Clinical signs and histopathology of brain, spinal cord and muscle of the pelvic limb of rats experimentally infected with Trypanosoma evansi

The aim of this study was to investigate whether rats infected with Trypanosoma evansi had neurological and locomotor signs, as well as histological lesions in the central nervous system (CNS) and pelvic muscles. To carry out this study, 52 rats were used and divided into two groups. The animals in Group A (n = 40) were infected with T. evansi, and the rats in Group B (n = 12) were used as negative controls (non-infected). Neurological examination was performed at Days 5, 15, 30 and 150 post-infection (PI) with eventual euthanasia of the rats. Samples of brain, spinal cord and skeletal muscle (biceps femoris and gastrocnemius muscles) were collected. The neurological tests evaluated motor capacity, balance and pain sensitivity. At Day 5 PI in Subgroup A1, the rats showed high parasitemia, became apathetic and presented with slow movements and signs of disorientation. After Day 15 PI in Subgroup A2 and Day 30 PI in Subgroup A3, no more clinical abnormalities were observed. Histologically, there was no damage to the CNS in these three subgroups, but within Subgroup A3, mononuclear infiltration of the muscle was observed. Rats chronically infected (Subgroup A4 - Day 150 PI) showed muscle atrophy, walking dysfunction and paralysis of the hind limbs. Mild mononuclear inflammatory infiltrates and perivascular cuffs were observed in the CNS of some of the animals in Subgroup A4. In these rats, severe muscle damage was observed in the skeletal muscle which included atrophy and loss of muscle fibers, multinucleated giant muscle cells, mononuclear myositis, Wallerian degeneration of the innervating fibers and mononuclear inflammatory infiltrate in the perineurium and adipose tissue. Based upon these findings, we conclude that infection by T. evansi in rats leads to muscle damage, which is probably the cause of the paralysis of hind limbs.