The phylogeny of Neospora caninum

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.

Comparison of the large subunit ribosomal DNA of Neospora and toxoplasma and development of a new genetic marker for their differentiation based on the D2 domain

The latest release of the large subunit ribosomal database contains 429 sequences, yet only 10 (six nuclear and four mitochondrial) are derived from parasites of the phylum Apicomplexa. Three of these (all Toxoplasma gondii) were previously contained in the 1994 release of the database. As an initiative towards an understanding of ribosomal gene organization in the Apicomplexa, the primary sequence of the large subunit (LSU) rDNA of Neospora caninum is presented, and compared with a consensus sequence derived for the LSU rDNA of T. gondii. Nucleotide differences observed between these two taxa in the D2 expansion segment (or domain) (also called the C1/C1' region) of the LSU rDNA were incorporated into a primer that forms the basis of a species-specific polymerase chain reaction (PCR) for N. caninum. The D2 domain of the LSU rDNA, therefore, represents a new genetic marker that can be used for the differentiation and identification of Neospora from other cyst-forming coccidia.

Toxoplasma gondii sporozoites form a transient parasitophorous vacuole that is impermeable and contains only a subset of dense-granule proteins

Toxoplasma gondii sporozoites form two parasitophorous vacuoles during development within host cells, the first (PV1) during host cell invasion and the second (PV2) 18 to 24 h postinoculation. PV1 is structurally distinctive due to its large size, yet it lacks a tubulovesicular network (C. A. Speer, M. Tilley, M. Temple, J. A. Blixt, J. P. Dubey, and M. W. White, Mol. Biochem. Parasitol. 75:75-86, 1995). Confirming the finding that sporozoites have a different electron-dense-granule composition, we have now found that sporozoites within oocysts lack the mRNAs encoding the 5' nucleoside triphosphate hydrolases (NTPase). NTPase first appears 12 h postinfection. Other tachyzoite dense-granule proteins, GRA1, GRA2, GRA4, GRA5, and GRA6, were detected in oocyst extracts, and antibodies against these proteins stained granules in the sporozoite cytoplasm. In contrast to tachyzoite invasion of host cells, however, sporozoites did not exocytose the dense-granule proteins GRA1, GRA2, or GRA4 during PV1 formation. Even after NTPase induction, these proteins were retained within cytoplasmic granules rather than being secreted into PV1. Only GRA5 was secreted by the sporozoite during host cell invasion, becoming associated with the membrane surrounding PV1. Microinjection of sporozoite-infected cells with fluorescent dyes showed that PV1 is impermeable to fluorescent dyes with molecular masses as small as 330 Da, indicating that PV1 lacks channels through which molecules can pass from the host cytoplasm into the vacuole. By contrast, lucifer yellow rapidly diffused into PV2, demonstrating the presence of molecular channels. These studies indicate that PV1 and PV2 are morphologically, immunologically, and functionally distinct, and that PV2 appears to be identical to the tachyzoite vacuole. The inaccessibility of PV1 to host cell nutrients may explain why parasite replication does not occur in this vacuole.

Cloning and characterization of two recombinant Neospora protein fragments and their use in serodiagnosis of bovine neosporosis

Bovine neosporosis causes fetal abortion and/or congenital neurologic disease in cattle. For the serodiagnosis of this parasitic disease, two immunodominant clones from a bovine Neospora lambda gt11 library were identified, characterized, and expressed as recombinant proteins for the development of an enzyme-linked immunosorbent assay (ELISA). These two clones, designated N54 and N57, were 29 and 20 kDa, respectively, when expressed as histidine fusion proteins from the pRSET expression vector. Antibodies to recombinant protein N54 recognized five major bands from a Neospora tachyzoite lysate with molecular masses of 97, 87, 77, 67, and 64 kDa. Antibodies to recombinant protein N57 recognized four primary bands with molecular masses of 34, 31, 30, and 28 kDa. When a defined "gold standard" panel of bovine sera from confirmed Neospora-positive and Neospora-negative cattle were characterized by immunoblotting, 57 of the 60 Neospora-positive serum samples recognized proteins with the molecular masses of the N54 heptuplet. Binding to the N57 quadruplet was more variable. The same gold standard panel was used to evaluate and compare an N54-based ELISA, an N57-based ELISA, and a whole-tachyzoite lysate-based ELISA. The sensitivities and specificities were 95 and 96% (N54 ELISA), 82 and 93% (N57 ELISA), and 74 and 93% (lysate ELISA). Thus, compared to the whole-tachyzoite lysate-based ELISA, both recombinant-protein-based ELISAs had higher sensitivities and higher or the same specificities and can be used to replace the whole-tachyzoite lysate ELISA for the serodiagnosis of bovine neosporosis.

