Prevalence of antibodies to Neospora sp. in horses from Alabama and characterisation of an isolate recovered from a naturally infected horse [corrected]

Seroprevalence and risk factors for Neospora spp. infection in equine in Egypt

Neospora infections in equine are associated with reproductive disorders and neurological diseases. Nevertheless, Egypt has no epidemiological information on this parasite in equine. This study determined the prevalence of Neospora spp. infection in 325 equines from three Egyptian governorates located at Northern Egypt using cELISA. The prevalence of antibodies against Neospora spp. was 19% (95% CI: 14.09-25.05) in horse, 34.1% (95%CI: 24.92-44.69) in donkey and 26.7% (95% CI: 15.97-41.04) in mule. In comparison to horse, donkey had a considerably higher chance of contracting Neospora spp. infection (OR = 1.80, 95% CI: 0.78-4.13; P = 0.016). The risk was also higher in freely grazing animals (OR = 3.49, 95% CI: 0.95-12.78; P = 0.059). Moreover, yearling animals (12-24 months) (OR = 5.03, 95% CI: 1.51-16.80; P = 0.009) and those with natural breeding (OR = 11.80, 95% CI: 3.24-42.99, P < 0.0001) and a history of early abortion (OR = 7.04, 95% CI: 3.01-16.47; P < 0.0001) also showed a greater risk of seropositivity. The risk of Neospora infection increased significantly in equines contacted with dogs (OR = 5.16, 95% CI: 1.76-15.10; P = 0.003). This the first serological study to determine the seroprevalence of Neospora spp. in equine in Egypt. Further studies are necessary to identify the species of Neospora and to understand the role of above-mentioned risk factors in spreading of infection.

Neospora spp. Seroprevalence and Risk Factors for Seropositivity in Apparently Healthy Horses and Pregnant Mares

Simple Summary

Neosporosis, caused by the parasite Neospora species, is recognized as one of the major causes of abortion in cattle worldwide causing large economic losses. Over the past few years, Neospora infection and parasite transmission from the mare to the fetus has been documented in horses and was associated with reproduction failure. In the present study, we investigated parasite prevalence and associated risk factors in the general equine population and in a group of pregnant mares during pregnancy and after parturition. Our findings revealed high exposure of horses to Neospora spp. parasites, with significantly higher prevalence in pregnant mares.

Abstract

Equine Neospora infection has been linked to neurological disorders and infertility in horses. This study looked into the risk factors for infection and the exposure to Neospora spp. in horses. The study was performed in two independent populations in Israel. The first consisted of apparently healthy horses, and the second consisted of mares examined during pregnancy and after parturition. Sera samples collected from horses and mares were tested for Neospora exposure by the indirect fluorescent antibody test (IFAT). The study revealed seroprevalence of 24% in apparently healthy horses and 66.4% and 48.6% in mares during gestation and after parturition, respectively. Among the investigated risk factors, older age (p = 0.026) and housing in both stalls and paddocks (p = 0.033) in apparently healthy horses, and Arabian breeds (p = 0.005) in pregnant mares, were found to be significantly associated with Neospora spp. seropositivity in univariable, but not multivariable, statistical analysis. This study revealed high exposure of equines to Neospora parasites, especially mares. Horse farm management, in combination with active surveillance, including serological testing and follow up, could help reduce the spread of the parasite among horses in endemic areas.

Equine Protozoal Myeloencephalitis

Advances in the understanding of equine protozoal myeloencephalitis (EPM) are reviewed. It is now apparent that EPM can be caused by either of 2 related protozoan parasites, Sarcocystis neurona and Neospora hughesi, although S neurona is the most common etiologic pathogen. Horses are commonly infected, but clinical disease occurs only infrequently; the factors influencing disease occurrence are not well understood. Epidemiologic studies have identified risk factors for the development of EPM, including the presence of opossums and prior stressful health-related events. Attempts to reproduce EPM experimentally have reliably induced antibody responses in challenged horses, but have not consistently produced neurologic disease. Diagnosis of EPM has improved by detecting intrathecal antibody production against the parasite. Sulfadiazine/pyrimethamine (ReBalance) and the triazine compounds diclazuril (Protazil) and ponazuril (Marquis) are effective anticoccidial drugs that are now available as FDA-approved treatments for EPM.

Invited review: Sarcocystis neurona, Neospora spp. and Toxoplasma gondii infections in horses and equine protozoal myeloencephalitis (EPM): five decades of personal experience, perspectives, and update

Sarcocystis neurona, Neospora spp. and Toxoplasma gondii are related protozoans; they were considered the same parasite until 1970s. Two of these parasites, S. neurona and Neospora spp. are associated with a neurological syndrome in horses, called equine protozoal myeloencephalitis (EPM). The diagnosis and treatment of EPM are difficult. Most cases of EPM are related to S. neurona while only a few are due to Neospora spp. infections. There are two species of Neospora, Neospora caninum that has a wide host range and Neospora hughesi that has been found only in horses. Currently, T. gondii is not considered as a cause of EPM in horses, although it causes neurological illness in many other hosts, including humans. The present review provides an update on history, life cycle, diagnosis and treatment of these three infections in horses.

Global seroprevalence of Neospora spp. in horses and donkeys: A systematic review and meta-analysis

Neospora infections due to Neospora caninum and N. hughesi are prevalent among equids of the world. The disease may affect reproductive and neurological consequences. The present systematic review and meta-analysis was performed to evaluate the global Neospora seroprevalence among horses and donkeys. A number of 57 out of 1575 total retrieved studies were included by searching the PubMed, Scopus, Science Direct, Web of Science and ProQuest. A total of 25,783 horses and 4377 donkeys were examined serologically, yielding a weighted seroprevalence of 13.46 % (95 % CI: 10.26 %-17.42 %) globally. Subgroup analysis revealed that there were statistically significant differences in the overall prevalence of Neospora spp. in the examined animals according to year, continent, WHO region, country, host, and diagnostic method. Age and sex in horses as well as sex in donkeys were significantly associated with the Neospora seroprevalence (P < 0.001). Our findings showed a relatively high exposure to Neospora spp. in horses and donkeys worldwide. Considering the possible economic impact, as well as the importance in animal health, more studies are needed to clarify the species causing equine neosporosis, correlate serological findings with clinical outcomes and assess the risk factors, in order to define adequate prevention and control strategies.

