Using a new combination of virus genetic material, which carries a single gene from a virulent strain of Marek’s disease virus, they are hopeful that further research and trials could lead to the production of an effective MD vaccine that is cheaper and easier to produce - and crucially has no possibility of reverting to a virulent strain.

Marek’s disease virus (MDV), is a highly contagious airborne pathogen that infects poultry, costing the industry around £1 billion a year. MD is currently controlled through vaccination and over 20 billion vaccine doses are administered annually worldwide.

‘Classical’ MD vaccines are live non-virulent viruses and are highly protective against mortality and disease. But as industry pressure increases to develop more efficient and effective vaccines, scientists are looking to vector-based vaccines that do not require a cold chain, are easier and cheaper to produce, and are more easily distinguished from the pathogenic virus. These new types of vaccine also have no risk of reverting to a virulent form, which means they will not cause disease in susceptible birds.

Dr Susan Baigent and colleagues from The Pirbright Institute’s Avian Oncogenic Virus group (led by Professor Venugopal Nair), examined the efficacy of using non-replicating adenovirus expressing a gene called MDV envelope glycoprotein (Ad5-gB) as a potential Marek’s disease vaccine in chickens.

A double dose of the new vaccine, given in the egg and post-hatch, gave similar levels of protection to the classic Marek's disease vaccine. However, it did not reduce virus shedding or the transmission of virulent virus.

Dr Baigent said: “Although it was slightly disappointing that the Ad5-gB vaccine did not significantly reduce transmission or shedding, it is very encouraging that this vectored vaccine was as effective in protecting birds against disease as the current live vaccine, and resulted in lower levels of virulent virus in infected birds’ blood when given as a double dose.

“What we don’t know is whether a single dose post-hatch would be as effective as a double-dose or whether using a higher dose of Ad5-gB vaccine would be more effective in reducing shedding and transmission. Clearly further research is needed on optimising the dose and time of vaccination in order to begin trials of Ad5-gB as a potential vectored vaccine candidate for Marek’s disease.”