Current research on Sarcocystis species of domestic animals

Identification of Sarcocystis capracanis in cerebrospinal fluid from sheep with neurological disease

Protozoal merozoites were identified in the cerebrospinal fluid of two sheep with neurological disease in the UK. Polymerase chain reaction (PCR) identified the merozoites as Sarcocystis capracanis, a common protozoal pathogen of goats. This is the first report of this species infecting sheep and may represent an aberrant infection with sheep acting as dead end hosts, or alternatively could indicate that sheep are able to act as intermediate hosts for S. capracanis, widening the previously reported host range of this pathogen. It is possible that S. capracanis is a previously unrecognised cause of ovine protozoal meningoencephalitis (OPM) in the UK.

Molecular detection of Sarcocystis species in slaughtered sheep by PCR-RFLP from south-western of Iran

Sarcocystis spp. are the cyst forming protozoan parasites that prevalent in livestock all around the world. In the presented work, we examined 40 macroscopic and 40 microscopic sarcocysts from Khouzestan and Lorestan provinces, south-western Iran, utilizing PCR-RFLP based on amplification of 18S rRNA gene. Using AvaI, HindII, TaqI and EcoRI restriction enzymes the results represented Sarcocystis gigantea in both macroscopic and microscopic cysts. This result supports the importance of molecular investigations on characterization of Sarcocystis species when we aimed to assess the reliable control and preventive programs.

Morphological and molecular characterization of Sarcocystis miescheriana from pigs in the central region of China

Sarcocystosis is an important food-borne parasitosis in humans and various animals. Sarcocystis miescheriana and Sarcocystis suihominis are pathogenic to pigs; S. suihominis is also distinctly pathogenic to humans. Intermediate and final hosts can harbor more than one Sarcocystis species, so the exact identification for Sarcocystis infection in various hosts is essential to control sarcocystosis in humans and important economic animals including pigs. In this study, four isolates of sarcocysts from slaughtered pigs (SmJY1-SmJY4) in the central region of China, in Henan province, were collected and examined by transmission electron microscopy and 18S rRNA sequence analysis to identify the Sarcocystis species in pigs in China. The results showed that cysts in the diaphragm muscles have a thick cyst wall with a number of palisade-like protrusions up to 4.38 μm in length. Inside these protrusions, there were 13-16 fibrils per protrusion. Bradyzoites in cysts showed typical characteristics of Apicomplexa including a conoid, many micronemes, dense bodies, one big nucleus, and a number of amylopectin granules. These ultrastructural results suggest that characteristics of tissue cysts of the isolates SmJY1-SmJY4 were similar to those of S. miescheriana. The sequence similarities of SmJY1-SmJY4 with S. miescheriana were 99-99.5 %, and the sequence similarities of SmJY1-SmJY4 with S. suihominis were much lower. Results of the ultrastructural observation in combination with molecular characterization based on the 18S rRNA sequence represent the first demonstration of S. miescheriana in pigs in China. In addition, results of the histological examination showed that the cysts of S. miescheriana had two types of cyst wall, a palisade-like thick wall and another smoothly thin wall, and could cause obvious atrophy, degeneration, and necrosis of muscle fibers in the diaphragm of naturally infected pigs. These findings will provide an important reference for the examination of Sarcocystis species in the slaughter quarantine of live pigs and in the control of sarcocystosis in pigs.

Molecular diagnostics of Sarcocystis spp. infections

Protozoa of the genus Sarcocystis (phylum Apicomplexa, family Sarcocystidae) is one of the most common parasites affecting animals. Interspecies diagnostic of Sarcocystis genus was based on electron microscopy for many years. Because of absence of visible differences between species with reachable magnifications, light microscopy is useless. In many cases serological diagnostic method have lack of sensitivity. A variety of molecular methods have been developed and used to detect and identify Sarcocystis spp. and to assess the genetic diversity among this protozoan from different population/hosts. Nowadays, molecular diagnostic is the common, time/cost effective method used all over the world to interspecies differentiation.

In vitro culture systems for the study of apicomplexan parasites in farm animals

In vitro culture systems represent powerful tools for the study of apicomplexan parasites such as Cryptosporidium, Eimeria, Sarcocystis, Neospora, Toxoplasma, Besnoitia, Babesia and Theileria, all with high relevance for farm animals. Proliferative stages of these parasites have been cultured in vitro employing a large variety of cell culture and explant approaches. For some, such as Cryptosporidium and Eimeria, the sexual development has been reproduced in cell cultures, while for others, animal experimentation is required to fulfill the life cycle. In vitro cultures have paved the way to exploit the basic biology of these organisms, and had a major impact on the development of tools for diagnostic purposes. With the aid of in vitro cultivation, studies on host-parasite interactions, on factors involved in innate resistance, stage conversion and differentiation, genetics and transfection technology, vaccine candidates and drug effectiveness could be carried out. The use of transgenic parasites has facilitated high-throughput screening of anti-microbial compounds that are active against the proliferative stages. Here, we review the basic features of cell culture-based in vitro systems for apicomplexan parasites that are relevant for farm animals, and discuss their applications with a focus on drug identification and studies of stage differentiation.