Seroprevalence of Neospora caninum Infection in Dog Population Worldwide: A Systematic Review and Meta-analysis

PURPOSE

Neospora caninum is an obligate intracellular apicomplexan protozoan that causes neurological disorders in dogs. This systematic review and meta-analysis targeted at evaluating the worldwide seroprevalence rate of N. caninum in dogs.

METHODS

Five electronic databases, including PubMed, Scopus, Web of Science, Science Direct, and Google Scholar, until December 2018 were thoroughly searched for relevant English language articles. Papers were selected based on inclusion criteria. Data were analyzed in StatsDirect statistical software (version 2.7.9).

RESULTS

The searching process yielded a total number of 156 papers. The total prevalence (95% confidence intervals) of N. caninum infection in dog population worldwide was measured as 17.14% in data analyses (15.25-19.10). In addition, a significant association was also detected between neosporosis infection in dogs and continent, country, year, WHO regions, sample size and diagnostic method (P < 0.001).

CONCLUSION

Dogs are a matter of concern to public health officials as a source of N. caninum infection. Therefore, it is of paramount importance to provide comprehensive data and systematically analyze the prevalence of N. caninum infection in dogs. Accordingly, it is recommended that researchers carry out further studies to prevent and control neosporosis among dog population worldwide.

Serological survey of Neospora spp. and Besnoitia spp. in horses in Portugal

Equine neosporosis is regarded to be caused either by Neospora hughesi or Neospora caninum and equine besnoitiosis is caused by Besnoitia bennetti, both of which are apicomplexan parasites. N. caninum is the only known Neospora species in Europe, where equine N. caninum infections have been reported as being associated to abortion and reproductive failure. N. hughesi is prevalent in North America and was predominantly linked to neurological disorders. B. bennetti is considered an emergent disease in donkeys in North America and evidence for B. bennetti infection was recently reported in Europe. Though N. caninum and Besnoitia besnoiti are prevalent in cattle in Portugal, little is known about neosporosis in horses and, to the best of our knowledge, no information was hitherto available for Besnoitia spp. The aim of this study was thus to carry out a serological survey to determine the seroprevalence of these parasites in naturally exposed horses in Portugal. A total of 385 animals were screened by the Indirect Fluorescent Antibody Test at the cut-off value 1:50 and positive results were confirmed by Western blot. Exposure to Neospora spp. and Besnoitia spp. was confirmed in 9.1% (95% Confidence Interval [CI]: 6.6-12.4%) and 0.3% (95% CI: 0.0-1.5%) of horses, respectively. Considering the putative economic and animal health impact of neosporosis in horses and the consequences of a possible spread of equine besnoitiosis in Europe and elsewhere, more comprehensive studies are needed to characterize the species detected in serological surveys, evaluate the geographical distribution and assess possible risk factors that could favor transmission.

Prevalence and risk factors for IgG antibodies to Neospora spp. in three types of equids from Southern Punjab, Pakistan

Equine hosts suffer from neurological disease, congenital infection, and reproductive problems associated with Neospora spp. infection. We conducted a cross sectional study using sera from 631 equids (324 horses, 218 donkeys and 89 mules) from the southern region of Punjab province, Pakistan to determine the prevalence of antibodies against Neospora spp. in this diverse group of equines. Fisk factors associated with seropositivity were evaluated statistically based on equine type, breed, age, husbandry, breeding methods, and reproductive history. Prevalence of antibodies to Neospora spp. was detected using a commercially available competitive ELISA kit. We detected IgG antibodies to Neospora spp. in 23.3% of the equids with prevalence by host being 16.0% in horses, 32.6% in donkeys and 26.9% in 89 mules. Statistically significant (P < 0.05) differences in prevalence were observed among these hosts. Prevalence ranged in breeds of horses from 3.7% in the Morna breed, 12.4% in breeding stock, 26.8% in draughting stock, to 31.4% in unknown breeds. No significant (P > 0.05) difference in prevalence was noted among age groups. Prevalence was significantly (P < 0.05) higher in female equines with a history of abortion than those with no history of abortion. This is the first report documenting Neospora spp. in equines from Pakistan and it provides evidence that Neospora spp. is associated with abortions in female equines in Pakistan.

Effects of Blood Contamination of Cerebrospinal Fluid on Results of Indirect Fluorescent Antibody Tests for Detection of Antibodies against Sarcocystis Neurona and Neospora Hughesi

The purpose of this study was to determine the effect of blood contamination of cerebrospinal fluid (CSF) on the results of indirect fluorescent antibody tests (IFATs) for Sarcocystis neurona and Neospora hughesi. The in vitro study used antibody-negative CSF collected from non-neurologic horses immediately after euthanasia and blood samples from 40 healthy horses that had a range of IFAT antibody titers against S. neurona and N. hughesi. Serial dilutions of whole blood were made in seronegative CSF to generate blood-contaminated CSF with red blood cell (RBC) concentrations ranging from 10 to 100,000 RBCs/μl. The blood-contaminated CSF samples were then tested for antibodies against both pathogens using IFAT. Blood contamination of CSF had no detectable effect on IFAT results for S. neurona or N. hughesi at any serologic titer when the RBC concentration in CSF was <10,000 RBCs/μl. At concentrations of 10,000-100,000 RBCs/μl of CSF, positive CSF results (IFAT titer ≥5) for S. neurona and N. hughesi were detected only when the corresponding serum titers were ≥160 and ≥80, respectively. The IFAT performed on CSF is reliable for testing horses for equine protozoal myeloencephalitis caused by S. neurona or N. hughesi, even when blood contamination causes the RBC concentration in CSF to be up to 10,000 RBCs/μl.

