A new haemosporidian of lizards, Saurocytozoon tupinambi gen.nov., sp.nov., in Tupinambus nigropunctatus (Teiidae)

Insights into the Biology of Leucocytozoon Species (Haemosporida, Leucocytozoidae): Why Is There Slow Research Progress on Agents of Leucocytozoonosis?

Blood parasites of the genus Leucocytozoon (Leucocytozoidae) only inhabit birds and represent a readily distinct evolutionary branch of the haemosporidians (Haemosporida, Apicomplexa). Some species cause pathology and even severe leucocytozoonosis in avian hosts, including poultry. The diversity of Leucocytozoon pathogens is remarkable, with over 1400 genetic lineages detected, most of which, however, have not been identified to the species level. At most, approximately 45 morphologically distinct species of Leucocytozoon have been described, but only a few have associated molecular data. This is unfortunate because basic information about named and morphologically recognized Leucocytozoon species is essential for a better understanding of phylogenetically closely related leucocytozoids that are known only by DNA sequence. Despite much research on haemosporidian parasites during the past 30 years, there has not been much progress in taxonomy, vectors, patterns of transmission, pathogenicity, and other aspects of the biology of these cosmopolitan bird pathogens. This study reviewed the available basic information on avian Leucocytozoon species, with particular attention to some obstacles that prevent progress to better understanding the biology of leucocytozoids. Major gaps in current Leucocytozoon species research are discussed, and possible approaches are suggested to resolve some issues that have limited practical parasitological studies of these pathogens.

Under the light: high prevalence of haemoparasites in lizards (Reptilia: Squamata) from Central Amazonia revealed by microscopy

Blood samples from 330 lizards of 19 species were collected to investigate the occurrence of haemoparasites. Samplings were performed in areas of upland (terra-firme) forest adjacent to Manaus municipality, Amazonas, Brazil. Blood parasites were detected in 220 (66%) lizards of 12 species and comprised four major groups: Apicomplexa (including haemogregarines, piroplasms, and haemosporidians), trypanosomatids, microfilarid nematodes and viral or bacterial organisms. Order Haemosporida had the highest prevalence, with 118 (35%) animals from 11 species. For lizard species, Uranoscodon superciliosus was the most parasitised host, with 103 (87%; n = 118) positive individuals. This species also presented the highest parasite diversity, with the occurrence of six taxa. Despite the difficulties attributed by many authors regarding the use of morphological characters for taxonomic resolution of haemoparasites, our low-cost approach using light microscopy recorded a high prevalence and diversity of blood parasite taxa in a relatively small number of host species. This report is the first survey of haemoparasites in lizards in the study region. It revealed a high diversity of lizard haemoparasites and highlights the need to understand their impacts on hosts.

Further parasites of the family Garniidae (Coccidiida: Haemosporidiidea) in Brazilian lizards. Fallisia effusa gen.nov., sp.nov. and Fallisia modesta gen.nov., sp.nov

Fallisia effusa gen.nov., sp.nov. (Haemosporidiidea: Garniidae) is described in the teiid lizard, Neusticurus bicarinatus, from Pará State, north Brazil. Schizogony and gametogony both take place within thrombocytes and white cells of the peripheral blood. There is no development in the red blood cells, by which character the organism is differentiated from Garnia, the other known genus within the family. Another species, Fallisia modesta gen.nov., sp.nov., is described in the iguanid lizard, Tropidurus torquatus hispidus, also from Pará, Brazil. It is distinguished from F. effusa by its development principally in the lymphocytes, as opposed to the thrombocytes. There are other, striking morphological differences between the two species. It is recommended that great care is needed in the interpretation of so-called ‘exo-erythrocytic stages’ of saurian plasmodia, which may well really belong to members of the Garniidae, in mixed infections.

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.