Polyparasitism is associated with increased disease severity in Toxoplasma gondii-infected marine sentinel species

In 1995, one of the largest outbreaks of human toxoplasmosis occurred in the Pacific Northwest region of North America. Genetic typing identified a novel Toxoplasma gondii strain linked to the outbreak, in which a wide spectrum of human disease was observed. For this globally-distributed, water-borne zoonosis, strain type is one variable influencing disease, but the inability of strain type to consistently explain variations in disease severity suggests that parasite genotype alone does not determine the outcome of infection. We investigated polyparasitism (infection with multiple parasite species) as a modulator of disease severity by examining the association of concomitant infection of T. gondii and the related parasite Sarcocystis neurona with protozoal disease in wild marine mammals from the Pacific Northwest. These hosts ostensibly serve as sentinels for the detection of terrestrial parasites implicated in water-borne epidemics of humans and wildlife in this endemic region. Marine mammals (151 stranded and 10 healthy individuals) sampled over 6 years were assessed for protozoal infection using multi-locus PCR-DNA sequencing directly from host tissues. Genetic analyses uncovered a high prevalence and diversity of protozoa, with 147/161 (91%) of our sampled population infected. From 2004 to 2009, the relative frequency of S. neurona infections increased dramatically, surpassing that of T. gondii. The majority of T. gondii infections were by genotypes bearing Type I lineage alleles, though strain genotype was not associated with disease severity. Significantly, polyparasitism with S. neurona and T. gondii was common (42%) and was associated with higher mortality and more severe protozoal encephalitis. Our finding of widespread polyparasitism among marine mammals indicates pervasive contamination of waterways by zoonotic agents. Furthermore, the significant association of concomitant infection with mortality and protozoal encephalitis identifies polyparasitism as an important factor contributing to disease severity in marine mammals.

Severity of toxoplasmosis, a water-borne zoonosis, varies widely from chronic and benign to acutely fatal. Here, we investigate polyparasitism (infection with multiple parasite species) as one factor governing the spectrum of disease in Toxoplasma gondii infections. This study utilized wild marine mammals as sentinels to detect contamination of waterways by T. gondii and a similar protozoan, Sarcocystis neurona, which have been linked to water-borne outbreaks in humans and wildlife along North America's Pacific Coast. Using genetic tools, we found high rates of protozoal infection, predominantly concomitant infections, in animals inhabiting major waterways of the Pacific Northwest. These dual infections of T. gondii and S. neurona were more frequently associated with mortality and protozoal encephalitis than single infections, indicating a role for polyparasitism in disease severity. Finally, rare T. gondii genotypes linked to a major human outbreak in the Pacific Northwest were abundant in marine mammals of the region, emphasizing wildlife as relevant sentinels for evaluation of human health risks. Our data implicate polyparasitism as a critical factor associated with the severity of protozoal disease. We also identify the need for vigilant surveillance of public waterways to prevent fecal contamination recurrently threatening human and wildlife health along the Pacific coast.

Sarcocystis sinensis is an ultrastructurally distinct parasite of water buffalo that can cause foodborne illness but cannot complete its life-cycle in human beings

In this study, we compared the morphology of Sarcocystis sinensis and Sarcocystis hominis, and assessed the infectiousness of S. sinensis for human volunteers. The cysts of S. sinensis were from water buffalo (Bubalus bubalis) and those of S. hominis were from cattle (Bos taurus). Transmission electron microscopy of S. sinensis cysts revealed that the cyst wall had leaning, finger-like protrusions measuring 1.44-5.08 μm in length and without invaginations on the tip surface of the protrusions. In contrast, the cyst wall of S. hominis had upright, finger-like protrusions measuring 9.43 μm×2.42 μm and with vesicle-like invaginations on the tip surface of the protrusions. Scanning electron microscopy revealed that surface of the protrusions was arranged as rectangles in S. sinensis, as compared to tongue-shaped in S. hominis. Other distinguishing features of S. sinensis include a thin ground substrate (GS) zone with microtubules and small, circle-like structures located at the base of the protrusions. Human volunteers, after consuming S. sinensis cysts, produced no sporocysts or oocysts in feces, suggesting that humans could not serve as definitive hosts for S. sinensis. By contrast, many sporocysts and oocysts were passed in feces of a human volunteer 11-29 days after ingestion of S. hominis cysts. These results showed that S. sinensis and S. hominis are separate species and S. sinensis cannot use human being as the definitive host.