Equine Protozoal Myeloencephalitis: An Updated Consensus Statement with a Focus on Parasite Biology, Diagnosis, Treatment, and Prevention

Equine protozoal myeloencephalitis (EPM) remains an important neurologic disease of horses. There are no pathognomonic clinical signs for the disease. Affected horses can have focal or multifocal central nervous system (CNS) disease. EPM can be difficult to diagnose antemortem. It is caused by either of 2 parasites, Sarcocystis neurona and Neospora hughesi, with much less known about N. hughesi. Although risk factors such as transport stress and breed and age correlations have been identified, biologic factors such as genetic predispositions of individual animals, and parasite‐specific factors such as strain differences in virulence, remain largely undetermined. This consensus statement update presents current published knowledge of the parasite biology, host immune response, disease pathogenesis, epidemiology, and risk factors. Importantly, the statement provides recommendations for EPM diagnosis, treatment, and prevention.

Equine protozoal myeloencephalitis

Equine protozoal myeloencephalitis (EPM) can be caused by either of 2 related protozoan parasites, Sarcocystis neurona and Neospora hughesi, although S. neurona is the most frequent etiologic pathogen. Horses are commonly infected, but clinical disease occurs infrequently; the factors influencing disease occurrence are not well understood. Risk factors for the development of EPM include the presence of opossums and prior stressful health-related events. Attempts to reproduce EPM experimentally have reliably induced antibody responses in challenged horses but have not consistently produced acute neurologic disease. Diagnosis and options for treatment of EPM have improved over the past decade.

Serum antibodies from a subset of horses positive for Babesia caballi by competitive enzyme-linked immunosorbent assay demonstrate a protein recognition pattern that is not consistent with infection

Tick-borne pathogens that cause persistent infection are of major concern to the livestock industry because of transmission risk from persistently infected animals and the potential economic losses they pose. The recent reemergence of Theileria equi in the United States prompted a widespread national survey resulting in identification of limited distribution of equine piroplasmosis (EP) in the U.S. horse population. This program identified Babesia caballi-seropositive horses using rhoptry-associated protein 1 (RAP-1)-competitive enzyme-linked immunosorbent assay (cELISA), despite B. caballi being considered nonendemic on the U.S. mainland. The purpose of the present study was to evaluate the suitability of RAP-1-cELISA as a single serological test to determine the infection status of B. caballi in U.S. horses. Immunoblotting indicated that sera from U.S. horses reacted with B. caballi lysate and purified B. caballi RAP-1 protein. Antibody reactivity to B. caballi lysate was exclusively directed against a single ∼50-kDa band corresponding to a native B. caballi RAP-1 protein. In contrast, sera from experimentally and naturally infected horses from regions where B. caballi is endemic bound multiple proteins ranging from 30 to 50 kDa. Dilutions of sera from U.S. horses positive by cELISA revealed low levels of antibodies, while sera from horses experimentally infected with B. caballi and from areas where B. caballi is endemic had comparatively high antibody levels. Finally, blood transfer from seropositive U.S. horses into naive horses demonstrated no evidence of B. caballi transmission, confirming that antibody reactivity in cELISA-positive U.S. horses was not consistent with infection. Therefore, we conclude that a combination of cELISA and immunoblotting is required for the accurate serodiagnosis of B. caballi.

Prevalence of antibodies to Sarcocystis neurona and Neospora hughesi in horses from Mexico

Equine protozoal myeloencephalitis (EPM) is a debilitating disease of horses caused by Sarcocystis neurona and Neospora hughesi. Sera from 495 horses in Durango State, Mexico were tested for anti-protozoal antibodies using enzyme-linked immunosorbent assays (ELISAs) based on major surface antigens of these two parasites. Antibodies to S. neurona were detected in 240 (48.5%) of the 495 horse sera tested with the rSnSAG2/4/3 trivalent ELISA. Multivariate analysis showed that exposure to S. neurona was associated with age, feeding grains and crops, and small herd size. Antibodies to N. hughesi were found in 15 (3.0%) of the 495 horse sera tested with the rNhSAG1 ELISA and confirmed by Western blot of N. hughesi tachyzoite antigen. This is the first report of S. neurona and N. hughesi exposure in horses in Mexico, and it affirms that EPM should be in the differential diagnosis for horses exhibiting signs of neurologic disease in this country.

A review of the infection, genetics, and evolution of Neospora caninum: from the past to the present

This paper is a review of current knowledge on Neospora caninum in the context of other apicomplexan parasites and with an emphasis on: life cycle, disease, epidemiology, immunity, control and treatment, evolution, genomes, and biological databases and web resources. N. caninum is an obligate, intracellular, coccidian, protozoan parasite of the phylum Apicomplexa. Infection can cause the clinical disease neosporosis, which most notably is associated with abortion in cattle. These abortions are a major root cause of economic loss to both the dairy and beef industries worldwide. N. caninum has been detected in every country in which a study has been specifically conducted to detect this parasite in cattle. The major mode of transmission in cattle is transplacental (or vertical) transmission and several elements of the N. caninum life cycle are yet to be studied in detail. The outcome of an infection is inextricably linked to the precise timing of the infection coupled with the status of the immune system of the dam and foetus. There is no community consensus as to whether it is the dam's pro-inflammatory cytotoxic response to tachyzoites that kills the foetus or the tachyzoites themselves. From economic analysis the most cost-effective approach to control neosporosis is a vaccine. The perfect vaccine would protect against both infection and the clinical disease, and this implies a vaccine is needed that can induce a non-foetopathic cell mediated immunity response. Researchers are beginning to capitalise on the vast potential of -omics data (e.g. genomes, transcriptomes, and proteomes) to further our understanding of pathogens but especially to identify vaccine and drug targets. The recent publication of a genome for N. caninum offers vast opportunities in these areas.

