Identification of synapomorphic characters in the genus Sarcocystis based on 18S rDNA sequence comparison

First findings of Sarcocystis species in game deer and feral pigs in Australia

Several wild game meat species, including deer and feral pigs are hunted and consumed in Australia. Feral pigs and deer are not indigenous to Australia, but they have proliferated extensively and established their presence in every state and territory. Following the report of a sambar deer displaying Sarcocystis like white cysts in its rump muscles, the present study was conducted to explore the prevalence of Sarcocystis infections in wild deer and feral pigs in the southeastern regions of Australia. Oesophagus, diaphragm, and heart tissue from 90 deer and eight feral pigs were examined visually for sarcocysts. All results were negative. PCR testing of randomly selected deer and feral pigs yielded positive results, which were subsequently supported by histopathology. This is the first study to report the presence of Sarcocystis spp. in deer and feral pigs in Australia. As no visual cysts were found on the heart or oesophagus that came back positive with PCR, infected animals, particularly those reared free-range, could be passing through meat quality checks unidentified. If people consume this meat without cooking it properly, it may lead to a human infection of Sarcocystis. However, a more targeted study focused on determining the parasite's prevalence and assessing its risks is necessary to determine if it constitutes a food safety issue. As this species has been found not only in feral pigs but also in domestic pigs, the potential for infection spreading between feral pigs and pigs in free-range livestock systems is high, potentially posing a large problem for the Australian pork industry, particularly with the increased emphasis on free-range pig husbandry. Future studies should concentrate on determining the species of Sarcocystis in feral animals commonly consumed as game meat to determine potential zoonotic risks. This could also include a more in-depth look at the prevalence of Sarcocystis infections in other game animals. Identifying where these parasites are present and to what extent, are important areas for future studies.

Recent insights into the morphology, molecular characterization and tissue localization of the caprine Sarcocystis species infecting domestic goats (Capra hiricus): Sarcocystis moulei, Sarcocystis capracanis, and Sarcocystis hircicanis

Ninety-seven (64.67%) out of 150 domestic goats (Capra hiricus) carcasses were found to be infected by Sarcocystis moulei, Sarcocystis capracanis, and Sarcocystis hircicanis sarcocysts. Sarcocystis moulei macrosarcocysts were detected in the cardiac, esophageal, skeletal, lingual, and diaphragmatic muscles of seven goats (4.67%) out of the 150 examined animals, whereas the microscopic Sarcocystis species were found in (90/150 = 60%). Two morphotypes of S. moulei were observed. Morphotype (I) macrosarcocysts were large-sized oval, ovoid, spherical, and measured 2-7 mm in length x 2-6 mm in width. Sarcocystis moulei morphotype (II) macrosarcocysts were spindle-shaped, spheroid, sometimes elongated, and measured 1.8-6 x 0.5-2 mm. By TEM, all S. moulei morphotypes were ultrastructurally the same and had a sarcocyst wall that was characterized by highly branched or cauliflower-like villar protrusions (VP) with dumbbell-like structures. The VP interior was packed with well-developed microtubules in longitudinal and cross arrangements. Sarcocystis moulei cyst wall was 3-6 μm thick. Sarcocystis capracanis microsarcocysts detected herein had a cyst wall that ranged from 4-8 μm in thickness. The VP was upright finger-like or cylindrical. The PVM had electron-dense corrugations in the region of the VP. Few amounts of microfilaments were detected inside the cores of VP. Sarcocystis hircicanis had a thinner cyst wall (~1-3 μm) with hairy long VP that ranged from 1 to 7.5 μm in length. Microtubules were missing inside the cores of the VP. The three caprine Sarcocystis species were molecularly characterized on the level of the 18S rRNA, 28S rRNA, and Cox1 genes.

