The evidence for rapid gametocyte viability changes in the course of parasitemia in Haemoproteus parasites

Abstract

Avian haemosporidian parasites of the genus Haemoproteus (Haemoproteidae, Haemosporida) are widespread, and some species cause diseases both in vertebrate hosts and blood-sucking insects. Parasitemia of Haemoproteus species usually is long-lasting, with gametocytes present in the circulation for several months. However, the viability of gametocytes and their ability to produce sexual cells have been insufficiently understood in the course of parasitemia. We initiated the sexual development in vitro conditions and calculated proportions of normal and anomalous ookinetes, which developed in two species of Haemoproteus. Mature gametocytes of the parasites were obtained from naturally infected avian hosts at different days of parasitemia. Haemoproteus (Parahaemoproteus) lanii (cytochrome b lineage hRB1) was isolated from one red-backed shrike Lanius collurio. Two isolates of Haemoproteus (Parahaemoproteus) tartakovskyi (cytochrome b lineage hSISKIN1) were used: one was obtained from a siskin Carduelis spinus and one from a common crossbill Loxia curvirostra. The wild-caught birds were kept indoors under controlled conditions, and blood was taken from them every 1 or 2 days during 10–14 days. After each blood sampling, the sexual process and ookinete development were initiated in vitro by exposure of infected blood containing mature gametocytes to air. Smears were prepared at intervals of 15 min, 3 h, and 12 h after the exposure; they were examined microscopically. In all, 25 experiments were performed; each experiment was repeated two times. The ratios of macro- and microgametocytes did not change in all experimental infections during this study. Sexual process occurred, and both normal and anomalous ookinetes developed in all parasites. The proportion of normal ookinetes did not change significantly in both isolates of H. tartakovskyi. Between 8 and 10 days of observation, the proportion of normal ookinetes of H. lanii decreased 6 times compared to the beginning of the experiment. That was accompanied with the rapid decrease of parasitemia and the inability of the majority of mature gametocytes to escape from erythrocytes and produce gametes, indicating disorder of the gametogenesis. There was clear difference in the gametogenesis between H. tartakovskyi and H. lanii from this point of view. This study shows that the viability of Haemoproteus gametocytes might change dramatically in the course of parasitemia within 1–2 days, and the presence of mature gametocytes in the circulation does not necessarily indicate their ability to exflagellate and produce ookinetes. We predict that this finding is important epidemiologically due to relationship with sporogony success.