Rosetting ability and adhesion of P. vivax gametocytes to endothelial cells and their influence on infectivity in Anopheles aquasalis

Malaria is a public health problem, with around 3.2 billion people at risk of infection, of which 2.5 billion are at risk of infection with Plasmodium vivax (Pv), the most prevalent form of malaria outside Africa Sub-Saharan. The recent evidence that erythrocytes parasitized by asexual Pv stages has the ability to cytoadhere in endothelial cells, suggest that this ability may be present in the sexual stages of the parasite, which may be related to an increase in the transmission to the mosquito vector. For this reason, the present study evaluated the ability of rosetting and the cytoadhesion of Pv gametocytes in endothelial cells of the bone marrow (HBMEC) and the relation of these factors in the infectivity in the insect vector. In addition, some receptors involved in the cytoadhesion process were also evaluated using transfected CHO cells. The assays were performed by isolating the Pv gametocytes from peripheral blood samples from infected patients, the cytoadhesion assays were performed and the parasite ability to cytoadhere in different receptors were evaluated. The ability of gametocytes to form rosettes was evaluated and in parallel the same sample was given to fed Anopheles aquasalis mosquitoes for evaluation of infectivity rate and intensity. A total of 85 samples were collected, 45 were used for cytoadhesion tests on HBMEC and CHO cells and 40 samples were used for rosette assay formation, from those 24 of these samples were used for the mosquito vector infection assays. It was observed cytoadhesion of Pv gametocytes to all cell types tested. we observed a greater cytoadhesion to CHOCD36 compared to the control (CHO745) (p = 0.031). The isolates were split in two groups: the ones that form a low number of rosettes (<10% of parasites in rosette formation) and the ones that form a high number of rosettes (≥10%). The infection rate was higher in the second group (p = 0.001). These observations showed that Pv gametocytes were able to cytoadhere to endothelial cells and to form rosettes. Importantly this is the first study to show that cytoadhesive phenomenon may be involved in mosquito infection.