Research

The brushtail possum is an introduced predator from Australia. It is the main vector (transmitter of TB in cattle and deer) in New Zealand.

TB battles won, not the war

By Samantha Tennent

Scientists have been fighting the war on TB eradication for decades and can finally see the finish line.

OSPRI lead veterinary epidemiologist Dallas New has been leading the team working on eradicating TB and says while they have many challenges, good progress is being made. Nearing the home straight for TB eradication in New Zealand, the team at Ospri know they need to keep the accelerator flat to the floor. With close to 1700 herds infected 30 years ago, it almost seemed impossible, but there are less than 40 herds infected now.

“It’s great we’ve made so much progress, but there are a few challenges with only small numbers of infected herds left,” Ospri lead veterinary epidemiologist Dallas New says.

“We need to access the land where possums preside and when there were a lot of areas to cover if we had trouble accessing one area, we had the option to go somewhere else.

“But now that we’re down to the remaining 30 to 40 infected herds, we need access to areas that are tougher to reach.”

The goal is to have TB eradicated from livestock by 2026, but NZ presents an interesting challenge for TB. In the 1800s, both cattle and possums were imported to NZ and some cattle were infected with TB. When the number of possums exploded, bovine TB jumped into possums.

“This hasn’t happened anywhere else, so that’s what makes the TB situation so tricky, we have to get rid of the possums that are spreading the TB,” she says.

The best combat against possums includes traditional pest control methods on the ground and in the air, as well as wildlife surveys. Most control is done using ground-based traps and handlaid toxins, but in some areas the most efficient is aerial control.

“There are some areas that just aren’t accessible to reach for ground control,” she explains.

“Applying baits containing biodegradable 1080 from helicopters is efficient, cost-effective and extremely successful at reducing possum numbers to low levels.”

“And it’s our best defence to get those numbers down, we know we can expect to eradicate TB from an area if we

“But now that we’re down to the remaining 30 to 40 infected herds, we need access to areas that are tougher to reach.”

reduce the number of possums to a low and even level, which means about one possum per 10 hectares, for a period of at least five years.”

Before an area can be classed as TBfree, Ospri carries out surveys to find out if TB is still present in local wildlife. That includes trapping possums and other species that can spread TB (such as pigs and ferrets) doing post-mortems and testing them for it.

They also survey areas where TB is believed to be eradicated to ensure there are no newly TB-infected possums or other wildlife. And like with humans and covid-19, monitoring animal movements is critical to track and trace TB to make sure it is not being spread that way.

“Most people now know why ‘movement control’ is so important, covid-19 has opened up a whole different language that now makes sense to people,” she says.

TB receives a lot of attention because it is a zoonotic disease that passes from animals to humans. If a person drinks milk from animals infected with TB they will get sick.

The risk is managed with pasteurisation, but it still remains a trade issue and the health and happiness of animals are important.

As the lead epidemiologist, New looks at the disease from a national level and provides guidance for anything that might be out of the ordinary.

“We develop protocols for what testing the vets around the country should do, what movements animals can or can’t do

While possum control is mostly done using ground-based traps and handlaid toxins, for inaccessible areas the most efficient method of control is aerial which is efficient, cost-effective and extremely successful at reducing possum numbers to low levels. Ten-eighty (1080) bait is highly water soluble and naturally breaks down in the environment into harmless substances through the process of biodegradation and dilution.

and other guidelines in the programme,” she says.

“We help to analyse tricky wholegenome sequencing, which gives us clues pointing to the source of infection and we organise research trials to make sure our tests are performing exactly how they should be.

“Our vets in the regions are at the coalface of bovine TB and the vet epi team is there to support them and strengthen our eradication programme.”

New describes this as her dream job. She moved from Canada in 2019 where she had been a field veterinary epidemiologist. And following a stint working with DairyNZ as a policy advisor on biosecurity, she began her current role at Ospri in January 2021.

She has a background in ‘One Health’, which are problems that touch on animals, humans and the environment, and wildlife and TB is exactly that.

“It’s a disease in cows, but to manage it you have to go into wildlife and kill possums to get rid of it, so it’s a perfect ‘One Health’ example,” she says.

“Most problems in the world are way more interconnected than we realise. So, when you think of something in the ‘One Health’ context, it makes you step outside your own expertise and consider other factors.”

She is a bit like a disease detective and she looks forward to seeing more progress towards TB eradication.

“My mentor is very well-known in the Irish and Australian TB eradication programmes and he’s been consulting on TB since the 1990s. He never thought New Zealand would get to where we are now,” she says.

“We are so close to getting rid of it, we must keep our eye on the ball and that’s exactly what I’m here to do.” n

Showcasing the science

With the rapid growth of New Zealand’s sheep milk industry, Crown Research Institute AgResearch has launched a new online resource to showcase the science supporting the industry.

The suite of research undertaken to prove the quality of product from the industry, and how it is produced and what impacts it has, is captured on the website agresearch.co.nz/sheep-milk

“In this world of high consumer expectation, we need to provide knowledge to support the farmer, the exporter and to inform new customers,” AgResearch senior scientist David Stevens says.

“This emerging food industry must understand their footprint and be able to quantify the nutritional benefits of their products. This empowers the consumer to balance their nutritional outcomes with the production systems that deliver that nutrition.”

The culmination of a six-year research programme, the online resource houses the new knowledge generated in milk composition and processing, milk nutritional values, farming systems and environmental impacts.

The programme funded by the Ministry of Business Innovation and Employment (MBIE), Boosting the Export Earnings of the Emerging Dairy Sheep Industry, involved industry partners and aimed to provide relevant knowledge through a joint process that kept researchers and the industry fully involved in the discovery and development work.

“The programme was split into four parts, to directly answer industry questions,” AgResearch science team leader Linda Samuelsson says.

“Parts of the programme delivered answers to underlying questions such as ‘what makes New Zealand sheep milk unique?’ and ‘how big is our environmental footprint?’.

“Other questions addressed the best ways to convert our raw milk into highvalue consumer-ready products and what types of functional benefits can we expect from consuming New Zealand sheep milk.

“At the same time we investigated how our farming and feeding systems provide subtle variations in the composition of our milk.

Samuelsson says a significant objective of the industry is to ensure high ethical standards of our farming practices.

“Lamb rearing, as an important part of production, has received special attention. This has led to the development of a suite of options and practices ensuring the care and best possible outcomes for each lamb crop,” she says.

The online resource guides the user through each objective to link farmers, industry and consumers to the range of new knowledge developed in the research programme. This includes, for example, fact sheets about lamb rearing practices, environmental impacts and composition of NZ sheep milk.

“At the other end of the spectrum we have papers defining the effects of onfarm practices on milk composition, as well as the functional properties of sheep milk in immune function and bone growth,” she says. n

AgResearch science team leader Linda Samuelsson has been part of a team researching how science is supporting the sheep milk industry.

AgResearch senior scientist David Stevens says the online resources showcasing science is the culmination of a six-year research programme.