Meningoencephalomyelitis caused by Neospora caninum in a juvenile fallow deer (Dama dama)

Seroprevalence of infectious pathogens of zoonotic and veterinary importance in wild ruminants from Slovenia

Introduction

Wildlife represents an increasingly important source of pathogens of medical and veterinary importance. Surveillance in wildlife offers an insight on current epidemiological status of selected pathogens and help to prevent spillovers to humans and livestock.

Material and methods

Our study included 312 wild ruminants belonging to five species: Roe deer (n = 134), red deer (n = 113), Alpine chamois (n = 53), European mouflon (n = 10) and Alpine ibex (n = 2). Seven pathogens that may have profound effect on human/livestock health and economic viability of the farms were tested using serological methods.

Results

Antibodies against Toxoplasma gondii, Neospora caninum, Coxiella burnetii, Brucella spp., Chlamydophila abortus, Mycobacterium avium subsp. paratuberculosis (MAP) and Mycobacterium bovis were detected in 34.62% (108/312), 0.96% (3/312), 2.24% (7/312), 0, 0.96% (3/312), 0, 0.64% (2/312) of animals tested, respectively. Because of low prevalences, risk factors were assessed only for T. gondii. Sex (female>male) and species (roe deer>red deer, roe deer>Alpine chamois) were significantly associated with the T. gondii positive outcome, while age was not.

Discussion

Adult males had the lowest T. gondii prevalence which offers future research opportunities. The lower seroprevalence of most investigated pathogens suggests game meat, if properly cooked, as being relatively safe for human consumption. This is the first study investigating the seroprevalence and associated risk factors of selected pathogens in wild ruminants in Slovenia.

Congenital transmission of Neospora caninum in wild ungulates and foxes

Introduction

Neospora caninum is one of the main causes of abortion in cattle. In wildlife, the occurrence and relevance of vertical infection have not been yet clearly evaluated. The aim of this study was to verify the possibility of vertical transmission of N. caninum in three wild species extensively distributed in Europe, namely roe deer Capreolus capreolus, wild boar Sus scrofa and red fox Vulpes vulpes.

Methods

A total of 190 fetuses (72 wild boars, 67 foxes and 51 roe deer) from 61 females were included in the study. All animals, which were either found dead or culled within selective control plans in North-western Italy, were tested, in parallel by PCR on central nervous system, skeletal muscle and kidney.

Results and discussion

The efficiency of vertical transmission in the three target species was of 87.5% (95% CI 69.00-95.66).

Epidemic abortions due to Neospora caninum infection in farmed red deer (Cervus elaphus)

This study describes for the first time an abortion outbreak caused by Neospora caninum in farmed red deer. During a 5-year period, farmed hinds, naturally mated, were regularly ultrasound monitored to detect reproductive losses over their gestation. During the 4 years previous to the outbreak, abortion rates ranged from 4.7 to 8.6% (average 6.5%), and serology for indirect diagnosis of neosporosis and toxoplasmosis was performed. At the fifth year, the abortion rate increased to 25.3%. During this outbreak, three aborted foetuses and their placentas were recovered and submitted to laboratory for etiological diagnosis. Blood samples were collected from the 81 hinds at the end of the gestational period and the seropositivity rate for N. caninum, Toxoplasma gondii, Brucella abortus, bovine viral diarrhoea virus and bovine alphaherpesvirus type 1 was 66.7%, 67.9%, 0.0%, 8.6% and 0.0%, respectively. Neospora caninum-seropositive hinds (OR = 5.7, P = 0.0271) and hinds with high antibody titres to N. caninum (OR = 7.4, P = 0.0130) were more likely to abort than seronegative hinds. In addition, N. caninum seropositivity rate in the aborted hinds was higher (OR = 5.4, P = 0.033) than the non-aborted hinds. No association was found between T. gondii nor BVDV-seropositivity and abortions. Typical protozoal histopathologic findings (necrotizing non suppurative encephalitis, meningitis, myocarditis, hepatitis, among others) were observed in all foetuses. Neospora caninum was immunolabelled by immunohistochemistry in several tissues from two foetuses, and infection was also confirmed in the three foetuses by serology and/or DNA detection. No other abortifacient agent was detected in the foetuses. Their dams showed high N. caninum antibody titres (≥ 6400). Serologic evidence and epidemiological data recorded suggested a point-source of N. caninum infection before the occurrence of the outbreak, probably related with contaminated feedstuff with oocysts. Moreover, the intensive production system with a high stocking rate could be also considered a factor which might have increased the risk of horizontal N. caninum infection in this herd.

