MEM INST OSWALDO CRUZ, RIO DE JANEIRO, 94(2) Mar/Apr 1999
PAGES: 261-268 DOI: Full paper
Characterization of Endotrypanum (Kinetoplastida: Trypanosomatidae), a Unique Parasite Infecting the Neotropical Tree Sloths (Edentata)

Antonia M Ramos Franco +, Gabriel Grimaldi Jr

Laboratório de Leishmaniose, Departamento de Imunologia, Instituto Oswaldo Cruz, Av. Brasil 4365, 21045-900 Rio de Janeiro, RJ, Brasil

Abstract

This article reviews current concepts of the biology of Endotrypanum spp. Data summarized here on parasite classification and taxonomic divergence found among these haemoflagellates come from our studies of molecular characterization of Endotrypanum stocks (representing an heterogenous population of reference strains and isolates from the Brazilian Amazon region) and from scientific literature. Using numerical zymotaxonomy we have demonstrated genetic diversity among these parasites. The molecular trees obtained revealed that there are, at least, three groups (distinct species?) of Endotrypanum, which are distributed in Central and South America. In concordance with this classification of the parasites there are further newer molecular data obtained using distinct markers. Moreover, comparative studies (based on the molecular genetics of the organisms) have shown the phylogenetic relationships between some Endotrypanum and related kinetoplastid lineages.

Biological characteristics of Endotrypanum spp. - Parasitic protozoa of the genus Endotrypanum are unique among the Kinetoplastida in that they infect erythrocytes of their mammalian host. Infection with Endo-trypanum appears to be restricted to edentates, principally of forest-dwelling two-toed sloths of the genus Choloepus, but rarer infections with these flagellates seems to occur in three-toed sloths (genus Bradypus) (Fig. 1). As shown in Fig. 2, inside the erythocyte the Endotrypanum assumes an epimastigote or trypomastigote form, while in the sandfly or during in vitro culture the parasite assumes promastigote morphology (Shaw 1992). However, the complete life cycle of Endotrypanum spp. has not been reproduced in experimental studies. Other developmental stages of the parasite may occur within the mammalian host (Deane 1961).

In nature, Endotrypanum parasites are probably transmitted by the bite of infected phlebotomine sandflies (Diptera: Psychodidae). Arias et al. (1985) identified E. schaudinni and other Endotrypanum sp. infections in sandflies and sloths captured in the Amazon Region of Brazil. Studies using kinetoplast DNA probe for detecting parasites in sandflies also demonstrated Endotrypanum infections in Lutzomyia shannoniLu. umbratilis and Lu. anduzei (Rogers et al. 1988). Further evidence for the development of Endotrypanum in phlebotomines was obtained by feeding several laboratory-reared sandfly species on infected sloths (Shaw 1964, 1969, 1981, Christensen & Herrer 1977, 1979). In these studies, infections developing within the insect gut (Shaw 1964, 1969) were similar to those found in wild caught sandflies (Johnson et al. 1963, Arias et al. 1985). Moreover, we have reported (Franco et al. 1997b) the developmental biology of Brazilian strains of Endotrypanum for three sandfly species. Development of Endotrypanum varied for each parasite-host species association. After feeding on culture forms of E. schaudinni, significantly more Lu. shannoni (100%, 9/9) became infected than did Lu. longipalpis (62.3%, 33/53) or Phlebotomus papatasi (27.3%, 15/55). The greatest number of infections were in the midgut and hindgut from 6 to 16 days after feeding, but flagellates also were present in the Malpighian tubules. Moreover, distinct development patterns in the sandfly gut were obtained when the Callejon Lu. longipalpis colony was fed on cultures of other Endotrypanum strains. There were also individual variation in the distribution and survival of parasites within the guts of flies in each group. These data indicate that there is variation in the susceptibility to infection with Endotrypanum among and within sandfly species.

Laboratory diagnosis - The finding that Endotrypanum and Leishmania, as well as other distinct groups of Trypanosomaare commonly found in the same vertebrate and insect hosts in Neotropical forests (Table) has led to an increased interest in developing simple methods to distinguish these parasites for epidemiological purposes. Several methods based on parasite-specific markers have been proposed to discriminate these organisms. Endotrypanum can be distinguished from Leishmania species and other trypanosomatids by enzymatic profiles (Arias et al. 1985, Shaw et al. 1991, Franco et al. 1996b), monoclonal antibodies (Lopes & McMahon-Pratt 1989, Franco et al. 1997a), total DNA probes (Greig et al. 1989), hybridization probes based on kDNA (Pacheco et al. 1990), mini-exon gene repeats (Fernandes et al. 1993a), lectin reactivity (Lopes et al. 1987) and sialidase/trans-sialidase activities (Medina-Acosta et al. 1994). However, the classical methods used for direct demonstration of the parasite in tissues is difficult because of the paucity of organisms in infected hosts. Work is now in progress to evaluate (employing PCR and serological assays) the prevalence of Endotrypanum and Leishmania infections in sloths captured in distinct sylvan areas of the Neotropics (Pirmez et al. 1997, Mayrink et al. 1998).

