Molecular phylogeny of Besnoitia and the genetic relationships among Besnoitia of cattle, wildebeest and goats

Knowledge on parasites of the genus Besnoitia is sparse, which are classified in the subfamily Toxoplasmatinae of the phylum Apicomplexa. This arrangement hypotheses that Besnoitia represents the sister group to species such as Toxoplasma gondii and Hammondia hammondi. In order to test this hypothesis, phylogenetic analyses of 18S ribosomal DNA (rDNA) from Besnoitia, Hammondia, Isospora, Frenkelia, Eimeria, Neospora, Sarcocystis and Toxoplasma were performed. The 18S rDNA of Besnoitia besnoiti, Besnoitia jellisoni and Eimeria alabamensis were amplified by PCR and sequenced. Phylogenetic analyses by parsimony and maximum-likelihood methods showed Besnoitia to be reproducibly the sister group to a clade containing Hammondia, Neospora and Toxoplasma. Furthermore, Besnoitia of cattle, wildebeest and goats had identical ITS1 rDNA sequences, which questions the use of the taxon Besnoitia caprae to describe the Besnoitia found in goats.

Evolution of ruminant Sarcocystis (Sporozoa) parasites based on small subunit rDNA sequences

We present an evolutionary analysis of 13 species of Sarcocystis, including 4 newly sequenced species with ruminants as their intermediate host, based on complete small subunit rDNA sequences. Those species with ruminants as their intermediate host form a well-supported clade, and there are at least two major clades within this group, one containing those species forming microcysts and with dogs as their definitive host and the other containing those species forming macrocysts and with cats as their definitive host. Those species with nonruminants as their intermediate host form the paraphyletic sister group to these clades. Most of the species have considerable genotypic differences (differing in more than 100 nucleotide positions), except for S. buffalonis and S. hirsuta. There is a large suite of genotypic differences indicating that those species infecting ruminant and nonruminant hosts have had very different evolutionary histories, and similarly for the felid- and canid-infecting species. Furthermore, the rDNA sequences that represent the different structural regions of the rRNA molecule have very different genotypic behavior within Sarcocystis. The evolution of these regions should be functionally constrained, and their differences can be explained in terms of the importance of the nucleotide sequences to their functions.

Oral Neospora caninum inoculation of neonatal calves

Four calves born to cows seronegative for Neospora caninum were dosed orally within 6 h after birth with tachyzoites of the bovine N. caninum Nc-SweB1 isolate added to colostrum. Two of the calves were dosed via stomach tube and two by feeding bottle. The latter two calves showed transient fever and passed blood-stained diarrhoea 1-2 weeks after inoculation. From 5 weeks after inoculation they developed a significant antibody response which remained high until the calves were euthanised and necropsied at 15 and 19 weeks after inoculation, respectively. The two calves inoculated by stomach tube showed no clinical signs and they remained seronegative throughout the study. At necropsy of the seropositive calves, no pathological lesions were seen, and parasites were not detected by immunohistochemistry. Neospora caninum was not re-isolated in cell culture from the brains of the seropositive calves; however, N. caninum DNA was detected in brain from both of them by PCR. The data suggest that oral infection of N. caninum via colostrum might be a possible route of vertical transmission in newborn calves, in addition to transplacental infection.

An indirect enzyme-linked immunoassay (ELISA) for demonstration of antibodies to Neospora caninum in serum and milk of cattle

An indirect enzyme-linked immunosorbent assay (ELISA) for detection of antibodies to Neospora caninum in serum from cattle is described. Extracted tachyzoite proteins incorporated into immunostimulating complexes (iscoms) were used as coating antigen and a mouse monoclonal antibody to bovine immunoglobulin G1 as conjugate. Western blot analysis of the iscom preparation revealed a restricted number of antigens compared with whole parasite homogenates. When probed with a serum from an experimentally infected calf, heavily stained antigens with apparent molecular masses of 28, 35, 45 and 78 kDa were seen. The sensitivity and specificity of the ELISA was 100% and 96%, respectively, against an indirect fluorescent antibody test as indicator of true status. The applicability of the ELISA for demonstration of antibodies in milk was evaluated and the agreement between serum and milk ELISA was 95%.

Characterization of a Swedish bovine isolate of Neospora caninum

The brain of a stillborn calf, seropositive to Neospora caninum and born to a seropositive cow, was homogenized and cultured on Vero cells, where growth of Neospora-like tachyzoites was detected after 8 weeks. The ultrastructural features of the new isolate (Nc-SweB1) corresponded to those of previously published Neospora isolates. In indirect immunofluorescence tests, antigens on Nc-SweB1 tachyzoites were recognized by antibodies raised to a canine N. caninum isolate (Nc-1) but not by antibodies to Toxoplasma gondii, Sarcocystis cruzi, S. tenella, Eimeria alabamensis, Babesia divergens, or B. motasi. Immunoblot analyses revealed no major antigenic difference between Nc-SweB1 and Nc-1, whereas several differences were seen between Nc-SweB1 and protozoa related to N. caninum. The sequences of 16S-like rRNA and the internal transcribed spacer 1 of Nc-SweB1 revealed complete homology with corresponding sequences of two canine N. caninum isolates. Thus, no dissimilarity between Nc-SweB1 and the canine isolates was found, confirming that Nc-SweB1 is N. caninum and suggesting that Neospora-like organisms isolated from cattle are indeed N. caninum.