Neospora caninum and Toxoplasma gondii infections and their relationship with reproductive losses in farmed red deer (Cervus elaphus)

The aims of the present study were to determine the Neospora caninum and Toxoplasma gondii seropositivity rates in farmed red deer hinds from Argentina and their relationship with reproductive losses. Over a 2-year period, 449 hinds from 4 commercial farms were serologically tested at late gestation for N. caninum and T. gondii by IFAT. During the first year, a sequential serological analysis was carried out at 3 different time points to analyze antibody dynamics from mating until the end of the gestation period. Fetal and postnatal mortality rates were estimated by 3 successive ultrasound scannings (us) annually and a breeding control carried out after the calving period. Ultrasound fetal measurements were used to estimate conception date and gestational age of abortions. The seropositivity rate for N. caninum was 25.5% (37/145) for the yearlings and 34.2% (104/304) for the adults, while for T. gondii was 64.3% (93/145) and 78.3% (238/304), respectively. Abortions detected at us1 and us2 were 13/21 (61.9%) with a range of gestational age of 30-87 days, while abortions detected at us3 were 8/21 (38.1%) with a range of gestational age of 49-209 days. The fetal mortality rate was 4% and 5.8%, while the postnatal mortality rate was 18.8% and 4.1% of 101 yearlings and 294 adult pregnant hinds, respectively. Most seropositive hinds to both protozoans showed a stable antibody titer pattern from mating to the end of gestation, and a lower proportion developed an increase in titers suggesting infection recrudescence. Seroconversion during the gestational period was demonstrated in 6 and 50 hinds for N. caninum and T. gondii, respectively. Hinds with fetal mortality were more likely to be seropositive to N. caninum (OR = 3.1) or have N. caninum titers ≥400 (OR = 27.4) than hinds that weaned a fawn. No statistical associations were detected for T. gondii seropositivity and reproductive losses. The pregnancy rate was not affected by N. caninum or T. gondii infection, while the serological evidence of N. caninum causing postnatal mortality was marginal. Based on serological evidence, N. caninum would be a potential abortigenic agent in red deer hinds.

Comparative health assessment of urban and non-urban free-ranging mule deer (Odocoileus hemionus) in southeastern British Columbia, Canada

Background

The provincial wildlife management agency, British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development, performed a translocation to control the urban mule deer (Odocoileus hemionus; uMD) overpopulation and supplement the declining non-urban mule deer (nuMD) population in the Kootenay region, British Columbia, Canada. The objectives of this cross-sectional study were to evaluate the health of the urban and nuMD populations by comparing pathogen exposure, body condition scores (BCS) and pregnancy rates, to characterize the health risks associated with the translocation and to investigate the role of infectious diseases in the decline of the nuMD deer population.

Methods

Two hundred free-ranging mule deer were captured in urban and non-urban environments in the Kootenay region from 2014 to 2017. BCS and morphometric examinations were performed for each deer. Blood samples collected from each deer were tested for exposure to selected pathogens and pregnancy status.

Results

Body condition scores averaged 3.4 on a five-point scale, was greater in nuMD, and significantly differed between years. Antibodies were detected for adenovirus hemorrhagic disease virus (38.4% (uMD 43.7%, nuMD 33.3%)), bluetongue virus (0.6% (uMD 1.2%, nuMD 0%)), bovine respiratory syncytial virus (8.4% (uMD 4.6%, nuMD 12.1%)), bovine viral diarrhea virus (1.1% (uMD 0%, nuMD 2.2%)), bovine parainfluenza-3 virus (27.0% (uMD 27.6%, nuMD 26.4%)), Neospora caninum (22.1% (uMD 24.4%, nuMD 19.7%)) and Toxoplasma gondii (8.2% (uMD 12.3%, nuMD 3.9%)). No antibodies against epizootic hemorrhagic disease virus were detected. Pregnancy rates did not differ between the two deer populations (90.7% (uMD 90.6%, nuMD 90.9%)). Exposure to N. caninum was associated with a reduced probability of being pregnant. uMD were more likely to be exposed to T. gondii than nuMD.