Neospora spp. and Toxoplasma gondii antibodies in horses in the Czech Republic

During January 2007, blood samples were collected from 552 healthy horses from nine different regions of the Czech Republic. Sera were tested for serum antibodies to Neospora caninum by a competitive-inhibition enzyme-linked immunosorbent assay and confirmed by an indirect fluorescent antibody test. The same samples were tested for serum antibodies against Toxoplasma gondii by a latex agglutination test. In total, 131 of 552 (24%) horses reacted positively for Neospora antibodies in competitive-inhibition enzyme-linked immunosorbent assay; seven of them had > or =50% of inhibition. Samples were confirmed in indirect fluorescence test, and only two samples were positive with final titres 50 and 100, while others were negative. Antibodies against T. gondii were found in 125 (23%) horses. This is the first serologic survey for Neospora spp. antibodies performed on horses in the Czech Republic.

Seroprevalence of Neospora spp. among asymptomatic horses, aborted mares and horses demonstrating neurological signs in Israel

Sera from 800 asymptomatic horses were examined for the presence of antibodies to Neospora caninum by immunofluorescence antibody test (IFAT). The presence of antibodies to N. caninum was also tested in sera from 52 mares that had aborted and 40 horses exhibiting neurological signs. A total of 95 (11.9%) of the 800 sera had antibodies for Neospora. Significantly higher seropositivity was obtained from horses that had neurological signs (21.2%) and from aborted mares (37.5%). There was significant linear-by-linear association between age and seropositivity. This is the first serologic survey for Neospora spp. antibodies performed on horses from the Middle East and the first to report significant difference in seropositivity between asymptomatic horses and horses exhibiting neurological signs.

Epidemiology and control of neosporosis and Neospora caninum

Neospora caninum is a protozoan parasite of animals. Until 1988, it was misidentified as Toxoplasma gondii. Since its first recognition in dogs in 1984 and the description of the new genus and species Neospora caninum in 1988, neosporosis has emerged as a serious disease of cattle and dogs worldwide. Abortions and neonatal mortality are a major problem in livestock operations, and neosporosis is a major cause of abortion in cattle. Although antibodies to N. caninum have been reported, the parasite has not been detected in human tissues. Thus, the zoonotic potential is uncertain. This review is focused mainly on the epidemiology and control of neosporosis in cattle, but worldwide seroprevalences of N. caninum in animals and humans are tabulated. The role of wildlife in the life cycle of N. caninum and strategies for the control of neosporosis in cattle are discussed.

Neospora caninum in wildlife

Neosporosis, which is caused by the coccidian parasite Neospora caninum, is recognized as a major disease of domestic animals that causes high abortion rates in cattle and fatal neurological disease in dogs. A life cycle of N. caninum in wild animals (i.e. sylvatic) has long been suspected because neosporosis has been detected in several wildlife species. Recently, the transmission of N. caninum has been confirmed in coyotes and white-tailed deer. The newly confirmed wild hosts and other wild animals are probably involved in the sylvatic cycle of the parasite. Control measures for neosporosis could now become more complicated, given the participation of wildlife in the life cycle of N. caninum.

Prevalence of Sarcocystis neurona and Neospora spp. infection in horses from Brazil based on presence of serum antibodies to parasite surface antigen

Sera from 961 horses from Brazil were tested for antibodies against the major surface antigens SnSAG4 and NhSAG1 to determine the seroprevalence of Sarcocystis neurona and Neospora hughesi, respectively. Antibodies against SnSAG4 were detected in 669 (69.6%) of the horses, while antibodies against NhSAG1 were detected in only 24 (2.5%) of the horses. These serologic results suggest that there is a high concentration of S. neurona in the environment of Brazil, which results in marked exposure of horses to this parasite. Additionally, the data further confirm that infection with Neospora spp. is relatively uncommon in horses.

Investigation of Neospora sp. and Toxoplasma gondii antibodies in mares and in precolostral foals from Parana State, Southern Brazil

Antibodies to Neospora sp. and Toxoplasma gondii were measured in mares and precolostral foals from a farm in Parana State, Brazil. An indirect fluorescent antibody test (IFAT) was used to determine specific antibodies. Three sampling points, 2003, 2004 and at parturition were included in the study, but not all horses are represented at a parturition time point. In 2003, antibodies to Neospora were detected in 17 mares (47%) at 1:50 dilution and in 5 mares (13.8%) at 1:100 dilution. In 2004, antibodies to Neospora were found in 11/36 (30%) horses with titers of 1:50 and in 6 mares (16.6%) at 1:100 dilution. The prevalence of antibodies against T. gondii was 2.7% in mares, either in 2003 and 2004. Evidence for the role of Neospora sp. in equine reproduction failure was not observed in the farm. Immunoglobulin G antibodies to Neospora were found in two of the nine precolostrum foals. Four seronegative foals were born from seronegative mothers, and three seronegative foals were born from seropositive mothers (1:50). Two seropositive precolostrum foals were born from seropositive mothers (1:50). The foals were born clinically normal, and T. gondii antibodies were not detected in their serum samples. The total immunoglobulins values detected on seronegative precolostrum foals were lower than the levels observed in the seropositive foals. This data warrants additional studies to differentiate N. hughesi and N. caninum serologically and determination if these parasites were associated with equine neurological disease and reproductive failure.