Sarcocystis cruzi: comparative studies confirm natural infections of buffaloes

Controversy exists concerning whether cattle and water buffalo sustain infections with cysts of distinct arrays of species in the genus Sarcocystis. In particular, morphologically similar parasites have been alternately ascribed to Sarcocystis cruzi or to Sarcocystis levinei, depending on their occurrence in cattle or water buffalo. We used light and transmission electron microscopy, genetic analysis, and experimental infections of definitive canine hosts to determine whether consistent differences could be identified from parasites derived from several natural infections of each host, examining several tissue types (esophagus, skeletal muscles, and heart). Cysts derived from cattle and water buffalo shared similar structure; variation among 18S rRNA sequences did not segregate consistently according to intermediate host type; parasites derived from cattle and water buffalo induced similar outcomes in the canine definitive host. One cattle specimen harbored unusually large (macroscopic) sarcocysts which nonetheless conformed to previously reported ultrastructural and genetic features of S. cruzi. Finding no consistent basis to differentiate between them, we conclude that the parasites infecting each host and tissue type correspond to S. cruzi. In our sample, no phylogenetically distinct taxon was sampled which might correspond to a distinct taxon previously described as S. levinei. Either that taxon was missed by our sampling effort, or it may represent a junior synonym to S. cruzi, which would then cycle between dogs and a broader range of intermediate bovine hosts than was previously considered.

Diagnosis of Sarcocystis spp. in cattle (Bos taurus) and water buffalo (Bubalus bubalis) in Northern Vietnam

Our aim was to develop a method for species diagnosis and to obtain data on the prevalence of Sarcocystis infections in cattle and water buffalo in the Son La Province of Northern Vietnam. Meat samples of naturally infected animals were examined by light and electron microscopy as well as by molecular methods. A PCR of part of the 18S rDNA gene followed by RFLP analysis was modified to detect infections with different Sarcocystis spp. in cattle and water buffaloes slaughtered in the Son La Province. It showed to be an economical method to detect multiple infections with Sarcocystis spp. Sequence analysis of the PCR amplicons was performed with selected samples and the results were compared with published sequences. With these methods the following Sarcocystis spp. were identified in cattle: Sarcocystis hirsuta, Sarcocystis cruzi and Sarcocystis hominis. Water buffaloes were infected with Sarcocystis fusiformis, S. cruzi, S. hominis and S. hirsuta. The results indicate that Sarcocystis spp. infecting cattle are also able to infect water buffaloes. So the validity of certain Sarcocystis spp. of water buffalo is discussed. Bovine lifestock in Northern Vietnam were commonly infected with Sarcocystis spp.

The inadequacy of morphology for species and genus delineation in microbial eukaryotes: an example from the parabasalian termite symbiont coronympha

Background

For the majority of microbial eukaryotes (protists, algae), there is no clearly superior species concept that is consistently applied. In the absence of a practical biological species concept, most species and genus level delineations have historically been based on morphology, which may lead to an underestimate of the diversity of microbial eukaryotes. Indeed, a growing body of molecular evidence, such as barcoding surveys, is beginning to support the conclusion that significant cryptic species diversity exists. This underestimate of diversity appears to be due to a combination of using morphology as the sole basis for assessing diversity and our inability to culture the vast majority of microbial life. Here we have used molecular markers to assess the species delineations in two related but morphologically distinct genera of uncultivated symbionts found in the hindgut of termites.

Methodology/Principal Findings

Using single-cell isolation and environmental PCR, we have used a barcoding approach to characterize the diversity of Coronympha and Metacoronympha symbionts in four species of Incisitermes termites, which were also examined using scanning electron microscopy and light microcopy. Despite the fact that these genera are significantly different in morphological complexity and structural organisation, we find they are two life history stages of the same species. At the same time, we show that the symbionts from different termite hosts show an equal or greater level of sequence diversity than do the hosts, despite the fact that the symbionts are all classified as one species.

Conclusions/Significance

The morphological information used to describe the diversity of these microbial symbionts is misleading at both the genus and species levels, and led to an underestimate of species level diversity as well as an overestimate of genus level diversity. The genus ‘Metacoronympha’ is invalid and appears to be a life history stage of Coronympha, while the single recognized species of Coronympha octonaria inhabiting these four termites is better described as four distinct species.

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.

Surveillance of endoparasitic infections and the first report of Physaloptera sp. and Sarcocystis spp. in farm rodents and shrews in central Taiwan

A total of 95 rodents and shrews including 82 Rattus norvegicus, 7 Rattus rattus, and 6 Suncus murinus were trapped from different localities of Taichung, Taiwan. The overall prevalence of parasites was 93.7%. The infection rates for R. norvegicus, R. rattus, and S. murinus were 93.9%, 85.7%, and 100%, respectively. The rats were infected with four cestodes, Taenia taeniaeformis (48.4%), Hymenolepis diminuta (38.9%), Hymenolepis nana (5.3%), and Raillietina celebensis (45.3%); ten nematodes, Angiostrongylus cantonensis (16.8%), Capillaria hepatica (49.5%), Gongylonema neoplasticum (1.1%), Heterakis spumosa (35.8%), Nippostrongylus brasiliensis (57.9%), Physaloptera sp. (1.1%), Strongyloides ratti (81.1%), Syphacia muris (2.1%), Trichosomoides crassicauda (29.5%), and Trichurus sp. (1.1%), and one protozoan, Sarcocystis spp. (33.7%). Physaloptera sp. from S. murinus and Sarcocystis spp. from both R. norvegicus and R. rattus were reported for the first time in Taiwan. The importances of zoonotic species were discussed.

