Brown-headed cowbirds (Molothrus ater) harbor Sarcocystis neurona and act as intermediate hosts

Sarcocystis neurona and related Sarcocystis spp. shed by opossums (Didelphis spp.) in South America

Protozoan parasites of the genus Sarcocystis are obligatory heteroxenous cyst-forming coccidia that infect a wide variety of animals and encompass approximately 200 described species. At least four Sarcocystis spp. (S. falcatula, S. neurona, S. lindsayi and S. speeri) use opossums (Didelphis spp.) as definitive hosts, and two of them, S. neurona and S. falcatula, are known to cause disease in horses and birds, respectively. Opossums are restricted to the Americas, but their distribution in the Americas is heterogeneous. Five Didelphis spp. are distributed in South America (D. aurita, D. albiventris, D. marsupialis, D. imperfecta and D. pernigra) whereas just one opossum species (D. virginiana) is found in North America. Studies conducted in the last decades show that Sarcocystis spp., derived from South American Didelphis spp., have biological and genetic differences in relation to Sarcocystis spp. shed by the North American opossum D. virginiana. The aim of this review was to address the peculiar scenario of Sarcocystis species shed by South American opossums, with a special focus on diagnosis, epidemiology, and animal infections, as well as the genetic characteristics of these parasites.

Serologic reactivity of canine sera to Sarcocystis neurona and Sarcocystis cruzi antigens

Sarcocystis neurona, a coccidian parasite shed by opossums (Didelphis spp.) in the Americas, is the major cause of equine protozoal myeloencephalitis (EPM) and induces disease in other domestic and wild animal species, including domestic dogs. Sarcocystis cruzi, despite its low pathogenicity for cattle (intermediate hosts), is worldwide distributed and uses mostly dogs as definitive hosts. The aims of this study were to test serological reactivities of dog sera to S. neurona and S. cruzi antigens, and to investigate potential serological cross-reactivity to these parasites. Sera from 353 Brazilian dogs were obtained from rural areas in the municipality of Ilhéus, Bahia, and examined by immunofluorescent antibody tests (IFAT). Antigens used in serological reactions consisted of S. neurona merozoites from a North American strain (SN138), and bradyzoites of S. cruzi obtained from Brazilian bovine hearts, with parasite species identity confirmed by PCR and sequencing of the 18S gene of the rDNA. Seropositivity to S. neurona and to S. cruzi were detected in 3.39% (12/353) and 4.81% (17/353) of the dogs, respectively. Ten canine sera reacted solely to S. neurona and 15 serum samples reacted only to S. cruzi. Two serum samples were simultaneously positive for both parasites. Sera from 14 dogs that tested positive by IFAT (9 for S. neurona and 3 for S. cruzi) and from two dogs that were negative by IFAT for the two parasites, were examined by Western blot using S. neurona as antigen; these sera reacted to a great number of protein bands, including antigens on the 16 and 30 KDa positions, which encompass immunodominant antigens for S. neurona in horses. Western blot did not show any specific pattern for S. neurona infection/exposure using canine sera. Dogs act as definitive hosts for several Sarcocystis spp. that infect farm animals, including horses, sheep, goats, water buffaloes and pigs, and for this reason, should contain antibodies to a broad repertoire of Sarcocystis spp. antigens. In conclusion, low percentages of dogs from rural areas of Ilhéus, Bahia, were reactive to both S. neurona and S. cruzi antigens. It is possible that other Sarcocystis species, besides S. neurona and S. cruzi, might have contributed for the seropositivity observed in this study. IFAT was more specific than Western blot to differentiate canine serological reactions to S. neurona and S. cruzi antigens.

Prevalence of Sarcocystis calchasi in free-ranging host species: Accipiter hawks and Common Woodpigeon in Germany

The apicomplexan parasite Sarcocystis calchasi (S. calchasi) triggers pigeon protozoal encephalitis, a neurologic disease in columbids. Accipiter hawks have been identified as the final host, and Columbidae and Psittaciformes as intermediate hosts. In this study, 368 free-ranging Accipiter hawks and 647 free-ranging common woodpigeons were sampled in a country-wide study in order to identify the prevalence of S. calchasi in these populations. A semi-nested PCR specific for S. calchasi tested positive in 7.3% (4.9–10.5) of submitted samples from Accipiter hawks. Juvenile Accipiter hawks (13.7%; 7.7–22.0) had a significantly higher infection rate with S. calchasi than adult Accipiter hawks (5.8%; 2.7–9.3). The prevalence of S. calchasi in common woodpigeons was 3.3% (5.4–9.7). Positive pigeons were identified in 14/16 federal states, and a region-dependency was detected, with higher rates of infection in the eastern parts of Germany. The results of this study suggest that the common woodpigeon is a natural reservoir for S. calchasi. In a study of one region for four consecutive years, an increase in prevalence was not detected. Findings indicate that the parasite is not newly introduced to Germany, but rather long established. The prevalence suggests that there is a substantial risk of S. calchasi infections in other free-ranging as well as captive host species.

