Haemolytic Complement and Class-specific Antibody Levels in Goats during Infection with< i> Trypanosoma evansi</i> and after treatment with Diminazene Aceturate

Abstract

Following infection with Trypanosoma evansi, goats mounted a strong class-specific antibody response, characterized by elevation of IgM and IgG antibody levels. Concomitant with the rising antibody levels and parasitaemia, was a drop (P < 0.0001) in the total haemolytic complement. These changes were accompanied by pyrexia (> 39 °C), slight dyspnoea, and fall in haematocrit levels (P < 0.01). Clinical examination revealed evidence of muscle wasting, lethargy and paleness of mucous membranes. Post-mortem examination carried out on one goat showed enlargement of lymph nodes, spleen and liver and oedema of the lungs and kidneys and a flabby heart. There was accumulation of sero-sanguineous fluid in the peritoneal, thoracic and pleural cavities and petechial haemorrhages on the serosa, pleura and intestinal mucosae. The brain was oedematous and showed evidence of congestion and meningeal petechiation. Cerebrospinal fluid (CSF) taken from infected goats did not show changes suggestive of any central nervous system (CNS) invasion by the parasites. Following treatment with diminazene aceturate, and the disappearance of parasites from the blood, the haematocrit status and haemolytic complement levels recovered by the 4th week. There was a rapid fall in the IgM-specific antibodies to near pre-infection levels. However, IgG-specific antibody levels were still elevated by the end of the study. The study shows that infection with this parasite may significantly affect goat production, because it causes changes which may lead to immunosuppression and organ failure. With the exception of IgG class-specific antibodies, these changes are quickly reversed by chemotherapeutic intervention. Levels of IgM and IgG class-specific antibodies may be a suitable indicator of the exposure status of goats to this parasite because the former fall rapidly after treatment or cure, while the latter may persist for long periods.