Sarcocystis in moose (Alces alces): molecular identification and phylogeny of six Sarcocystis species in moose, and a morphological description of three new species

Muscle tissues from 34 moose from Southeastern Norway and two moose from Canada were examined. Sarcocysts were excised and morphologically classified by light microscopy, and some cysts were further examined by scanning electron microscopy or DNA amplification and sequencing at the small subunit (ssu) rRNA gene. In Norwegian moose, three sarcocyst types were recognized, yet five Sarcocystis species were found by sequence analysis. New names were proposed for three species which could be characterised by both morphological and molecular methods, i.e., Sarcocystis alces, Sarcocystis ovalis, and Sarcocystis scandinavica. S. alces was the most prevalent species, whereas S. scandinavica and the two unnamed species were rare and might either use another principal intermediate host or a rare definitive host. The five species in Norwegian moose were different from Sarcocystis alceslatrans isolated from a Canadian moose. Phylogenetic analyses based on complete ssu rRNA gene sequences revealed a close relationship between the six Sarcocystis species from moose and species from reindeer and Sika deer. We conclude that molecular methods are necessary for unequivocal species identification, as different cervid hosts harbour morphologically indistinguishable sarcocysts.

Aborto ovino associado com infecção por Sarcocystis sp

Infecções por protozoários têm distribuição mundial e podem causar aborto, nascimentos prematuros e ou morte fetal em diversas espécies animais. Em julho de 2004, oito ovinos Corriedale apresentaram problemas reprodutivos caracterizados por aborto e natimortalidade no terço final da gestação. Dessas oito perdas, um natimorto macho foi enviado ao Setor de Patologia Veterinária para necropsia. Alterações macroscópicas não foram observadas durante a necropsia. Lesões histológicas foram observadas principalmente no cérebro e coração e se caracterizaram por encefalite não-supurativa multifocal acentuada associada à presença de protozoários no interior de células endoteliais e vasos sanguíneos e miocardite não-supurativa focal leve. Alguns desses organismos apresentaram formato de roseta. O teste de imunoistoquímica anti-Toxoplasma gondii foi negativo, mas houve reação cruzada com anticorpo anti-Neospora caninum. O exame de imunofluorescência direta para Leptospira sp. foi negativo. A bacteriologia aeróbica e micro-aeróbica não revelou crescimento significativo. Esses achados foram compatíveis com o diagnóstico de Sarcocystis sp.

Molecular-based identification of Sarcocystis hominis in Belgian minced beef

Sarcocystis hominis, one of the three species of Sarcocystis that cause muscular cysts in cattle, is a protozoan parasite that can infect the human intestinal tract. The objective of the present study was to develop a new molecular identification method capable of discriminating among the bovine Sarcocystis species and to apply this tool in combination with stereomicroscopy to determine the presence of Sarcocystis spp. in minced beef in Belgium, with special attention to Sarcocystis hominis. A PCR technique based on the 18S rRNA sequence and by sequencing of the amplicon was highly specific. Sequence analysis of PCR products from thick-walled cysts collected from minced beef in Belgium revealed that S. hominis was present in 97.4% of the samples. Because the consumption of raw minced beef is common in Belgium and certain other European countries, these findings may point to an underestimated risk to public health.

Genetic characterisation of six Sarcocystis species from reindeer (Rangifer tarandus tarandus) in Norway based on the small subunit rRNA gene

Six Sarcocystis species, i.e. Sarcocystis grueneri, Sarcocystis rangi, Sarcocystis tarandivulpes, Sarcocystis hardangeri, Sarcocystis rangiferi and Sarcocystis tarandi have previously been described from reindeer based on sarcocyst morphology. In order to validate and expand the species descriptions, the complete small subunit (ssu) rRNA gene was sequenced and used to genetically characterise the six species. The aim was to reveal possible genetic variation in the ssu rRNA gene within each Sarcocystis species, between the species from reindeer, but also between the reindeer species and related Sarcocystis species characterised in other studies. Muscle tissue from the heart and diaphragm was sampled from 18 adult semi-domesticated reindeer at a field abattoir in northern Norway. Sarcocysts were excised from the tissue and classified into one of the six known Sarcocystis species based on their morphology. Two cysts of each of the six species from two different animals were randomly selected for further DNA analyses. The complete ssu rRNA gene was amplified by the polymerase chain reaction (PCR) and subsequently sequenced. The complete ssu rRNA gene sequences were used to compare the six species with each other and with other previously sequenced Sarcocystis species retrieved from GenBank. There was little sequence variation between two isolates of the same species, but the six species differed from each other by insertions, deletions and single nucleotide polymorphisms (SNPs), mainly located in variable regions of the gene. The identity between the six species from reindeer was approximately the same as when other Sarcocystis species using a different intermediate host were compared with each other. This study supported previous findings of reindeer being the intermediate host for at least six Sarcocystis species and the results also indicated the existence of certain nucleotide positions within the ssu rRNA gene that are unique to Sarcocystis species with a canine definitive host.