Sarcocystis neurona and Neospora caninum in Brazilian opossums (Didelphis spp.): Molecular investigation and in vitro isolation of Sarcocystis spp

Sarcocystis neurona and Neospora spp. are protozoan parasites that induce neurological diseases in horses and other animal species. Opossums (Didelphis albiventris and Didelphis virginiana) are definitive hosts of S. neurona, which is the major cause of equine protozoal myeloencephalitis (EPM). Neospora caninum causes abortion in cattle and infects a wide range of animal species, while N. hughesi is known to induce neurologic disease in equids. The aims of this study were to investigate S. neurona and N. caninum in tissues from opossums in the northeastern Brazil, and to isolate Brazilian strains of Sarcocystis spp. from wild opossums for comparison with previously isolated strains. Carcasses of 39 opossums from Bahia state were available for molecular identification of Sarcocystis spp. and N. caninum in their tissues, and for sporocyst detection by intestinal scraping. In addition, Sarcocystis-like sporocysts from nine additional opossums, obtained in São Paulo state, were tested. Sarcocystis DNA was found in 16 (41%) of the 39 opossums' carcasses; N. caninum DNA was detected in tissues from three opossums. The sporocysts from the nine additional opossums from São Paulo state were tested by bioassay and induced infection in nine budgerigars, but in none of the gamma-interferon knockout mice. In vitro isolation was successful using tissues from all nine budgerigars. The isolated strains were maintained in CV-1 and Vero cells. Three of nine isolates presented contamination in cell culture and were discarded. Analysis of six isolates based on five loci showed that these parasites were genetically different from each other and also distinct from S. neurona, S. falcatula, S. lindsayi, and S. speeri. In conclusion, opossums in the studied regions were infected with N. caninum and Sarcocystis spp. and represent a potential source of infection to other animals. This is the first report of N. caninum infection in tissues from black-eared opossum (D. aurita or D. marsupialis) and white-eared opossum (D. albiventris). Brazilian opossums are probably infected by different Sarcocystis spp. distinct from S. neurona and S. falcatula, or present a high level of genetic recombination.

Molecular characterization and development ofSarcocystis speerisarcocysts in gamma interferon gene knockout mice

The North American opossum (Didelphis virginiana) is the definitive host for at least three named species ofSarcocystis: Sarcocystis falcatula, Sarcocystis neuronaandSarcocystis speeri.The South American opossums (Didelphis albiventris, Didelphis marsupialisandDidelphis aurita) are definitive hosts forS. falcatulaandS. lindsayi. The sporocysts of theseSarcocystisspecies are similar morphologically. They are also not easily distinguished genetically because of the difficulties of DNA extraction from sporocysts and availability of distinguishing genetic markers. Some of these species can be distinguished by bioassay;S. neuronaandS. speeriare infective to gamma interferon gene knockout (KO) mice, but not to budgerigars (Melopsittacus undulatus); whereasS. falcatulaandS. lindsayiare infective to budgerigars but not to KO mice. The natural intermediate host ofS. speeriis unknown. In the present study, development of sarcocysts ofS. speeriin the KO mice is described. Sarcocysts were first seen at 12 days post-inoculation (p.i.), and they became macroscopic (up to 4 mm long) by 25 days p.i. The structure of the sarcocyst wall did not change from the time bradyzoites had formed at 50–220 days p.i. Sarcocysts contained unique villar protrusions, ‘type 38’. The polymerase chain reaction amplifications and sequences analysis of three nuclear loci (18S rRNA, 28S rRNAandITS1) and two mitochondrial loci (cox1andcytb) ofS. speeriisolate from an Argentinean opossum (D. albiventris) confirmed its membership among species ofSarcocystisand indicated an especially close relationship to another parasite in this genus that employs opossums as its definitive host,S. neurona.These results should be useful in finding natural intermediate host ofS. speeri.

