Seroprevalence of Sarcocystis neurona and Neospora hughesi in healthy horses from the province of Alberta, Canada.

Overview

• This study assessed the presence of antibodies against the parasites Sarcocystis neurona and Neospora hughesi in healthy horses living in Alberta, Canada, to understand their exposure to these pathogens that cause equine protozoal myeloencephalitis (EPM).

Background

• Equine protozoal myeloencephalitis (EPM) is a neurological disease in horses caused mainly by Sarcocystis neurona and less commonly by Neospora hughesi.
• These parasites infect horses and can cause debilitating neurological symptoms.
• Seroprevalence studies, which look for antibodies against these pathogens in blood, help determine how widespread exposure is among horse populations.
• Limited data existed on exposure rates in Canadian horses, especially in Alberta.

Objectives

• To establish the prevalence of antibodies against S. neurona and N. hughesi in horses residing exclusively in Alberta, Canada.
• To use commercially available immunodiagnostic tests to evaluate antibody presence in horses that show no neurological symptoms.

Methods

• Samples were drawn from a biobank containing serum from 116 healthy horses in Alberta collected during 2021-2022.
• Only horses that had continuously lived in Alberta and had no neurologic signs were included, based on owner survey information.
• Serological testing methods used included:
  • Indirect Fluorescent Antibody Test (IFAT) for both S. neurona and N. hughesi.
  • Enzyme-Linked Immunosorbent Assays (ELISAs) specific for S. neurona (rSnSAG2/4/3 ELISA) and N. hughesi (NhSAG1 ELISA).
  • A subset of 30 samples underwent Western blot testing for S. neurona antibodies.
• The study design was cross-sectional, analyzing the antibody status at one point in time.

Results

• For anti-S. neurona antibodies:
  • 26 of 116 horses tested positive by IFAT.
  • 4 of 116 were positive by ELISA.
  • 5 of 30 tested positive by Western blot in the subset.
  • No horse was positive on all three tests simultaneously, indicating poor agreement between tests.
• For anti-N. hughesi antibodies:
  • 18 of 116 were positive by IFAT.
  • 2 of 116 were positive by ELISA.
  • No horses were positive on both tests concurrently.
• The disparate results across testing methods suggest variable test sensitivities or specificity challenges in detecting exposure.

Conclusions

• The study supports that some horses in Alberta have been exposed to S. neurona and N. hughesi despite appearing healthy and neurologically normal.
• Commercially available serological tests for detecting antibodies showed poor concordance and may have low sensitivity in this population.
• Results imply caution when interpreting serological tests for EPM pathogens in healthy horses due to possible false positives or negatives.
• Further research is necessary to improve diagnostic accuracy and clarify the significance of antibody presence in asymptomatic horses.