Prevalence and characteristics of Plasmodium vivax Gametocytes in Duffy-positive and Duffy-negative populations across Ethiopia

Plasmodium parasites replicate asexually in the human host. The proportion of infections that carries gametocytes is a proxy for human-to-mosquito transmissibility. It is unclear what proportion of P. vivax infections in Duffy-negatives carries gametocytes. This study aims to determine the prevalence of P. vivax in Duffy-negatives across broad regions of Ethiopia and characterize parasite stages. Finger-prick blood samples were collected for microscopic and molecular screening of Plasmodium parasites and Duffy status of individuals. Molecular screening of plasmodium species and Duffy blood group genotyping was done using SYBR green and Taqman qPCR method. Among the total 447 samples, 414 (92.6%) were P. vivax confirmed and, 16 (3.9%) of them were from Duffy-negatives. Of these, 5/16 (31.3%) Duffy-negative P. vivax-infected samples were detected with gametocytes. Of the 398 Duffy-positive P. vivax-infected samples, 150 (37.7%) were detected with gametocytes, slightly higher than that in Duffy-negatives. This study highlights the presence of P. vivax gametocytes in Duffy-negative infections, suggestive of human-to-mosquito transmissibility. Although P. vivax infections in Duffy-negatives are commonly associated with low parasitemia, some of these infections were shown with relatively high parasitemia and may represent better erythrocyte invasion capability of P. vivax and hidden reservoirs that can contribute to transmission. A better understanding of P. vivax transmission biology and gametocyte function particularly in Duffy-negative populations would aid future treatment and management of vivax malaria in Africa