Small sarcocysts can be a feature of experimental infections with Sarcocystis neurona merozoites.

This research article investigates the existence of small tissue cysts, called sarcocysts, in animals experimentally infected with a parasite called Sarcocystis neurona. The study re-examines previously collected tissue samples from experimentally infected animals to determine if the small-sized sarcocysts were initially overlooked due to their size.

Background

• Sarcocystis neurona is a parasite associated with a disease in horses known as Equine Protozoal Myeloencephalitis (EPM).
• Previous studies trying to replicate the life cycle of the parasite in a laboratory setting have failed to produce tissue cysts in potential intermediate hosts.
• The studies showed no detectable sarcocysts based on histology (study of tissues) and in vivo feeding trials.

Objective of the Study

• A recent report showing the successful production of small sarcocysts led the researchers to revisit archived tissues from earlier experiments.
• The aim was to determine if small sarcocysts may have been overlooked due to their size and rarity compared to larger sarcocysts.

Methodology

• The researchers re-examined tissues from two previous inoculation studies involving parasites produced in vitro (in the lab) and then infected into cats and raccoons.
• These tissues were re-examined using a process known as immunohistochemistry staining, to make it easier to identify tissue cysts.

Findings

• In the cat study, no small cysts were found – this was consistent with the original findings.
• In the raccoon study, one raccoon was found to have small sarcocysts that had not been reported in the original publication. This led the researchers to speculate that smaller S. neurona sarcocysts may have been overlooked in the initial experimental inoculations.

Conclusions

• The researchers concluded that a closer examination of tissues, particularly using immunohistochemistry, is necessary to detect the smaller S. neurona sarcocysts that may be associated with experimental inoculations.
• This indicates that sarcocysts formed by S. neurona may be smaller than previously thought and potentially overlooked when using conventional methods of histology.