Investigating phylogenetic relationships within the Apicomplexa using sequence data: the search for homology

Whether stated explicitly or not, all molecular studies that seek to infer "homologies" among sequences or that attempt to determine the "relatedness" of taxa based on sequence comparisons are evolutionary studies. The generation of a reliable evolutionary hypothesis based on molecular sequences is dependent almost exclusively on the ability to align sequences such that bases or amino acids in the same position of two sequences are positionally homologous (i.e., they share the same position in the gene under study). The selection of suitable gene targets (commonly 18S small subunit rRNA gene sequences in the Apicomplexa) and appropriate ingroup and outgroup taxa will affect the ability to align sequences unambiguously. Mathematically derived alignments based on local sequence similarity have been shown to be less reliable than alignments based on conserved secondary structures coupled with an analysis of compensatory base changes. Use of staggered sequence alignments through hypervariable regions of 18S small subunit rRNA gene sequences in which subsets of taxa are aligned independently may permit inclusion of more of the primary sequences with an associated increase in information content in the data set. The use of these highly variable regions is critical for determining the branching order of closely related terminal taxa in the phylum Apicomplexa.

Targeting the secretory pathway of Toxoplasma gondii

Little is known about the extent of conservation in the organization of the secretory pathway in organisms as different as prokaryotes, eukaryotes, and humans. The protozoan parasite Toxoplasma gondii allows easy genetic manipulations, and numerous vectors for selection of transgenic parasites have been developed. One approach to study the molecular mechanism of protein sorting and trafficking is the expression of foreign proteins. Here we describe the design and application of a vector that targets proteins to the secretory pathway of T. gondii and yields high-level expression of Escherichia coli reporter proteins. The general strategies and potential problems in expressing foreign proteins in T. gondii are discussed.

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.

Detection of Neospora from tissues of experimentally infected rhesus macaques by PCR and specific DNA probe hybridization

Neospora is a newly recognized Toxoplasma-like cyst-forming coccidian parasite that causes abortion or congenital infections in naturally or experimentally infected animals. In this study, pregnant rhesus macaques were inoculated with culture-derived tachyzoites of a bovine Neospora isolate, and tissue samples from various major organs were collected from dams and fetuses for the detection of parasite DNA by using oligonucleotide primers COC-1 and COC-2 for PCR amplification of a conserved coccidial nuclear small-subunit rRNA gene sequence, and amplification products were confirmed by hybridization with a Neospora-specific DNA probe. PCR products were amplified from DNAs of different fetal monkey tissues, including brain, heart, lung, liver, spleen, skeletal muscle, skin, and placenta. In addition, Neospora DNA was amplified from the brain, heart, and lung tissues of infected rhesus macaque dams. The PCR and probe hybridization system may provide an effective method for the detection of Neospora infection in fetuses and dams from nonhuman primates and may be useful in determining the zoonotic potential of Neospora.

