Identification and production of recombinant antigens for a vaccination against the screw-worm fly (Chrysomya bezziana)

• Inter-University Centre on Biotechnology, Indonesia
• Research Institute for Veterinary Science, Indonesia
• Agency for Agricultural Research and Development, Indonesia
• Queensland Department of Primary Industries, Australia

Chrysomya bezziana, is a serious pest of buffalo, cattle, goats, sheep and pigs. Adult flies lay their eggs on wounds and undamaged skin. As the larvae develop they form deep wounds and within eight days they drop from the animal to pupate. The effect on the animal is loss of condition and appetite, anaemia, infertility, and death.

In Southeast Asia, some areas have 20-30% of cattle infested and 30% mortality in calves. On small farms screwworm infestations are frequently controlled by picking larvae out of the wounds and treating with tobacco, sump oil, petrol or battery acid.

On larger farms control is difficult, with treatment requiring the removal of larvae in conjunction with regular applications of insecticides which give little protection. Projected increases in stock numbers in the region and progression toward less intensive management of stock may mean greater losses due to screwworm.

The aim of this project is to develop a vaccine to combat infestations of Screwworm Fly Chrysomya bezziana. The high cost of the insecticides and the problems of resistance, residues and their effects on non-target organisms have led to the search for cheaper more effective and environmentally safe control strategies.

Vaccinations as a control measure have proved effective against cattle tick. Considerable progress has been made in vaccinating sheep against sheep blow fly. Sheep vaccinated against sheep blow fly have also been shown to inhibit the growth of screwworm larvae.

Methods used in this project will be to:

. establish a colony of screwworm from which to set up a vaccine assay against the fly and to harvest peritrophic membranes (the membranes lining the 'stomach') from the larvae;
. identify and isolate antigens from whole larvae and the peritrophic membranes which cause the production of an immune response in the host which protects the animal against the fly: this will use biochemical purification, immunoassay and recombinant DNA technology.
. successfully collaborate with Indonesian scientists and train Indonesian staff in DNA technology; and
. prepare and test native and recombinant antigens in vaccine trials and begin discussions on collaboration on vaccine trials in cattle or sheep using recombinant antigens.

The project will involve staff in Australia and Indonesia with expertise in screwworm and methods of its control, oligonucleotide synthesis, gene isolation, DNA library construction and screening and immunological aspects of vaccine research.