Trypanocidal drugs and their effect on parasitaemia, specific IgG production and protective immunity in rats infected with Trypanosoma lewisi.

In rats infected with Trypanosoma lewisi, parasitaemia normally resolves by day 32; thereafter, the rodents become solidly immune to re-infection. Rats treated on day 5 of infection with a single i.m. dose of 35 mg/kg of the trypanocidal drug ethidium bromide (EB) had recovered from parasitaemia by day 12, whereas berenil (BE) given at 100 mg/kg, more than twice the recommended dose, had no effect on parasitaemia. However, rats treated for 4 consecutive days beginning on day 5 of infection with Lampit (LA) and Radanil (RA) at 350 mg/kg showed no parasitaemia on days 16 and 20, respectively. EB was the most effective drug in lowering the total IgG antibody as compared with the control animals, whose specific IgG titres remained elevated for over 200 days after the parasitaemia had been cleared. LA also significantly reduced the antibody levels through day 240, whereas RA only transitorily depressed the antibody levels on days 20 and 30. BE, which had no effect on parasitaemia, correspondingly failed to depress the total IgG levels. Re-challenge infection of the drug-treated, recovered animals on day 240 (208 days after the normal resolution of the infection) revealed that except for the EB group, which displayed transitory parasitaemia for 4 days, other treated and control rats completely resisted the challenge; pre-challenge antibody titres were lower than 1:160 in EB-treated animals in contrast to the levels of 1:320 or higher measured in the other drug-treated and control animals, which resisted the infection.(ABSTRACT TRUNCATED AT 250 WORDS)