A comparative study of the responses of the thymus, spleen, lymph nodes and bone marrow of the albino rat to infection with Trypanosoma congolense and Trypanosoma brucei.

Using 90 albino rats, a comparison was made between the response to experimental infections of Trypanosoma brucei and T congolense of approximately three weeks duration by observation of parasitaemia, packed cell volume values, post mortem spleen and lymph weights, and histology of thymus, spleen, lymph nodes and bone marrow. In T congolense infection, phagocytosis of trypanosomes in the spleen appeared to be the main response of the host's haemopoietic tissues to the parasites, which were observed only intravascularly. In T brucei infection immunological responses occurred in the spleen and lymph nodes in addition to trypanosome phagocytosis. Trypanosomes were seen intercellularly in thymus, mediastinal tissue and lymph node sinuses and parasitaemia reached considerably higher values than in T congolense infection. Erythrophagocytosis in the spleen was the only histological feature which could account for the reduction in packed cell volume which occurred near death in both infections, medullary haemopoiesis being increased. Changes in the thymus, incorporating plasma cell production and depletion of cortical small lymphocytes, occurred in both infections.