Discussion

Comparison of BCS, pregnancy rates and pathogen exposure of uMD and nuMD showed that the health of the two populations did not significantly differ, suggesting uMD translocations do not pose a severe risk of pathogen transmission between mule deer populations and that these selected pathogens do not factor in the decline of the nuMD population. However, inclusion of additional health indicators and creation of a robust predictive disease model are warranted to further characterize the health of mule deer and the health risks associated with uMD translocations. These results should be considered as part of a formal risk assessment for future uMD translocations in southeastern British Columbia.

Transplacental transmission of Neospora caninum in moose (Alces alces)

A 5-years-old moose (Alces alces) cow kept in a zoo in the German Federal State of Brandenburg aborted a female foetus of 44cm crown rump length (CRL). Pathohistological analysis revealed several Neospora (N.) caninum infected cells and cysts, as well as multifocal gliosis, necrosis, haemorrhages, dystrophic mineralisation and haemosiderosis in the brain, predominantly in cerebrum and brainstem. In addition, mild lymphocytic meningitis was present. Together with the fresh foetus, a mummified foetus of 16cm CRL was expelled. Neither focal necrosis, nor inflammation was detected in the brain of the mummified foetus. By two polymerase chain reactions (PCR) targeting the pNc5 gene of N. caninum (i.e. an end point PCR and a real-time PCR), by two serological methods (immunofluorescence test and immunoblot), by histological and immunohistochemical analyses, transplacental N. caninum infection was confirmed in the fresh foetus and interpreted as possible cause of abortion. Infection with other agents causing abortion including Bovine Herpesvirus 1 (BHV1), Bluetongue Virus (BTV), Bovine Virus Diarrhoea Virus (BVDV), Brucella spp., Chlamydia spp., Coxiella burnetii and Toxoplasma gondii were excluded. Our findings show that control measures may be necessary to protect captive moose against accidental N. caninum infection. Further studies are needed to explore the importance of neosporosis in wild and captive moose.

Myofasciitis in the Domestic Ferret

Since late 2003, an inflammatory disease of muscle and fascia has been diagnosed in several ferrets at Northwest ZooPath, and this report describes the condition in 17 ferrets. It is a disease of young ferrets, characterized by rapid onset of clinical signs, high fever, neutrophilic leukocytosis, treatment failure, and death (or euthanasia). Gross lesions include atrophy of skeletal muscle; red and white mottling and dilatation of the esophagus; and splenomegaly. Histologically, moderate to severe suppurative to pyogranulomatous inflammation is in the skeletal muscle and the fascia at multiple sites, including esophagus, heart, limbs, body wall, head, and lumbar regions. Myeloid hyperplasia of spleen and/or bone marrow also is a prominent feature. Ultrastructural lesions include mitochondrial swelling, intracellular edema, disruption of myofibrils and Z bands. Bacterial and viral cultures, electron microscopy, immunohistochemistry, and polymerase chain reaction were negative for a variety of infectious agents. The clinical presentation and distribution of lesions suggests that polymyositis in domestic ferrets is likely a distinct entity. The etiopathogenesis if this condition is not known.

Sarcocystis spp. Infection in two Red Panda Cubs (Ailurus fulgens)

Two neonatal male red panda (Ailurus fulgens) littermates were submitted for necropsy examination. One animal was found dead with no prior signs of illness; the other had a brief history of laboured breathing. Post-mortem examination revealed disseminated protozoal infection. To further characterize the causative agent, transmission electron microscopy (TEM), immunohistochemistry (IHC), polymerase chain reaction (PCR) and amplification and nucleic acid sequencing were performed. IHC was negative for Toxoplasma gondii and Neospora caninum, but was positive for a Sarcocystis spp. TEM of cardiac muscle and lung revealed numerous intracellular apicomplexan protozoa within parasitophorous vacuoles. PCR and nucleic acid sequencing of partial 18S rRNA and the internal transcribed spacer (ITS)-1 region confirmed a Sarcocystis spp. that shared 99% sequence homology to Sarcocystis neurona and Sarcocystis dasypi. This represents the first report of sarcocystosis in red pandas. The histopathological, immunohistochemical, molecular and ultrastructural findings are supportive of vertical transmission resulting in fatal disseminated disease.