Molecular Detection and Characterization of Sarcocystis Infection in Naturally Infected Buffaloes, Brazil

ABSTRACT

Sarcocystosis is a disease caused by various Sarcocystis species, a coccidian protozoan parasite that infects humans and animals and is commonly found in ruminants. Although Sarcocystis occurs all over the world, the species responsible for infecting buffaloes in Brazil have not been identified. In this study, we used molecular methods to estimate the prevalence of natural Sarcocystis infection in buffaloes. Phylogenetic analyses were conducted for the first time to identify the species of this protozoan that are responsible for infecting buffalos in southern Brazil, Rio Grande do Sul state. Heart samples from 80 buffaloes were subjected to microscopic examination followed by molecular analysis. Microcysts were present in 19 (23.75%) of 80 samples. The genomic DNA from the 19 cyst samples was extracted and amplified, and six sequences were obtained. The analysis was performed with the StandenPackage software, and the nucleotide sequences generated were analyzed by comparison with sequences in GenBank. All the sequenced samples were identified as Sarcocystis levinei.

HIGHLIGHTS

Morphologic and molecular identification of three macroscopic Sarcocystis species infecting domestic sheep (Ovis aries) and cattle (Bos taurus) in Egypt

In a survey study on the macroscopic species of Sarcocystis infecting domestic sheep (Ovis aries) and cattle (Bos taurus) in Egypt, the macrosarcocysts of Sarcocystis gigantea and Sarcocystis medusiformis were detected in the carcasses of 33 domestic sheep out of a total of 250 (13.20%), whereas Sarcocystis hirsuta macrosarcocysts were found in 17 out of 150 cattle (11.33%) slaughtered at the municipal abattoirs of two different provinces in Egypt. The sarcocysts of each species were thoroughly described morphologically through gross inspection, histopathologic and transmission electron microscopic (TEM) examination. By TEM, S. gigantea primary cyst wall was 6-7.5 μm thick and had irregular highly branched cauliflower-like villar protrusions (VP).The VP contained microtubules (mt) and multiple electron dense granules (edg) that were dispersed inside the cores of the branched VP. Besides, the parasitophorous vacuolar membrane (PVM) had minute blister-like invaginations all over the entire surface of the sarcocyst. S. medusiformis cyst had a thin sarcocyst wall (~2 μm thick) as compared to that of S. gigantea. The cyst wall had trapezoidal or nearly pyramidal VP that were surrounded by thick PVM in addition to a ground substance GS that contained electron-dense fine particles. S. hirsuta sarcocyst wall was 7-9 μm thick and possessed rhomboid-shaped VP that contained microtubules (mt) and electron-dense granules (edg) of variable sizes. The edg were arranged in rows and running parallel to the longitudinal axis of the protrusions. The VP had characteristic narrow neck-like constrictions at their bases, dilated middle portions, and tapered distal ends. The detected macrosarcocysts were eventually confirmed by molecular characterization on the levels of 18S rRNA, 28S rRNA, and Cox1 sequences. Phylogenetic analyses based on the sequences of the 18S rRNA and Cox1 genetic markers gave rise to robust associations of the currently identified isolates of S. gigantea, S. medusiformis, and S. hirsuta within a major clade of Sarcocystis species with felines as presumed or known definitive hosts.

Sarcocystis infection in red deer (Cervus elaphus) with eosinophilic myositis/fasciitis in Switzerland and involvement of red foxes (Vulpes vulpes) and hunting dogs in the transmission

