Sleeping sickness in the Lambwe Valley in 1978.

Even though tsetse control measures were discontinued in the Lambwe Valley in 1974 the prevalence of Rhodesian sleeping sickness remained at low levels. A survey conducted in 1978 verified a low prevalence of disease (0.1%). Thirty-four per cent of the individuals tested were positive for malaria with the highest prevalence (44%) in children aged 0-9 years. Thirteen of 1340 individuals (0.97%) tested and found negative for sleeping sickness in 1978 developed the disease by 1985. Fourteen individuals with moderate titres (2+) in the IFAT but who showed no evidence of disease were traced and found to be alive and well seven years later. Three of these patients still had positive titres but the others had converted to negative. Sera from four patients infected and treated in 1978 were also positive, but only one of five patients treated in 1977 reacted in the test. The CFT as described did not appear useful as a diagnostic test.

Expression of two variant surface glycoproteins on individual African trypanosomes during antigen switching.

Individual Trypanosoma brucei rhodesiense organisms were observed in the process of switching variant surface glycoproteins (VSG's). During this switch, trypanosomes simultaneously expressed both pre- and postswitch VSG's uniformly over their surface as detected with monoclonal antibodies. Analysis of this switching event showed that trypanosomes expressing any one of three distinct preswitch VSG's could switch to expression of from one to three different postswitch VSG's. Up to 2.7 percent of the trypanosome population was in the process of switching at one time.

Trypanosoma rhodesiense blood forms express all antigen specificities relevant to protection against metacyclic (insect form) challenge.

Monoclonal antibodies were used to demonstrate the expression of four distinct metacyclic (infective insect form) trypanosome antigens on blood forms of T. rhodesiense. Metacyclic antigens were consistently expressed on the blood forms on days 4 and 5 of the first parasitemia after metacyclic infection of C57BL/6 mice. In different mice examined, the percent of blood forms expressing metacyclic antigens ranged from 46 to 85%. Immunization with irradiated day-5 blood form trypanosomes was protective against metacyclic challenge, indicating that all antigen specificities relevant to protective immunization against metacyclic challenge are expressed on blood form trypanosomes. Blood forms, in contrast to metacyclic forms, can be isolated in quantities sufficient for purification of antigens and genetic cloning.