Parasites Of Reptiles Research Articles

Entamoeba Shows Reversible Variation in Ploidy under Different Growth Conditions and between Life Cycle Phases

Under axenic growth conditions, trophozoites of Entamoeba histolytica contain heterogenous amounts of DNA due to the presence of both multiple nuclei and different amounts of DNA in individual nuclei. In order to establish if the DNA content and the observed heterogeneity is maintained during different growth conditions, we have compared E. histolytica cells growing in xenic and axenic cultures. Our results show that the nuclear DNA content of E. histolytica trophozoites growing in axenic cultures is at least 10 fold higher than in xenic cultures. Re-association of axenic cultures with their bacterial flora led to a reduction of DNA content to the original xenic values. Thus switching between xenic and axenic growth conditions was accompanied by significant changes in the nuclear DNA content of this parasite. Changes in DNA content during encystation-excystation were studied in the related reptilian parasite E. invadens. During excystation of E. invadens cysts, it was observed that the nuclear DNA content increased approximately 40 fold following emergence of trophozoites in axenic cultures. Based on the observed large changes in nuclear size and DNA content, and the minor differences in relative abundance of representative protein coding sequences, rDNA and tRNA sequences, it appears that gain or loss of whole genome copies may be occurring during changes in the growth conditions. Our studies demonstrate the inherent plasticity and dynamic nature of the Entamoeba genome in at least two species.

An Entamoeba cysteine peptidase specifically expressed during encystation

Protozoan parasites of the genus Entamoeba possess a considerable number of cysteine peptidases (CPs), the function of most of these molecules for amoeba biology needs to be established. In order to determine whether CPs may play a role during Entamoeba stage conversion from trophozoites into cysts and vice versa, expression of cp genes was analysed in the reptilian parasite Entamoeba invadens, a model organism for studying Entamoeba cyst development. By homology search, 28 papain-like cp genes were identified in public E. invadens genome databases. For eight of these genes the expression profiles during stage conversion was determined. By Northern blot analysis, transcripts for eicp-a9, -b7, -b8 and -c2, respectively, were detected neither in trophozoites or cysts nor at any of the point of times analysed during stage conversion. On the other hand, eicp-a5 is constitutively expressed during all developmental stages, whereas eicp-a3 and eicp-a11, respectively, are trophozoite-specific. Only eicp-b9 was found to be cyst-specific as it is expressed exclusively 18 to 28 h after cyst induction. Cyst-specific expression was confirmed by immunofluorescence microscopy of the corresponding protein EiCP-B9. In immature cysts, the molecule is located in structures that accumulate near the cyst wall, but which are uniformly distributed in mature cysts. The precise function of EiCP-B9 during Entamoeba encystation remains to be determined. However, colocalisation studies with an Entamoeba marker for autophagosomes suggest that EiCP-B9 is not associated with Entamoeba autophagy.

Development of a Polymerase Chain Reaction Test for Entamoeba invadens

Entamoeba invadens is a protozoal parasite of reptiles that causes colitis, abscesses of liver and other organs, and sometimes acute death. It is generally considered a commensal of chelonians but has also been implicated as a cause of colitis, diarrhea, and death in gopher (Gopherus polyphemus) and leopard (Geochelone pardalis) tortoises. Diagnosis of E. invadens is currently by detection of trophozoites and/or cysts upon direct fecal examination. However, definitive diagnosis of E. invadens has been difficult due to the very similar morphology of nonpathogenic Entamoeba spp., including E. ranarum, E. insolita, E. barreti, and E. terrapinae. Definitive speciation of Entamoeba spp. is important to avoid misdiagnosis or overtreatment for nonpathogenic protozoa. It is also important for consideration of mixed species reptile collections to avoid exposing snakes and lizards to E. invadens. In this study, we developed polymerase chain reaction (PCR) primers for E. invadens, E. ranarum, E. terrapinae, and E. insolita and conducted PCR amplification of purified DNA from cell cultures, as well as purified DNA from reptile stool samples with E. invadens trophozoites added. As a result of this study, a naturally occurring infection of E. invadens was confirmed in a giant South American river turtle (Podocnemis expansa). This study has developed successful PCR primers for four species of Entamoeba and demonstrates that PCR is a promising diagnostic tool for the definitive identification of E. invadens.

Dealing with reptile parasites in general practice

(2007). Dealing with reptile parasites in general practice. Veterinary Nursing Journal: Vol. 22, No. 11, pp. 18-21.