An update on Sarcocystis neurona infections in animals and equine protozoal myeloencephalitis (EPM)

Equine protozoal myeloencephalitis (EPM) is a serious disease of horses, and its management continues to be a challenge for veterinarians. The protozoan Sarcocystis neurona is most commonly associated with EPM. S. neurona has emerged as a common cause of mortality in marine mammals, especially sea otters (Enhydra lutris). EPM-like illness has also been recorded in several other mammals, including domestic dogs and cats. This paper updates S. neurona and EPM information from the last 15 years on the advances regarding life cycle, molecular biology, epidemiology, clinical signs, diagnosis, treatment and control.

Exposure of free-living jaguars to Toxoplasma gondii, Neospora caninum and Sarcocystis neurona in the Brazilian Pantanal

Toxoplasma gondii, Neospora caninum and Sarcocystis neurona are related apicomplexan parasites that cause reproductive and neurological disorders in a wide range of domestic and wild animals. In the present study, the immunofluorescence antibody test (IFAT) was used to investigate the presence of antibodies against T. gondii, N. caninum and S. neurona in the sera of 11 free-living jaguars (Panthera onca) in two protected areas in the Pantanal region of Mato Grosso state, Brazil. Ten jaguars (90.9%) showed seropositivity for T. gondii, eight (72.7%) for S. neurona, and seven (63.6%) for N. caninum antigens. Our findings reveal exposure of jaguars to these related coccidian parasites and circulation of these pathogens in this wild ecosystem. To the best of our knowledge, this is the first serological detection of N. caninum and S. neurona in free-living jaguars.

Frequency of antibodies against Sarcocystis neurona and Neospora caninum in domestic cats in the state of Bahia, Brazil

Sarcocystis neurona is the major agent of equine protozoal myeloencephalitis. It infects several mammalian species in the Americas, where the definitive hosts, marsupials of the genus Didelphis (D. virginiana and D. albiventris) are found. Domestic cats are one of the confirmed intermediate hosts of the parasite; however, antibodies against S. neurona had never before been demonstrated in Brazilian cats. The aim of this study was to determine whether cats in Bahia, Brazil, are exposed to the parasite. A total of 272 feline serum samples (134 from feral and 138 from house cats) were subjected to an indirect fluorescent antibody test using cultured merozoites of S. neurona as antigen. Positivity was detected in 4.0% (11/272) of the tested samples, with titers ranging from 25 to 800. The feline sera were also tested for antibodies against the protozoan Neospora caninum, with an observed antibody frequency of 2.9%. To the author's knowledge, this is the first study to report antibodies against S. neurona in Brazilian cats. We conclude that cats are exposed to the parasite in the region of this study. Further investigations are needed to confirm the role of cats in the transmission cycle of S. neurona in Brazil.

Modulation of the host Th1 immune response in pigeon protozoal encephalitis caused by Sarcocystis calchasi

Pigeon protozoal encephalitis (PPE) is an emerging central-nervous disease of domestic pigeons (Columba livia f. domestica) reported in Germany and the United States. It is caused by the apicomplexan parasite Sarcocystis calchasi which is transmitted by Accipter hawks. In contrast to other members of the Apicomplexa such as Toxoplasma and Plasmodium, the knowledge about the pathophysiology and host manipulation of Sarcocystis is scarce and almost nothing is known about PPE. Here we show by mRNA expression profiling a significant down-modulation of the interleukin (IL)-12/IL-18/interferon (IFN)-γ axis in the brains of experimentally infected pigeons during the schizogonic phase of disease. Concomitantly, no cellular immune response was observed in histopathology while immunohistochemistry and nested PCR detected S. calchasi. In contrast, in the late central-nervous phase, IFN-γ and tumor necrosis factor (TNF) α-related cytokines were significantly up-modulated, which correlated with a prominent MHC-II protein expression in areas of mononuclear cell infiltration and necrosis. The mononuclear cell fraction was mainly composed of T-lymphocytes, fewer macrophages and B-lymphocytes. Surprisingly, the severity and composition of the immune cell response appears unrelated to the infectious dose, although the severity and onset of the central nervous signs clearly was dose-dependent. We identified no or only very few tissue cysts by immunohistochemistry in pigeons with severe encephalitis of which one pigeon repeatedly remained negative by PCR despite severe lesions. Taken together, these observations may suggest an immune evasion strategy of S. calchasi during the early phase and a delayed-type hypersensitivity reaction as cause of the extensive cerebral lesions during the late neurological phase of disease.

