Comparison of Prevalence Factors in Neurologic Horses with and Without Seropositivity to Neospora hughesi and/or Sarcocystis neurona

The results of this retrospective study show that Neospora hughesi is, alone or in combination with Sarcocystis neurona, associated with equine protozoal myeloencephalitis (EPM) cases. The wide geographic origin of N. hughesi seropositive horses highlights the need to test for both protozoal pathogens in horses with suspected EPM.

1. Introduction

Although equine protozoal myeloencephalitis (EPM) due to Sarcocystis neurona is well recognized throughout the United States, the occurrence of EPM due to Neospora hughesi has remained poorly investigated. The aim of this study was to determine the frequency of suspected EPM horses testing seropositive to N. hughesi and to compare prevalence factors among suspected EPM horses testing seropositive or seronegative to N. hughesi and/or S. neurona.

2. Materials and Methods

Epidemiological information from neurologic horses tested for specific antibodies to N. hughesi and S. neurona by means of an indirect immunofluorescent antibody test were reviewed, using forms submitted to the School of Veterinary Medicine at Davis from December 1, 2010, to November 30, 2011. The submission forms for each horse contained information pertaining to the date of sample collection, the state of residence, signalment, and clinical signs. Horses were allocated to one of four groups, depending on the serological results: Neospora seropositive only group, S. neurona seropositive only group, N. hughesi and S. neurona seropositive group, and N. hughesi and S. neurona seronegative group. 

3. Results and Discussion

A total of 3,123 submissions were evaluated. EPMsuspected horses seropositive for N. hughesi and S. neurona originated from 25 and 41 states, respectively. Significant associations were made between states, months of submission, breeds, clinical signs, and serological groups. There was no association between age or sex and serological groups.