Cultivation and multiplication of viable axenic trypanosoma vivax in vitro and in vivo

Abstract

Trypanosoma vivax was isolated from the blood of an infected laboratory mouse, washed and introduced into the prepared culture media, ME-99 and minimum essential medium (MEM), both containing laboratory prepared (commercial) horse serum and antibiotics (streptomycin and penicillin). The cultures were monitored in vitro for 12 days. There was an initial decline in parasitaemia in the first 48 h in both media, which later picked up to reach the peak of about 1.10 x 102 parasites/ml in ME-99 on day 5 and 6.2 x 10 parasites/ml in MEM on day 4. Thereafter, the parasites number tapered off to reach zero on day 9 in ME-99 and day 10 in MEM. No growth was recorded in the control, which contained normal saline (pH 7), horse serum and antibiotics. The result of the in vivo culture showed a different trend when compared to the in vitro. Multiplication was tremendous with a peak of about 3 x 10 parasites/ml of blood on day 22 (high inoculum) and day 24 (low inoculum) post infection. The slender trypomastigote parasites recovered in the in vitro culture was short and had a long, free flagellum and measured 23-25 um while that of the in vivo culture was long, slender, clongated, torpedo shaped body measuring between 30 and 32 um. During the course of the in vivo culture congenital transmission of trypanosomes was observed. The in vitro attenuated parasite conferred a degree of protection to 25% of the mice that were later infected with viable parasites indicating possible prophylactic effect of in vitro attenuated parasites. The study showed that T. vivax could not be cultured in large numbers on their own axenically in MEM and ME-99. However, ME-99 can be said to be more suitable compared to MEM for axenic cultivation of T. vivax as a result of the additional nutrients supplied by the tissue culture medium 199 present in medium ME-99. Also, the parasites multiplied better in vivo compared to the in vitro study, which could mean that the best means of culturing trypanosomes still remains the in vivo method.