Mapping of quantitative trait loci affecting resistance/susceptibility to Sarcocystis miescheriana in swine

The outcome of infectious diseases in vertebrates is under genetic control at least to some extent. In swine, e.g., marked differences in resistance/susceptibility to Sarcocystis miescheriana have been shown between Chinese Meishan and European Pietrain pigs, and these differences are associated with high heritabilities. A first step toward the identification of genes and polymorphisms causal for these differences may be the mapping of quantitative trait loci (QTLs). Considering clinical, immunological, and parasitological traits in the above model system, this survey represents the first QTL study on parasite resistance in pigs. QTL mapping was performed in 139 F(2) pigs of a Meishan/Pietrain family infected with S. miescheriana. Fourteen genome-wide significant QTLs were mapped to several chromosomal areas. Among others, major QTLs were identified for bradyzoite numbers in skeletal muscles (F = 17.4; p < 0.001) and for S. miescheriana-specific plasma IgG(2) levels determined 42 days p.i. (F = 20.9; p < 0.001). The QTLs were mapped to different regions of chromosome 7, i.e., to the region of the major histocompatibility complex (bradyzoites) and to an immunoglobulin heavy chain cluster, respectively. These results provide evidence for a direct and causal role for gene variants within these gene clusters (cis-acting) in differences in resistance to S. miescheriana.

Effects of frozen storage on the structure of sarcocysts in pig muscle and implications in taxonomic studies

The morphology of the cyst wall of Sarcocystis has unique characteristics that can be used in species identification. To find a suitable way to preserve Sarcocystis cyst samples for species identification, by light microscopy and electron microscopy, we recorded the morphological changes in the cysts of Sarcocystis suihominis and Sarcocystis miescheriana from pig muscle, induced by storage at -20 degrees C. Comparisons were made between fresh cysts and those subjected to frozen storage for periods of 3 days, 20 days and 30 days.

RESULTS

cyst wall of the two Sarcocystis species appeared unaffected by storage. There was no obvious change in the length, nor in the width of the protrusions after storage (P>0.05), but the structure of the bradyzoite in the sarcocyst was in many cases disintegrated at -20 degrees C in 20 days for S. miescheriana and 30 days for S. suihominis. To our knowledge this is the first report that Sarcocystis cyst in muscle can be stored at -20 degrees C before and remain suitable for ultrastructural morphological study. Consequently, this paper proposes freezing as a convenient storage method for samples used in taxonomic studies of Sarcocystis.

The parasite connection in ecosystems and macroevolution

In addition to their obvious negative effects ("pathogens"), endoparasites of various kinds play an important role in shaping and maintaining modern animal communities. In the long-term, parasites including pathogens are indispensable entities of any ecosystem. To understand this, it is essential that one changes the viewpoint from the host's interests to that of the parasite. Together with geographic isolation, trophic arms race, symbiosis, and niche partitioning, all parasites (including balance strategists, i.e. seemingly non-pathogenic ones) modulate their hosts' population densities. In addition, heteroxenic parasites control the balance between predator and prey species, particularly if final and intermediate hosts are vertebrates. Thereby, such parasites enhance the bonds in ecosystems and help maintain the status quo. As the links between eukaryotic parasites and their hosts are less flexible than trophic connections, parasite networks probably contributed to the observed stasis and incumbency of ecosystems over geologic time, in spite of continuous Darwinian innovation. Because heteroxenic parasites target taxonomic levels above that of the species (e.g. families), these taxa may have also become units of selection in global catastrophies. Macroevolutionary extrapolations, however, are difficult to verify because endoparasites cannot fossilize.

Neosporosis, Toxoplasmosis, and Sarcocystosis in Ruminants

Neospora caninum, Sarcocystis spp, and Toxoplasma gondii are related coccidian parasites that can cause abortion and neonatal mortality in animals. In addition, T gondii and certain species of Sarcocystis are zoonotic. This article reviews information on the etiology, diagnosis, control, and prevention of these diseases.

Naturally occurring Sarcocystis neurona-like infection in a dog with myositis

Tissue stages similar to those of Sarcocystis neurona, the causative agent of equine protozoal myeloencephalitis, were identified in skeletal muscles of a dog. The dog, a 6-year-old Labrador retriever, was seropositive for Toxoplasma gondii infection and euthanized due to a history of polymyositis and progressive muscular atrophy. Histologically, 30, variably sized, microscopic, intracellular sarcocysts were observed in 60 sections of skeletal muscles taken from the neck, fore limbs and hind limbs. The cysts were only observed in inflamed skeletal muscles, but were mostly in myocytes at the periphery of areas infiltrated with leukocytes. Ultrastructurally, the cyst wall had villar protrusions consistent with sarcocysts. Immunohistochemistry with monoclonal S. neurona antibodies demonstrated positive labeling of zoites in merozoites or schizonts in the skeletal muscle interstitium, but no labeling of the sarcocysts. Initial PCR analysis with primers amplifying a genetic sequence encoding Apicomplexan 18s rRNA, and subsequent PCR analysis with differentiating primers indicated that the genetic sequences had 100% identity with sequences reported for S. neurona.