A review of neosporosis and pathologic findings of Neospora caninum infection in wildlife

Neospora caninum is an apicomplexan parasite that is the etiologic agent of neosporosis, a devastating infectious disease regarded as a major cause of reproductive loss in cattle and neuromuscular disease in dogs worldwide. This protozoan pathogen is maintained in the environment by a heteroxenous life cycle that involves a definitive canid host and a wide range of intermediate hosts. In recent years, a number of wildlife species have been investigated for their possible involvement in the N. caninum life cycle and many have been implicated as intermediate hosts. However, in many instances these studies have utilized serological and molecular techniques to detect infection in clinically normal animals, and investigation of possible associated morbidity, mortality, and pathology has been neglected. As such, the occurrence and importance of Neospora-associated disease in wildlife species are unknown. In order to improve our understanding of the significance of N. caninum infection in nondomestic species, the present review provides an up-to-date summary of clinical neosporosis and N. caninum-associated pathologic lesions in naturally and experimentally infected wildlife species. We provide a list of all free-ranging and captive wildlife species identified with N. caninum infection to date using currently available diagnostic tools. The advantages and disadvantages of diagnostic methods in wildlife are addressed in order to recommend optimal diagnosis of confirming N. caninum infection and neosporosis in nondomestic species. Although current data would suggest that N. caninum infection does not adversely impact wildlife populations, there is a need for greater international uniformity in the diagnosis of N. caninum infection and neosporosis in nondomestic species in order to assess the true consequences of parasite infection.

Neospora caninum is a cause of perinatal mortality in axis deer (Axis axis)

Neospora caninum is a worldwide distributed protozoan that may cause neuromuscular disease in dogs and reproductive failure in domestic and wild ruminants. One axis fawn (Axis axis) and four neonates from the same deer herd died at a zoo in Argentina within a four-month period. The fawn presented with dilatation of the anal sphincter at birth and incontinence, developed weakness and ataxia and died at 14 days of age. At necropsy, a mega formation of the distal large intestine was observed. Microscopically, non-suppurative encephalitis, suppurative bronchopneumonia, fibrin necrotic enteritis and degenerative changes in the liver were observed in hematoxilin and eosin-stained tissue sections, and thick-walled N. caninum-like cysts were observed in fresh brain samples. Serologic studies for N. caninum revealed an IFAT titer of 1:6400 in the fawn and 1:25, 1:400, 1:3200 and 1:6400 in the neonates. N. caninum DNA was detected in brain samples from the fawn and from one neonate by PCR, and the parasite was isolated in vitro from the fawn' brain after passage through gerbils (Meriones unguiculatus) and gamma-interferon knock-out mice. N. caninum DNA obtained from the fawn, neonate and isolated parasites showed the same microsatellite pattern. This suggests a common infection source for both animals. The diagnosis of N. caninum infection was confirmed, suggesting its association with perinatal mortality in captive axis deer. To the best of our knowledge, this is the first report of clinical disease associated to N. caninum infection in axis deer and of isolation of the parasite from this wild ruminant species.

Neospora caninum and Wildlife

Bovine neosporosis caused by Neospora caninum is among the main causes of abortion in cattle nowadays. At present there is no effective treatment or vaccine. Serological evidence in domestic, wild, and zoo animals indicates that many species have been exposed to this parasite. However, many aspects of the life cycle of N. caninum are unknown and the role of wildlife in the life cycle of N. caninum is still not completely elucidated. In North America, there are data consistent with a sylvatic cycle involving white tailed-deer and canids and in Australia a plausible sylvatic cycle could be occurring between wild dogs and their macropod preys. In Europe, a similar sylvatic cycle has not been established but is very likely. The present review is a comprehensive and up to date summary of the current knowledge on the sylvatic cycle of N. caninum, species affected and their geographical distribution. These findings could have important implications in both sylvatic and domestic cycles since infected wildlife may influence the prevalence of infection in cattle farms in the same areas. Wildlife will need to be taken into account in the control measures to reduce the economical losses associated with this important disease in cattle farms.

Cutaneous toxoplasmosis in two dogs

Cutaneous toxoplasmosis has been previously reported in human beings, rarely reported in cats, and reported in 1 dog with systemic toxoplasmosis. The present report describes 2 cases of cutaneous toxoplasmosis in 2 dogs treated with immunosuppressive therapy. One of the dogs developed generalized cutaneous pustules and pruritus, and the other dog only had a single subcutaneous nodule. Microscopically, skin biopsies showed moderate to severe pyogranulomatous and necrotizing dermatitis and panniculitis, with multifocal vasculitis and vascular thrombosis. Single or aggregates of protozoal tachyzoites were mostly intracytoplasmic and occasionally extracellular. The etiology was confirmed in both cases by immunohistochemistry and by polymerase chain reaction assays, which were followed by nucleic acid sequencing. Both patients were treated with clindamycin. The dog with generalized lesions developed pulmonary and neurological signs and was euthanized. The dog with a single nodule recovered completely with no remission of cutaneous lesions.