Population genetics of Toxoplasma gondii: new perspectives from parasite genotypes in wildlife

Toxoplasma gondii, a zoonotic protozoal parasite, is well-known for its global distribution and its ability to infect virtually all warm-blooded vertebrates. Nonetheless, attempts to describe the population structure of T. gondii have been primarily limited to samples isolated from humans and domesticated animals. More recent studies, however, have made efforts to characterize T. gondii isolates from a wider range of host species and geographic locales. These findings have dramatically changed our perception of the extent of genetic diversity in T. gondii and the relative roles of sexual recombination and clonal propagation in the parasite's lifecycle. In particular, identification of novel, disease-causing T. gondii strains in wildlife has raised concerns from both a conservation and public health perspective as to whether distinct domestic and sylvatic parasite gene pools exist. If so, overlap of these cycles may represent regions of high probability of disease emergence. Here, we attempt to answer these key questions by reviewing recent studies of T. gondii infections in wildlife, highlighting those which have advanced our understanding of the genetic diversity and population biology of this important zoonotic pathogen.

Self-mating in the definitive host potentiates clonal outbreaks of the apicomplexan parasites Sarcocystis neurona and Toxoplasma gondii

Tissue-encysting coccidia, including Toxoplasma gondii and Sarcocystis neurona, are heterogamous parasites with sexual and asexual life stages in definitive and intermediate hosts, respectively. During its sexual life stage, T. gondii reproduces either by genetic out-crossing or via clonal amplification of a single strain through self-mating. Out-crossing has been experimentally verified as a potent mechanism capable of producing offspring possessing a range of adaptive and virulence potentials. In contrast, selfing and other life history traits, such as asexual expansion of tissue-cysts by oral transmission among intermediate hosts, have been proposed to explain the genetic basis for the clonal population structure of T. gondii. In this study, we investigated the contributing roles self-mating and sexual recombination play in nature to maintain clonal population structures and produce or expand parasite clones capable of causing disease epidemics for two tissue encysting parasites. We applied high-resolution genotyping against strains isolated from a T. gondii waterborne outbreak that caused symptomatic disease in 155 immune-competent people in Brazil and a S. neurona outbreak that resulted in a mass mortality event in Southern sea otters. In both cases, a single, genetically distinct clone was found infecting outbreak-exposed individuals. Furthermore, the T. gondii outbreak clone was one of several apparently recombinant progeny recovered from the local environment. Since oocysts or sporocysts were the infectious form implicated in each outbreak, the expansion of the epidemic clone can be explained by self-mating. The results also show that out-crossing preceded selfing to produce the virulent T. gondii clone. For the tissue encysting coccidia, self-mating exists as a key adaptation potentiating the epidemic expansion and transmission of newly emerged parasite clones that can profoundly shape parasite population genetic structures or cause devastating disease outbreaks.

The parasites Toxoplasma gondii and Sarcocystis neurona have lifecycles that include a sexual stage in a definitive host and an asexual stage in intermediate hosts. For T. gondii, laboratory studies have demonstrated that the sexual stage can serve the dual purpose of producing new, virulent genotypes through recombination and promoting expansion of single clones via self-mating. Self-mating and other life history traits of T. gondii, including transmission of asexual stages among intermediate hosts, are assumed to account for the clonal population genetic structure of this organism. However, the relative contributions of sexual recombination and self-mating verses other life history traits in causing disease outbreaks or in shaping Toxoplasma's population genetic structure have not been verified in nature, nor have these traits been extensively examined in related parasites. To address this knowledge gap, we conducted population genetic analyses on T. gondii and S. neurona strains isolated from naturally occurring outbreaks affecting humans and sea otters, respectively. Our results identify self-mating as a key trait potentiating disease outbreaks through the rapid amplification of a single clone into millions of infectious units. Selfing is likely a key adaptation for enhancing transmission of recently emerged, recombinant clones and reshaping population genetic structures among the tissue-cyst coccidia.