The alien and native pentastomids fauna of an exotic lizard population from Brazilian Northeast

Pentastomids are common parasites of reptiles’ respiratory tract with more than 130 species described (de Oliveira Almeida and Christoffersen 1999; Rego 1983). The knowledge on the infection by the pentastomid Raillietiella in Brazil is scarce. Few works has been reported: Raillietiella freitasi in the lungs of Thrachylepis atlanticus (formerly Mabuya punctata; Motta 1963; Motta and Gomes 1968; Rego 1983, 1984); larvae of Raillietiella sp. in the skink Mabuya agilis (Vrcibradic et al. 2002) and a likely new species of Raillietiella aff. furcocerca infecting Cnemidophorus abaetensis and Cnemidophorus ocellifer (Dias et al. 2005). The house gecko Hemidactylus mabouia Moreau de Jonnes, 1818, is a broadly distributed species in the tropics and has invaded the New World after accidental introductions, becoming a successful colonizer, widely represented in southern North America, in Central and South America (Federico and Cacivio 2000). Along its range, H. mabouia has harboured an extensive parasitic fauna composed of protozoans, platyhelminthes, acanthocephalans, nematodes, pentastomids, and mites (Ali et al. 1985; Simonsen and Sarda 1985; Lainson and Paperna 1999; Martinez-Rivera et al. 2003; Anjos et al. 2005). We collected the specimens of H. mabouia from January to April 2006 in human buildings (houses) in the municipality of Barbalha (7°18′S; 39°18′W), Ceara state, in Northeastern Brazil. The climate of the region is predominantly mild hot semi-arid (mean annual temperature varying from 24°C to 26°C) and an annual rainfall of 1,153 mm. The vegetation in the area is composed of plant species common to Caatinga, Cerrado, wet forest, and transitional zones between these adjacent biomes (IPECE 2005). Lizards were collected by hand, promptly euthanized with ether and fixed with formalin 10% and posterior preserved in ethanol 70%. Lizard snout–vent length (SVL) was measured with a ruler (to the nearest 1 mm). Voucher specimens were housed in the Zoological Collection of the Universidade Regional do Cariri (LZ-URCA): 323–332, 334, 336, 338, 339, 341–355, 368–375. The lungs of the geckos were removed and carefully checked under a stereomicroscope to search for pentastomids. After that, the body cavity was checked and no pentastomid was found in the body cavity. The pentastomids were either preserved in ethanol 70% or mounted on slides and treated with a Hoyer medium. All the pentastomids found were adults because we noticed that the uterus of the females were full of eggs and that their single hooks had no chitinous accessories, which make Parasitol Res (2007) 101:627–628 DOI 10.1007/s00436-007-0526-7

Helminth parasites of reptiles (Reptilia) in Romania

Necropsy of 82 specimens of reptiles (snakes, lizards, and turtles) was performed between 2002 and 2006 to determine the helminth fauna. We examined 7 species of reptiles: Natrix natrix (n=25), Natrix tessellata (n=20), Vipera berus (n=5), Coluber caspius (n=12), Anguis fragilis (n=2), Lacerta agilis (n=10), and Emys orbicularis (n=8). Overall prevalence of helminthic infections in Romanian reptiles was 81.71%. In snakes, the most prevalent group of helminths was trematodes. The helminth species, their prevalence, intensity, and abundance are shown in Table 1. In two reptile species, all individuals were infected with helminths (N. natrix and E. orbicularis). The lowest prevalence of helminthic infection was in C. caspius. Three digenean trematodes, namely, Leptophallus nigrovenosus, Metaleptophallus gracillimus, and Spirhapalum polesianum, and three nematodes, Entomelas entomelas, Strongyloides mirzai, and Hexametra quadricornis, are new records for Romania. N. natrix has a new host record for infection with nematode genus Eustrongylides.

Identification of developmentally regulated genes in Entamoeba histolytica: insights into mechanisms of stage conversion in a protozoan parasite

Developmental switching between life-cycle stages is a common feature among many pathogenic organisms. The protozoan parasite Entamoeba histolytica converts between cysts (essential for disease transmission) and trophozoites (responsible for tissue invasion). Identification of genes involved in the developmental pathway has been severely hindered by the inability to generate E. histolytica cysts in vitro. Using parasite strains derived from recent human infections and whole-genome transcriptional profiling, we determined that 1439 genes (approximately 15% of annotated genes) were potentially developmentally regulated. Genes enriched in cysts (672 in total) included cysteine proteinases and transmembrane protein kinases, which may be involved in signal transduction. Genes enriched in trophozoites (767 in total) included genes typically thought of as important in tissue invasion by trophozoites, including the Gal/GalNAc lectin light subunit and cysteine protease 1. Putative regulators of differentiation including possible G-protein coupled receptors, signal transduction proteins and transcription factors were identified. A number of E. histolytica stage-specific genes were also developmentally regulated in the reptilian parasite E. invadens, indicating that they likely have conserved functions in Entamoeba development. These advances lay the groundwork for dissection of the molecular signals that initiate stage conversion and development of novel diagnostic and therapeutic measures targeting E. histolytica cysts.