Toxoplasma gondii infection in adult llamas (Lama glama) and vicunas (Vicugnavicugna) in the Peruvian Andean region

The present study was designed to investigate Toxoplasma gondii infection in adult llamas (Lama glama) and vicunas (Vicugna vicugna) in the Peruvian Andean region, for which to date no information has been available. Serum samples from 43 llamas (L. glama) and 200 vicunas were tested by IFAT detecting titres of 1:50 or higher in 55.8% (33.9-70.9%) and 5.5% (2.8-9.6%), respectively. IFAT titres ranged from 1:50 to 1:6400. In order to avoid cross reactions with closely related coccidian parasites and to confirm the existence of T. gondii specific antibodies, IFAT positive sera from both ruminant species were also analysed by western blot. T. gondii specific antigens were recognised by IFAT positive sera, although different IFAT cut-off points could be selected for llamas (1:200) and vicunas (1:50) meaning seroprevalence of 44.2% (29.1-60.1%) and 5.5% (2.8-9.6%), respectively. Based on the frequency and intensity of tachyzoite antigen recognition, at least three immunodominant antigens with apparent molecular weights of 22-24, 30, and 38-40 kDa were detected, together with other minor protein fractions located in the 18-73 kDa range. This study documents for the first time the presence of T. gondii infection and reports the target T. gondii antigens in adult llamas and vicunas in Peru.

RISK OF TRANSPLACENTAL TRANSMISSION OF SARCOCYSTIS NEURONA AND NEOSPORA HUGHESI IN CALIFORNIA HORSES

The study objective was to assess the risk of transplacental transmission of Sarcocystis neurona and Neospora hughesi in foals from 4 California farms during 3 foaling seasons. Serum of presuckle foals and serum and colostrum of periparturient mares were tested using indirect fluorescent antibody tests for S. neurona and N. hughesi. Serum antibody titers were < or =10 in 366 presuckle foals tested. There was no serologic or histologic evidence of either parasite in aborted fetuses or placentas examined. Positivity for S. neurona and N. hughesi in mares increased with age. Mares < or =9 yr that originated from Kentucky were 3.8 and 1.4 times more likely to be positive for S. neurona and N. hughesi, respectively, than mares from California. The strength of association between positivity to either parasite and state of birth decreased as age increased. Mares positive for S. neurona and N. hughesi were 2.2 and 1.7 times more likely, respectively, to have a previous abortion than negative mares, adjusted for age and state of birth. The annual mortality rate for mares was 4%. The annual incidence rate of equine protozoal myeloencephalitis was 0.2%. In conclusion, there was no detectable risk of transplacental transmission of S. neurona and N. hughesi. Prevalence of antibodies against both parasites in mares increased with age.

Seasonal variation in Sarcocystis species infections in goats in northern Iraq

We investigated the prevalence of sarcocystosis in 826 goats slaughtered in the winter season from November to April in northern Iraq. The prevalence of macrocysts was on average 34%, with only 20% infected animals in November, but 46% in February. The infection rate in 1-, 3- and 6-year-old goats was 4%, 48%, and 83%, respectively. The highest specificity of infection was in the oesophagus (99%) and the lowest in the diaphragm (3%). Grossly, we identified 2 forms of macroscopic sarcocysts, fat and thin, with different morphological characteristics. The prevalence of microcysts was 97% and no effects of age, sex and seasonal variations were observed. Development of microcysts in the small intestine of dogs and cats has also been investigated. The pre-patent period in experimentally infected dogs was 12–14 days and the patent period lasted 64–66 days. A dog shed about 155 million sporocysts, but no sporocysts were shed by cats that had been fed the same infected tissues, thus identifying the microcysts as Sarcocystis capracanis.

First report of Neospora caninum infection in adult alpacas (Vicugna pacos) and llamas (Lama glama)

Neospora caninum is a cyst-forming coccidian that mainly affects bovines, although Neospora infection has also been described in other domestic and wild ruminant species. Serum samples from 78 alpacas (Vicugna pacos) and 73 llamas (Lama glama) at a unique dilution of 1:50 tested by indirect fluorescent antibody test (IFAT) were further analyzed serologically by IFAT and Western blot in both ruminant species to avoid cross-reactions with closely related coccidian parasites and to confirm the existence of N. caninum-specific antibodies. IFAT titers ranging between 1:50 and 1:800 were found. When using Western blot, N. caninum tachyzoite-specific immunodominant antigens with apparent molecular weights of 17-18, 34-35, 37, and 60-62 kDa were also recognized, although some sera with 1:50 IFAT titers proved not to have N. caninum-specific antibodies. As expected, higher IFAT titers were associated with higher anti-N. caninum reactivity in Western blot. This report documents for the first time the presence of N. caninum infection in adult alpacas and llamas from Peru.

