Systemic Toxoplasmosis in a Horse.

This study documents the first known case of clinical toxoplasmosis—a type of parasitic disease—in an American Quarter Horse gelding. The horse showed symptoms of weight loss, colic, fever, and soft feces, and after death, its autopsy showed signs of gastric mass, necrosis in cecal region, and presence of protozoal tachyzoites, which was eventually identified as toxoplasma gondii.

Case Description

• The article starts with the case of an adult American Quarter horse gelding. This horse had been experiencing weight loss and suddenly developed additional symptoms such as colic, fever, soft feces and elevated liver enzymes.
• The horse was presented for necropsy—essentially an autopsy on an animal—where they found multiple masses on the gastric mucosa, or lining of the stomach, and signs of necrosis, or tissue death, in the cecum, a part of the large intestine.

Histological Evaluation

• The investigation continued with histological evaluation, which refers to the study of microscopic structure of tissues. It was found that the masses consisted of lymph nodes with granulomatous inflammation, a special type of chronic inflammatory reaction, and areas showing tissue breakdown and dissolution, also known as liquefactive necrosis.
• Within and surrounding these necrotic areas were clusters of rapidly developing protozoan form known as tachyzoites. These clusters were found both free in the tissue and inside the cells that are part of the body’s immune response, known as histiocytes.
• Mild inflammation of similar kind was present in the spleen, lungs and liver. Necrotizing typhitis, i.e., severe inflammation of the cecum leading to tissue death, was also evident.

Identification of Toxoplasma gondii

• The researchers used immunolabeling, a technique that uses antibodies to identify a specific protein or antigen, in this case for Toxoplasma gondii, a protozoan parasite.
• The immunolabeling was found to be positive, confirming the presence of this parasite.
• The ultrastructural morphology, or the detailed structure of the protozoa as seen through an electron microscope, was found to be compatible with that of T. gondii.

Significance of the Case

• Although horses across the world have been found to test positive for T. gondii, indicating they have been exposed to this parasite, this is the first time the disease, toxoplasmosis, caused by this parasite has been clinically documented in this species.
• This study shows that horses can not only be carriers of Toxoplasma gondii, but they can also be affected by the disease caused by this parasite.