Prospects for the control of sheep blowfly strike by vaccination.

Research into vaccination against flystrike is aimed at either controlling the predisposing condition, fleece rot, or direct control of the fly maggots. A vaccine against the major bacterial species found in fleece rot lesions, Pseudomonas aeruginosa, is undergoing field trials and results suggest that this vaccine may reduce fleece rot incidence. Problems to be investigated include the existence of variants of P. aeruginosa in the field and the involvement of other species of bacteria in fleece rot. Strategies for direct vaccination include immunization with larval products involved in wound formation and larval nutrition and immunization against novel antigens usually from the gut of first instar larvae. Both methods have resulted in significant inhibition of larval growth. Analysis of larval products has revealed a number of active proteases which degrade skin proteins such as collagen. Inhibition of these enzymes with plasma enzyme inhibitors also affects larval growth in vitro. Antibodies raised against these enzymes are being tested for inhibitory effects against larvae and used to isolate cDNA clones from Lucilia cuprina libraries. Antigens from the gut are able to induce antibodies inhibitory to larval growth both in vitro and in vivo. Isolation of these antigens is proceeding in a number of laboratories. Problems still to be analysed include whether growth inhibition produces effective protection in the field and whether sufficient antibody will have early access to the larvae to significantly affect them.