Identification of Sarcocystis hominis-like (Protozoa: Sarcocystidae) cyst in water buffalo (Bubalus bubalis) based on 18S rRNA gene sequences

DNA templates were extracted from isolates of Sarcocystis hominis-like cysts collected from cattle and water buffalo, as well as from Sarcocystis fusiformis cysts and Sarcocystis suihominis cysts. The 18S rRNA genes were amplified using DNA from a single cyst as the templates. Approximately 1,367-1,440 bp sequences were obtained. The sequence difference in isolates of Sarcocystis hominis-like cysts from water buffaloes, and isolates of S. hominis cysts from cattle were very low, only about 0.1%, much lower than the lowest value (1.7%) among different species. Combined with their morphological structure, these sequence data indicate that the 4 isolates from cattle and water buffalo might be the same species, i.e., S. hominis, suggesting that both cattle and water buffalo may serve as the intermediate hosts for this parasite. Apparently, this is the first report using a single cyst to do such work and is a useful way to distinguish the Sarcocystis cyst in an intermediate host that may be simultaneously infected by several different Sarcocystis species.

Immunoconversion against Sarcocystis neurona in normal and dexamethasone-treated horses challenged with S. neurona sporocysts

Equine protozoal myeloencephalitis is a common neurologic disease of horses in the Americas usually caused by Sarcocystis neurona. To date, the disease has not been induced in horses using characterized sporocysts from Didelphis virginiana, the definitive host. S. neurona sporocysts from 15 naturally infected opossums were fed to horses seronegative for antibodies against S. neurona. Eight horses were given 5x10(5) sporocysts daily for 7 days. Horses were examined for abnormal clinical signs, and blood and cerebrospinal fluid were harvested at intervals for 90 days after the first day of challenge and analyzed both qualitatively (western blot) and quantitatively (anti-17kDa) for anti-S. neurona IgG. Four of the challenged horses were given dexamethasone (0.1mg/kg orally once daily) for the duration of the experiment. All challenged horses immunoconverted against S. neurona in blood within 32 days of challenge and in CSF within 61 days. There was a trend (P = 0.057) for horses given dexamethasone to immunoconvert earlier than horses that were not immunosuppressed. Anti-17kDa was detected in the CSF of all challenged horses by day 61. This response was statistically greater at day 32 in horses given dexamethasone. Control horses remained seronegative throughout the period in which all challenged horses converted. One control horse immunoconverted in blood at day 75 and in CSF at day 89. Signs of neurologic disease were mild to equivocal in challenged horses. Horses given dexamethasone had more severe signs of limb weakness than did horses not given dexamethasone; however, we could not determine whether these signs were due to spinal cord disease or to effects of systemic illness. At necropsy, mild-moderate multifocal gliosis and neurophagia were found histologically in the spinal cords of 7/8 challenged horses. No organisms were seen either in routinely processed sections or by immunohistochemistry. Although neurologic disease comparable to naturally occurring equine protozoal myeloencephalitis (EPM) was not produced, we had clear evidence of an immune response to challenge both systemically and in the CNS. Broad immunosuppression with dexamethasone did not increase the severity of histologic changes in the CNS of challenged horses. Future work must focus on defining the factors that govern progression of inapparent S. neurona infection to EPM.

A European perspective on Neospora caninum

Since the identification of Neospora caninum in 1984 as a parasite separate from Toxoplasma gondii by Bjerkas et al., and its subsequent characterization and classification in 1988 by Dubey and co-workers, this parasite has attracted increasing attention, primarily as an important causative agent of abortion in cattle and neuromuscular disease in dogs, but also as a complementary model system to T. gondii for investigating the basic biology of intracellular parasitism. During November 11-14, 1999, the COST 820 Annual meeting (Vaccines against coccidioses) took place in Interlaken, Switzerland. Almost half of the papers presented at that meeting were on N. caninum and neosporosis, reflecting the increasing awareness of the importance of this parasite on part of the scientific community in Europe. On the occasion of the meeting, participants in this COST Action involved in Neospora research in Europe were asked to participate in this invited review in order to document the growing interest in N. caninum and the disease it causes. Thus, this paper is a unique collection of contributions provided by several European experts in the field. It is comprised of 10 reviews or original papers on different aspects of Neospora research including epidemiology, immunology, application and development of serological tools, and molecular characterisation of the parasite currently carried out throughout Europe. In addition, two distinguished invited speakers from overseas (Milton McAllister and John Ellis) provided valuable contributions. This invited review demonstrates that the COST 820 Action has brought together scientists from all over Europe and other parts of the world, and has laid the basis for many fruitful collaborations. The studies described here will contribute in assessing the relevance of neosporosis as a potential risk factor not only for animals, but also for human health.

