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.     

Prevalence of agglutinating antibodies to Sarcocystis neurona in raccoons, Procyon lotor, from the United States

Equine protozoal myeloencephalitis (EPM) is the most important protozoal disease of horses in North America and it is caused by Sarcocystis neurona. Natural cases of encephalitis due to S. neurona have been reported in raccoons, Procyon lotor. We examined 99 raccoons for agglutinating antibodies to S. neurona using the S. neurona agglutination test (SAT) employing formalin-fixed merozoites as antigen. Raccoons originated in Florida (N=24, collected in 1996), New Jersey (N=25, collected in 1993), Pennsylvania (N=25, collected in 1999), and Massachusetts (N=25, collected in 1993 and 1994). We found that 58 (58.6%) of the 99 raccoons were positive for antibodies to S. neurona using the SAT; 44 of 99 raccoons (44%) had titers of ≥1:500. This prevalence is similar to the reported seroprevalence of 33–60% for S. neurona antibodies in horses from the United States using the Western blot test.     

Antigen-specific antibodies in cerebrospinal fluid after intramuscular injection of ovalbumin in horses

Eighteen normal horses were assigned to 1 of 3 treatment groups to investigate the effects of IM or intrathecal (IT) administration of ovalbumin on serum and cerebrospinal fluid (CSF) antibody production. Horses of group 1 were injected intramuscularly with ovalbumin and adjuvant, while horses in treatment groups 2 and 3 received ovalbumin intrathecally or intravenously, followed by IM injection as in group 1. Serum and CSF antibody titers were tested in group I every 30 days for 4 months, while serum and CSF were collected in group 2 and 3 horses at postvaccination day 60. Horses of group 1 (IM) developed a serum antibody titer that peaked at postadministration day 60 (1:24,320 +/- 7,680) (mean +/- I SEM). Anti-ovalbumin antibodies were detected in CSF, and titers paralleled that of the serum, although at a much lower concentration (peak, 1:166 +/- 87). Horses of groups 2 and 3 developed significantly (P = .02) lower serum titers (1:720 and 1:2,067, respectively), but the difference in CSF titers did not achieve statistical significance (P = .06). The results confirm that antigen-specific antibody can be found in the CSF of horses in which antigen is not administered intrathecally. This may affect the interpretation of CSF analysis in diseases such as equine protozoal myeloencephalitis. Further, the findings suggest that IT injection of the soluble antigen ovalbumin induces a state of antigenic tolerance in the horse. The clinical significance of this finding remains unknown at this time.     

Sarcocystis neurona-specific immunoglobulin G in the serum and cerebrospinal fluid of horses administered S neurona vaccine

A vaccine against Sarcocystis neurona, which induces equine protozoal myeloencephalitis (EPM), has received conditional licensure in the United States. A major concern is whether the immunoglobulin G (IgG) response elicited by the vaccine will compromise the use of Western blotting (WB) as a diagnostic tool in vaccinated horses with neurologic disease. Our goals were to determine if vaccination (1) causes seroconversion: (2) causes at least a transient increase in S neurona-specific IgG in the cerebrospinal fluid (CSF); and (3) induces an IgG response that can be differentiated from that induced by natural exposure. Horses included in the study (n = 29) were older than 6 months with no evidence of neurologic disease. The presence or absence of anti-S neurona antibodies in the serum of each horse was determined by WB analysis. Seropositive horses had CSF collected and submitted for cytology, CSF index, and WB analysis. The vaccine was administered to all the horses and boostered 3-4 weeks later. On day 14 after the 2nd administration, serum and CSF were collected and analyzed. Eighty-nine percent (8 of 9) of the initial seronegative horses seroconverted after vaccination, of which 57% (4 of 7) had anti-S neurona IgG in their CSE Eighty percent (16 of 20) of the seropositive horses had an increase in serum S neurona IgG after vaccination. Of the 6 of 20 horses that were initially seropositive/CSF negative, 2 were borderline positive for anti-S neurona IgG in the CSF, 2 tested positive, and 2 were excluded because the CSF sample had been contaminated by blood. There were no WB banding patterns that distinguished samples from horses that seroconverted due to vaccination versus natural exposure. Caution must be used in interpreting WB analysis from neurologic horses that have been recently vaccinated for EPM.     

Prevalence of agglutinating antibodies to Sarcocystis neurona in raccoons, Procyon lotor, from the United States.

Equine protozoal myeloencephalitis (EPM) is the most important protozoal disease of horses in North America and it is caused by Sarcocystis neurona. Natural cases of encephalitis due to S. neurona have been reported in raccoons, Procyon lotor. We examined 99 raccoons for agglutinating antibodies to S. neurona using the S. neurona agglutination test (SAT) employing formalin-fixed merozoites as antigen. Raccoons originated in Florida (N=24, collected in 1996), New Jersey (N=25, collected in 1993), Pennsylvania (N=25, collected in 1999), and Massachusetts (N=25, collected in 1993 and 1994). We found that 58 (58.6%) of the 99 raccoons were positive for antibodies to S. neurona using the SAT; 44 of 99 raccoons (44%) had titers of ≥1:500. This prevalence is similar to the reported seroprevalence of 33–60% for S. neurona antibodies in horses from the United States using the Western blot test.     