Experimental infection of non-pregnant and pregnant sheep with Neospora caninum

In an initial experiment, 21 sheep in groups of five or six were inoculated subcutaneously (sc) with 10(8), 10(6) or 10(4) Neospora caninum tachyzoites (Liverpool isolate), or with control inoculum, and monitored for clinical signs and for "seroconversion". Animals given the two higher doses showed febrile responses and all three groups inoculated with the parasite showed seroconversion. In a second experiment, 12 pregnant sheep were each inoculated sc at 90 days' gestation with 10(6) tachyzoites, and at 25, 40 and 53 days post-inoculation (dpi) groups of four were killed for examination of the fetuses and placentas. Appropriate control ewes were included in the study. All fetuses were alive immediately before their dams were killed, except for one, which was found to be mummified at 40 dpi. Histopathological lesions were found consistently in both fetal central nervous system (CNS) and placental tissues. In the latter, focal necrosis, which was mild at 25 dpi, was much more severe at 40 dpi and much less severe at 53 dpi. Lesions in the fetal CNS consisted of focal microgliosis (with or without central necrosis), lymphoid cuffing and non-suppurative meningitis. Lesions were also found in fetal liver, heart and lung. Neospora antigen was demonstrated in fetal brain and placental tissues and, at 25 dpi, in single samples of fetal liver and heart. The prescapular lymph nodes did not differ in size from those of control fetuses but were more mature in that they contained a significantly greater number of secondary follicles. Both IgM and IgG antibodies to N. caninum were detected in the serum of fetuses from infected ewes. Thus, N. caninum readily infected pregnant ewes and caused lesions in fetal tissues and placentas which resembled those of ovine toxoplasmosis. In addition, the changes were similar to those of bovine neosporosis; the infected pregnant ewe therefore offers a good model for the bovine disease.

Serological response over time to recombinant Neospora caninum antigens in cattle after a neosporosis-induced abortion

Recombinant Neospora caninum tachyzoite antigens were evaluated in an enzyme-linked immunosorbent assay (ELISA) for recognition by serum antibodies (Ab) from Neospora-infected cattle. Serum samples were obtained every 2 to 3 weeks for 8 to 15 months from 10 cows with histories of Neospora-associated abortion. Serum samples were also obtained from offspring of these animals and from a large number of cows that had aborted a fetus, due to infection by Neospora or other organisms, at various times during gestation. All 10 cows had positive ELISA Ab titers to both recombinant N. caninum tachyzoite antigens after abortion, during subsequent gestation, and after parturition. In three cows, there was a noticeable peak in Ab titers early in gestation. Calves born to Neospora-infected cows also had positive titers of Ab to the recombinant tachyzoite antigens, and these titers remained elevated for at least 4 months after birth. A portion of the serum immunoglobulin in calves may have been derived from colostrum of infected cows. A calf born from a seronegative mother had a positive ELISA titer only after being fed colostrum from a seropositive cow. However, precolostral titers in calves born from Neospora-infected cows were high at birth, suggesting that the parasite was transmitted to the fetus via the placenta and induced a humoral immune response therein. The recombinant tachyzoite antigens were also useful for corroborating clinical diagnoses of Neospora-induced abortion. A significant difference (P < 0.05) between anti-recombinant antigen Ab titers in cows that aborted due to Neospora and those in cows that aborted from other causes was found.

Phylogenetic relationships of entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) inferred from partial 18S rRNA gene sequences

Aligned 265-bp sequences of partial 18S rRNA gene were used to infer phylogenetic relationships among entomopathogenic nematodes by using maximum parsimony and likelihood methods. Phylogenetic analyses support Heterorhabditidae and Steinernematidae belonging to different monophylies. There was more sequence divergence in Steinernema species than in Heterorhabditis species. These results are congruent with the phylogenies based on morphological, life cycle, and distributional evidence. Examination of all trees within 1% of the length of the most parsimonious trees and bootstrap analyses support most relationships among Steinernema species but the relationships among Heterorhabditis species were not supported. We suggest that the partial 18S rRNA gene sequences may be too conserved for phylogenetic inference among Heterorhabditis species, but are well suited for phylogenetic inference within and among closely related families and genera of entomopathogenic nematodes and for inferring phylogenetic relationships among Steinernema species.

Bovine fetal neosporosis: a comparison of epizootic and sporadic abortion cases and different age classes with regard to lesion severity and immunohistochemical identification of organisms in brain, heart, and liver

Eighty bovine fetuses with confirmed neosporosis were used to score lesion severity and presence of parasites in brain, heart, and liver. A comparison was made between epizootic and sporadic abortion cases. The possible influence of fetal age was also investigated. Histologic lesions of multifocal encephalitis, myocarditis, and periportal hepatitis with or without focal hepatocellular necrosis were almost always observed. Neospora caninum tachyzoites were identified immunohistochemically in 85% of the brains, 14% of the hearts, and 26% of the livers. Tissue cysts were observed in 21% of the brains. Significant differences between epizootic and sporadic abortion cases were found only in the liver. Hepatic lesions were more prominent and N. caninum tachyzoites were observed more frequently and in higher numbers in epizootic cases. Examination by immunohistochemistry of the liver in addition to the brain can be highly contributive diagnostically, particularly in epizootic cases. There were no significant age-related differences except for a higher presence of tachyzoites in the hearts of younger fetuses (3-4 months gestational age).

