Demonstration of erythrophagocytosis in Trypanosoma congolense-infected goats

Anaemia is the most prominent clinical sign of trypanosomosis in domestic a nimals but little is known about its pathogenesis. This work investigated e rythrophagocytosis as the possible cause of anaemia. Pathogenic Trypanosoma congolense (IL3000) was intravenously inoculated into six goats at 3 x 10( 6) trypanosomes per goat. Six other goats were maintained as controls. The infection was studied for 10 weeks and parasitaemia, packed cell volume (PC V) and serum protein levels were determined. The amount of erythrophagocyto sis was determined from the amount of Cr-51-labelled red blood cells (RBCs) phagocytosed by self mononuclear cells (MNCs) in vitro and by microscopica lly counting phagocytosed RBCs on Giemsa stained smears of incubated mixtur es of RBCs and self MNCs. The infection resulted in trypanosomosis with rap id progressive anaemia and mean peaks of parasitaemia of about 3 x 10(3) ml (-1). In infected goats, a significant (P < 0.05) mean reduction in PCV (of 37-22%) was observed starting from about 20 days up to 56 days post-infect ion. Within this same phase, significant (P < 0.05) differences in mean rad ioactivity counts of Cr-51 incorporated into MNCs were observed with infect ed goats' samples having counts 50% higher than the control goats' samples. Microscopically, the mean number of phagocytosed RBCs in infected goats' M NCs was noted to be 80% higher (P < 0.05) than that of central goats. Appre ciable increases (P < 0.05) in mean serum globulin levels, from 3.5 to 4.7 g/dl, were observed within 3 weeks of infection. The study showed that eryt hrophagocytosis is an important mechanism leading to anaemia in the pathoph ysiology of I: congolense infection in Zambian goats. (C) 2001 Elsevier Sci ence B.V. All rights reserved.