Seroprevalence of Sarcocystis neurona and Its Association With Neurologic Disorders in Argentinean Horses

Equine protozoal myeloencephalitis (EPM) is generally caused by Sarcocystis neurona and can produce substantial economic losses on equine production in America. The aims of the present study were to evaluate the seroprevalence of S. neurona in the main horse-production area of Argentina and associate it with the occurrence of neurologic disorders. Serum samples were collected from 640 horses in nine Argentinean provinces. Most of the samples correspond to animals ≥1.5-year-old from different breeds (n = 628); 12 samples were from younger horses. Further seroprevalence comparison was conducted from the older animals grouped with (n = 148) or without neurologic signs (n = 480). Immunoblot: proteins from 2 × 10⁷S. neurona merozoites were used as antigen on each membrane. Reactivity to antigens with relative mobility of 7, 10, and 16 kDa was considered specific for antibodies against S. neurona; reactivity at 30 kDa was recorded separately. The overall seroprevalence for S. neurona was 26.1% (167/640), and all the provinces had positive horses. Seroprevalence of animals with neurologic signs was greater (P < .001) than what was observed in normal horses (39.2% vs. 22.1%), with an odds ratio of 2.27. Reactivity at 30 kDa was detected in 71% of all samples. This study identified a wide distribution of S. neurona–positive animals in Argentina and horses with neurologic signs having a greater seroprevalence than normal horses. Sarcocystis neurona infection should be considered for early differential diagnosis and treatment of animals with neurologic disorders to decrease the economic impact of EPM in Argentina.     

Has Sarcocystis neurona Dubey et al., 1991 (Sporozoa: Apicomplexa: Sarcocystidae) cospeciated with its intermediate hosts?

The question of how Sarcocystis neurona is able to overcome species barrier and adapt to new hosts is central to the understanding of both the evolutionary origin of S. neurona and the prediction of its field host range. Therefore, it is worth reviewing current knowledge on S. neurona host specificity. The available host range data for S. neurona are discussed in relation to a subject of evolutionary importance—specialist or generalist and its implications to understand the strategies of host adaptation. Current evidences demonstrate that a wide range of hosts exists for S. neurona. This parasite tends to be highly specific for its definitive host but much less so for its intermediate host (I.H.). The unique specificity of S. neurona for its definitive host may be mediated by a probable long coevolutionary relationship of the parasite and carnivores in a restricted ecological niche ‘New World’. This might be taken as evidence that carnivores are the ‘original’ host group for S. neurona. Rather, the capacity of S. neurona to exploit an unusually large number of I.H. species probably indicates that S. neurona maintains non-specificity to its I.H. as an adaptive response to insure the survival of the parasite in areas in which the ‘preferred’ host is not available. This review concludes with the view that adaptation of S. neurona to a new host is a complex interplay that involves a large number of determinants.     

Perception of Equine Practitioners Regarding the Occurrence of Selected Equine Neurologic Diseases in the Northeast Over a 10-Year Period

A survey was developed to examine the perception of equine practitioners regarding the occurrence of five equine neurologic diseases in the northeastern United States over the 10-year period between June 1, 1997 and June 1, 2007. This information was then compared with trends at Cornell University's Equine Hospital during the same time span, which in general agreed with practitioners' opinions. Equine herpes virus-1 (EHV-1) neurologic disease, equine motor neuron disease (EMND), and equine protozoal myelitis (EPM) have historic and current relevance. Results showed that the frequency of EMND and EPM has remained relatively stationary or decreased somewhat, whereas the frequency of the neurologic strain of EHV-1 may have increased slightly over the last decade. Less historical information on clinical disease associated with Borrelia burgdorferi infection (Lyme disease) and Parelaphostrongylus tenuis exists; however, results suggest that P. tenuis in the equine is presently emergent. Opinions regarding the existence and rate of occurrence of clinical borreliosis in horses appear divided. A better understanding of the frequency with which these diseases occur, as well as possible associated positive risk factors, will aid the equine practitioner in making an appropriate diagnosis in cases of neurologic disease in their equine patients.     

Equine Proliferative Enteropathy Caused by Lawsonia intracellularis in a Foal in Brazil

An 8-month-old foal in Brazil presented with fever, colic, diarrhea, hypoproteinemia (especially hypoalbuminemia), leukocytosis, and hyperfibrinogenemia and became lethargic and anorexic with a poor body score. A diagnosis of Lawsonia intracellularis proliferative enteropathy was confirmed by fecal polymerase chain reaction and serologic testing, and the foal was successfully treated with oxytetracycline followed by azithromycin.     

