Effects of Samorin Treatment and Delayed Infection on the Establishment of Trypanosomes in Glossina Pallidipes

The protective role of Samorin (isometamidium chloride) when given with the bloodmeal, and the effect of the age of flies at infective feed, on the establishment of Trypanosoma congolense and Trypanosoma vivax in Glossina pallidipes Austen was evaluated. G. pallidipes was fed on fresh bovine blood containing 0, 6, 8, 10, 12 and 14 {mu}g of Samorin/mL of blood on day 0. A control group was fed in vivo on an infected goat as first feed on the same day (day 0). On day 3 post-Samorin treatment, the flies were infected in vivo by feeding them on a goat infected with either T. congolense or T. vivax. Similar procedures were followed for the experimental groups infected 5, 10 and 20 days post-Samorin treatment. Thereafter flies were maintained on rabbits for 15 and 20 days for the T. vivax and T. congolense groups, respectively. Fly survival was assessed, and the flies were dissected to determine infection rates. Results showed that the age of a fly at infection significantly affected the refractoriness of G. pallidipes to T. congolense ( F{sub 4,20} = 5.241; P=0.0047) and T. vivax ( F{sub 4,20} = 5.410; P=0.0040) infections. However, the effect of Samorin treatment on infection per se was not shown to be significant (F{sub 5,19} = 2.383; P=0733 and F{sub 4,20} = 1.106; P=0.3900) for T. congolense and T. vivax, respectively. The age of flies at infection significantly reduced tsetse survival (F{sub 4,20} = 7.584; P 0.67 and F{sub 5,19} = 0.485; P=0.783). These results indicated that, for T. congolense and T. vivax, combining Samorin treatment at a concentration of at least 8 {mu}g/mL, and delaying exposure of tsetse to infective feed for at least 3 days post emergence, induces sufficient refractoriness that may counter the increased challenge posed by the mass release of flies in sterile insect technique (SIT) programmes. (author)