During the past year, results of vaccine trials against hydatid infection in sheep and goats have proven the EG95 vaccine to be reliable and highly effective. Results are available from seven trials in which sheep or goats were vaccinated with EG95 and subsequently given an experimental challenge infection with E. granulosus eggs. These data have been reported in Lightowlers et al. Parasite Immunol.18:457-462, 1996 and by David Heath during the XVIII International Congress of Hydatidology in Lisbon last year. The following table summarizes these results and the figure illustrates the regions in which the trials have been carried out.

EG95 vaccine Trial Results Summary

Field trials of the vaccine have been set up in China and Argentina. In Lisbon, David Heath reported on the results obtained in Hejing and Bayenguolen, China, where 81-83% protection was afforded by the vaccine against natural field challenge infection in sheep. Oscar Jensen also has a field trial is in progress in Samiento, Argentina the results of which are expected in November. Other trials using the EG95 vaccine which are in progress in Samiento are investigating the duration of immunity, colostral transfer of immunity from ewe to lamb and protection in different breeds of sheep. Information concerning some of these aspects is available at present from trials conducted by David Heath in New Zealand and the data from Argentina will provide additional useful information, particularly from a country which includes areas of high parasite endemicity.

Research on the EG95 is being conducted by David Woollard in Melbourne in an attempt to identify the host protective epitope(s) of the antigen which may allow the development of a synthetic peptide based vaccine. Vaccine trials are underway in sheep using four synthetic peptide epitopes selected from the EG95 sequence based on their strong immunogenicity.

Conan Chow in Melbourne is undertaking a research program in which he is cloning and sequencing the family of genes which encode EG95 and closely related proteins in E. granulosus. This information will be able to be used to assess the extent to which the EG95 gene and the encoded protein vary in E. granulosus isolates from around the world. This will allow us to predict the possibility that variants of the parasite may exist which could be antigenically different and insusceptible to the EG95 vaccine. The same information would allow the rapid modification of the vaccine to overcome such difficulties if they were to occur.

Completion of vaccine trials already underway and, hopefully, the establishment of trials in other endemic countries, will allow us to develop a strategy by which vaccination of the natural domestic animal intermediate hosts of cystic hydatid disease will be able to make a valuable contribution to the effectiveness of hydatid control campaigns.

Editor's note: The figure from the paper version of Echinonews will be added as soon as possible .

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