Discovery of the pre-erythrocytic stages of a saurian malaria parasite, hypnozoites, and a possible mechanism for the maintenance of chronic infections throughout the life of the host

Re-examination of tissue sections from four Takydromus tachydromoides (Sauria: Lacertidae) naturally infected with Plasmodium sasai found liver parenchymal cells, containing uninucleate parasites which may correspond to the hypnozoite stage of primate malaria parasites, schizonts and segmenters in parenchymal cells, and hepatic macrophages which contained numerous schizonts. Following destaining of the original H&E and prolonged restaining with warm Giemsa stain, encysted schizonts, protected by a hyaline wall, were discovered in the connective tissue or capillary endothelium of lung, liver, brain, heart, pancreas, kidney, intestine wall, testis, and both intra- and intermuscularly in the femoral muscles. Unencysted schizonts in the pulmonary endothelium apparently represent the phanerozoic stages, which, following encystment in the various tissues, are recognized as a new stage in the life cycle of reptilian malarial parasites, the chronozoic schizonts. A hypothesis is presented to describe the life cycle of P. sasai, which may be characteristic of other saurian malaria parasites. It interprets the sequence of pre-erythrocytic stages found as follows: sporozoites enter hepatic parenchymal cells where some may become dormant as hypnozoites, and others form cryptozoic schizonts. The cryptozoites parasitize hepatic macrophages and form metacryptozoic schizonts. Metacryptozoites produce phanerozoic schizonts in the capillary endothelium and connective tissue of the lung and other organs. Phanerozoites and possibly metacryptozoites then invade the erythrocytes to begin the erythrocytic cycle. Some of the phanerozoites in endothelium, connective tissue and skeletal muscle become encysted as chronozoic schizonts, and their progeny, chronozoites, renew the erythrocytic cycle throughout the life of the host and produce seasonal relapses of gametocytemia, in spring, at the end of hibernation by the lizard.

Remarks on the status of the genus Leucocytozoon Sambon, 1908

Authorship of the genus Leucocytozoon has been variously assigned to several investigatiors, especially Danilewsky and Ziemann. Recently Hsu, Campbell & Levine (1973) have credited it to Berestneff. It is herein submitted that they erred in doing so and in relegating Akiba Bennett, Garnham & Fallis, 1965 and Saurocytozoon Lainson & Shaw, 1969 to synonymy with it. An attempt is made to clarify the confusion that has increasingly surrounded the genus Leucocytozoon, and it is recommended that the type species (by designation) should be Leucocytozoon majoris (Laveran, 1902), one of a mixture of organisms earlier lumped together under a name (Haemamoeba Grassi & Feletti, 1890) currently reserved for an avian subgenus of Plasmodium Marchiafava & Celli, 1885. We conclude that the generic name should be credited to Sambon, the 1st author to present an unequivocal description of the genus.

Observations on non-pigmented haemosporidia of Brazilian lizards, including a new species of Saurocytozoon in Mabuya mabouya (Scincidae)

Of 63 specimens of the lizardMabuya mabouya(Scincidae) examined in Pará State, Brazil, 31 showed one or more haemosporidians in the peripheral blood. These includedGarnia(Plasmodium)morula(Telford, 1970), Lainson, Landau & Shaw, 1971;Plasmodium tropiduriandP. diploglossiAragão & Neiva, 1909; aPlasmodiumspecies close toP. diminutivumTelford, 1973a; and a new species ofSaurocytozoonLainson & Shaw, 1969a. Eleven different combinations of these parasites were noted, emphasizing the care needed in avoiding erroneous descriptions based on mixed infections. This is especially so whenG. morulais mixed withP. tropidurior other species with small, rounded gametocytes occupying a polar position in the red blood cells. Of 18 skinks infected withG. morula, 10 had pure infections, as judged by repeated examinations over long periods. The morphology of the Brazilian parasite is very similar to that described forG. morulafrom Panama (Telford, 1970): no malarial pigment could be demonstrated in any stage of the infection, including ookinetes and possible early oocysts which were studied in experimentally infectedCulex pipiens fatigans. Ookinetes and rounded forms, possibly representing uninucleate oocysts, persisted in these insects up to 24 h after the blood-meal, but developed no further.C. p. fatigansis thus unlikely to be a natural vector ofG. morula. Saurocytozoon mabuyisp.nov. is described inM. mabouya: the gametocytes develop in the lymphocytes and monocytes of the circulating blood and reach maximum size in 19–28 days. The parasite can be distinguished from the other known species,S. tupinambiof the teiid lizardTupinambus nigropunctatus, by its smaller gametocytes. Nothing is known of the sporogonic cycle. Differences between the sporogonic stages ofS. tupinambiandLeucocytozoonare listed.