Fresh thinking in the fight against Tb
A world-first effort to develop a vaccine to make possums immune to tuberculosis (Tb) could one day be an effective tool for reducing the levels of this problematic disease in livestock both in New Zealand and overseas.
In a trial in the Orongorongo Valley, the team from Otago Innovation, AgResearch and Landcare Research have recently shown that a new, orally deliverable form of the tuberculosis vaccine, BCG, works in wild possums. This trial, led by Dr Dan Tompkins of Landcare Research, was the basis of a paper published in the prestigious journal Proceedings of the Royal Society B: Biological Sciences.
The Orongorongo trial was the first anywhere in the world to demonstrate that orally delivered bacterial vaccines can protect wildlife against natural disease exposure. It indicates that wildlife vaccination, along with existing control methods, could be used to totally prevent the spread of Tb to domestic animals such as cattle.
The latest step in this ongoing work is a new trial to determine how long vaccination remains effective in a wild possum population.
Oral vaccine delivery, considered essential for wide-scale application to wildlife, is much less straightforward than the intramuscular injection with BCG that humans receive. To ensure the vaccine is absorbed through the possum gut wall and remains active, the vaccine is incorporated into a digestible lipid matrix recently developed by Otago Innovation and AgResearch.
Dr Tompkins believes the work to be essential because it will provide another ‘tool in the toolbox’ to fight the transmission of Tb.
‘It’s an exciting step in the search for different ways to control possums and Tb. We want to be able to use the vaccine in conjunction with more effective poisoning methods to control Tb in possum populations and therefore stop the transmission from possums to cattle.
‘This is a big step, but it is important to note that for possums in New Zealand it is unlikely to be a complete replacement for toxins, or future technologies currently in development like fertility control where the aim is to control the possums themselves by suppressing reproduction.’
The longer term plan is to develop biodegradable sachets or pellets that contain the vaccine, which would be particularly useful around livestock, near waterways, or in a populated area.
The teams’ study in the Orongorongo Valley has shown the vaccine is highly effective. The new trial is to establish whether protection from Tb lasts one, two, three years or longer, which will eventually dictate how it is used.
Dr Tompkins says the same vaccine could also be applied in other situations, including in the United Kingdom and Ireland, where it will soon be trialled with badgers.
‘Over there, badgers play the same role as possums in the transmission of Tb. The problem is that badgers are protected and also cherished by many as part of the rural landscape.’