TRANSMISSION BLOCKING VACCINE STUDIES IN LEISHMANIASIS: 11. EFFECT OF IMMUNISATION USING LEISHMANIA MAJOR DERIVED 63 KILODALTON GLYCOPROTEIN, LIPOPHOSPHOGLYCAN AND WHOLE PARASITE ANTIGENS ON THE COURSE OF L. MAJOR INFECTION IN BALBIC MICE

Abstract

Background: Safe, effective and inexpensive vaccines may be the most practical tool for controlof any form of leishmaniasis. Leishmaniasis produces a state of pre-immunition which is theunderlying mechanism for prolonged immunity to re-infection. Low doses of parasites has beenshown to beable to induce protection in mice. It is not known, however, how immunesel-a froma susceptible host imrnunised with Leishmania-derived antigens when taken in by the sandflyaffects the development and the subsequent transmission of the parasite to naive hosts.Objective: To monitor the course of disease in BALBlc mice following challenge using L.rnajor infected P. duboscqi which had previously fed on immunised mice.Methods: BALBIc mice were immunised adequately withLeishrnania major-derived antigensnamely, crude whole parasite (WPA), recombinant 63 kilodalton glycoprotein (rgp63),lipophosphoglycan (LPG;) ancl a cocktail composed of rgp63 plus LPG antigens. Laboratoryreared Phlebotornus duboscqi sandflies, the natural vector for L. major were later allwwed tofeed on immunised animals, interrupted and allowed to continue feeding on infected animalsfor an equal amount of time until they became fully engorged. The sandflies were maintainedon apples as a carbohydrate source in an insectary maintained at a temperature of 2S°C and80% relative humidity. On the seventh day these sandflies were used to infect naivc B:ALB/c mice and the course of infection followed for a period of at least three months.Results: Mice infected usingsandflies which had previously fed on WPA or rgp63-immunizedmice showed disease exacerbation as the infection progressed, whereas those infected usingsandflies which had previously fed on LPG-immunised mice had the least lesion sizescompared to control mice infected using sandflies which had fed on saline immunised mice(p<0.05).Conclusions: Results from this study indicate that the course of L. major infection in BALBIc mice was dependent on the infective dose of parasites transmitted by the sandflies. R~:sultsfrom this study suggests that sub-infective doses of the parasite from sandflies previously fedon animals immunised with Leishmania-derived antigens needs to be evaluated for theirpotential in vaccine development against Leishmania infections