood, with transcription levels similar to those of infections out of pregnancy. These findings are of interest for the design of malaria vaccines for pregnant women.