Astrocytic and microglial response and histopathological changes in the brain of horses with experimental chronic Trypanosoma evansi infection.

The research article examines how the brain of horses respond and change due to a chronic infection of Trypanosoma evansi, which is an experimentally placed parasite. The study observes the reactions of different types of cells in the central nervous system (CNS) and the severity of the consequent lesions.

Study design and methodology

• The subject of the study was a group of male and female horses, with differing levels of crossbreeding, and aged between four and seven years.
• The researchers injected the horses with trypomastigotes of T. evansi. This parasite was originally taken from an infected dog.
• After injection, the horses were monitored until they began showing signs of CNS disturbance. This was characterized by motor incoordination, specifically in the pelvic limbs. Symptoms appeared between 67 and 124 days after inoculation.
• A control group of horses that were not infected were observed over the same period of time for comparative purposes.
• To observe the changes in the CNS, specifically lesions, the horses’ tissues were stained with Hematoxylin and Eosin (HE) and probed with the avidin-biotin peroxidase method.

Findings and implications

• The infected horses developed a widespread non-suppurative meningoencephalomyelitis, an inflammative condition of the brain and spinal cord. The severity of the lesions varied across the CNS, reflecting an irregular pattern of inflammatory vascular changes.
• The study also observed an infiltration of mononuclear cells, anisomorphic gliosis (a type of cellular reaction in the CNS), and reactive microglia which were identified in the affected regions. The intensity of the astrocytic response (another type of cellular response in the CNS) emphasizes the critical role of these cells in trypanosomiasis, a disease caused by trypanosomes.
• The gliosis observed indicates these cells’ ability as mediators of immune response. This suggests a strong reaction of the body’s immune system to the presence of the parasites.
• Notably, the parasites themselves were not found in the nervous tissues, which suggests that their effects might be systemic, or felt indirectly in the nervous system.

This research provides insight into the mechanisms of parasitic infections, specifically T. evansi, in the CNS of equines, deepening our understanding of the pathology of trypanosomiasis. The findings emphasize the importance of astrocytic response in combating the infection and may guide future research and treatment approaches.