Formation of filopodia in Trypanosoma congolense by crosslinking the variant surface antigen

Trypanosoma congolense was exposed to various substances binding to the variant surface antigen (VSG). All methods of crosslinking VSG molecules caused the rapid accumulation of ligands along the line of flagellar attachment and their shedding by formation of coat-covered vesicles and filopodia. This phenomenon was observed after treatment of the parasites with concanavalin A (Con A), anti-VSG-IgG plus protein A-gold, attachment of the cells to surfaces coated with poly-L-lysine and Con A and to Formvar films before negative staining. Moreover, trypanosomes aggregated by primary antibodies formed vesicles and filopodia at the points of contact. Those antibodies bound to the remaining cell surface, however, remained distributed uniformly. This indicates that primary antibodies alone do not cause crosslinking of VSG on the surface of T.congolense.

Selection for drug resistance in Trypanosoma congolense during cyclic transmissions through Glossina morsitans morsitans and drug treated rabbits

A drug-sensitive Trypanosoma congolense (IL 1180 strain), with a known CD50 and CD90 (doses required to cure 50 and 90% of the infected animals) was cyclically passaged through tsetse flies. The infected flies were then fed on rabbits which received weekly prophylactic treatment of Samorin. It was observed that the infections arising from flies maintained for over 60 days on drug-treated rabbits required higher curative doses to achieve a 50 and 90% cure. The results of this work suggest that a selection for drug resistance occurs when trypanosome stage in Glossina is continuously exposed to drug-treated animals.

The role of lectins and trypanosome genotype in the maturation of midgut infections in Glossina morsitans

Feeding D + Glucosamine to Glossina morsitans throughout their life significantly reduced the proportions of midgut infections which developed into mature infections with three different stocks of Trypanosoma congolense. In one stock of T. congolense, maturation was completely blocked by this carbohydrate, which is known to specifically inhibit tsetse midgut lectin activity. Similar experiments with T. brucei showed that D + Glucosamine also inhibited maturation and, when combined with results from previous experiments with the same carbohydrate, indicated that lectin inhibition also had significant effects on T. brucei infections. It is concluded that midgut lectin secreted by the fly is responsible for triggering maturation of procyclic T. congolense and T. brucei. The maturation response of midgut trypanosomes to lectin stimulation varies between species and between stocks of the same trypanosome species, probably reflecting differences in numbers of lectin binding sites which are determined by trypanosome genotypes.

Ro 15-0216: a nitroimidazole compound active in vitro against human and animal pathogenic African trypanosomes

In vitro systems for the continuous cultivation of Trypanosoma brucei brucei, T. b. gambiense, T. b. rhodesiense, T. congolense and T. vivax were used to determine the antitrypanosomal activity of the 2-substituted nitroimidazole Ro 15-0216. For all trypanosome species, the concentration which inhibited parasite growth by 50% (IC50 value) was established: 0.0957 microgram ml-1 (T. b. brucei TC221), 0.1327 microgram ml-1 (T. b. gambiense STIB 754-A), 0.0450 microgram ml-1 (T. b. rhodesiense STIB 704-BABA), 0.0896 microgram ml-1 (T. congolense ILNat 3.1) and 0.0109 microgram ml-1 (T. vivax ILRAD 1392). The IC50 value of its major metabolite Ro 19-9638 was 0.0341 microgram ml-1 (T. b. rhodesiense STIB 704-BABA). Furthermore, minimum exposure times required to render T. b. brucei non-infective for mice as well as preventing their growth in vitro have been established to be three, four, six and ten hours at drug concentrations of 30, 10, 3 and 1 microgram ml-1, respectively.

Trypanocidal activity of a 5-substituted 2-nitroimidazole compound (Ro 15-0216) in mice

The trypanocidal activity of a 5-substituted 2-nitroimidazole compound (Ro 15-0216, 2-(dimethylamino)-4'-[(1-methyl-2-nitroimidazole-5-yl) methoxy] acetanilid) was tested in stocks of T.b. brucei, T.b. evansi, T. vivax, and T. congolense. The trypanosome stocks showed different sensitivities, the Trypanozoon group was most sensitive followed by T. vivax and T. congolense. Administration of the compound in the drinking water was superior to single intraperitoneal injections. A T.b. brucei stock with reduced sensitivity to Mel B and insensitive to diminazene aceturate was cured by a dose 13 times greater than that necessary for the drug-sensitive T.b. brucei stock, administered in the drinking water. Quinapyramine- and quinapyramine/suramin-resistant stocks of T.b. evansi were eliminated with doses of 63 and 160 mg/kg i.p., respectively; to eliminate the drug-sensitive T.b. brucei stock, 250 mg/kg i.p. were required. The combination of Ro 15-0216 with suramin showed a synergistic effect in suramin-sensitive and in suramin-resistant stocks of T.b. evansi, although high doses of suramin were applied in the latter. Synergism of Ro 15-0216 with diminazene aceturate was demonstrated in T. congolense-infected mice.

