Toxoplasma-like sporozoa in an aborted equine fetus.

The study discusses a case where protozoa—similar to the commonly known Toxoplasma gondii—were found in a horse fetus that was aborted two months prior to its expected due date. The protozoa were located in the lung tissue, a fact confirmed through laboratory examination methods, which however failed to formally identify the organisms as Toxoplasma gondii.

Identification of lesion sites and protozoa

• The study centered on the lung specimens of a prematurely aborted equine fetus. Upon examination, these tissues manifested signs of damage and disease in the form of areas of necrosis and infiltrations of mononuclear cells, a type of white blood cell.
• More importantly, researches found protozoans (single-celled, usually parasitic organisms) both in and outside (extracellular and intracellular) the lung’s alveolar tissue—a key part of the lungs that facilitates gas exchange.

Protozoan measurements and characteristics

• The individual organisms measured about 4 microns by 2.5 microns. In comparison, bigger cyst-like structures, also noted in the specimens, were around 25 microns by 18 microns in size.
• The biological characteristics of these organisms and structures led researchers to compare them to the Toxoplasma gondii, a common cause of toxoplasmosis, a disease that can lead to severe health consequences in horses, and can also be transmitted to humans and other animals.

Exclusion of Toxoplasma gondii

• Zoologists made use of particular staining methods—periodic acid-Schiff and the immunoperoxidase and peroxidase-antiperoxidase—to test whether these organisms were indeed Toxoplasma gondii.
• These tests were negative, indicating that the organisms found did not belong to the known Toxoplasma gondii species.
• Additionally, antibody tests from the mare that carried the fetus were conducted twelve days after the abortion. These tests returned low serum antibody titers (less than 1:10) against T. gondii, further suggesting that the organisms were not T. gondii.