Detection of Trypanosoma evansi in brains of the naturally infected hog deer by streptavidine-biotin immunohistochemistry.

Twenty-four percent of hog deer (Cervus porcinus) that ranged free on a farm in Samut Prakarn province, Thailand, died showing nervous signs between September 1997 and February 1998. The nervous signs shown by most of them included ataxis, paresis of hind limbs, lateral recumbency, excitation and convulsion. Six animals and one carcass were submitted for diagnosis at the National Institute of Animal Health, Bangkok. Trypanosoma evansi was detected in blood and cerebrospinal fluid of four and five animals, respectively. Antibodies to T. evansi were found in all the hog deer by indirect enzyme-linked immunosorbent assay. Histopathological observation revealed a generalised non-suppurative meningoencephalitis affecting the white and grey matter at all levels of the brain. Typically, there were broad perivascular cuffs of mononuclear inflammatory cells, including lymphocytes, and some Mott cells. No trypanosomes were found in any tissue examined by conventional histopathology. However, numerous T. evansi were demonstrated by streptavidine-biotin immunohistochemistry in neuropil and Virchow-Robin spaces of brain in three animals.