Chemotherapy of trypanosomiasis: the use of guanylhydrazone compounds in the treatment of experimental murine trypanosomiasis

The efficacy of 1,3,5-triacetylbenzene tris(guanylhydrazone) trihydrochloride i.e. [(TBG)] in the treatment of early and late stage infections of Trypanosoma brucei in mice was investigated. Successful treatment on day 3 after infection could be achieved by doses of 2 X 2.5 mg kg-1. If treatment was delayed to 21 days after infection then the mice had to be given either suramin (1 X 20 mg kg-1) or difluoromethyl-ornithine (DFMO) 2% solution for 14 days in addition to either 15 mg kg-1 (TBG) daily for 4 days or 10 mg kg-1 twice daily for 4 days to obtain permanent cures. Other guanylhydrazone compounds were investigated for the treatment of chronic T. brucei infections and, at the limited dose levels used, failed to give any permanent cures. The use of (TBG) in the treatment of early and late stage infections of T. congolense and T. evansi indicated that treatment on day 3 after infection could be successful but on day 21 after infection the results were disappointing.

Morphological changes in Trypanosoma congolense after proteolytic removal of the surface coat

Bloodstream forms of Trypanosoma congolense were exposed to proteases at various concentrations, and the consequences of this treatment were continuously examined by electron microscopy. Unexpectedly, proteolysis did not simply result in the removal of the surface coat, but in dramatic morphological changes characterized by membrane adhesions, subsequently leading to flagella/plasmamembrane and to plasmamembrane/plasmamembrane fusions. The resulting axonemal internalization and rearrangement of cell organelles were followed by profound changes in cell shape. The axonemal motility, however, was maintained.

Effects of vasopressor drugs on number of Trypanosoma congolense in ruminant blood

The effects of intravenous administration of vasopressor drugs on parasite concentration was studied in cows and sheep infected with Trypanosoma congolense. Ephedrine (USP), adrenaline (BP) and insulin increased jugular concentration of the parasite. Maximum effects were reached between 1 1/2 and 2 h with ephedrine and at 2 1/2-3 h with adrenaline. Increases in parasitaemia resulting from epinephrine were sustained only in sheep and adrenaline gave similar effects in both ruminants. Only epinephrine significantly increased parasitaemia within 45 min of administration. Ephedrine, hydralazine and guanethidine had no significant effects on parasitaemia. It is suggested that one of the mechanisms by which trypanocides increase jugular concentration of T. congolense may be by vasoconstriction of the capillary endothelium.

The appearance of isometamidium resistant Trypanosoma congolense in West Africa

The frequent reappearance of patent parasitemia, mainly Trypanosoma congolense, in cattle maintained under isometamidium prophylaxis in the Upper Volta indicated that drug-resistant forms might be appearing. To investigate this possibility, trypanosome stocks were isolated in mice, their isometamidium sensitivity estimated and compared to that of stocks isolated before drug use was widespread. Most T. congolense stocks isolated in 1982-1983 were 4-8 times less sensitive to isometamidium than those isolated in 1979-1980.

Effect of trypanocides on jugular concentration of Trypanosoma congolense in the West African dwarf sheep

The effects of various trypanocides on parasitaemia was investigated in sheep experimentally-infected with Trypanosoma congolense strain 58/98. Intravenous injection of Berenil at the height of the first parasitaemic wave increased jugular parasite concentration by 12 and 16 times at the 9th and 20th minute post-treatment, respectively. With Pentamidine, maximum counts were 5.0-8.6 times zero-time concentration during the same periods. Peak effects of Samorin, Novidium and Ethidium were observed between the 60th and 90th minutes after drug administration and were 9.5, 6.3 and 3.5 times initial values, respectively. Injection of trypanocides resulted in double peaks of parasitaemia in which the second was usually higher than the first, except with Antrypol and Germanin which had no significant effect on parasitaemia. The amplitude, but not the onset of the increase in parasitaemia in sheep, was found to be related to the therapeutic efficacy of the trypanocides in the treatment of Trypanosoma congolense infection in rats. Animals treated with the diamidines (Berenil and Pentamidine) exhibited apparent parasitologic cure of infection in sheep two to four days after treatment. However, administration of any of the drugs one week after the first treatment resulted in flushing of cryptic trypanosomes into the jugular vein and counts as high as 7.63 X 10(3) microliter -1 were observed within ten minutes with Berenil. It is suggested that besides their therapeutic use, the diamidines may be of value in the parasitologic diagnosis of sub-patent trypanosomiasis due to Trypanosoma congolense.

Observation on drug resistance of Trypanosoma (Nannomonas) congolense and Trypanosoma (Duttonella) vivax in cattle at a feedlot in the Northern Ivory Coast

Studies carried out on feedlot cattle show Berenil at 7 mg/kg to be the treatment of choice in trypanosomiasis although repeated doses may be necessary. Resistant strains of Trypanosoma (Duttonella) vivax and Trypanosomas (Nannomonas) congolense survived dosages of between 0.5 mg/kg and 1.0 mg/kg of Trypamidium and were cross resistant to Homidium bromide.