Recombinant NhSAG1 ELISA: a sensitive and specific assay for detecting antibodies against Neospora hughesi in equine serum

Neospora hughesi is a recently identified cause of equine protozoal myeloencephalitis. However, the significance of this parasite is poorly understood. An enzyme-linked immunosorbent assay (ELISA) with a recombinant form of the N. hughesi 29-kDa surface antigen (rNhSAG1) was developed for serodiagnosis of equine N. hughesi infections. Parallel ELISA analysis showed that animals immunized or infected with N. hughesi exhibited greater antibody reactivity with rNhSAG1 than with the Neospora caninum homolog, rNcSAG1. The rNhSAG1 ELISA showed 94.4% sensitivity and 95.0% specificity when compared with N. hughesi western blot results for 1,006 samples. The N. hughesi seroprevalence was 3.4% for the 1,917 samples tested by ELISA, which is less than earlier reports. Importantly, western blot analysis of ELISA-positive sera revealed only 18 true seropositive samples for an even lower seroprevalence of 0.9%. These results imply that Neospora spp. infections are uncommon in horses. The sensitivity and specificity exhibited by the rNhSAG1 ELISA suggest that it has a potential use for serodiagnosis of N. hughesi infection in equids. Furthermore, the high-throughput capability of the ELISA will allow for screening large sample sets, which should provide a better understanding of N. hughesi epidemiology.

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.

Risk of postnatal exposure to Sarcocystis neurona and Neospora hughesi in horses

OBJECTIVE

To estimate risk of exposure and age at first exposure to Sarcocystis neurona and Neospora hughesi and time to maternal antibody decay in foals.

ANIMALS

484 Thoroughbred and Warmblood foals from 4 farms in California.

PROCEDURE

Serum was collected before and after colostrum ingestion and at 3-month intervals thereafter. Samples were tested by use of the indirect fluorescent antibody test; cutoff titers were > or = 40 and > or = 160 for S neurona and N hughesi, respectively.

RESULTS

Risk of exposure to S neurona and N hughesi during the study were 8.2% and 3.1%, respectively. Annual rate of exposure was 3.1% for S neurona and 1.7% for N hughesi. There was a significant difference in the risk of exposure to S neurona among farms but not in the risk of exposure to N hughesi. Median age at first exposure was 1.2 years for S neurona and 0.8 years for N hughesi. Highest prevalence of antibodies against S neurona and N hughesi was 6% and 2.1 %, respectively, at a mean age of 1.7 and 1.4 years, respectively. Median time to maternal antibody decay was 96 days for S neurona and 91 days for N hughesi. There were no clinical cases of equine protozoal myeloenchaphlitis (EPM).

CONCLUSIONS AND CLINICAL RELEVANCE

Exposure to S neurona and N hughesi was low in foals between birth and 2.5 years of age. Maternally acquired antibodies may cause false-positive results for 3 or 4 months after birth, and EPM was a rare clinical disease in horses < or = 2.5 years of age.

Seroprevalence of Neospora spp. in asymptomatic horses in Italy

One hundred and fifty horses from Italy were tested for serum antibodies to Neospora caninum by indirect fluorescence antibody test (IFAT). Antibodies were present in 42 horses (28%). The positive titres were: 1:50 (16/150-10.5%), 1:100 (26/150-17%), 1:200 (8/150-5.3%) and 1:800 (1/150-0.6%). No neurological anomalies were observed in the seropositive horses. This is the first serologic survey for Neospora spp. antibodies performed on horses born and raised in Italy.

Investigation of Neospora sp. antibodies in aborted mares from Normandy, France

Neospora caninum, an apicomplexan protozoan parasite, is recognized as a major cause of abortion in cattle while limited information is presently available on association between equine Neospora infections and abortions. The aim of the present study was to document prevalence of antibodies against Neospora sp. in aborted mares as a clue to the role of N. caninum in mare reproductive failure in Normandy, France. Using an agglutination test, the number of animals with elevated (>80) anti-Neospora sp. antibody titer was higher in a group of 54 aborted mares than in randomly chosen groups of 45 mares and 76 horses sampled for equine arteritis virus and Fasciola hepatica antibodies, respectively (P<0.001). N. caninum DNA was found in 3/91 fetal brains, 2/77 fetal hearts, and 1/1 placenta, and present in both brains and hearts of two fetuses. In 13 cases for which both mare serum and fetus were available, no fetal N. caninum amplification product was present while a large variation of maternal antibody titers was found. Data prompt at additional surveys of association between equine reproductive failure and Neospora sp. infection.

Prevalence of antibodies to Neospora caninum, Sarcocystis neurona, and Toxoplasma gondii in wild horses from central Wyoming

Sarcocystis neurona, Neospora caninum, N. hughesi, and Toxoplasma gondii are 4 related coccidians considered to be associated with encephalomyelitis in horses. The source of infection for N. hughesi is unknown, whereas opossums, dogs, and cats are the definitive hosts for S. neurona, N. caninum, and T. gondii, respectively. Seroprevalence of these coccidians in 276 wild horses from central Wyoming outside the known range of the opossum (Didelphis virginiana) was determined. Antibodies to T. gondii were found only in 1 of 276 horses tested with the modified agglutination test using 1:25, 1:50, and 1:500 dilutions. Antibodies to N. caninum were found in 86 (31.1%) of the 276 horses tested with the Neospora agglutination test--the titers were 1:25 in 38 horses, 1:50 in 15, 1:100 in 9, 1:200 in 8, 1:400 in 4, 1:800 in 2, 1:1,600 in 2, 1:3,200 in 2, and 1:12,800 in 1. Antibodies to S. neurona were assessed with the serum immunoblot; of 276 horses tested, 18 had antibodies considered specific for S. neurona. Antibodies to S. neurona also were assessed with the S. neurona direct agglutination test (SAT). Thirty-nine of 265 horses tested had SAT antibodies--in titers of 1:50 in 26 horses and 1:100 in 13. The presence of S. neurona antibodies in horses in central Wyoming suggests that either there is cross-reactivity between S. neurona and some other infection or a definitive host other than opossum is the source of infection. In a retrospective study, S. neurona antibodies were not found by immunoblot in the sera of 243 horses from western Canada outside the range of D. virginiana.