Novel ELISA for detection of Neospora-specific antibodies in cattle

An enzyme-linked immunosorbent assay (ELISA) to detect antibodies to Neospora species in cattle was developed. Whole formalin-fixed Neospora caninum (NC-Liverpool) tachyzoites were used as antigen and a monoclonal antibody to bovine immunoglobulin light chain and an anti-mouse horseradish peroxidase conjugate were used to reveal bound antibody. A panel of 46 sera, negative by the immunofluorescent antibody test (IFAT), were used in the ELISA at a serum dilution of 1:500 to calculate the negative cut-off value of OD405 = 0.77. There was a 95 per cent agreement between the results of the ELISA and the IFAT with 104 serum samples. The specificity and sensitivity of the ELISA were 96 per cent and 95 per cent, respectively, when compared with the IFAT. No significant cross-reaction was observed with the sera from cattle infected experimentally with Toxoplasma gondii, Cryptosporidium parvum, Babesia divergens, Sarcocystis cruzi, Eimeria alabamensis or E bovis. A significantly modified version of the test is now commercially available.

Herd-based diagnosis of Neospora caninum-induced endemic and epidemic abortion in cows and evidence for congenital and postnatal transmission

Aborting and nonaborting cows and their dams or daughters were studied to determine if herd abortion problems were associated with the presence of Neospora caninum antibodies and to estimate when aborting cows may have acquired the infection. Cows were sampled from 20 herds that had experienced an abortion epidemic presumed to have been caused by N. caninum and from 2 herds experiencing endemic abortion. Seroprevalence for 14 herds experiencing an epidemic ranged from 7% to 70%, as estimated by enzyme-linked immunosorbent assay. A strong association between seropositivity and abortion was found for only 5 of 14 herds with a presumed diagnosis of N. caninum abortion (P < or = 0.015, lower 95% confidence interval of odds ratio > or = 1.2), indicating N. caninum may be overdiagnosed as the cause of an abortion epidemic in some herds. No association was found between dam and daughter seropositivity for herds experiencing an epidemic (P > or = 0.17), suggesting that most cows aborting during an epidemic were infected postnatally. For the 2 herds with endemic abortion (A, B), odds of an aborting cow having N. caninum antibodies were 3.4-fold (herd A) and 7.0-fold (herd B) higher than odds for nonaborting cows (P < or = 0.05). Cows that aborted a fetus infected with N. caninum were more likely to have had a previous seropositive daughter than were nonaborting seronegative cows (P < or = 0.0025), suggesting that infection had been acquired before conception of the aborted fetus.

A review of Neospora caninum and neosporosis

Neospora caninum is a recently recognized protozoan parasite of animals, which until 1988 was misidentified as Toxoplasma gondii. Its life cycle is unknown. Transplacental transmission is the only recognized mode of transmission. It has a wide host range, but its zoonotic potential is unknown. Neosporosis is a major cause of abortion in cattle in many countries. It is also an important cause of neuromuscular paralysis in dogs. This paper reviews information on parasite structure, life cycle, biology, clinical signs, diagnosis, treatment and control.

Serological diagnosis of bovine neosporosis by Neospora caninum monoclonal antibody-based competitive inhibition enzyme-linked immunosorbent assay

