In Indonesia infectious bursal disease, also known as Gumboro, has been a cause of significant economic losses in small rural poultry holdings. In particular, strains of Gumboro known as very virulent infectious bursal disease viruses (vvIBDV) have caused high morality since 1991. Existing vaccines developed to control less virulent Gumboro strains have not been effective and this sector has been reluctant to adopt these vaccines in spite of heavy losses. Australia is one of the few countries that are free from vvIBDV. Incursion and spread of such strains would seriously impact on the profitability and the sustainability of the local poultry industry. For that reason CSIRO - AAHL has developed a test to differentiate vvIBDV from other Gumboro strains. The objectives of this project are:

For Indonesia: to develop an effective vaccine from a local strain of vvIBDV which could then be manufactured cheaply by a local vaccine company
For Australia: to evaluate ELISA for differentiation of vvIBDV on farms with outbreaks of Gumboro in order to ascertain the performance of this test under field conditions

The project is collaboration between Research Institute for Veterinary Science, Balai Penelitian Veteriner (BALITVET), Bogor, Indonesia & CSIRO Livestock Industries, Australian Animal Health Laboratory (AAHL), Geelong. Duration 1 January 2001 to 31 December 2003. Project was finalised and signed on 6 October 2001.

From mid October to 31 December 2001 the following work was done. Two Indonesian IBDV strains and one vaccine strain were selected for passage in tissue culture, as planned. Selection of strains was based on the previously available sequence of 17 IBDV strains. In October/November there were shortages in availability of SPF eggs from Vaksindo Pty Ltd that has prevented continuing passage of viruses. Passaging of viruses continued in December using eggs from another source, and two IBDV strains received 5 and 11 passages in primary chicken embryo fibroblasts. During this time the major part of preparatory work has been undertaken such as purchase of reagents and consumables, some equipment such as CO2 incubator & preparation of experimental facility for work with chicken. In Australia, position of technical officer was advertised and reagents to be used in ELISA produced in large quantities and standardized. There was no travel during this period.

Currently we anticipate hat the project will be competed about 6 months after the end date of 31 December 2003. There will be some increase in activity during the year 2 (travel, laboratory and field work, capital purchase) that will consume part of the budget surplus from year 1. There are currently no changes to the budget.

Six strains were selected as candidates for vaccine development from infectious bursal disease virus (IBDV) strains isolated and characterised previously in Indonesia. Strains selected were either very virulent (vvIBDV) or classical strains. After five blind passages in chicken embryo fibroblasts, only four strains were recovered indicating differences in IBDV strains ability to replicate in tissue culture. Of these four strains, one strain based on a vvIBDV, has been selected for further passage and vaccine development after cloning in tissue culture. After more than thirty passages in chicken embryo fibroblasts, virulence of this strain was reduced for both specific pathogen free chickens and commercial broilers. Although this virus is currently the prime candidate for vaccine development three other strains are also being passaged in tissue culture and will be evaluated as vaccine candidates.

To evaluate the performance of a test developed in Australia for discrimination of vvIBDV samples of bursal tissue were collected from broiler farms with acute IBDV. Testing on these samples indicated that in some flocks vvIBDV were involved, whereas in other flocks classical IBDV were detected. These results will be confirmed by sequencing of bursal samples in order to correlate sequence data with ELISA results.

Two vvIBDV strains were selected as candidates for vaccine development. After more than 30 passages in tissue culture the virulence of one strain was reduced for chickens and commercial broilers. However this preparation was still too pathogenic to be used as a vaccine. Therefore the two strains were further passaged in tissue culture. Both strains were also cloned in order to insure that the vaccine contained a single, genetically uniform virus population. All viruses were characterised at the molecular level during passaging to monitor genetic changes that were occurring and to achieve desired genetic changes in the virus.

In total, five viruses at different passage levels and with different genetic characteristics were selected for trials in specific pathogen-free chickens. Samples collected from poultry flocks in Indonesia with Gumboro-like mortalities, and typed by an ELISA to be vvIBDV, were genetically characterised. Sequencing confirmed the ELISA results as suspected samples had almost identical seque
nces to those of other vvIBDV viruses isolated previously in Indonesia. Additionally, an experimental IBD killed vaccine was also prepared. This vaccine will be trialed in breeder hens to booster their IBD immunity and to provide protective maternal antibodies to hatching chicks until the age of their first IBD vaccination.

Five clones from two vvIBDV strains, at different passage levels and with different genetic characteristics, were selected during the previous phase of the project as vaccine candidates. The safety and efficacy of these five clones were compared in laboratory trials using specific pathogen-free chickens. These laboratory evaluations established that three vaccine clones were safe and efficacious; however, they differed in pathogenicity for the bursa of Fabricius of vaccinated chickens. These three vaccine clones that were shown to be safe and efficacious in laboratory trials were then propagated in tissue culture in large quantities which are needed for field trails. Laboratory trials in specific pathogen-free chickens were also undertaken in Balitvet to determine the optimum age at which broiler and layer chicks should be vaccinated, as well as to determine the optimum route by which vaccine should be administered to chicks. An external review of the project was completed in January 2004, and a recommendation made to ACIAR that the project be extended in order to complete field trials of three vaccine candidates, prepare the laboratory manual for the vaccine production and commercialise the vaccine. In accordance with this recommendation, a project extension document was prepared and submitted to ACIAR for consideration. Several promotional activities for the Gumboro vaccine under development were undertaken in Indonesia and a scientific paper on an ELISA for detection of vvIBDV was prepared for journal submission.

Laboratory evaluations of five developed candidate vaccine clones were conducted during 2004 in specific-pathogen free chicks. These evaluations established that of five vaccine clones three were safe and efficacious; however, they differed in pathogenicity for the bursa of Fabricius of vaccinated chickens. During 2005 period, safety and efficacy of three finally selected vaccine clones was evaluated in field trails using village, layer and meat type-chickens. For each type of chickens three farms, at different locations, were used. Two vaccine clones were equally efficacious in all type of chickens, whereas the third vaccine clone was safe, but was not efficacious. All flocks vaccinated with two vaccines had good vaccination response, showed no mortality from Gumboro during the entire growing period, no signs of immunosuppression and growth performance at the end of growing period was not affected. A scientific paper on an ELISA for detection of vvIBDV was published in scientific journal Avian Pathology

Documentation necessary for commercialisation of developed IBDV vaccine, including manual for commercial vaccine production, was completed. Several vaccine manufacturers in Indonesia were approached and their expression of interest sought. It was established that various options for commercialisation of Gumboro vaccine should be considered and pathway most appropriate chosen.