Review of Neospora caninum and neosporosis in animals

Neospora caninum is a coccidian parasite of animals. It is a major pathogen for cattle and dogs and it occasionally causes clinical infections in horses, goats, sheep, and deer. Domestic dogs are the only known definitive hosts for N. caninum. It is one of the most efficiently transmitted parasite of cattle and up to 90% of cattle in some herds are infected. Transplacental transmission is considered the major route of transmission of N. caninum in cattle. Neospora caninum is a major cause of abortion in cattle in many countries. To elicit protective immunity against abortion in cows that already harbor a latent infection is a major problem. This paper reviews information on biology, diagnosis, epidemiology and control of neosporosis in animals.

Comparison of a serum indirect fluorescent antibody test with two Western blot tests for the diagnosis of equine protozoal myeloencephalitis

A serum indirect fluorescent antibody test (IFAT) was compared with a Western blot (WB) and a modified Western blot (mWB) for diagnosis of equine protozoal myeloencephalitis (EPM). Using receiver-operating characteristic (ROC) analysis, the area under the curve of the IFAT was greater than the areaunder the curves of the WB and the mWB (P = 0.025 and P = 0.044, respectively). There was no statistically significant difference between the areas under the curves of the WBs (P > 0.05). On the basis of an arbitrarily chosen cut-off titer for a positive test result of 1:80 for the IFAT and interpreting weak positive WB results as positive test results, the sensitivities and 95% confidence intervals (CI) of all 3 tests were identical and equal to 88.9% (51.8-99.7%). The specificities and 95% CIs of the IFAT, WB, and mWB test were 100% (91-100%), 87.2% (72.6-95.7%), and 69.2% (52.4-83%), respectively. The overall accuracy of the IFAT was shown to be better than that of the WBs and, therefore, the test has potential for use in the diagnosis of EPM caused by Sarcocystis neurona.

The comparative pathogenesis of neosporosis

Since its first description in dogs in 1984, the protozoan parasite Neospora caninum has been found to infect a wide range of animals, worldwide. In cattle, N. caninum has particular significance as a cause of abortion in which persistence of infection in the mother, recrudescence of the parasite during pregnancy, and the vulnerability of the placenta and foetus to invasion are important features. This article discusses how Neospora invades cells, how it infects and causes disease in several animal species, and particularly how it has evolved a special niche in cattle and dogs that ensures its survival.

Qualitative evaluation of selective tests for detection of Neospora hughesi antibodies in serum and cerebrospinal fluid of experimentally infected horses

Neospora hughesi is a newly recognized protozoan pathogen in horses that causes a myeloencephalitis similar to Sarcocystis neurona. There are no validated serologic tests using the gold standard sera that are currently available to detect specific N. hughesi antibodies and, thus, no tests available to detect antemortem exposure or estimate seroprevalence in the horse. The objectives of the present study were to establish a bank of gold standard equine sera through experimental infections with N. hughesi and to assess several serologic tests for the detection of related protozoan antibodies. Seven horses were inoculated with N. hughesi tachyzoites, and 7 horses received uninfected cell culture material. The horses were monitored, and blood and cerebrospinal fluid were collected repeatedly over a 4-mo period. With the sera, 4 different serologic techniques were evaluated. including a whole-parasite lysate enzyme-linked immunosorbent assay (ELISA), a recombinant protein ELISA, a modified direct agglutination test, and an indirect fluorescent antibody test. Qualitative and quantitative evaluation of the results showed that the N. hughesi indirect fluorescent antibody test (IFAT) consistently discriminated between experimentally infected and noninfected horses, using a cutoff of 1:640. Sera from 3 naturally infected horses had titers >1:640. Cerebrospinal fluid in all but I infected horse had very low N. hughesi IFAT titers (<1:160), starting at postinoculation day 30.

Redescription of Neospora caninum and its differentiation from related coccidia

Neospora caninum is a protozoan parasite of animals, which before 1984 was misidentified as Toxoplasma gondii. Infection by this parasite is a major cause of abortion in cattle and causes paralysis in dogs. Since the original description of N. caninum in 1988, considerable progress has been made in the understanding of its life cycle, biology, genetics and diagnosis. In this article, the authors redescribe the parasite, distinguish it from related coccidia, and provide accession numbers to its type specimens deposited in museums.

Seroprevalence of Neospora, Toxoplasma gondii and Sarcocystis neurona antibodies in horses from Jeju island, South Korea

Parasite-specific antibody responses to Neospora spp. and Toxoplasma gondii, antigens were detected using the indirect fluorescent antibody test (IFAT) and immunoblot analysis in a korean equine population located on Jeju island, South Korea (126 degrees 12' E and 33 degrees 34' N). For comparison, a naturally infected Neospora hughesi horse and an experimentally inoculated T. gondii equid (pony) were used. In addition, all samples were tested for antibodies to Sarcocystis neurona by immunoblot analysis. A total of 191 serum samples from clinically normal horses were evaluated. Only 2% (4 out of 191) and 2.6% (5 out of 191) of the samples had showed reactivity at 1:100 using the IFAT for Neospora spp. and T. gondii, respectively. For T. gondii, two samples matched the antigen banding pattern of the positive control by immunoblot analysis. No sample was positive for N. hughesi by immunoblot analysis in this study. Overall, there was a 1% seroprevalence for T. gondii antibodies in the horses tested based on immunoblot analysis. The seroprevalence for S. neurona and N. hughesi antibodies was 0%. We concluded that these horses are either not routinely exposed to these parasites or antibody titers are not sufficiently elevated to be detectable. It is most likely the former explanation since Jeju island equine farms are isolated from the main land, and the horses were all less than 3 years of age. This naïve population of horses could be useful when evaluating S. neurona serodiagnostic tests or evaluating potential S. neurona vaccines since exposure risks to S. neurona and closely related parasites are negligible.