Neospora caninum, a protozoan parasite closely related to Toxoplasma gondii, causes abortion and congenital infection in cattle. To investigate specific methods of antemortem diagnosis, the antibody responses of infected cows were evaluated by immunoblot assay and competitive inhibition enzyme-linked immunosorbent assay (CI-ELISA) by using a monoclonal antibody (MAb), MAb 4A4-2, against N. caninum tachyzoites. MAb 4A4-2 bound diffusely to the exterior surface of N. caninum tachyzoites and recognized a single 65-kDa band in immunoblots. MAb 4A4-2 was unreactive to antigens of two closely related apicomplexan protozoa, Toxoplasma gondii and Sarcocystis cruzi. Binding of MAb 4A4-2 was inhibited by mild periodate treatment of N. caninum antigen, demonstrating the carbohydrate nature of the epitope. Immunoblot analysis of N. caninum tachyzoite antigens with sera from cows with confirmed Neospora-induced abortion revealed at minimum 14 major antigens ranging from 11 to 175 kDa. Although the recognized antigens varied from cow to cow, antigens of 116, 65, and 25 kDa were detected in all cows with abortion confirmed to be caused by N. caninum. The binding of MAb 4A4-2 to N. caninum tachyzoite antigen was consistently inhibited by sera from Neospora-infected cows in a CI-ELISA format and was not inhibited by sera from Neospora antibody-negative cows. Furthermore, sera from cattle experimentally infected with T. gondii, S. cruzi, Sarcocystis hominis, or Sarcocystis hirsuta, which had cross-reactive antibodies recognizing multiple N. caninum antigens by immunoblot assay, did not inhibit binding of MAb 4A4-2 in the CI-ELISA. Thus, MAb 4A4-2 binds a carbohydrate epitope on a single N. caninum tachyzoite surface antigen that is recognized consistently and specifically by Neospora-infected cattle.

Phylogenetic tree-building

Cladistic analysis is an approach to phylogeny reconstruction that groups taxa in such a way that those with historically more-recent ancestors form groups nested within groups of taxa with more-distant ancestors. This nested set of taxa can be represented as a branching diagram or tree (a cladogram), which is an hypothesis of the evolutionary history of the taxa. The analysis is performed by searching for nested groups of shared derived character states. These shared derived character states define monophyletic groups of taxa (clades), which include all of the descendants of the most recent common ancestor. If all of the characters for a set of taxa are congruent, then reconstructing the phylogenetic tree is unproblematic. However, most real data sets contain incongruent characters, and consequently a wide range of tree-building methods has been developed. These methods differ in a variety of characteristics, and they may produce topologically distinct trees for a single data set. None of the currently-available methods are simultaneously efficient, powerful, consistent and robust, and thus there is no single ideal method. However, many of them appear to perform well under a wide range of conditions, with the exception of the UPGMA method and the Invariants method.

Identification of bovine Neospora parasites by PCR amplification and specific small-subunit rRNA sequence probe hybridization

Neospora is a newly recognized genus of pathogenic coccidia, closely related to Toxoplasma gondii, that can cause abortion or congenital disease in a variety of domestic animal hosts. On the basis of the small-subunit rRNA gene sequences of Neospora spp. and other apicomplexa coccidia, oligonucleotide primers COC-1 and COC-2 were used for PCR amplification of conserved sequences of approximately 300 bp in size. A Neospora-specific chemiluminescent probe hybridized to Southern blots of amplification products from Neospora DNA but not to Southern blots with amplified DNA from the other coccidian parasites tested. A Toxoplasma-specific probe whose sequence differed from that of the probe for Neospora spp. by a single base pair was used to distinguish these parasites by specific Southern blot hybridization. The PCR system detected as few as one Neospora tachyzoite in the culture medium or five tachyzoites in samples of whole blood or amniotic fluid spiked with Neospora parasites. In addition, Neospora PCR products were successfully amplified from whole blood and amniotic fluid samples of experimentally infected bovine and rhesus macaque fetuses. These results indicate that this PCR and probe hybridization system could be a valuable adjunct to serology and immunohistochemistry for the diagnosis of Neospora infections in bovine or primate fetuses.

Codon usage in Cryptosporidium parvum differs from that in other Eimeriorina

Codon usage of Crytosporidium parvum was compared with those of other Eimeriorina Toxoplasma gondii and Eimeria tenella and revealed a biased use of synonymous codons with a preference for NNU (40.0%) and NNA (33.4%). There was no close resemblance of the codon usage of C. parvum to T. gondii (correlation coefficient, r = 0.14) or E. tenella (r = 0.14) but it was similar to Entamoeba histolytica (r = 0.75) and Plasmodium falciparum (r = 0.5). Analysis of the codon usage in homologous gene sequences (actin, beta-tubulin) also failed to reveal a close relationship between C. parvum and T. gondii or E. tenella. The low usage codons in C. parvum were most frequently used codons in T. gondii and E. tenella. These observations are consistent with 18S rRNA sequence analysis which shows no close relationship of Cryptosporidium with other Eimeriorina (Sarcocystis, Toxoplasma and Eimeria) and questions the validity of the current classification of C. parvum.

