Progress on vaccines against parasites.

There has been significant progress in attempts to develop effective vaccines against parasitic diseases, including malaria, leishmaniasis and schistosomiasis. In malaria, in addition to field trials with SPf66, the Colombian malaria vaccine, several Plasmodium falciparum candidate vaccines are under Phase I testing, including NYVAC-7, a multi-antigen, attenuated recombinant vaccinia virus. Additional candidate antigens are at an advanced stage of pre-clinical development. In leishmaniasis, Phase III clinical trials on first generation vaccines (killed Leishmania, with or without BCG) are proceeding in several countries. Use of IL-12 as an adjuvant for use with killed Leishmania vaccine is being studied in non-human primates. A genetically constructed (gene knock-out) live avirulent Leishmania is being developed in preclinical studies as a potential live vaccine. Research is also underway to evaluate several recombinant proteins. The genes coding for such leading candidate antigens are also being incorporated into various live vectors to yield recombinant organisms with vaccination potential. In schistosomiasis, a strategy for the development of a vaccine against Schistosoma mansoni has been established, focussing on six priority recombinant antigens. An Asian S. japonicum vaccine development network has also been established, initially to develop a vaccine to block transmission in cattle and oxen, important reservoirs of the disease in Asia, and ultimately a human vaccine. As all of the above-mentioned vaccines will be used in the field in disease-endemic tropical countries, optimal stability will be of paramount importance.