Digital PCR reveals high PvDBP1 but not PvEBP/DBP2 and PvRBP2b copies in Plasmodium vivax from Duffy-negative Individuals in Central Africa.

BACKGROUND

Vivax malaria, once thought rare in Duffy-negative Africans, is now reported in various parts of Africa, suggesting alternate invasion mechanisms and parasite adaptability to Duffy-null cells. One hypothesis is that copy number variation (CNV) of genes involved in erythrocyte invasion may impact parasite invasion capability and/or host immune evasion particularly in Duffy-negative individuals.

METHOD

Using novel digital PCR, we assessed CNV of three key erythrocyte-binding genes of Pv isolated from DN individuals in three eco-epidemiological zones of Cameroon. For a subset of samples, we compare dPCR results with qPCR and PCR diagnostic approaches.

RESULTS

PvDBP1 duplications were detected in ∼92% of DN Pv samples, compared to ∼10% of the samples with multi-copy PvEBP/DBP2 and PvRBP2b. A significant positive correlation was detected between PvDBP1 CNV and parasite load among the samples. Both Malagasy- and Cambodian-type PvDBP1 duplications were detected. About one-third of the samples harbored both duplication types and these samples were exclusively in northern highland of Cameroon, suggesting either polyclonal infections or a third duplication type.

CONCLUSION

Multi-copy PvDBP1 across all study sites may imply significant parasite adaptability, and improved parasite invasion, potentially influencing parasitemia. This was confirmed with the significantly higher parasitemia observed in samples with Cambodian and those with both duplication types compared to ones with no duplication. Further, our data showed CNV analysis by qPCR may not be as precise as dPCR particularly for low-parasitemia DN Pv samples. Predominantly low PvEBP/DBP2 and PvRBP2b copy raise question to their role in parasite adaptation to invading DN erythrocytes.