Congenital neosporosis in goats from the State of Minas Gerais, Brazil

Congenital Neospora caninum infection was diagnosed in two Saanen goat kids from two distinct herds with a history of abortion and weak newborn goat kids in the Southern region of the State of Minas Gerais, Brazil. The first kid was weak at birth, had difficulty to rise and was unable to nurse. Gross lesions of porencephaly and hydrocephalus ex vacuo were seen. Multifocal necrosis, gliosis and non-supurative encephalitis were observed in the brain. Several parasitic cysts with a thick wall that reacted strongly only with polyclonal antiserum to Neospora caninum were seen in the cerebral cortex, brain stem and cerebellum. The second kid was born from a Neospora caninum seropositive mother that aborted in the last pregnancy. It was born without clinical signs. The diagnosis of neosporosis was based on antibody titer of 1:800 to N. caninum by indirect fluorescence antibody test obtained from blood collected before the goat kid ingested the colostrum and Neospora caninum DNA was detected by polymerase chain reaction and sequenced from placenta. This is the first report of neosporosis in goats in the southeast region of Brazil.

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.

Seroprevalence of Neospora caninum in non-carnivorous wildlife from Spain

Serum samples from 1034 non-carnivorous wildlife from Spain were tested for antibodies to Neospora caninum by competitive screening enzyme linked immunosorbent assay (ELISA) and confirmed by an indirect fluorescent antibody test (IFAT). High agreement was observed between results in both techniques (kappa value higher than 0.9). Prevalences of N. caninum antibodies positive by both techniques were 11.8% of 237 red deer (Cervus elaphus), 7.7% of 13 barbary sheep (Ammotragus lervia), 6.1% of 33 roe deer (Capreolus capreolus) and 0.3% of 298 wild boar (Sus scrofa). In one of 53 hares (Lepus granatensis), antibodies were found in the ELISA but could not be confirmed by IFAT due to lack of sample. Antibodies to N. caninum were not found in any of 251 wild rabbits (Oryctolagus cuniculus), 79 fallow deer (Dama dama), 27 mouflon (Ovis ammon), 40 chamois (Rupicapra pyrenaica) and three Spanish ibex (Capra pyrenaica). Statistically significant differences were observed between N. caninum seroprevalence in red deer and management of hunting estates (open versus fenced) with higher prevalence in fenced estates, and among sampling sites. Seroprevalence was particularly high in some areas (MO estate in South-Central Spain or some estates of Catalonia, North-East Spain), while no contact with N. caninum was observed in others. Results indicate that in certain areas of Spain, N. caninum is present in wildlife, especially in red deer. These results have important implications in both sylvatic cycles and may influence the prevalence of infection in cattle farms in those areas. To our knowledge, this is the first report of antibodies to N. caninum in wildlife from Spain and the first report of N. caninum antibodies in barbary sheep and wild boar.

Diagnosis of bovine neosporosis

The protozoan parasite Neospora caninum is a major cause of abortion in cattle. The diagnosis of neosporosis-associated mortality and abortion in cattle is difficult. In the present paper we review histologic, serologic, immunohistochemical, and molecular methods for dignosis of bovine neosporosis. Although not a routine method of diagnosis, methods to isolate viable N. caninum from bovine tissues are also reviewed.

Seroprevalences of antibodies to Neospora caninum and Toxoplasma gondii in zoo animals

