High frequency of the Duffy-negative genotype and absence of Plasmodium vivax infections in Ghana

Abstract

Background The Duffy-negative phenotype is a condition which is thought to confer complete resistance against blood infection with Plasmodium vivax. However, recent studies from different malaria-endemic regions including western Africa have now shown that P. vivax can infect red blood cells (RBCs) and cause clinical disease in Duffy-negative people. The actual prevalence of P. vivax in local populations in Ghana is unknown. In addition, little information is available about the distribution of Duffy genotypes in Ghana. We determined the prevalence of P. vivax and the distribution of Duffy genotypes in Ghana. Methods DNA was extracted from dried blood spots (DBS) collected from 952 subjects (845 malaria patients and 107 asymptomatic persons) from nine locations in Ghana. Plasmodium species identification was carried out by nested polymerase chain reaction (PCR) amplification of the small-subunit rRNA genes; P. vivax was further characterized by PCR analysis of the central region of the Pvcsp gene. Duffy blood group genotyping was performed by PCR with sequence-specific primers (PCR-SSP) to detect the presence of the FYES allele. Results No cases of P. vivax were detected in any of the samples by both PCR methods used. Majority of infections (542, 94.8%) in the malaria patient samples were due to P. falciparum with only 1 infection (0.0017%) and 2 infections (0.0034%) due to P. malariae and P. ovale, respectively. No case of mixed infection was identified. Of the samples tested for the FYES allele from all the sites, 90.5% (862/952) had the FYES allele. All positive samples were genotyped as FY*B-33/FY*B-33 (Duffy-negative homozygous) and therefore classified as Fy(a-b-). Conclusions No cases of P. vivax were detected by both PCRs and 90.5% of the subjects tested carried the FYES allele. The lack of P. vivax infections observed can be attributed to the high frequency of the FYES allele that silences erythroid expression of the Duffy. These results provide insights on the host susceptibility for P. vivax infections that has before not been investigated in Ghana.