Parasites of domestic and wild animals in South Africa. XLVII. Ticks of tortoises and other reptiles

A total of 586 reptiles, belonging to 35 species and five subspecies, were examined in surveys aimed at determining the species spectrum and geographic distribution of ticks that infest them. Of these reptiles 509 were tortoises, 28 monitor or other lizards, and 49 snakes. Nine ixodid tick species, of which seven belonged to the genus Amblyomma, and one argasid tick, Ornithodoros compactus were recovered. Seven of the ten tick species are parasites of reptiles. Amongst these seven species Amblyomma marmoreum was most prevalent and numerous on leopard tortoises, Geochelone pardalis; Amblyomma nuttalliwas present only on Bell's hinged tortoises, Kinixys belliana; and most Amblyomma sylvaticum were collected from angulate tortoises, Chersina angulata. Amblyomma exornatum (formerly Aponomma exornatum) was only recovered from monitor lizards, Varanus spp.; most Amblyomma latum (formerly Aponomma latum) were from snakes; and a single nymph of Amblyomma transversale (formerly Aponomma transversale) was collected from a southern African python, Python natalensis. All 30 Namaqualand speckled padloper tortoises, Homopus signatus signatus, examined were infested with O. compactus. The seasonal occurrence of A. sylvaticum and the geographic distribution of this tick and of A. marmoreum, A. nuttalli, A. exornatum, A. latum and O. compactus are illustrated.

Effects of a combinations of emodepside and praziquantel on parasites of reptiles and rodents

A new combination of two anthelmintic compounds containing emodepside and praziquantel (Profender, Bayer AG, Levekusen, Germany) was tested in pet rodents and reptiles. Topical application of the two compounds led to the quick disappearance of nematodes and cestodes from a broad spectrum of hosts including mice, jirds, snakes, anole lizards, turtles, monitor lizards, etc. In reptiles the dosage had to be increased, since the thick outer layer of the epidermis hinders the penetration of the compounds. In animals with an extremely thick epidermis (e.g. monitor lizards, leguans) the new product was applied under the armpits.

Efficacy of a combination of imidacloprid and moxidectin against parasites of reptiles and rodents: case reports

A new compound containing imidacloprid 10% (w/v) and moxidectin 2.5% (w/v) (Advantage multi, Advocate) was applied as a spot-on treatment to mice experimentally infected with Trichuris muris. Case reports of reptiles found positive for nematode and mite infections following parasitological examination and treated with this compound are also discussed. The results demonstrated that the registered, recommended 2.5% moxidectin concentration for use in dogs was sufficient to eliminate nematodes and mites in reptiles. Infections with nematodes were successfully treated with a single application. Mite infestations in reptiles were eliminated using a treatment repeated on 3 consecutive days.

Analysis of the ITS region and partial ssu and lsu rRNA genes ofBlastocystisandProteromonas lacertae

Blastocystis is a common single-celled enteric parasite found in a large variety of hosts. Recent molecular analysis supports the concept that this eukaryotic organism is a stramenopile most closely related to Proteromonas lacertae, a parasite of reptiles. In this study, the internal transcribed spacer region, partial small subunit rRNA and large subunit rRNA genes from 7 Blastocystis isolates (5 human, 1 pig and 1 sheep), and a Proteromonas lacertae isolate were amplified by PCR, cloned and sequenced. Blastocystis was found to be a typical eukaryote with both ITS1 and ITS2 regions present. Phylogenetic analysis based on the entire PCR amplicon revealed that the Blastocystis isolates did not segregate according to host or geographic origin. The highest sequence identities with the conserved Blastocystis 5.8S rDNA sequence were with the stramenopiles Fibrocapsa japonica, Chattonella marina, Cylindrotheca closterium and Hyphochytrium catenoides. The most parsimonious tree based on the 5.8S rDNA sequence from P. lacertae, 11 other stramenopiles, 2 fungi, 3 algae and 3 alveolates showed Blastocystis positioned within the stramenopiles, with P. lacertae as its closest relative. This work therefore supports the hypothesis that Blastocystis is most closely related to P. lacertae, and that it should be regarded as an unusual stramenopile.

