Seroprevalence of Sarcocystis spp., Neospora spp. and Besnoitia spp. in horses (Equus caballus) intended for slaughter in the state of Rio Grande do Sul, Brazil.

Overview

• This study investigated the prevalence of three parasitic infections—Sarcocystis neurona, Neospora caninum, and Besnoitia besnoiti—in horses in Rio Grande do Sul, Brazil, by testing blood samples and attempting parasite detection in brain tissues.

Background and Objectives

• The parasites investigated are protozoan parasites that can infect horses and other animals, potentially causing disease:
• Sarcocystis neurona: Known to cause equine protozoal myeloencephalitis (EPM), a neurological disease in horses.
• Neospora caninum: Primarily causes disease in cattle and dogs but can infect other mammals.
• Besnoitia besnoiti: Causes besnoitiosis, mainly in cattle, and the significance in horses is less clear.
• The study aimed to assess how common exposure (seroprevalence) to these three parasites is among horses intended for slaughter in Rio Grande do Sul, Brazil.

Methods

• A total of 354 equine serum samples were collected at slaughterhouses.
• The Immunofluorescent Antibody Test (IFAT) was used to detect antibodies indicating exposure to the parasites:
• Cut-off titers of 1:80 for S. neurona and 1:50 for N. caninum and B. besnoiti were used to define positive results.
• To attempt direct parasite detection, brain samples from seropositive horses for N. caninum underwent:
• Polymerase Chain Reaction (PCR) testing.
• Bioassay using gerbils (Meriones unguiculatus), an animal model commonly used to check for viable parasites.
• Samples positive by IFAT for B. besnoiti were further tested by Western blot, a confirmatory method.

Results

• Seroprevalence rates (percentage of horses with antibodies) were:
• 44.63% (158/354) positive for Sarcocystis neurona.
• 9.32% (33/354) positive for Neospora caninum.
• Some horses showed combined positivity:
• 3.38% (12) positive for both N. caninum and S. neurona.
• 1.41% (5) positive for S. neurona and B. besnoiti.
• 0.84% (3) positive for B. besnoiti and N. caninum.
• However, none of the B. besnoiti IFAT positive samples were confirmed by Western blot, suggesting false positives or cross-reactivity in IFAT for this parasite.
• Brain samples from N. caninum seropositive horses tested negative by PCR and bioassay, indicating no detectable active infection in those tissues at the time of sampling.

Interpretation and Implications

• The relatively high seroprevalence for S. neurona suggests widespread exposure among horses slaughtered in this region, which could have implications for equine health and EPM risk.
• The lower seroprevalence for N. caninum indicates less frequent exposure, and the lack of detected parasite DNA or viable organisms in brain tissue suggests limited active infection or parasite presence in the central nervous system of these horses.
• The B. besnoiti results indicate that IFAT alone may not be reliable for diagnosing exposure in horses and that further testing (e.g., Western blot) is necessary to confirm infection.
• The combined positive reactions hint at possible co-exposures but require cautious interpretation as cross-reactivity in serological tests can occur.
• Overall, these findings provide important epidemiological data useful for veterinary surveillance and may guide disease control strategies in Brazilian equine populations.