Discrimination of Neospora caninum from Toxoplasma gondii and other apicomplexan parasites by hybridization and PCR

Neospora caninum is a protozoan parasite which causes neurological problems in dogs and abortion in cattle. As N. caninum is difficult to distinguish morphologically from Toxoplasma gondii, we developed a molecular tool capable of discriminating between the two parasites. Genomic DNA was isolated from in vitro cultured N. caninum tachyzoites and cloned into a plasmid vector. Resulting colonies were subsequently screened by differential hybridization using N. caninum and T. gondii DNA. Two clones were characterized in detail: one clone, termed pNc5, was found to be specific for N. caninum whereas the second clone, pNc1, hybridized with DNA from both parasites. The sequence of pNc5 was determined and different oligonucleotide primers were designed for use in the polymerase chain reaction (PCR). A 944 bp fragment was specifically amplified from N. caninum DNA, but not from DNA extracted from T. gondii or different Sarcocystis species. Positive signals in PCR were obtained with as little as 100 pg parasite template DNA. In addition, dual PCR with primer pairs specific for N. caninum and T. gondii allowed the detection of either parasite in mixed samples.

Neospora species infection in a herd of dairy cattle

OBJECTIVE

To investigate the route of transmission of Neospora sp in a herd of dairy cattle in which sporadic abortions had been observed since the establishment of the farm in 1980.

DESIGN

Serum samples were screened for antibodies to Neospora sp, and records from an artificial insemination program were analyzed.

ANIMALS

58 female cattle.

PROCEDURE

An ELISA was used to screen serum samples of antibodies to Neospora sp. Fertility, calf mortality, and relationships between specific cattle were investigated. Statistical analysis was performed on the fertility data.

RESULTS

Antibodies were detected in 17 of 58 (29%) tested cattle. All seropositive cattle were descendants of 2 cows purchased in 1980. Cattle that were descendants of those 2 cows were compared with their herdmates, but significant differences were not detected in the number of inseminations per confirmed pregnancy or in the number of cattle that required more than 1 insemination/ pregnancy. Since 1980, there were 323 confirmed pregnancies in the herd, and calf mortality (prenatal and perinatal mortality) was 24 of 323 (7%).

CLINICAL IMPLICATIONS

Congenital transmission of Neospora organisms together with the apparent lack of horizontal transmission observed in the herd reported here indicated that Neospora sp has the ability to be transmitted from dam to offspring for several generations. This mode of transmission would explain the maintenance of infection in a population of cattle despite the lack of a definitive host for the parasite.

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.

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.

A case of Neospora associated bovine abortion in Sweden

Neospora caninum is a recently recognized protozoan organism that causes fatal neuromuscular disease in dogs and abortions and stillbirths in cattle and other animals (Dubey & Lindsay 1993). The parasite is morphologically similar and phylogenetically very closely related to the cyst-forming coccidium Toxoplasma gondii (Ellis et al. 1994, Holmdahl et al. 1994). This group of parasites has a two-host life cycle principally involving a carnivorous definitive host and a herbivorous or omnivorous intermediate host. However, with N. caninum, there is as yet no knowledge of any definitive host harbouring sexual stages of the parasite. The only known route of transmission is vertical from mother to foetus (Dubey & Lindsay 1993).

The phylogeny of Neospora caninum and Toxoplasma gondii based on ribosomal RNA sequences

Neospora caninum is a newly described cyst-forming coccidium which is the cause of severe neurological disease in dogs. The parasite is morphologically similar to Toxoplasma gondii, but the two species can be differentiated serologically. In order to define the phylogenetic position of N. caninum, we have determined 16S-like rRNA sequences from three members of the family of Sarcocystidae: N. caninum, T. gondii, and Sarcocystis fusiformis. The 16S-like rRNA genes from the three parasites were amplified by polymerase chain reaction and the sequences were determined by direct solid-phase sequencing. The sequences derived were computer aligned with several other 16S-like rRNA sequences from protozoan parasites to construct phylogenetic trees. The study confirmed that N. caninum should be classified as a member of the family Sarcocystidae. However, because of the close relationship to T. gondii it seems questionable that N. caninum should be placed in a new genus.

Oligonucleotide probes complementary to variable regions of 18S rRNA from Sarcocystis species

Sarcocystis is a large genus of cyst-forming coccidian parasites in the phylum Apicomplexa (Protista). Stable RNA was extracted from cystozoites of Sarcocystis cruzi, S. tenella, S. fusiformis, S. gigantea and Toxoplasma gondii. The partial sequences of the small sub-unit ribosomal RNA (18S rRNA) were determined by direct RNA sequencing with reverse transcriptase. The rRNA sequences were computer aligned with the published partial sequence of T. gondii, and three oligonucleotides complementary to different variable regions of the 18S rRNA were synthesized. The three probes were end-labelled with 32P and tested in filter hybridization experiments. One of the probes designed to be Sarcocystis genus-specific, did not cross-hybridize to stable RNA from T. gondii. Two of the probes were designed to be species-specific for S. cruzi and S. tenella, and these probes hybridized specifically with their respective targets.