Seroprevalence of antibodies against Neospora caninum in diagnostic equine serum samples and their possible association with fetal loss

A case-control study of the association between the presence of serum antibodies against Neospora spp. and fetal loss was performed on serum samples submitted to a veterinary diagnostic laboratory in northwestern United States. Control sera were randomly selected from those submitted from healthy horses for routine equine infectious anemia testing required for regulatory health certification. Case sera were randomly selected from those submitted from aborting mares for diagnostic workup. Based on a 1:50 or greater titer on the indirect fluorescent antibody test, 8% of the 160 control sera and 13% of the 140 case sera were titer positive. The association odds ratio of 1.67 fell short of statistical significance (p=0.124).

Characterization of the Oregon isolate of Neospora hughesi from a horse

Neospora hughesi was isolated in cell cultures inoculated with homogenate of spinal cord from a horse in Oregon. Tachyzoites of this Oregon isolate of N. hughesi were maintained continuously by cell culture passage and tachyzoites were infective to immunosuppressed mice. Gamma interferon gene knockout (KO) mice injected with tachyzoites developed fatal myocarditis and numerous tachyzoites were seen in lesions. Gerbils (Meriones unguiculatus) inoculated with tachyzoites developed antibodies (> or = 1:500) as indicated by the Neospora caninum agglutination test but did not develop clinical signs, and Neospora organisms were not demonstrable in their tissues. Tissue cysts were not found in gerbils, nude mice, KO mice, immunosuppressed outbred Swiss Webster mice, or BALB/c mice injected with the Oregon isolate of N. hughesi. Ultrastructurally, tachyzoites of the Oregon isolate from the myocardium of infected KO mice and from cell culture were similar to N. caninum tachyzoites. Western blot analysis using NcSAG1 and NcSRS2 polyclonal and monoclonal antibodies and characterization of the internal transcribed spacer 1 sequences from the equine isolates and different isolates of N. caninum from dogs and cattle indicated that the Oregon isolate of N. hughesi is distinct from N. caninum isolates from cattle and dogs.

Molecular comparison of the dense granule proteins GRA6 and GRA7 of Neospora hughesi and Neospora caninum

Neospora hughesi is a recently described apicomplexan parasite that has been associated with several cases of equine protozoal myeloencephalitis. The biology of this new parasite is just beginning to be defined. Towards this understanding, we report important differences between the nucleotide and deduced amino acid sequences of the dense granule proteins GRA6 and GRA7 of N. hughesi and Neospora caninum. This information can be used to differentiate the two species and contribute to further understanding of the prevalence and biology of N. hughesi. The newly defined proteins of N. hughesi are referred to as NhGRA6 and NhGRA7 in keeping with the protocol for naming homologous proteins of the Apicomplexa. Genes of the two dense granule proteins of N. hughesi (isolate Nh-A1) and four different isolates of N. caninum were isolated via PCR and their DNA sequences were determined. Computer analysis indicated that the two gene sequences were identical among all four N. caninum isolates. However, the gene for NhGRA6 was found to be 96 nucleotides longer at the 3' end than that of NcGRA6, resulting in a protein product that is 32 amino acids larger than NcGRA6. Two tandem repeat sequences were identified at the 3' end of the NhGRA6 gene. These repeat sequences contributed to the lengthening of the carboxy terminus of NhGRA6 in comparison with that of NcGRA6. The larger size of NhGRA6 was further confirmed by Western blot analysis in which NcGRA6 monospecific antibodies recognised a protein of approximately 42 kDa in N. hughesi whole tachyzoite preparation but a protein of 37 kDa in N. caninum whole tachyzoite preparation. Analysis of GRA7 gene sequences indicated a 6 and 14.8% difference at nucleotide and amino acid sequence level, respectively, between NcGRA7 and NhGRA7. Despite the same number of residues in the deduced amino acid sequences of all the GRA7 proteins, Western blot analysis indicated a difference in the migration pattern of NhGRA7 in comparison with NcGRA7. Results of our study indicate that diagnostic tests based on differences in dense granule sequences and antigenicity may have potential to differentiate between N. hughesi and N. caninum. Such diagnostic tests would be valuable tools to aid in our understanding of the epidemiology of these parasites. Additionally, dense granule proteins are immunogenic and they may have potential as use in recombinant vaccines against neosporosis.

A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM)

Equine protozoal myeloencephalitis (EPM) is a serious neurological disease of horses in the Americas. The protozoan most commonly associated with EPM is Sarcocystis neurona. The complete life cycle of S. neurona is unknown, including its natural intermediate host that harbors its sarcocyst. Opossums (Didelphis virginiana, Didelphis albiventris) are its definitive hosts. Horses are considered its aberrant hosts because only schizonts and merozoites (no sarcocysts) are found in horses. EPM-like disease occurs in a variety of mammals including cats, mink, raccoons, skunks, Pacific harbor seals, ponies, and Southern sea otters. Cats can act as an experimental intermediate host harboring the sarcocyst stage after ingesting sporocysts. This paper reviews information on the history, structure, life cycle, biology, pathogenesis, induction of disease in animals, clinical signs, diagnosis, pathology, epidemiology, and treatment of EPM caused by S. neurona.