Neospora caninum is an apicomplexan parasite that causes neuromuscular disease in dogs and abortions in cattle. Little is known about the prevalence of antibodies to this parasite in zoo animals. Sera from 556 animals, from 13 Czech and Slovak zoos were tested for antibodies to N. caninum and Toxoplasma gondii by indirect fluorescent antibody test. Antibodies to N. caninum were found in 31 of 556 zoo animals (5.6%), representing 18 of 114 species tested: Eurasian wolf (Canis lupus lupus), Maned wolf (Chrysocyon brachyurus), fennec (Vulpes zerda), cheetah (Acinonyx jubatus), jaguarundi (Herpailurus yaguarondi), Eurasian lynx (Lynx lynx), Indian lion (Panthera leo goojratensis), fisher (Martes pennanti), blackbuck (Antilope cervicapra), European bison (Bison bonasus), lechwe (Kobus leche), African buffalo (Syncerus caffer caffer), eland (Taurotragus oryx), sitatunga (Tragelaphus spekei gratus), Thorold's deer (Cervus albirostris), Eastern elk (C. elaphus canadensis), Vietnam sika deer (C. nippon pseudaxis) and Père David's deer (Elaphurus davidianus). Titres ranged from 1:40 to 1:2560. The highest prevalence 50% was found in family mustelidae of the order carnivora. Antibodies to T. gondii were detected in 193 of 556 zoo animals (34.7%) representing 72 of 114 species tested, with titres ranging from 1:40 to 1:40960. The highest prevalence 100% was found in families: hyaenidae, mustelidae, ursidae and viveridae of the order carnivora. The results of this study indicate that zoo animals have more exposure to T. gondii than to N. caninum. It is the first report of seroprevalence of antibodies to N. caninum in European zoo animals.

The sylvatic cycle of Neospora caninum: where do we go from here?

Bovine abortions due to Neospora caninum infection are a major cattle-production problem worldwide. The parasite is readily maintained in cattle populations by vertical transmission. The domestic dog excretes oocysts in its feces and, after sporulation, these oocysts are infectious to cattle. Current control measures are aimed at culling infected cows and limiting the access of cattle to infective oocysts. The recent revelations that coyotes (Canis latrans) can excrete N. caninum oocysts in their feces and that white-tailed deer (Odocoileus virginianus) are natural intermediate hosts of the parasite demonstrate the existence of a sylvatic cycle of neosporosis in North America. This complicates parasite-prevention programs but opens many new and exciting avenues of research. Similar canid-ruminant sylvatic cycles might exist in other countries and, if so, need to be investigated.

Evidence to support horses as natural intermediate hosts for Sarcocystis neurona

Opossums (Didelphis spp.) are the definitive host for the protozoan parasite Sarcocystis neurona, the causative agent of equine protozoal myeloencephalitis (EPM). Opossums shed sporocysts in feces that can be ingested by true intermediate hosts (cats, raccoons, skunks, armadillos and sea otters). Horses acquire the parasite by ingestion of feed or water contaminated by opossum feces. However, horses have been classified as aberrant intermediate hosts because the terminal asexual sarcocyst stage that is required for transmission to the definitive host has not been found in their tissues despite extensive efforts to search for them [Dubey, J.P., Lindsay, D.S., Saville, W.J., Reed, S.M., Granstrom, D.E., Speer, C.A., 2001b. A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM). Vet. Parasitol. 95, 89-131]. In a 4-month-old filly with neurological disease consistent with EPM, we demonstrate schizonts in the brain and spinal cord and mature sarcocysts in the tongue and skeletal muscle, both with genetic and morphological characteristics of S. neurona. The histological and electron microscopic morphology of the schizonts and sarcocysts were identical to published features of S. neurona [Stanek, J.F., Dubey, J.P., Oglesbee, M.J., Reed, S.M., Lindsay, D.S., Capitini, L.A., Njoku, C.J., Vittitow, K.L., Saville, W.J., 2002. Life cycle of Sarcocystis neurona in its natural intermediate host, the raccoon, Procyon lotor. J. Parasitol. 88, 1151-1158]. DNA from schizonts and sarcocysts from this horse produced Sarcocystis specific 334bp PCR products [Tanhauser, S.M., Yowell, C.A., Cutler, T.J., Greiner, E.C., MacKay, R.J., Dame, J.B., 1999. Multiple DNA markers differentiate Sarcocystis neurona and Sarcocystis falcatula. J. Parasitol. 85, 221-228]. Restriction fragment length polymorphism (RFLP) analysis of these PCR products showed banding patterns characteristic of S. neurona. Sequencing, alignment and comparison of both schizont and sarcocyst DNA amplicons showed 100% identity. Although Koch's postulates have not been demonstrated in this case study, the finding of mature, intact S. neurona schizonts and sarcocysts in the tissues of this single horse strongly suggests that horses have the potential to act as intermediate hosts. Further studies are needed to demonstrate Koch's postulates with repeated transfer of S. neurona between opossums and horses.