Reptile trade and the risk of exotic tick introductions into southern South American countries

Ticks exotic for the Neotropical region were found on Python regius imported into Argentina and Chile. All ticks (7 males and 3 females) were classified as Amblyomma latum Koch, 1844 ( = Aponomma latum). Additionally, four lots comprising 18 males of the Argentinean tortoise tick, Amblyomma argentinae Neumann, 1904, were found on a terrestrial tortoise, Chelonoidis chilensis, and on three terrestrial tortoises (probably C. chilensis) imported to Uruguay presumably from Argentina). These findings alert us to the risk of expanding the distribution of reptile parasites and their diseases into regions previously free of these parasites.

Characterization of Chitin Synthases from Entamoeba

A major component of the Entamoeba cyst wall is chitin, a homopolymer of beta-(1,4)-linked N-acetyl-D-glucosamine. Polymerization of chitin requires the presence of active chitin synthases (CHS), a group of enzymes belonging to the family of beta-glycosyl transferases. CHS have been described for fungi, insects, and nematodes; however, information is lacking about the structure and expression of this class of enzymes in protozoons such as Entamoeba. In this study, the primary structures of two putative E. histolytica CHS (EhCHS-1 and EhCHS-2) were determined by gene cloning and homologous proteins were identified in databases from E. dispar and the reptilian parasite E. invadens. The latter constitutes the widely used model organism for the study of Entamoeba cyst development. The two ameba enzymes revealed between 23% and 33% sequence similarity to CHS from other organisms with full conservation of all residues critically important for CHS activity. Interestingly, EhCHS-1 and EhCHS-2 differed substantially in their predicted molecular weights (73 kD vs. 114 kD) as well as in their isoelectric points (5.04 vs. 8.05), and homology was restricted to a central stretch of about 400 amino acid residues containing the catalytic domain. Outside the catalytic domain, EhCHS-1 was predicted to have seven transmembrane helices (TMH) of which the majority is located within the C-terminal part, resembling the situation found in yeast; whereas, EhCHS-2 is structurally related to nematode or insect chitin synthases, as it contained 17 predicted TMHs of which the majority is located within the N-terminal part of the molecule. Northern blot analysis revealed that genes corresponding to CHS-1 and CHS-2 are not expressed in Entamoeba trophozoites, but substantial amounts of CHS-1 and CHS-2 RNA were present 4 to 8 hours after induction of cyst formation by glucose deprivation of E. invadens. The time-courses of expression differed slightly between the two ameba CHS genes, as in contrast to CHS-1 RNA, expression of CHS-2 RNA was more transient and no plateau was observed between 8 and 16 hours of encystation. However, both CHS RNAs were no longer detectable after 48 hours when most of the cells had been transformed into mature cysts.

Gene discovery in the Entamoeba invadens genome.

Entamoeba invadens, a parasite of reptiles, is a model for the study of encystation by the human enteric pathogen Entamoeba histolytica, because E. invadens form cysts in axenic culture. With approximately 0.5-fold sequence coverage of the genome, we were able to get insights into E. invadens gene and genome features. Overall, the E. invadens genome displays many of the features that are emerging from ongoing genome sequencing efforts in E. histolytica. At the nucleotide level the E. invadens genome has on average 60% sequence identity with that of E. histolytica. The presence of introns in E. invadens was predicted with similar consensus (GTTTGT em leader A/TAG) sequences to those identified in E. histolytica and Entamoeba dispar. Sequences highly repeated in the genome of E. histolytica (rRNAs, tRNAs, CXXC-rich proteins, and Leu-rich repeat proteins) were found to be highly repeated in the E. invadens genome. Numerous proteins homologous to those implicated in amoebic virulence, (Gal/GalNAc lectins, amoebapores, and cysteine proteinases) and drug resistance (p-glycoproteins) were identified. Homologs of proteins involved in cell cycle, vesicular trafficking and signal transduction were identified, which may be involved in en/excystation and cell growth of E. invadens. Finally, multiple copies of a number of E. invadens genes coding for predicted enzymes involved in core metabolism and the targets of anti-amoebic drugs were identified.