Sporocyst size of isolates of Sarcocystis shed by the Virginia opossum (Didelphis virginiana)

The Virginia opossum (Didelphis virginiana) is a definitive host for multiple Sarcocystis species including Sarcocystis neurona, one of the causative agents of equine protozoal myeloencephalitis (EPM), a severe, neuromuscular disease of horses. Size and morphologic characteristics of isolates of Sarcocystis shed by the opossum were examined to determine if differences were useful in discriminating between the isolates and/or species. Collections of sporocysts from 17 opossums were molecularly characterized and measured using an ocular micrometer. The mean sporocyst size of isolates of S. neurona was 10.7 microm x 7.0 microm, Sarcocystis falcatula 11.0 microm x 7.1 microm, Sarcocystis speeri 12.2 microm x 8.8 microm, 1085-like isolate 10.9 microm x 6.8 microm, and 3344-like isolate 19.4 microm x 10.5 microm. The length and width of S. speeri were statistically different (p < 0.05) from the sporocysts of other types. The length of S. neurona and S. falcatula sporocysts were statistically different (p < 0.05) from each other and the width of S. falcatula and 1085 differed (p < 0.05). The fifth sporocyst type (3344) was observed, but due to pronounced morphological characteristics, statistical analysis was not performed. There was no consistent difference between the taxa based on internal structure of the sporocyst.

Viability of Sarcocystis neurona sporocysts and dose titration in gamma-interferon knockout mice

Gamma-interferon knockout mice have become the model animal used for studies on Sarcocystis neurona. In order to determine the viability of S. neurona sporocysts and to evaluate the course of the disease in these mice, sporocysts were collected from opossums (Didelphis virginiana), processed, and stored for varying periods of time. Gamma-interferon knockout mice were then inoculated orally with different isolates at different doses. These animals were observed daily for clinical signs until they died or it appeared necessary to humanely euthanize them. 15 of 17 (88%) mice died or showed clinical signs consistent with neurologic disease. The clinical neurologic symptoms observed in these mice appeared to be similar to those observed in horses. 15 of 17 (88%) mice were euthanized or dead by day 35 and organisms were observed in the brains of 13 of 17 (77%) mice. Dose appeared not to effect clinical signs, but did effect the amount of time in which the course of disease was completed with some isolates. The minimum effective dose in this study was 500 orally inoculated sporocysts. Efforts to titrate to smaller doses were not attempted. Direct correlation can be made between molecularly characterized S. neurona sporocysts and their ability to cause neurologic disease in gamma-interferon knockout mice.

Equine protozoal myeloencephalitis

Recent advances in the understanding of the parasite life cycle, epidemiology, clinical signs, diagnosis, treatment, and prevention of EPM are reviewed. The NAHMS Equine '98 study and a controlled retrospective study from The Ohio State University College of Veterinary Medicine identified a number of risk factors associated with development of the disease. The national annual incidence of EPM was 1% or less depending on the primary use of the animals. Increased disease risk was associated with age (1-5 and > 13 years of age), season (lowest in winter months and increasing with ambient temperature), previous stressful events, the presence of opossums, the use of nonsurface water drinking systems, and failure to restrict wildlife access to feed. Horses that received treatment were 10 times more likely to improve, and those that improved were 50 times more likely to survive. A number of recent studies confirmed that horses can be experimentally infected with S. neurona; however, large numbers of sporocysts are apparently necessary to achieve infection, and clinical signs and abnormal CNS histology are only seen inconsistently. Results suggest that CNS infection and positive CSF immunoblot findings may be transient phenomena among naturally infected horses. Although immunosuppression may be involved in the development of EPM, some element of the immune response seems to be necessary for the development of clinical signs. Use of the standard immunoblot test for the detection of anti-S. neurona antibodies in CSF continues to provide the most useful adjunct to a detailed neurologic examination for the diagnosis of EPM. Test sensitivity and specificity were 89% in 295 horses euthanatized because of neurologic disease, of which 123 were confirmed cases of EPM. The PPV was 85%, and the NVP was 92%. A number of promising new EPM treatments are under investigation. In addition to standard SDZ/PYR therapy, toltrazuril, ponazuril, diclazuril, and NTZ have shown promise as possible alternatives.

A random amplified polymorphic DNA polymerase chain reaction technique that differentiates between Neospora species

Neospora caninum is a recently described coccidial parasite that was first isolated from a dog in 1988 and has subsequently been shown to infect a wide range of mammals. Neospora hughesi, a new species of this genus, has recently been isolated from the spinal cord of horses showing clinical signs of equine protozoal myeloencephalitis. The random amplified polymorphic DNA polymerase chain reaction technique is capable of differentiating between N. caninum and N. hughesi.

Neospora hughesi: experimental infections in mice, gerbils, and dogs

Neospora hughesi is a recently described cause of equine protozoal myeloencephalitis (EPM). A rodent model for pathogenicity would facilitate development of therapies to be used in horses. In the present study, we examined the susceptibility of BALB/c gamma-interferon gene knockout (gamma-INFKO), BALB/c, CD-1, and C57BL/6 strains of mice and gerbils to infection with tachyzoites of the Nh-A1 strain of N. hughesi isolated from a horse from AL, USA. Only the gamma-IFNKO mice developed severe clinical disease following infection with N. hughesi and died 19-25 days after infection and exhibited severe cardiac lesions. In contrast, experimental infection of gamma-INFKO mice with tachyzoites of the NC-1 or NC-Liverpool strains of Neospora caninum resulted in deaths 8-10 days after infection. The most severe lesions were in the livers, spleens, and lungs of these mice. Gerbils inoculated with N. hughesi did not develop clinical disease, had few microscopic lesions, but did seroconvert. Two dogs fed the brains of mice, shown to contain N. hughesi tissue stages by cell culture and gamma-IFNKO mouse bioassay, did not shed N. caninum-like oocysts over a 23 days observation period. The marked difference in pathogenicity between the two species of Neospora in gamma-IFNKO mice, and lack of oocyst excretion by dogs fed N. hughesi infected mice provide additional evidence that the species distinction between N. caninum and N. hughesi is valid.