Prevalence of Multi-Drug-Resistant Salmonella in Equids Maintained by Low Income Individuals and on Designated Equine Farms in India

We examined 872 equids (445 maintained by low-income individuals and 427 maintained on nine designated equine farms) and, using previously described methods for bacteria, isolated Salmonella from fecal samples of 59 (6.77%) animals. Of the 646 horses, 183 donkeys, and 43 mules that had feces cultured for Salmonella, 42 (6.5%), 7 (3.8%), and 10 (23.3%), respectively, were excreting Salmonella strains in feces. Six horse mares were excreting Salmonella enterica of two different serovars simultaneously. A total of 65 Salmonella enterica isolates belonged to 13 serovars, namely S. paratyphi B var Java (14), S. I. 4, 5, 12, 27: r, i: 1, 5 (11), S. Drogana (8), S. Newport (7), S. Saintpaul (5), S. Lagos (4), S. Typhimurium (5), S. Kottbus (3), S. Bovismorbificans (3), S. Dumfries (2), S. Tshiongwe (1) S. Weltevreden (monophasic) (1), and S. enterica ssp salamae (1). With Salmonella-specific polymerase chain reaction (PCR) using hisJ gene primers, 107 (12.3) fecal samples yielded a specific amplicon of 496 bp. On using PCR, prevalence of Salmonella in donkeys, horses, and mules was 4.9%, 10.8%, and 65.1%, respectively. With both methods of Salmonella detection in feces, prevalence was significantly higher in female than in male donkeys and horses. Salmonella shedding in feces was significantly higher in equids maintained by low-income people than those at designated equine farms. Almost all Salmonella isolates (63 of 65) had multiple-drug-resistance (MDR, resistance to three or more drugs). Salmonella isolates were commonly resistant to sulfamethoxazole (90.8%), tetracycline (70.8%), doxycycline (67.7%), furazolidone (66.2%), and colistin (55.4%). A few isolates had resistance to trimethoprim (3.1%), ciprofloxacin (3.1%), ceftriaxone (3.1%), ceftazidime (3.1%), cefoperazone (3.1%), chloramphenicol (4.6%), cefotaxime (6.2%), gentamicin (9.2%), ampicillin + cloxacillin (9.2%), cotrimoxazole (13.8%), kanamycin (13.8%), amoxicillin + clavulanic acid (16.9%), imipenem (16.9%), ampicillin (18.5%), amikacin (23.1%), neomycin (27.7%), nalidixic acid (33.8%), and streptomycin (36.9%). With the exception of 13 Salmonella isolates of S. Drogana (4), S. Newport (4), S. I. 4, 5, 12, 27: r, i: 1, 5 (4) and S. Kottbus (1) serovars, all had one or more than one plasmid. Molecular weight of plasmids ranged between 3 kDa and >87 kDa. One heavy plasmid (≥87 kda) was present in all the 52 plasmid-positive strains. Presence of plasmid could not be correlated with MDR in Salmonella isolates from equids.     

Clinical Experience Using MicroLactin for the Treatment of Equine Inflammatory Disease

MicroLactin is a patented milk protein concentrate whose mode of action is proposed to inhibit neutrophil activation in inflammation and to bolster the immune response in musculoskeletal diseases. MicroLactin was empirically used in the treatment of a series of equine clinical cases. MicroLactin was given in two trials to 166 horses in which neutrophils were associated with an inflammatory response. The primary clinical groups having the greatest positive responders to the use of MicroLactin were: respiratory (92%), joint lameness/foot trauma (90%), muscle injury/myositis (92%), equine protozoal myeloencephalitis (EPM) (81%), skin trauma/hypersensitivity (89%), and toxic enteritis (89%). Positive clinical results were seen within 10 to 14 days when MicroLactin was used as a daily treatment either alone or in combination with other anti-inflammatory agents or as an adjunct to the primary treatment.     

Clinical and Laboratory Findings in Equine Piroplasmosis

The objective of this study was to evaluate equine piroplasmosis (EP) as a cause of morbidity in horses in Sardinia (Italy), describe the clinical signs and altered hematologic and biochemical parameters, and illustrate response to different treatments. Among 44 horses suspected of tick-borne disease, 38 were polymerase chain reaction (PCR) positive for Theileria equi (n = 27) or Babesia caballi (n = 6), whereas five were positive for both protozoans. Typical clinical features of piroplasmosis were seen in some of the horses, whereas others had nonspecific mild symptoms. Hematologic findings revealed involvement of the three blood cell lineages (anemia, leukopenia or leukocytosis, thrombocytopenia), and biochemical variations were related to increased bilirubin, alteration of serum phosphorus, and hypoalbuminemia. We suggest that the two protozoans are the most important causative agents of equine tick-borne disease in this geographic area, and we observe that different clinical features are associated with the disease; in addition to the typical aspects of piroplasmosis, characterized by fever, pale mucous membranes, and icterus, we can signal other nonspecific mild signs such as weight loss, weight loss associated with an insignificant leukopenia, or weight loss associated with depression, anorexia, and mild hyperbilirubin. The study is intended as a practical contribution for veterinary practitioners because it describes different clinical presentations and laboratory findings of EP, suggests diagnostic and therapeutic approaches to the disease, and shows diffusion of the disease in a Mediterranean region.