High frequency of the erythroid silent Duffy antigen genotype and lack of Plasmodium vivax infections in Haiti

BACKGROUND: Malaria is a significant public health concern in Haiti where approximately 30,000 cases are reported annually with CDC estimates as high as 200,000. Malaria infections in Haiti are caused almost exclusively by Plasmodium falciparum, while a small number of Plasmodium malariae and an even smaller number of putative Plasmodium vivax infections have been reported. The lack of confirmed P. vivax infections in Haiti could be due to the genetic background of native Haitians. Having descended from West African populations, many Haitians could be Duffy negative due to a single nucleotide polymorphism from thymine to cytosine in the GATA box of the promoter region of the Duffy antigen receptor for chemokines (DARC) gene. This mutation, encoded by the FY(ES) allele, eliminates the expression of the Duffy antigen on erythrocytes, which reduces invasion by P. vivax. This study investigated the frequency of the FY(ES) allele and P. vivax infections in malaria patients with the goal of uncovering factors for the lack of P. vivax infections reported in Haiti. METHODS: DNA was extracted from dried blood spots collected from malaria patients at four clinic locations in Haiti. The samples were analysed by polymerase chain reaction (PCR) for the presence of the P. vivax small subunit ribosomal RNA gene. PCR, sequencing, and restriction enzyme digestion were used to detect the presence of the FY(ES) allele. Matched samples were examined for both presence of P. vivax and the FY(ES) allele. RESULTS: No cases of P. vivax were detected in any of the samples (0/136). Of all samples tested for the FY(ES) allele, 99.4% had the FY(ES) allele (163/164). Of the matched samples, 99% had the FY(ES) allele (98/99). CONCLUSIONS: In this preliminary study, no cases of P. vivax were confirmed by PCR and 99% of the malaria patients tested carried the FY(ES) allele. The high frequency of the FY(ES) allele that silences erythroid expression of the Duffy antigen offers a biologically plausible explanation for the lack of P. vivax infections observed. These results provide insights on the host susceptibility for P. vivax infections that has never before been investigated in Haiti.