Red deer (Cervus elaphus) carcasses showing grey-greenish discolouration have been increasingly observed in the canton of Grisons, Switzerland. We investigated whether Sarcocystis infections were associated with this pathology, and whether wild and domestic canids were involved in their transmission. Meat from affected red deer (n = 26), faeces and intestines from red foxes (Vulpes vulpes) (n = 126), and faeces from hunting dogs (n = 12) from the region, were analysed. Eosinophilic myositis and/or fasciitis were diagnosed in 69% of the deer, and sarcocysts were observed in 89% of the animals. Molecular typing targeting a ~700bp variable region of the 18S rRNA gene revealed Sarcocystis hjorti in 73%, S. venatoria/S. iberica in 54%, S. linearis/S. taeniata in 12%, S. pilosa in 8% and S. ovalis in 4% of the deer samples. No inflammatory changes were observed in red deer carcasses with normal appearance (n = 8); however, sarcocysts were observed in one sample, and S. hjorti, S. venatoria/S. iberica or S. silva DNA was detected in five samples. Sarcocystis oocysts/sporocysts were observed in 11/106 faecal and 6/20 intestinal fox samples, and in 2/12 canine samples. Sarcocystis tenella (n = 8), S. hjorti (n = 2), S. gracilis (n = 2), and S. miescheriana (n = 1) were identified in foxes, and S. gracilis (n = 2), S. capreolicanis (n = 1) and S. linearis/S. taeniata (n = 1) in dogs. This study provides first molecular evidence of S. pilosa and S. silva infection in red deer and S. linearis/S. taeniata in dogs and represents the first record of S. ovalis transmitted by corvids in Central Europe. Although Sarcocystis species infecting red deer are not regarded as zoonotic, the affected carcasses can be declared as unfit for human consumption due to the extensive pathological changes.

Sarcocystis entzerothi n. sp. from the European roe deer (Capreolus capreolus)

In the present study, we describe Sarcocystis entzerothi n. sp. from the European roe deer (Capreolus capreolus) based on the microscopical and DNA analysis. By light microscopy (LM), cysts of S. entzerothi were spindle-shaped with pointed tips, 950-1900 × 70-150 μm in size and had 5-6 μm long finger-like cyst wall protrusions. Cyst wall of S. entzerothi by transmission electron microscopy (TEM) was type 10a-like; villar protrusions were up to 1.2 μm wide, densely packed, lying about 0.1 μm between each other, had profuse microgranules and microfilaments, parasitophorous vacuolar membrane had many minute invaginations, and the ground substance layer measured up to 0.4 μm. This species is morphologically similar to Sarcocystis silva, previously found in the roe deer and the moose (Alces alces). By LM, cysts of S. silva were cigar-shaped with blunted tips, measured 1000-1500 × 130-184 μm, and had 7-8 μm long finger-like cyst wall protrusions. Under TEM, S. silva had no clear differences from S. entzerothi in their cyst wall ultrastructure. Having examined six roe deer hunted in Lithuania, cysts of S. entzerothi and S. silva were identified in four and two animals, respectively. These two Sarcocystis species could be morphologically differentiated according to the shape of the cysts and the length of protrusions. The species examined showed 95.6-96.1 % and 85.6-86.9 % sequence identity within 18S ribosomal DNA (rDNA) and cox1, respectively, and therefore they could be clearly distinguished by means of molecular methods. It should be noted that in the 18S rDNA phylogenetic tree, S. entzerothi from the roe deer was placed together with one sequence of Sarcocystis sp. from the Lithuanian red deer (Cervus elaphus) demonstrating the same species. Based on 18S rDNA and cox1 sequences, S. entzerothi was more closely related to Sarcocystis species transmitted via felids than canids.

Molecular differentiation of bovine sarcocysts

Cattle are common intermediate hosts of Sarcocystis, and the prevalence in adult bovine muscle is close to 100 % in most regions of the world. Three Sarcocystis spp. are known to infect cattle as intermediate hosts, namely, S. cruzi, S. hirsuta, and S. hominis. The aim of the present study was the molecular identification and differentiation of these three species, Neospora caninum and Besnoitia by PCR and RFLP methods. Tissue samples were obtained from diaphragmatic muscle of 101 cattle slaughtered in Shiraz, Fars Province, Iran, for both smear preparation and DNA extraction. The samples were digested by Pepsin, washed three times with PBS solution before taking smears, fixed in absolute methanol and stained with 10 % Giemsa. The slides were examined microscopically for Sarcocystis bradyzoites and DNA was extracted from 100 mg of Sarcocystis-infected meat samples. Since the primers also bind to 18S rRNA gene of some tissue cyst-forming coccidian protozoa, DNA was also extracted from 100 μl of tachyzoite-containing suspension of N. caninum and Besnoitia isolated from goat to compare RFLP pattern. Polymerase chain reaction (PCR) was performed on DNA of samples which were microscopically positive for Sarcocystis. Five restriction enzymes Dra1, EcoRV, RsaI, AvaI, and SspI were used for RFLP and DNA of one sample from protozoa was sequenced. Based on the RFLP results, 87 (98.9 %) DNA samples were cut with DraI, indicating infection by S. cruzi. One sample (1.1 %) of PCR products of infected samples was cut only with EcoRV which showed S. hominis infection. Forty-eight samples (53.3 %) of PCR products were cut with both DraI, EcoRV, or with DraI, EcoRV, and RsaI while none of them was cut with SspI, which shows the mixed infection of both S. cruzi and S. hominis and no infection with S. hirsuta. It seems by utilizing these restriction enzymes, RLFP could be a suitable method not only for identification of Sarcocystis species but also for differentiating them from N. caninum and Besnoitia.

