Neospora caninum-associated equine protozoal myeloencephalitis.

The research article investigates the occurrence of equine protozoal myeloencephalitis (EPM), a neurological disease in a 20-year-old horse, which was initially diagnosed as being caused by Sarcocystis neurona, but was ultimately found to be caused by Neospora caninum.

Background of the study

• This study focuses on equine protozoal myeloencephalitis (EPM), a common neurological disease in horses, usually associated with the parasite Sarcocystis neurona.
• In this particular case, a 20-year-old horse with severe ataxia (loss of full control of bodily movements) was clinically diagnosed with EPM. This preliminary diagnosis was based on the detection of S. neurona antibodies in the horse’s cerebrospinal fluid by western blot, an analytical technique used to detect specific proteins in a sample of tissue homogenate or extract.

Methodology

• The researchers administered corticosteroids to the horse to facilitate the in vitro culture of S. neurona from its spinal cord following necropsy, which is a post-mortem examination of the horse, akin to autopsy in humans.
• Microscopic examination of the horse’s brain and spinal cord revealed lesions characteristic of EPM, including multifocal inflammatory cellular infiltrates and large groups of protozoa.

Findings

• Interestingly, upon further immunohistochemical (a process to visually detect the presence of specific proteins in cells or tissues), light microscopic, and electron microscopic examinations, the researchers discovered that the protozoa infesting the horse’s brain and spinal cord were not S. neurona but another organism called Neospora caninum.
• Details such as the protozoan’s method of division (endodyogeny), the presence of rhoptries in tachyzoites (an intracellular infective form of the parasite), and reaction to N. caninum antibodies confirmed this identification.
• Therefore, despite the initial diagnosis and the horse’s clinical signs pointing towards S. neurona-induced EPM, the actual causative agent was found to be N. caninum.

Implications

• This finding highlights that N. caninum can also cause EPM, advising veterinarians to consider it as another potential causative agent when diagnosing and treating EPM.
• The research indicates a potential increase in the diagnosis of N. caninum as an etiological agent responsible for the lesions of EPM, suggesting a possible shift in epidemiological perspectives concerning this equine disease.