A Role for a Galactose Lectin and Its Ligands During Encystment of Entamoeba1

In the life cycle of Entamoeba parasites alternate between the colon-dwelling trophozoite and the infectious cyst forms. The physiologic stimuli that trigger differentiation of trophozoites into cysts remain undefined. On the surface of the human-infecting Entamoeba, parasites express a galactose/N-acetylgatactosamine (gal/galNAc)-binding lectin, which plays demonstrated roles in contact-dependent lysis of target cells and resistance to host complement. Using a reptilian parasite, Entamoeba invadens, to study cyst formation in vitro, we found that efficient encystation was dependent on the presence of gal-terminated ligands in the induction medium. Precise concentration ranges of several gal-terminated ligands, such as asialofetuin, gal-bovine serum albumin (gal-BSA), and mucin, functioned in encystation medium to stimulate differentiation. Greater than 10 mM levels of free gal inhibited the amoeba aggregation that precedes encystation and prevented formation of mature cysts. Inhibitory levels of gal also prevented the up-regulation of genes which normally occurs at 24 h of encystation. The surface of Entamoeba invadens was found to express a gal lectin which has a heterodimeric structure similar to that of Entamoeba histolytica. The 30 kDa light subunit (LGL) of the E. invadens lectin is similar in overall size and sequence to the LGL of E. histolytica. The heavy subunits, however, differ in size, have an identical spacing of cysteines in their extracellular domains, and have highly conserved C-terminal transmembrane and cytoplasmic domains. These results suggest a new role for the Entamoeba gal lectins in monitoring the concentrations of gal ligands in the colon and contributing to stimuli that induce encystment.

Subulura lacertilia sp.n. (Nematoda, Subuluridae) parasitizing the Brazilian lizard Tropidurus nanuzae Rodrigues (Lacertilia, Tropiduridae)

This report deals with the identification of samples of nematodes recovered from Tropidurus nanuzae Rodrigues, 1981, with the description of a new species, and is a part of a major study on helminth parasites of reptiles in Brazil, taking into account previous data on this subject. The main approach is that referring to the first occurrence of subulurid nematodes in a reptilian host, since they have been assigned previously to birds and mammals.

Effect of dinitroaniline herbicides on the growth of Entamoeba histolytica.

The effect of the dinitroaniline herbicides oryzalin and trifluralin on the growth of Entamoeba histolytica was examined. Oryzalin inhibited the growth of E. histolytica strain HM-1:IMSS. Trifluralin was less effective than oryzalin for this parasite. Entamoeba histolytica was more resistant to these dinitroanilines than other parasitic protozoa examined so far, including Leishmania spp., Trypanosoma brucei, Plasmodium falciparum, Toxoplasma gondii, and Cryptosporidium parvum. Colchicine, a potent microtubule inhibitor of animal cells, was much less effective for E. histolytica, even at very high concentrations. A reptilian parasite, Entamoeba invadens strain IP-1, examined for comparison, was more resistant to these dinitroanilines than E. histolytica. Accumulation of E. histolytica trophozoites in mitosis was observed after culture in 100 microM oryzalin. The inhibitory effect of oryzalin on the growth of E. histolytica trophozoites was abrogated by removal of the drug after exposure to 100 microM for 2 days. In parallel to the recovery of growth after removal of the drug, the percentage of trophozoites in mitosis was reduced to a normal level. The results indicate that treatment of trophozoites with oryzalin arrests mitosis and that its effect is reversible. Therefore, oryzalin is a useful tool for studies relating to the cell cycle of this parasite.

Comparative Analysis of Nematode Infection in Agama aculeata and Agama planiceps, and Its Effect on Body Condition and Fecundity