Molecular identification of Sarcocystis spp. in foxes (Vulpes vulpes) and raccoon dogs (Nyctereutes procyonoides) from Germany

More than 200 Sarcocystis spp. have been named and most of them appear to be involved in a particular predator-prey cycle. Among canids, the European fox (Vulpes vulpes) and the raccoon dog (Nyctereutes procyonoides) are widely distributed in Europe and probably play an important role as definitive hosts in the epidemiology of Sarcocystis spp. infections. A total of 50 small intestines from foxes and 38 from raccoon dogs were sampled in the Federal State of Brandenburg, Germany. Mucosal scrapings were collected and analyzed by sugar flotation and when oocysts or sporocysts were detected, an overnight sedimentation was performed and DNA extracted with a commercial kit. A PCR was conducted using primers targeting a fragment of the 18S rRNA gene (with a size of approximately 850 bp) and the amplicons were purified and sequenced. Samples with an inconclusive sequencing were cloned into plasmids and ≥ 3 plasmids from each amplicon were sequenced. Sarcocystis spp. oocysts/sporocysts were detected in 38% (19/50) of fox and 52.6% (20/38) of raccoon dog samples. Sequencing analysis of amplicons from oocyst DNA revealed mixed infections in 9 fox and 5 raccoon dog samples. In the fox samples, the most often identified Sarcocystis spp. were S. tenella or S. capracanis (10.0%); S. miescheriana (8.0%) and S. gracilis (8.0%) followed by Sarcocystis spp., which use birds as intermediate hosts (6.0%), and S. capreolicanis (4.0%). In the raccoon dog samples, sequences with a ≥99% identity with the following species were detected: S. miescheriana (18.4%), S. gracilis (13.1%), Sarcocystis spp. using birds as IH (10.5%), S. tenella or S.capracanis (2.6%) and S. capreolicanis (2.6%). The estimated prevalence of Sarcocystis spp. infections determined using mucosal scrapings was higher than in related studies performed by analyzing faecal samples. The methodology of 18S rRNA gene amplification, cloning and sequencing is suitable to identify mixed infections with Sarcocystis spp. and to gather information on potential definitive hosts of these parasite species.

Molecular identification of Sarcocystis spp. helped to define the origin of green pythons (Morelia viridis) confiscated in Germany

Sarcocystis spp. represent apicomplexan parasites. They usually have a heteroxenous life cycle. Around 200 species have been described, affecting a wide range of animals worldwide, including reptiles. In recent years, large numbers of reptiles have been imported into Europe as pets and, as a consequence, animal welfare and species protection issues emerged. A sample of pooled feces from four confiscated green pythons (Morelia viridis) containing Sarcocystis spp. sporocysts was investigated. These snakes were imported for the pet trade and declared as being captive-bred. Full length 18S rRNA genes were amplified, cloned into plasmids and sequenced. Two different Sarcocystis spp. sequences were identified and registered as Sarcocystis sp. from M. viridis in GenBank. Both showed a 95-97% sequence identity with the 18S rRNA gene of Sarcocystis singaporensis. Phylogenetic analysis positioned these sequences together with other Sarcocystis spp. from snakes and rodents as definitive and intermediate hosts (IH), respectively. Sequence data and also the results of clinical and parasitological examinations suggest that the snakes were definitive hosts for Sarcocystis spp. that circulate in wild IH. Thus, it seems unlikely that the infected snakes had been legally bred. Our research shows that information on the infection of snakes with Sarcocystis spp. may be used to assess compliance with regulations on the trade with wildlife species.