The ultrastructure of bradyzoites and tissue cysts of Neospora caninum in dogs: absence of distinguishing morphological features between parasites of canine and bovine origin

The fine structure of bradyzoites and tissue cysts of Neospora caninum in dogs is described. Original findings consisting of branching, septa-like structures of the cyst wall and peculiar, lipid-like inclusions in the cyst ground substance were described. Tubulo-vesicular structures in the cyst ground substance and distinctive, vesicular organelles containing short, membranous segments and smaller vesicles, described in Neospora parasites of bovine origin and previously undescribed in parasites of canine origin, were also observed. The findings in this study indicate that there are no distinct ultrastructural morphological criteria differentiating N. caninum in dogs and the Neospora-like protozoan of cattle. The previously reported morphological distinction between parasites of canine and bovine origin may be attributed to the relatively small numbers of tissue cysts examined, differences in tissue fixation and processing, and variation in developmental stage of the parasites examined.

Rapid and sensitive identification of Neospora caninum by in vitro amplification of the internal transcribed spacer 1

Neospora caninum and N. caninum-like organisms are cyst-forming coccidian parasites known to cause neuromuscular disorders in dogs and abortion in cattle. In this article we report on the use of the polymerase chain reaction (PCR) for the detection of DNA from N. caninum. After determining the sequence of the internal transcribed spacer 1 (ITS1) of N. caninum and Toxoplasma gondii, and part of the sequences for 4 species of Sarcocystis, we designed a primer set for the amplification of a 279-base-pair fragment of ITS1 from N. caninum. The PCR system made possible the specific detection of 5 N. caninum organisms and no amplification was observed from any of the other cyst-forming coccidia tested, including the closely related T. gondii. Furthermore, we were also able to demonstrate the presence of N. caninum in brain and lung tissue samples from experimentally infected mice. Our data also link the 5.8S rRNA gene for T. gondii and N. caninum to the 16S-like rRNA gene, within the rDNA unit.

Adhesion and invasion of bovine endothelial cells by Neospora caninum

Neospora caninum is a recently identified coccidian parasite which was, until 1988, misdiagnosed as Toxoplasma gondii. It causes paralysis and death in dogs and neonatal mortality and abortion in cattle, sheep, goats and horses. The life-cycle of Neospora has not yet been elucidated. The only two stages identified so far are tissue cysts and intracellularly dividing tachyzoites. Very little is known about the biology of this species. We have set up a fluorescence-based adhesion/invasion assay in order to investigate the interaction of N. caninum tachyzoites with bovine aorta endothelial (BAE) cells in vitro. Treatment of both host cells and parasites with metabolic inhibitors determined the metabolic requirements for adhesion and invasion. Chemical and enzymatic modifications of parasite and endothelial cell surfaces were used in order to obtain information on the nature of cell surface components responsible for the interaction between parasite and host. Electron microscopical investigations defined the ultrastructural characteristics of the adhesion and invasion process, and provided information on the intracellular development of the parasites.

Development of a polymerase chain reaction assay for the diagnosis of neosporosis using the Neospora caninum 14-3-3 gene

Neospora caninum is a recently described apicomplexan parasite which causes neuromuscular disease in dogs, and abortion and neonatal morbidity in cattle, sheep and horses. Morphological similarities and serological cross-reactivity between N. caninum and the closely related parasite Toxoplasma gondii, have resulted in the frequent misdiagnosis of neosporosis as toxoplasmosis. This report describes the isolation and characterization of an N. caninum cDNA clone encoding a 14-3-3 protein homologue. The 14-3-3 proteins are a class of proteins which show a high degree of amino acid sequence conservation across several eukaryotic taxa. Using less conserved regions of the N. caninum cDNA clone, nested primers were designed for the amplification of a 614-bp N. caninum DNA fragment by the polymerase chain reaction (PCR). The DNA fragment was amplified from N. caninum genomic DNA, but not from T. gondii, Sarcocystis muris, Sarcocystis tenella, or Sarcocystis cruzi genomic DNA. Additionally, the fragment was amplified from DNA prepared from the brains of N. caninum-infected mice, but not from the brain of a mouse infected with T. gondii. These results suggest that this PCR assay may be useful for the diagnosis of neosporosis.

