Australia’s turkey producers could soon benefit from a new vaccine against hemorrhagic enteritis virus (HEV), developed specifically for local turkey production.
There is no vaccine available in the country to protect turkey flocks against HEV, in part due to quarantine restrictions and concern over introducing new strains, but also because of the small market size.
While there have been few diagnosed outbreaks of acute hemorrhagic enteritis (HE) in Australia’s turkey flocks, the virus is now thought to be widespread, having first been reported in the 1980s.
The exact costs to the Australian poultry industry are unknown as, rather than causing clinical disease, HEV is thought to cause immunosuppression.
There may be sporadic outbreaks of disease in the country, but the more likely effect of the virus is increased mortality, reduced performance, and an increase in other diseases due to infection making birds more susceptible to other organisms. Secondary infections, for example severe colibaccilosis, can be treated, but there is no specific treatment for HEV infection.
Hemorrhagic enteritis has reduced the performance of Australia’s turkey sector, but a locally produced vaccine will give turkey flocks protection that has, to date, been unavailable.
The situation in Australia’s turkey sector is quite complex as, not only are birds serologically positive, they actually carry the virus. There would appear to be a lot of persistent infection in Australia’s poultry flocks, and when birds recover, they continue to harbor the virus in significant amounts.
Professor Steve Walkden-Brown, of the University of New England (UNE), together with industry colleagues, has been determining how widespread the disease is with the aid of Poultry CRC funding and has started work on developing an Australian vaccine.
HEV diagnostics now available
The project has already developed new molecular tests for the virus, both a standard PCR and a real-time quantitative PCR test, which can indicate the presence of the virus and the number of copies of the virus. A commercial ELISA kit from the U.S. has also been brought in to detect antibodies. Previously, there were no readily available diagnostic tools available in the country to detect HEV.
However, progress on HEV vaccine development has not been easy, and the team hit a stumbling block when it was unsuccessful in growing the virus in cell culture or chick embryos.
The virus, unlike many other adenoviruses, does not grow well in cell culture, and the one cell line in which it is known to grow, and which is used in vaccine production outside of Australia, cannot be used for this purpose in the country because of quarantine regulations.
The researchers found that they could, however, grow the virus in SPF chickens, and UNE has a isolator in which this can be done.
The team will use the SPF chickens to produce a master seed for the vaccine, and then the virus dose will be titrated and safety and efficacy trials undertaken following Australian Pesticides and Veterinary Medicines Authority (APVMA) guidelines. Finally, a production run will take place, and an AVPMA minor use permit sought.
Walkden-Brown, commenting the project, said: “We are 100 percent confident that we will be able to produce a viable vaccine. We have a good local candidate strain of HEV. We have shown that we can grow it. We’ve done experiments in turkeys and chickens.
“We know we can grow it to high titre, and we know that we can extract it from infectious material, so there is little risk of not being able to produce a vaccine. We have another 12 months to run on our project, and plan to have a viable product available for the project stakeholders by December 2016.”