Genetic assemblage of Sarcocystis spp. in Malaysian snakes

Background

Sarcocystis species are protozoan parasites with a wide host range including snakes. Although there were several reports of Sarcocytis species in snakes, their distribution and prevalence are still not fully explored.

Methods

In this study, fecal specimens of several snake species in Malaysia were examined for the presence of Sarcocystis by PCR of 18S rDNA sequence. Microscopy examination of the fecal specimens for sporocysts was not carried as it was difficult to determine the species of the infecting Sarcocystis.

Results

Of the 28 snake fecal specimens, 7 were positive by PCR. BLASTn and phylogenetic analyses of the amplified 18S rDNA sequences revealed the snakes were infected with either S. nesbitti, S. singaporensis, S. zuoi or undefined Sarcocystis species.

Conclusion

This study is the first to report Sarcocystis infection in a cobra, and S. nesbitti in a reticulated python.

Phylogenetic analysis of Sarcocystis nesbitti (Coccidia: Sarcocystidae) suggests a snake as its probable definitive host

Sarcocystis nesbitti was first described by Mandour in 1969 from rhesus monkey muscle. Its definitive host remains unknown. 18S rRNA gene of S. nesbitti was amplified, sequenced, and subjected to phylogenetic analysis. Among those congeners available for comparison, it shares closest affinity with those species of Sarcocystis which use snakes as definitive hosts. We therefore hypothesize that a snake may serve as the definitive host for S. nesbitti.

First identification of Sarcocystis tenella (Railliet, 1886) Moulé, 1886 (Protozoa: Apicomplexa) by PCR in naturally infected sheep from Brazil

Sarcocystis tenella is a dog-sheep protozoan parasite, causing a widespread enzootic muscle parasitosis and neurological disease mainly in lambs. This parasite is pathogenic to sheep and important to the economical production of sheep. The present study was initially aimed to determine Toxoplasma gondii infection and the occurrence of co-infection with other Apicomplexa parasites in 602 Brazilian sheep. Twenty of these sheep were positive with antibodies to T. gondii by MAT and IFAT-IgG tests, positive with PCR-RFLP genotyping at multiple loci, and parasites were isolated from mice infected with sheep tissue samples. Two additional sheep born in Brazil, a 2-year-old female Polwarth (Ideal) sheep, a breed originated from Australia (#1), and a 1-year-old male Corriedale sheep, a breed originated from New Zealand and Australia (#2) were positive to T. gondii antibodies by serum tests, and PCR, but negative for bioassay in mice. In genotyping at 12 loci, sheep #1 sample and #2 presented positive results only for some markers. PCR-RFLP of 18S ribosomal RNA (18S rRNA) was performed in all 22 animals to identify the possibility of co-infection of T. gondii with other Apicomplexa parasites, such as S. tenella, Neospora caninum and Hammondia hammondi, resulting in a T. gondii profile for the first 20 animals and a unique genotyping profile for sheep #1 and #2, identical to S. tenella. The 18S rRNA PCR products (approximately 310 bp) were sequenced and blasted to GenBank database at NCBI. Both samples were identical to S. tenella 18S rRNA gene (GenBank accession number L24383-1). These results suggest the existence of co-infection of S. tenella with T. gondii in ewes from Brazil.