Molecular characterization of the genus - The taxonomy of Endotrypanum spp. is still controversial. Since the original description of this parasite, by Mesnil and Brimont in 1908, only two species have been named as E. schaudinni Mesnil and Brimont, 1908 and E. monterogeii, Shaw, 1969. Croft et al. (1980) observed that the mobilities of the enzymes MDH, IDH and ME, in seven stocks of this parasite were different for the strains that had virus-like particles from those that did not. The two groups did not agree with the original identification of E. schaudinni and E. monterogeii since, ultrastructural and biochemical parameters were similar, in contrast to the description by Shaw (1969), who reported serological differences between these species. Lopes et al. (1990), also grouped both species in the same cluster by comparison of nuclear DNA restriction fragment patterns.

The main goal of our studies is to apply an integrated set of approaches towards the characterization of parasites within the genus Endotrypanum and to use this information in a coherent manner to address problems of parasite identification and taxonomy, diagnosis and developmental biology. Our results confirm previous studies reporting population diversity within this genus (Lopes et al. 1990).

Trans-sialidase and sialidase activities - By virtue of the differences observed in the rations of these enzyme activities, a large collection of trypanosomatids (comprising the major taxa of these parasites) could be separated into four expression types. Endotrypanum could be clustered into a group which could be easily differentiate from other trypanosomatids by their capacity of expressing comparable levels of both trans-sialidase and sialidase activities (Medina-Acosta et al. 1994). In general, the measurement of trans-sialidase and sialidase activities permits the differentiation of parasites frequently found in the same sylvatic vertebrate and invertebrate hosts that are difficult to distinguish, such as Leishmania and Endotrypanum.

Reactivities with monoclonal antibodies - Among the new approaches for identifying Endotrypanum is serodeme analysis using specific monoclonal antibodies, Mabs (Lopes & McMahon-Pratt 1989). In a recent study (Franco et al. 1997a), an heterogenous population of Endotrypanum strains have been screened against a panel of Mabs derived for selected species of Endotrypanum or Leishmania, to see whether this approach could be used to differentiate/group further among these parasites. Using different immunological assay systems, Mabs considered specific for the genus Endotrypanum[E-24, CXXX-3G5-F12] or strain M6159 of E. schaudinni [E-2, CXIV-3C7-F5] (Lopes & McMahon-Pratt 1989) reacted variably according to the test used but in the ELISA or immunofluorescence assay both reacted with all the strains tested. Analyses using these Mabs showed antigenic diversity occurring among the Endotrypanum strains, but no qualitative or quantitative reactivity pattern could be consistently related to parasite origin (i.e., host species involved) or geographic area of isolation. Western blot analyses of the parasites showed that these Mabs recognized multiple components and differences existed either in the epitope density or molecular forms associated with the antigenic determinants, which allowed the assignment of the strains to specific antigenic groups.

Multilocus enzyme electrophoresis (MLEE) - As a result of using numerical zymotaxonomy for classifying these organisms (Franco et al. 1996b), the taxonomic horizon of Endotrypanum spp. has been widened. We have analyzed enzyme polymorphism among a group of Endotrypanum parasites (17 stocks isolated from sloths in the Amazon Region in Brazil and 6 reference strains). The 16 enzymic loci were analyzed, and the strains were classified into zymodemes, each representing parasites with unique enzyme profiles. Using numerical analyses the genus was shown to be monophyletic and the 12 zymodemes characterized could be divided into three groups (A, B, C) (Fig. 3). The data indicate that E. schaudinni is a species complex. The heterogeneous population of parasites showed, however, no correlation with the origin of Endotrypanum stocks. Eight isolates from the State of Rondônia (Brazil) and a parasite strain from Panama were clustered together into a zymodeme (IOC/EZ01), which was phenetically closely related to theEmonterogeii from Costa Rica. All these data reinforce the discussion about the existence of the later parasite species.