Clinical, pathological and epidemiological findings in three outbreaks of ovine protozoan myeloencephalitis

Ovine protozoan myeloencephalitis is a disease of sheep associated with the apicomplexan protozoan Sarcocystis tenella. This paper describes the clinical, pathological and epidemiological findings in three affected flocks from a well-defined geographical area. Clinical signs were restricted to sheep under one year old in their first winter and were first observed at least 42 days after they had been moved off the hill grazing areas to low ground pasture, or after they were given conserved forage. The findings are discussed in relation to the timescale of the life cycle of S. tenella and it is suggested that clinical disease was precipitated by the change from a low level of exposure to infection on the hill to a high level of exposure through contaminated pasture or forage. Possible preventive strategies are discussed.

Dalmeny disease in an alpaca (Lama pacos): sarcocystosis, eosinophilic myositis and abortion

Disseminated eosinophilic myositis was diagnosed in an alpaca that had been imported to the USA from Peru 5 years earlier. The myositis was associated with macroscopically visible large sarcocysts that were characterized histologically by septate compartments containing bradyzoites, and ultrastructurally by cyst walls composed of anastomosing villous protrusions. Two hours before death, the alpaca aborted an 8-month-gestation fetus, but no lesions were found in the uterus, placenta or fetus. Additional macroscopical findings included haemoabdomen and myofibre haemorrhage, degeneration and necrosis. It is believed that this is the first described case of clinical disease associated with a Sarcocystis sp. (probably S. aucheniae) in camelids.

Development and validation of species-specific nested PCRs for diagnosis of acute sarcocystiosis in sheep

Sheep may be infected by four species of Sarcocystis. Two of these species, Sarcocystis tenella and Sarcocystis arieticanis, are pathogenic. They may cause abortion or acute disease during the early phase of infection, and chronic disease during the late phase of infection. Thus far, diagnosis of sarcocystiosis in sheep has been limited, because traditional diagnostic tests based on the detection of Sarcocystis-specific antibodies are only genus-specific and, thus, cannot differentiate between pathogenic and non-pathogenic species. In addition, most of these tests show a reasonable sensitivity only for the late phase of infection. Therefore, diagnosis of acute sarcocystiosis has been based mainly on post-mortem examination, i.e. after the animal had succumbed to the disease. Here we established species-specific nested PCR assays based on unique small subunit ribosomal RNA gene sequences of S. tenella and S. arieticanis. These PCR assays specifically detect DNA of the homologous species in blood samples of sheep. No cross-reactions were observed with the heterologous pathogenic species, the non-pathogenic species Sarcocystis gigantea, or the closely related coccidia Toxoplasma gondii and Neospora caninum. In sheep experimentally infected with S. tenella or S. arieticanis, positive PCR results were correlated with the early phases of multiplication (endopolygeny) of the parasites. By contrast, Sarcocystis-specific antibodies were detected by an enzyme-linked immunosorbent assay only during the terminal phase of endopolygeny or thereafter. Thus, the nested PCR assays developed here enable, for the first time, the diagnosis and differentiation of infections with S. tenella and S. arieticanis in living sheep during the acute phase of the disease and facilitate comprehensive studies on the epidemiology and importance of infections with pathogenic Sarcocystis species in sheep.

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.

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.

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

In order to further investigate synapomorphic characters in the genus Sarcocystis, the small subunit ribosomal RNA gene sequences of Sarcocystis capracanis and Sarcocystis moulei were determined and used to infer the phylogenetic position of these two organisms within the cyst-forming coccidia. Phylogenies derived using distance, maximum parsimony and maximum likelihood methods demonstrated that S. capracanis groups with Sarcocystis tenella and Sarcocystis arieticanis as a clade that shares the characteristic of using canids as their definitive host. S. moulei was shown to group with Sarcocystis gigantea and Sarcocystis fusiformis as a clade that shares the characteristic of using fields as their definitive host.

Production of a recombinant fusion protein of Sarcocystis tenella and evaluation of its diagnostic potential in an ELISA

We have isolated a cDNA clone encoding an antigenic polypeptide of Sarcocystis tenella by screening a cystozoite-derived cDNA library in lambda gt11 with antibodies from sheep infected experimentally with S. tenella. This clone, termed STC29, was subcloned and expressed in the vector pGEX-3X as a soluble fusion protein with glutathione S-transferase having an apparent molecular mass of 46 kDa. Antibody raised against the recombinant fusion protein recognized a native polypeptide of 25 kDa in cystozoites of S. tenella. In an ELISA with sera from experimentally infected sheep, the recombinant STC29 antigen could differentiate infections with S. tenella from those with Sarcocystis arieticanis or Toxoplasma gondii. Hence, the research described here reports the identification of the first recombinant S. tenella antigen that may be useful for standardization of a serological test for the diagnosis of S.tenella infections in sheep.