The current status of the small subunit rRNA phylogeny of the coccidia (Sporozoa)

There is no current comprehensive assessment of the molecular phylogeny of the coccidia, as all recently published papers either deal with subsets of the taxa or sequence data, or provide non-robust analyses. Here, we present a comprehensive and consistent phylogenetic analysis of the available data for the small-subunit ribosomal RNA gene sequence, including a number of taxa not previously studied, based on a Bayesian tree-building analysis and the covariotide model of evolution. The assumptions of the analysis have been rigorously tested, and the benefits and limitations highlighted. Our results provide support for a number of prior conclusions, including the monophyly of the families Sarcocystidae (cyst-forming coccidia) and Eimeriidae (oocyst-forming coccidia), but with bird-host Isospora species in the Eimeriidae and mammal-host species in the Sarcocystidae. However, it is clear that a number of previously reported relationships are dependent on the evolutionary model chosen, such as the placements of Goussia janae, Lankesterella minimia and Caryospora bigenetica. Our results also confirm the monophyly of the subfamilies Toxoplasmatinae and Sarcocystinae, but only some of the previously reported groups within these subfamilies are supported by our analysis. Similarly, only some of the previously reported groups within the Eimeriidae are supported by our analysis, and the genus Eimeria is clearly paraphyletic. There are unambiguous patterns of host-parasite relationship within the coccidia, as most of the well-supported groups have a consistent and restricted range of hosts, with the exception of the Toxoplasmatinae. Furthermore, the previously reported groups for which we found no support all have a diverse range of unrelated hosts, confirming that these are unlikely to be natural groups. The most interesting unaddressed questions may relate to Isospora, which has the fewest available sequences and host-parasite relationships apparently not as straightforward as elsewhere within the suborder.

The conceptual basis for a new classification of the coccidia

At the joint meeting of the 8th International Coccidiosis Conference and the Annual Scientific Meeting of the Australian Society for Parasitology in Palm Cove, Australia, in July 2001, a Controversial Roundtable was held on 'New classification of coccidia'. The aim of this Roundtable was to stimulate and encourage discussion and debate on current classification schemes for the group of parasitic protozoa known as the eimeriid coccidia. In the past, such classifications have been based only on phenotypic characters such as morphology, ultrastructure, life cycles, and host specificity. However, over the past 10-15 years, molecular phylogenetic studies on taxa of the eimeriid coccidia have revealed that several of the families, subfamilies, and genera that have been erected based on non-molecular characters are paraphyletic. Therefore, this Roundtable was an important forum for initial discussions on how a new and more comprehensive classification of the eimeriid coccidia, which takes into consideration both phenotypic and molecular characters, can be devised. The stimulus came from invited speakers who gave introductions into selected areas of taxonomy and classification. Following these introductions, a more general discussion with the audience addressed potential steps that may be taken in future work. This review is the immediate outcome of the Roundtable. It describes advantages and disadvantages of the use of phenotypic or molecular characters as the base for taxonomic schemes for eimeriid coccidia. It gives specific examples for drawbacks of current classifications based only on phenotypic characters as well as potential pitfalls associated with the use of only molecular phylogenies. It addresses current controversies as well as rules of taxonomy and nomenclature relevant for the eimeriid coccidia. Finally, it recommends the establishment of an international group of scientists to meet on a regular basis, stimulate further discussions, and give direction on how the final goal, i.e. a proposal for a revised, and widely accepted, classification of the eimeriid coccidia, may be achieved.

Molecular approaches for inferring evolutionary relationships among protistan parasites

Within the diverse group of parasites broadly recognized as protists, there are limited morphological characters that can be used to distinguish species and even fewer characters that can infer evolutionary relationships among species. For this reason, molecular data are commonly used to infer relationships among species and strains. These studies most commonly rely on sequences associated with the ribosomal RNA genes but increasingly other nuclear, mitochondrial or plastid genes are contributing data. Molecular systematics has been invaluable in expanding the range of characters that are available for inferring relationships among protistan taxa. As an adjunct to morphological characters, sequence data allow us to better understand the evolutionary history of this group of parasites and thereby erect a well-supported taxonomic framework that reflects these historical relationships. Importantly, the predictive nature of such a framework can aid the search for therapeutic compounds (e.g. via shared biochemical pathways) and highlight organisms that should be tested for cross-reactivity in immunological or molecular diagnostic methods (e.g. use of the closest relatives to assess test specificity). For emergent and poorly known parasites, molecular characterization and placement within the broader phylogenetic framework can help predict likely life history traits, including possible or likely definitive hosts.