Minicircle kDNA heterogeneity and molecular karyotypes - Comparisons of kDNA restriction enzyme fragments profiles from strains representing selected Endotrypanum zymodemes were carried out by polyacrylamide gradient gel electrophoresis. As the degree of heterogeneity within minicircles varied among species or strains of Endotrypanum, the stocks could be clustered into distinct groups of parasites, according to the major sequence classes (minicircle fragments or digests) released by the restriction endonucleases tested (Franco et al. 1996a). In parallel study using PFGE and appropriate gel running conditions, chromosomes were polymorphic in number (10-25) and size (290-2,200 kb) of bands among parasites of this genus. Distinct karyotypes were constructed among E. schaudinniE. monterogeii andEndotrypanum sp. strains. All of the isolates (5) of Endotrypanum sp. from the same species of sloth (C. juruanus) and geographical origin (Rondônia, Brazil) had the same karyotype (Franco et al. 1992). Interesting, these parasites were grouped in the same zymodeme (EZ01) with two other stocks originating from Central America (Franco et al. 1996b). However, RAPD analysis using selected primer was able to differentiate the EZ01 parasites, but the strains did not group on the basis of their geographic origin (Franco et al. 1998a).

Evolutionary links among parasites and taxonomic problems - The difficult taxonomy of Endotrypanum spp. is mainly because the parasite life cycle is unknown. Although this genus is unique among the Trypanosomatidae in that the parasites are found inside the erythrocyte of the mammalian host, both forms (epimastigotes of E. schaudinni and trypomastigotes of E. monterogeii) are found rarely in infected sloths. Endotrypanum spp. have other distinct form in their lyfe cycle: a motile flagellated promastigote stage that lives extracellularly within the alimentary tract of the vector, at least in experimentally infected phlebotomine sandfly (Franco et al. 1997b).

The Endotrypanum shares many characters with other trypanosomatids, particularly those of the genus Leishmania(Shaw 1992). Phylogenetic reconstruction studies of the various kinetoplastid lineages (Fernandes et al. 1993b, Maslov & Simpson 1995) have shown that Leishmania and Endotrypanum are more closely related organisms to each other than either is to T. cruzi. The genetic similarity between Endotrypanum and leishmanial parasites, such as L. (L.) herreriL.(L). hertigi/L. (L). deaneiL. (V.) colombiensis or L. (V.) equatorensis was demonstrated by (i) sequencing comparisons of the small subunit of ribosomal RNA and RNA Polymerase II genes (Croan & Ellis 1996, Noyes et al. 1996, 1997, Croan et al. 1997), (ii) numerical zymotaxonomy, (iii) intergenic region typing of the internal transcribed spacers of the rRNA genes, (iv) minicircle kDNA heterogeneity analysis, and (v) measurement of the sialidase activites of the parasites (Cupolillo et al. 1998). The data show that L. (L.) hertigi/L. (L.) deanei (Herrer 1971, Lainson & Shaw 1977) are genetically closest to the Endotrypanum/L. (L.) herreri group. Interesting, L. (L.) herreri was genetically closer toEndotrypanum than to the pathogenic Leishmania species (Croan et al. 1997, Noyes et al. 1997). The former parasite was originally isolated from two (C. hoffmanni) and three-toed (B. griseus) sloths, and sandflies (Lu. trapidoi, Lu. ylephiletor and Lu. shannoni) in Costa Rica (Zeledón et al. 1979). Studies employing monoclonal antibodies have also shown antigenic similarities among these parasites (Grimaldi et al. 1992, Shaw 1992, Franco et al. 1997a).

Moreover, studies by Touch-down PCR with primers from kinetoplastid housekeeping genes (ribosomal P proteins and repetitive sequences, SIRE) examine the relationships among Endotrypanum (N= 22 strains, comprising the major taxa of this genus) and L. (L.) herreri (ISHA/CR/74/LV341 and IYLE/CR/74/LV342 strains, both isolated from sandflies, and MCHO/CR/74/LV344 strain, isolated from sloth). The data reveal differences among the leishmanial strains, but showing closed genetic similarity between LV342 and Endotrypanum strains clustered within the same group (group A) by zymodeme analysis (Franco et al. 1996b). However, both strains LV341 and LV344 were distinct from all Endotrypanumstocks analyzed (Franco et al. 1998b). Comparative phylogenetic reconstruction studies are in progress to address the evolutionary links among these related kinetoplastid lineages.

The known vertebrate hosts of Endotrypanum spp., two and three-toed sloths, are considered as unique examples of South American fauna and they evolved some 60-70 million years ago during the Palaeocene period. The separation between these two genera of sloths occurred later during the Miocene period and their presence in Central America, is thought to be a result of migration from South America (Webb 1985, Sarich 1985). In Choloepus the body temperature ranges from 24º to 33º C. This variation results in a geographical barrier to these mammals (Nowak 1991) and consequently to the parasites. Lopes et al. (1990) based on results of restriction fragment hybridization conclude thatEndotrypanum originated in South America. Considering these observations, zymodeme EZ01 (Fig. 3) has migrated towards Central America and the parasites isolated in this area are representative of the most recent group (group A). Moreover, the results suggest that the dispersal of the genus Endotrypanum has arisen from group C, which is probably the most ancient organism (Franco et al. 1996b).

 

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