The development and persistence of phanerozoites in experimental infections of Plasmodium sasai

A new Haemocystidium (Apicomplexa: Plasmodiidae) species of the dhub lizard, Uromastyx aegyptia microlepis , in Abu Dhabi, distinguished by the absence of pigment

The spiny-tailed lizard, Uromastyx aegyptia microlepis , in Abu Dhabi is parasitized by Haemocystidium apigmentada n. sp., and 2 species of Hepatozoon . The elongate gametocytes of H. apigmentada are 13-19 × 6-9 µm, with length × width (LW) 90-133 µm(2), and L/W ratio 1.56-3.17. Gametocyte dimensions do not differ by sex. Gametocytes are unpigmented. Hepatozoon species 1 has gamonts with a consistently terminal nucleus, with dimensions of 13-16 × 4.5-7 µm, LW of 58-104 µm(2), and L/W ratio of 2.00-3.22. Hepatozoon species 2 gamonts have a broad nucleus at the midbody, and dimensions of 13-15.5 × 5-7 µm, LW of 71-109 µm(2), and L/W ratio of 1.93-3.00.

The biology of some intraerythrocytic parasites of fishes, amphibia and reptiles

Fishes, amphibia and reptiles, the ectothermic vertebrates, are hosts for a variety of intraerythrocytic parasites including protists, prokaryotes, viruses and structures of uncertain status. These parasites may experience host temperature fluctuations, host reproductive strategies, population genetics, host habitat and migratory behaviour quite unlike those of endothermic hosts. Few blood infections of fishes, amphibia and reptiles have proven pathogenicity, in contrast to the many intraerythrocytic parasites of mammals and some birds which harm their hosts. Although not given the attention afforded to intraerythrocytic parasites of endotherms, those of ectotherms have been studied for more than a century. This review reports on the diversity, general biology and phylogeny of intraerythrocytic parasites of ectotherms. The existence of taxonomic confusion is emphasized and the main taxonomic features of most of the 23 better characterized genera, particularly the kinetoplastid and apicomplexan protists, are summarized. Transmission of protistan infections of aquatic ectotherms is also discussed. Leeches can transfer sporozoties or merozoites to the vertebrate host during feeding. Dormant sporozoites of Lankesterella may permit transmission of species of this genus between vertebrates by predation. The fish haemogregarine, Haemogregarina bigemina, probably has gnathiid isopods, rather than leeches, as its definitive hosts. Hepatozoon spp. in aquatic hosts, and Progarnia of caiman, may also use invertebrate hosts other than leeches. Protistan infections of terrestrial or semi-terrestrial hosts are transmitted by a variety of arthropods, or, in some cases, leeches, contaminated paratenic hosts, or sporocysts free in water. Transfer of protists between vertebrates by predation and congenitally may also occur. The biology of the host cells of these infections, the red blood cells of ectotherm vertebrates, is summarized and compared with that of mammalian erythrocytes. Erythropoiesis, the nature of the surface molecules (especially the possible existence of a major histocompatibility complex), the haemoglobins, and the shape and size of erythrocytes are discussed. The exoerythrocytic sites in which protists, prokaryotes, viruses and structures of uncertain status exist before erythrocyte entry are described. Tissue merogony, tissue cysts and invasion of the white cell series occur in a variety of protistan infections. Intraerythrocytic stages of protistan infections are also discussed, including modes of entry to erythrocytes, survival mechanisms, and multiplication. The impact of infection on host populations is difficult to assess, in part because there is no agreement in the literature on the criteria used to evaluate parasite-induced cost to the host. Almost all studies have been on haemogregarine and Plasmodium infections in, mainly, lizards, but also fishes and snakes. Some infections may be responsible for mortality in their hosts, but hosts themselves may be short-lived, or have a limited ability to recover from infection.

Two malaria parasites (Apicomplexa: Plasmodiidae) of the Australian skink Egernia stokesii

The Australian skink Egernia stokesii is parasitized uncommonly by Plasmodium circularis n. sp. and by Plasmodium mackerrasae. Plasmodium circularis is distinguished from all other plasmodiids by immature schizonts that encircle host cell nuclei, forming an unbroken ring from apparent fusion of the attenuated ends. Mature schizonts contract into halteridial or dumbbell-shaped forms 15.6 x 4.3 microm, LW 66.2 microm2, with 19-52 nuclei. Rounded or oval gametocytes are 9.0 x 7.3 microm, LW 66.9 microm2, and L/W 1.24. Gametocyte LW is 2.63 x host erythrocyte nucleus size and 1.79X uninfected erythrocyte nuclei. Plasmodium mackerrasae occurs in high prevalence and often massive parasitemia in E. stokesii. Schizonts, often oblong, elongate, or oval, are 5.1 x 3.7 microm, LW 19.8 microm2, with 7.2 merozoites. Immature gametocytes, elongate with terminal nucleus, may produce multiple infections of 6 or more parasites. Mature gametocytes, usually rounded, are 5.8 x 4.6 microm, LW 26.7 microm2, and L/W 1.29. Gametocyte size is 0.98 x host erythrocyte nucleus size and 1.03 x uninfected erythrocyte nuclei. Phanerozoites, in endothelium or connective tissue of most organs, may appear in large numbers in circulating blood as seemingly intact bodies of regular form, similar to or larger than phanerozoites seen in sections. Previously unreported phenomena for hemosporidian parasites include extremely large, highly irregular exoerythrocytic schizonts, in circulating blood, perhaps torn from endothelial lining of blood vessels and sinuses, and a visible flooding of free merozoites into the blood stream.