Effects of sequence alignment and structural domains of ribosomal DNA on phylogeny reconstruction for the protozoan family sarcocystidae

Finding correct species relationships using phylogeny reconstruction based on molecular data is dependent on several empirical and technical factors. These include the choice of DNA sequence from which phylogeny is to be inferred, the establishment of character homology within a sequence alignment, and the phylogeny algorithm used. Nevertheless, sequencing and phylogeny tools provide a way of testing certain hypotheses regarding the relationship among the organisms for which phenotypic characters demonstrate conflicting evolutionary information. The protozoan family Sarcocystidae is one such group for which molecular data have been applied phylogenetically to resolve questionable relationships. However, analyses carried out to date, particularly based on small-subunit ribosomal DNA, have not resolved all of the relationships within this family. Analysis of more than one gene is necessary in order to obtain a robust species signal, and some DNA sequences may not be appropriate in terms of their phylogenetic information content. With this in mind, we tested the informativeness of our chosen molecule, the large-subunit ribosomal DNA (lsu rDNA), by using subdivisions of the sequence in phylogenetic analysis through PAUP, fastDNAml, and neighbor joining. The segments of sequence applied correspond to areas of higher nucleotide variation in a secondary-structure alignment involving 21 taxa. We found that subdivision of the entire lsu rDNA is inappropriate for phylogenetic analysis of the Sarcocystidae. There are limited informative nucleotide sites in the lsu rDNA for certain clades, such as the one encompassing the subfamily Toxoplasmatinae. Consequently, the removal of any segment of the alignment compromises the final tree topology. We also tested the effect of using two different alignment procedures (CLUSTAL W and the structure alignment using DCSE) and three different tree-building methods on the final tree topology. This work shows that congruence between different methods in the formation of clades may be a feature of robust topology; however, a sequence alignment based on primary structure may not be comparing homologous nucleotides even though the expected topology is obtained. Our results support previous findings showing the paraphyly of the current genera Sarcocystis and Hammondia and again bring to question the relationships of Sarcocystis muris, Isospora felis, and Neospora caninum. In addition, results based on phylogenetic analysis of the structure alignment suggest that Sarcocystis zamani and Sarcocystis singaporensis, which have reptilian definitive hosts, are monophyletic with Sarcocystis species using mammalian definitive hosts if the genus Frenkelia is synonymized with Sarcocystis.

Phylogenetic relationships of the genus Frenkelia: a review of its history and new knowledge gained from comparison of large subunit ribosomal ribonucleic acid gene sequences

The different genera currently classified into the family Sarcocystidae include parasites which are of significant medical, veterinary and economic importance. The genus Sarcocystis is the largest within the family Sarcocystidae and consists of species which infect a broad range of animals including mammals, birds and reptiles. Frenkelia, another genus within this family, consists of parasites that use rodents as intermediate hosts and birds of prey as definitive hosts. Both genera follow an almost identical pattern of life cycle, and their life cycle stages are morphologically very similar. However, the relationship between the two genera remains unresolved because previous analyses of phenotypic characters and of small subunit ribosomal ribonucleic acid gene sequences have questioned the validity of the genus Frenkelia or the monophyly of the genus Sarcocystis if Frenkelia was recognised as a valid genus. We therefore subjected the large subunit ribosomal ribonucleic acid gene sequences of representative taxa in these genera to phylogenetic analyses to ascertain a definitive relationship between the two genera. The full length large subunit ribosomal ribonucleic acid gene sequences obtained were aligned using Clustal W and Dedicated Comparative Sequence Editor secondary structure alignments. The Dedicated Comparative Sequence Editor alignment was then split into two data sets, one including helical regions, and one including non-helical regions, in order to determine the more informative sites. Subsequently, all four alignment data sets were subjected to different tree-building algorithms. All of the analyses produced trees supporting the paraphyly of the genus Sarcocystis if Frenkelia was recognised as a valid genus and, thus, call for a revision of the current definition of these genera. However, an alternative, more parsimonious and more appropriate solution to the Sarcocystis/Frenkelia controversy is to synonymise the genus Frenkelia with the genus Sarcocystis.