The vertebrate gut typically harbors a complex assemblage of parasite species of which the best known ones in reptiles are protozoans and helminths (Telford, 1988; Goldberg and Bursey, 1990; Brown et al., 1994). However, as far as the helminths are concerned, detailed studies of their community ecology, distribution patterns in individual hosts and among host species, and their effects on host biology have until now focused mainly on birds and mammals (Anderson, 1992; Anderson and Long, 1992; Delahay et al., 1995), with far less attention given to reptiles. This is in spite of such studies on reptiles that could provide interesting and important insights into vertebrate host-parasite relationships, when considering the vast diversity of life-history patterns, reproductive modes, body sizes, foraging modes, and trophic relations that exist among them (Aho, 1990). Reptile parasites affect their hosts in a variety of ways. These include the lowering of body condition (Dunlap and Mathies, 1993), a reduction in fat deposition (Schall, 1983), a reduction in fecundity (Pence and Selcer, 1988; Galan, 1996), and a lowering of locomotor capability (Oppliger et al., 1996), to name but a few. The distribution of parasites among individual hosts in a population can also provide information about their transmission dynamics and age-related effects (Anderson and Gordon, 1982; Sorci, 1996). In this study, seasonal prevalence, abundance, infection intensity, and dispersion of two types of nematode commonly found in Agama aculeata and Agama planiceps were compared and their effects on body condition and fecundity assessed. The study was conducted in Windhoek, Namibia (22?34'S; 17?06'E) where both lizards are common. Agama aculeata occurs throughout southern Africa, whereas A. planiceps is found only in Namibia (McLachlan, 1981; Branch, 1988). The former species inhabits sandveld areas in semidesert and savannah biomes, whereas the latter is found in rocky outcrops in semidesert and arid savannah biomes (Branch, 1988). Both are insectivorous (Heideman, 1992), breed during spring/summer (Heideman, 1992, 1994, 1995a), and show significant differences in their liver and abdominal fatbody masses between the breeding and nonbreeding seasons. However, no significant differences were found in the monthly mass fluctuations of these organs in each of these seasons (Heideman, 1992). Two types of nematode are frequently found in the gut of these agamas, a Pharyngodon sp. and an Abbreviata sp. (Heideman, 1995b), both of which have yet to be described. Two less common endoparasites are the gut cestode Oochoristica truncata (Heideman, 1991) and a pulmonary pentastomid arthropod Raillietiella n. sp. (J. Wiley and N. J. L. Heideman, unpubl.). Numbers per host reported for the Pharyngodon sp. varied from one to 61, whereas that for the Abbreviata sp. varied from one to 67 (Heideman, 1995b). Collectively, therefore, the numbers of these nematodes per host can be substantial. It was hypothesized that, because of differences in their microhabitats, the agamas should differ in their degree of contact with intermediate hosts of the two nematode species and therefore also differ in their degree of infection. It was further hypothesized that the nematodes should affect body condition of the agamas negatively through their appropriation of host food. This in turn was expected to impact negatively on fecundity which in reptiles is closely linked to the energy available in the liver and abdominal fatbodies (Ho et al., 1982).

Evolution of the genus Leishmania revealed by comparison of DNA and RNA polymerase gene sequences

Previous hypotheses of Leishmania evolution are undermined by limitations in the phylogenetic reconstruction method employed or due to the omission of key parasites. In this experiment, sequences of the gene encoding the DNA polymerase α catalytic polypeptide (POLA) were analysed phylogenetically in combination with those encoding the RNA polymerase II largest subunit gene (RPOIILS) to infer a comprehensive phylogeny of Leishmania. Nineteen species of parasites were studied, comprising representatives of each Leishmania species-complex ( Leishmania Leishmania tropica, Leishmania Leishmania donovani, Leishmania Leishmania mexicana, Leishmania Leishmania hertigi and Leishmania Viannia braziliensis), as well as parasites of questionable taxonomy ( Leishmania herreri, Sauroleishmania adleri, Sauroleishmania deanei, Sauroleishmania gymnodactyli and Sauroleishmania tarentolae). The analyses presented here provide strong support for the hypothesis that the Leishmania that infect reptiles (also known as Sauroleishmania ) evolved from mammalian Leishmania. One implication of this finding is that the taxonomic definition of Leishmania should be broadened to encompass characteristics of the reptilian parasites. However, this taxonomic revision is complicated in that Leishmania ( L.) hertigi, Leishmania ( L.) deanei and Leishmania herreri, which exhibit some biological properties of Leishmania, are more closely related to Endotrypanum on the basis of these sequence comparisons. Consequently, the taxonomic discrimination between Leishmania that infect mammals, Leishmania that infect reptiles and Endotrypanum may be more problematic than has been previously thought. Since our resulting phylogenetic hypothesis is supported by the analyses of two different genes, we speculate on the origin and evolutionary expansion of this lineage of kinetoplastid protozoa.

Encystation of entamoeba parasites.

Entamoeba histolytica is a protozoan parasite of humans, and the causitive agent of intestinal amebiasis. The disease-causing stage of the parasite is an osmotically sensitive ameboid form, which differentiates into a thick-walled cyst for transmission from person to person. The conditions within the human intestine that induce encystment of the amoeba are unknown, but studies using an amoebic parasite of reptiles are now yielding information about the molecules and host:parasite interactions involved in the process. An understanding of the amoeba's obligatory encystment pathway should provide an approach for interrupting the transmission of this parasite, for which there is currently no vaccine.