Characterization of the first European isolate of Neospora caninum (Dubey, Carpenter, Speer, Topper and Uggla)

Neospora caninum is an apicomplexan, protozoan parasite, which causes severe disease in dogs and cattle. It has previously been isolated only in the United States. A 5-week-old Boxer pup with a progressive hindlimb paresis was diagnosed as suffering from neosporosis on the basis of clinical signs and the presence of anti-Neospora antibodies in it, 2 litter-mates and its dam. Despite treatment with sulphonamides, the pup was euthanased 3 days later. The diagnosis of neosporosis was confirmed by immunohistochemical examination of muscle and CNS tissue sections from the pup. Parasites were isolated into Vero cell culture from the cerebrum, and confirmed as Neospora caninum by immunofluorescence with specific antibody, tachyzoite ultrastructure and 16S-like ribosomal RNA sequences. This isolate (designated NC-Liverpool) has been continuously passaged every 7-10 days. Its growth characteristics, ultrastructure and antigenic profile, as revealed by immunoblotting, have revealed no major differences from the American NC-1 isolate. Furthermore, no difference was seen when comparing the sequences of 16S-like ribosomal RNA and the ITS1 region of the two isolates.

Current research on Sarcocystis species of domestic animals

The genus Sarcocystis is composed of about 130 species of heteroxenous cyst-forming coccidia with differences in life cycle and pathogenicity. Pathogenic Sarcocystis spp. can cause disease in their intermediate hosts, in particular in ruminants. Research on Sarcocystis infections has been impeded by several facets of the parasites. Intermediate as well as definitive hosts can be parasitized by several different species with similarities in biology and morphology. Antigen preparations derived from pathogenic Sarcocystis spp. are highly cross-reactive with antibodies directed against non-pathogenic species. As a consequence, none of the currently available immunological tests is species-specific and can differentiate between pathogenic and non-pathogenic Sarcocystis spp. Over the last decade, new techniques in immunology, protein chemistry and molecular biology have facilitated more advanced studies on the molecular composition and molecular biology of Sarcocystis spp. in various laboratories. The development of species-specific monoclonal antibodies and analyses of the molecular composition of some life-cycle stages of Sarcocystis spp. of cattle and sheep showed that species-specific proteins and antigens exist in these species, although they are not highly abundant. In addition, comparisons of rRNA genes of different Sarcocystis spp. identified unique sequences in the rRNA of pathogenic Sarcocystis spp. that are suitable targets for species-specific identification. Thus, tools have become available that facilitate the development of methods for species-specific identification and differentiation of Sarcocystis spp. as well as the identification and study of molecules that are associated with pathogenicity of some of these parasites.

Interferon gamma inhibits the intracellular multiplication of Neospora caninum, as shown by incorporation of 3H uracil

An assay was developed to quantify the growth of two different isolates of the protozoon Neospora caninum within ovine fibroblast cells in vitro by differential uptake of 3H uracil. The NC-1 isolate of N. caninum multiplied more quickly in culture than the NC Liverpool isolate, as reflected by increased incorporation of isotope by the former over a shorter period of time. After the parasites had left the ruptured host cells, there was very little incorporation of isotope. This suggested that multiplication occurred within and not outside the cells. Treatment of the cells with ovine recombinant interferon gamma for 24 h before infection significantly inhibited intracellular multiplication of the parasite.

Evolutionary origin of Plasmodium and other Apicomplexa based on rRNA genes

We have explored the evolutionary history of the Apicomplexa and two related protistan phyla, Dinozoa and Ciliophora, by comparing the nucleotide sequences of small subunit ribosomal RNA genes. We conclude that the Plasmodium lineage, to which the malarial parasites belong, diverged from other apicomplexan lineages (piroplasmids and coccidians) several hundred million years ago, perhaps even before the Cambrian. The Plasmodium radiation, which gave rise to several species parasitic to humans, occurred approximately 129 million years ago; Plasmodium parasitism of humans has independently arisen several times. The origin of apicomplexans (Plasmodium), dinoflagellates, and ciliates may be > 1 billion years old, perhaps older than the three multicellular kingdoms of animals, plants, and fungi. Digenetic parasitism independently evolved several times in the Apicomplexa.

