Livestock parasites halved with a single dose vaccine
The bid to feed large populations in developing countries is burdened by the threat of livestock disease. The RECOMBINANT BCG project, funded by the EU, overall aimed to develop a multivaccine to address this agricultural problem. Diseases targeted were bovine tuberculosis together with parasites causing schistosomiasis and fascioliasis. Over a period of five years, the consortium of six universities from northern Europe and South America pitched their expertise at the microbial, genomic and immunological aspects of the project objectives. One of the teams of scientists based in Brazil focused their attention on the development of a vaccine to control schistosomiasis (caused by Schistosoma mansoni). Reliant on the presence of water and its intermediate host, a water snail, Schistosoma mansoni (S. mansoni) is a significant parasite both in cattle and humans. Not only that, but due to their large size and longevity, cows can act as very large reservoirs for the adult worms and increase maintenance and dissemination of the disease. The antigen Sm14 (S. mansoni14) had previously shown considerable promise as a component of vaccines. One special feature of Sm14 is its immunological activity against both S. mansoni and Fasciola hepatica, another predominant ruminant parasite that causes fascioliasis. The Sm14 antigen was cloned, fused with another protein and then lodged in the cell wall of the tuberculosis-causing bacterium, Mycobacterium bovis BCG. This resultant rBCG-Sm14 strain did not induce anti-Sm 14 antibodies in test mice. However, the rodents did produce more gamma interferon from white cells from the spleen, an indication of T-helper type 1 response. Further evidence of the effectiveness of rBCG-Sm14 emerged in mice infected with the water-borne borne stage of the schistosomiasis parasite. Mice immunised with only one, or at most two, doses showed a reduction of almost half the resulting worms – only achievable previously with three doses of the pure antigen. Clearly, a one-dose regime for the control of parasitic diseases in livestock is preferable from a practical point of view to a multiple-dose programme. The single dose format offers increased vaccination opportunities with potentially improved vaccine safety.
