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Investigations were undertaken to evaluate the immune response of trypanotolerant N'Dama (Bos taurus) and susceptible Boran (Bos indicus) cattle to two Trypanosoma congolense variable antigen types (VATs) expressed in both breeds following tsetse-transmitted challenge. The VAT-specific antibodies of both IgM and IgG1 isotypes produced by both breeds had similar neutralizing titres. The interaction between immune sera, trypanosomes and freshly isolated peripheral blood leucocytes (PBL) from uninfected N'Dama and Boran animals was studied. It was found that both N'Dama and Boran immune sera were able to induce adherence of trypanosomes to the N'Dama PBL, but not to Boran PBL. The adherence-inducing activity was exhibited by both IgM and IgG1 antibodies, but IgG1 antibodies were more efficient in this respect. These results suggest that there are qualitative and/or quantitative differences in the immunoglobulin receptor function of PBL between the two breeds of cattle.

The course of infection and the humoral immune response to Trypanosoma congolense clone ILNat 3.1 were studied in test goat kids receiving colostrum from dams immunized with the surface coat of ILNat 3.1 and control kids that received colostrum from nonimmunized dams. At 24-48 h after birth, all test kids had detectable serum antibodies to the trypanosome clone. There was no difference in the prepatent period between the test and control kids following challenge with 10(3) T. congolense ILNat 3.1 trypanosomes 8 days after birth. After the first 7 days of the experimental period, significantly lower parasitemia was recorded in test kids than in control kids. The mean packed red cell volume of test kids was not significantly different from that of control kids 7 days after infection. The test kids gained as much weight as noninfected control kids; both groups gained twice as much weight as infected control kids. Following infection, all kids developed antibodies against the infecting trypanosome clone. Fifteen test kids had titers equal to or greater than 1280 compared to only two control kids. The test kids survived longer after infection compared to control kids. The results suggest that colostrum from does immunized with the surface of a T. congolense clone did not prevent infection, but decreased parasitemia and prolonged survival of kids challenged with the same clone.

A purified protein, relative molecular weight 83 kilodalton (kD), and plasma membranes from Trypanosoma brucei were tested as potential vaccines against tsetse-transmitted T. vivax and T. brucei in goats and rabbits. The 83 kD protein was found in lysates of all clones of T. brucei examined, as well as in lysates of T. vivax, T. congolense and T. rhodesiense. Rabbits and goats were immunized with various amounts of antigen in Freund's complete adjuvant and boosted twice with antigen in Freund's incomplete adjuvant. Two weeks after the last inoculation, the goats were challenged with T. vivax-infected and the rabbits with T. brucei-infected Glossina morsitans morsitans. Although high antibody levels were detected in all the animals immunized with either antigen as measured by radioimmunoassay and immunodiffusion, they became infected and the course of disease was the same as that in unimmunized controls.

The metacyclic trypanosomes of a Trypanosoma brucei brucei clone (ILTat 2.1) were analysed with regard to their variable antigen (VAT) composition using monoclonal antibodies. The metacyclic population was antigenically heterogeneous. Despite the heterogeneity, however, the overall VAT composition of the metacyclic population appeared to be limited in number. A similar pattern of reactivity was observed when the monoclonal antibodies were tested on metacyclics of another clone (IL Tat 2.2) derived from a rabbit 30 days after infection with IL Tat 2.1 as well as those of the parent stock (STIB 247). The VAT characteristics of the metacyclics of this serodeme were consistent regardless of whether they were transmitted by Glossina morsitans morsitans or G.m. centralis. The monoclonal antibodies also reacted with some of the bloodstream VATs isolated within 72 h from cyclically infected mice. None of the monoclonal antibodies, however, reacted with metacyclics of a different stock (LUMP 227).

Specific antisera against sera of 46 species of vertebrates were prepared. The antisera to 21 Bovidae species were raised in goats except the antiserum to goat serum which was raised in sheep. The antisera to 3 Suidae species were produced either in domestic pigs or warthogs, while antisera to most of the other vertebrate species were raised in rabbits. The antisera were used in an enzyme-linked immunosorbent assay (ELISA) to identify the source of bloodmeals ingested by teneral and non-teneral tsetse at different time intervals after feeding. The bloodmeal donors were identifiable in 100% of the teneral tsetse up to 40 h post-feeding and in 87.5% in those tested up to 74 h post-feeding. Non-teneral tsetse digested the species-distinguishing bloodmeal components faster than the tenerals. Bloodmeals could be identified in 100% non-tenerals at 20 h post-feeding but only 67.5% and 50% of the bloodmeals could be identified 40 h and 74 h post-feeding, respectively. The antisera were also able to identify mixed bloodmeals from closely related species.

Six Boran steers were infected simultaneously with Trypanosoma congolense and T. brucei brucei while another group of 3 was inoculated with T. b. brucei one year after infection with T. congolense. Three further steers were infected with T. b. brucei alone. Whereas, the six animals which received simultaneous infections developed clinical signs of cerebral trypanosomiasis as evidenced by depression, ataxia and occasional circling, those infected with T. b. brucei alone did not. At necropsy, 4 out of the 6 simultaneously infected animals had a mild to severe disseminated non-suppurative meningoencephalitis. Trypanosoma b. brucei was isolated from the cerebrospinal fluid (CSF) of three out of the four animals with histological lesions. Two of the cattle superinfected with T. b. brucei one year after infection with T. congolense also developed both clinical and histological evidence of cerebral trypanosomiasis. Trypanosoma congolense was isolated from the CSF of one of these 2 animals. Specific antibodies to the variable surface glycoproteins (VSGs) of the infecting T. b. brucei and T. congolense clones were found in the CSF of the 8 animals that developed cerebral trypanosomiasis. In these animals however, there was neither temporal nor quantitative correlation between VSG-specific antibodies in serum and in CSF, implying a de novo synthesis of antibodies to the infecting trypanosomes in the CSF.