Phylogenetic relationships between Toxoplasma and Sarcocystis deduced from a comparison of 18S rDNA sequences

The current taxonomy of parasites in the genus Sarcocystis is largely based on morphological characteristics as well as on host specificity and life-cycle structure. Recently, phylogenetic analyses of partial ribosomal RNA (rRNA) sequences provided support for paraphyly of Sarcocystis. We have tested the validity of this hypothesis by sequencing the complete 18S rRNA genes of Sarcocystis arieticanis, Sarcocystis gigantea and Sarcocystis tenella and comparing them with gene sequences derived from other taxa of the phylum Apicomplexa. The results obtained from this study do not reject the hypothesis of monophyly of Sarcocystis species, although the bootstrap data were inconclusive for some species.

Identification of Eimeria bovis merozoite cDNAs using differential mRNA display

Differences in gene expression between Eimeria bovis sporozoites and first-generation merozoites were analyzed using the technique of differential mRNA display. Approx. 5% of the sequences detected in first-generation merozoites appear to be unique relative to sporozoites. Several of the bands corresponding to merozoite-specific gene expression were isolated and cloned. Northern blot analysis revealed that the cDNA fragments DMZ-7, DMZ-8 and NMZ-6 hybridized to mRNAs expressed at > 50-fold higher levels in merozoites relative to sporozoites. A fourth cDNA fragment, NMZ-4, hybridized to a mRNA expressed at 3-fold higher levels in merozoites. Further characterization demonstrated that expression of DMZ-8 in E. bovis-infected bovine cells begins as early as 12 h after sporozoite invasion and continues throughout the entire 14 days of first-generation schizogony. Sequence analysis of each of the four merozoite cDNAs failed to identify any significant similarity to any entries in the GenBank database, suggesting that these developmentally regulated genes may be unique to coccidian parasites.

Genetic comparison of Neospora caninum with Toxoplasma and Sarcocystis by random amplified polymorphic DNA-polymerase chain reaction

To determine the relationship of Neospora caninum to protozoa classified in the family Sarcocystidae of the phylum Apicomplexa, the genomes of N. caninum, three Toxoplasma gondii strains (RHa, CEP, TPR) and three Sarcocystis species (S. tenella, S. muris, S. gigantea) that were thought to be closely related coccidia were compared by the random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) technique. The genomic DNAs were amplified by the use of seven 10-mer arbitrary sequence primers to generate polymorphic DNA. Significant DNA polymorphisms were observed among Neospora, Toxoplasma and Sarcocystis. It appears that one primer tested may have value in a diagnostic RAPD-PCR to differentiate T. gondii from other closely related protozoa. The high level of genetic divergence of N. caninum from T. gondii strains and several Sarcocystis species observed in this study is consistent with the hypothesis that N. caninum is indeed an independent species of protozoan parasite. As compared with the Sarcocystis species tested, a closer genetic relationship of N. caninum to T. gondii was not observed. By contrast, a closer genetic relationship of S. muris to T. gondii was revealed in this study.

Effects of sequence alignment on the phylogeny of Sarcocystis deduced from 18S rDNA sequences

The family Sarcocystidae contains a wide variety of parasitic protozoa, some of which are important pathogens of livestock and humans. The taxonomic relationships between two of the genera in this family (Toxoplasma and Sarcocystis) have been debated for a number of years and remain controversial. Recent studies, from comparisons of 18S rDNA-sequence data, have suggested that Sarcocystis is paraphyletic, although a hypothesis supporting monophyly of Sarcocystis could not be rejected. The present study shows that the phylogenetically informative nucleotide positions within the 18S rDNA are primarily located in the regions that make up the helices in the secondary structure of the 18S rRNA. A phylogenetic analysis of 18S rDNA-sequence data aligned by secondary structure constraints, or a subset of the data corresponding to all nucleotides found in the helices, provide unambiguous evidence supporting monophyly of Sarcocystis.