Systemic sarcocystosis in a striped skunk (Mephitis mephitis)

A striped skunk with neurological signs was euthanized and examined via necropsy. Histologically, protozoa were found in multiple tissues. Protozoal schizonts measured 15 to 25 mum in diameter and contained 4 to 6 mum crescent-shaped merozoites. Protozoa were associated with necrosis and inflammation in the lung, brain, liver, and nasal epithelium. Immunohistochemistry labeled protozoa strongly positive for Sarcocystis neurona. Polymerase chain reaction-amplified products from the protozoan were 99.6% identical to the corresponding portion of the nuclear small subunit ribosomal RNA gene of S neurona. S neurona origin was further confirmed by amplifying a 451-base pair DNA fragment from the skunk lung, which differed by just 2 or 3 base pairs from the small subunit ribosomal RNA gene of S neurona. Striped skunks act as intermediate and aberrant hosts for S neurona; however, S neurona has rarely been found in extraneural tissues in any species, and systemic sarcocystosis has not been reported in skunks. Additionally, canine distemper virus infection was confirmed with histopathology and immunohistochemistry. Concurrent canine distemper suggests that immunosuppression may have played a role in S neurona infection in this skunk.

Rhinitis and disseminated disease in a ferret (Mustela putorius furo) naturally infected with Sarcocystis neurona

Naturally occurring Sarcocystis neurona infection in a ferret (Mustela putorius furo) with rhinitis and disseminated disease are described for the first time. The ferret exhibited severe rhinitis with intra-lesional S. neurona merozoites and schizonts. Diagnosis was confirmed immunohistochemically by staining with S. neurona-specific antibodies, and by phylogenetic analyses of conserved and variable portions of nuclear ribosomal DNA. On the basis of intense schizogony in the nasal mucosa, we propose the possibility of an olfactory nerve pathway route of infection for S. neurona meningoencephalitis.

Prevalence and risk factors associated with Sarcocystis neurona infections in opossums (Didelphis virginiana) from central California

Sarcocystis neurona, a protozoal parasite shed by opossums (Didelphis virginiana), has been shown to cause significant morbidity and mortality in horses, sea otters, and other marine mammals. Over the course of 3 years (fall 2005-summer 2008), opossums from central California were tested for infection with S. neurona. Of 288 opossums sampled, 17 (5.9%) were infected with S. neurona based on the molecular characterization of sporocysts from intestinal scrapings or feces. Risk factors evaluated for association with S. neurona infection in opossums included: age, sex, location, season, presence of pouch young in females, concomitant infection, and sampling method (live-trapped or traffic-killed). Multivariate logistic regression analysis identified that opossums in the Central Valley were 9 times more likely to be infected than those near the coast (p=0.009). Similarly, opossum infection was 5 times more likely to be detected during the reproductive season (March-July; p=0.013). This first investigation of S. neurona infection prevalence and associated risk factors in opossums in the western United States can be used to develop management strategies aimed at reducing the incidence of S. neurona infections in susceptible hosts, including horses and threatened California sea otters (Enhydra lutris neries).

Ultrastructural and molecular confirmation of the development of Sarcocystis neurona tissue cysts in the central nervous system of southern sea otters (Enhydra lutris nereis)

In 2004, three wild sea otters were diagnosed with putative Sarcocystis neurona-associated meningoencephalitis by histopathology and immunohistochemistry. Schizonts, free merozoites and tissue cysts were observed in the brains of all three infected animals. Tissue cysts walls from sea otter 1 (SO1) stained positively using anti-S. neurona polyclonal antiserum. However, positive staining does not preclude infection by closely related or cross-reactive tissue cyst-forming coccidian parasites. Two immature tissue cysts in the brain of SO1 were examined using transmission electron microscopy. Ultrastructural features included cyst walls with thin villous projections up to 1 microm long with tapered ends and a distinctive, electron-dense outer lining layer composed of linearly-arranged, semi-circular structures with a "hobnailed" surface contour. Small numbers of microtubules extended down through the villi into the underlying granular layer. Metrocytes were short and plump with an anterior apical complex, 22 sub-pellicular microtubules, numerous free ribosomes and no rhoptries. Some metrocytes appeared to be dividing, with two adjacent nuclear profiles. Collectively these ultrastructural features were compatible with developing protozoal cysts and were similar to prior descriptions of S. neurona tissue cysts. Panspecific 18S rDNA primers were utilized to identify protozoa infecting the brains of these otters and DNA amplification and additional sequencing at the ITS1 locus confirmed that all three otters were infected with S. neurona. No other Sarcocystis spp. were detected in the brains or skeletal muscles of these animals by immunohistochemistry or PCR. We believe this is the first ultrastructural and molecular confirmation of the development of S. neurona tissue cysts in the CNS of any animal.