Phylogenetic analysis of Sarcocystis spp. of mammals and reptiles supports the coevolution of Sarcocystis spp. with their final hosts

Sequences of the small subunit rRNA genes were obtained for two coccidians, Sarcocystis dispersa and an unnamed Sarcocystis sp. which parasitise the European barn owl and an African viperid snake as their final host, respectively, and share mouse as their intermediate host. Phylogenetic analysis of the sequence data showed that Sarcocystis sp. from the viperid snake is most closely related to another Sarcocystis sp. isolated from an American crotalid snake, while S. dispersa grouped with other bird-transmitted species. The available dataset failed to resolve the evolutionary relationships among four major branches into which all Sarcocystidae and Isospora spp. were split. However, within these branches, the phylogenetic relationships of the majority of analysed members of the genus Sarcocystis reflected coevolution with their final, rather than intermediate hosts.

Phylogenetic analysis of coccidia based on 18S rDNA sequence comparison indicates that Isospora is most closely related to Toxoplasma and Neospora

The phylogenetic relationships and taxonomic affinities of coccidia with isosporan-type oocysts have been unclear as overlapping characters, recently discovered life cycle features, and even recently discovered taxa, continue to be incorporated into biological classifications of the group. We determined the full or partial 18S ribosomal RNA gene sequences of three mammalian Isospora spp., Isospora felis, Isospora ohioensis and Isospora suis, and a Sarcocystis sp. of a rattlesnake, and used these sequences for a phylogenetic analysis of the genus Isospora and the cyst-forming coccidia. Various alveolate 18S rDNA sequences were aligned and analyzed using maximum parsimony to obtain a phylogenetic hypothesis for the group. The three Isospora spp. were found to be most closely related to Toxoplasma gondii and Neospora caninum. This clade in turn formed the sister group to the Sarcocystis spp. included in the analysis. The results confirm that the genus Isospora does not belong to the family Eimeriidae, but should be classified together with the cyst-forming coccidia in the family Sarcocystidae. Furthermore, there appear to be two lineages within the Sarcocystidae. One lineage comprises Isospora and the Toxoplasma/Neospora clade which share the characters of having a proliferative phase of development preceding gamogony in the definitive host and an exogenous phase of sporogony. The other lineage comprises the Sarcocystis spp. which have no proliferative phase in the definitive host and an endogenous phase of sporogony.

Molecular phylogenetic relatedness of Frenkelia spp. (Protozoa, Apicomplexa) to Sarcocystis falcatula Stiles 1893: is the genus Sarcocystis paraphyletic?

The coccidians Frenkelia microti and F. glareoli (Apicomplexa: Sarcocystidae) form tissue cysts in the brain of small rodents (intermediate hosts) while oocysts are formed in the intestine of final hosts, buzzards of the genus Buteo. The inclusion of the small subunit ribosomal RNA gene sequences (SSU rRNA) of both Frenkelia species into the SSU rRNA trees of other, tissue cyst-forming coccidia strongly supports paraphyly of the genus Sarcocystis. Frenkelia spp. exhibit close relatedness to Sarcocystis falcatula Stiles 1893, a bird-opossum parasite, recognized under its junior synonym S. neurona Dubey et al. 1991, as the causative agent of equine protozoan myeloencephalitis on the American continent. As the definition of the genus Frenkelia is based on a plesiomorphic character (affinity to the neural tissue) of supposedly low phylogenetic value, the synonymization of the genus Frenkelia with Sarcocystis is proposed. This renders the genus Sarcocystis monophyletic.