How wild pigs help eradicate TB

Narrator

New Zealand Tbfree program uses wild pigs to track with bovine tuberculosis still exists in wildlife. 

Wild pig surveys provide important data that guides the design of TB free's possum control programme.  

They help to show where TB has been removed from wildlife so that possum control for TB purposes can finish. 

How wild pigs help track TB

Narrator

Research shows that TB in pigs nearly always comes from some of the other species, mostly possums. 

Brent Rohloff — OSPRI programme manager 

"We use pigs as an indicator species of TB because they have a really large home range, significantly larger than possums. 

They're also a scavenging species so they tend to pick up TB pretty efficiently if there is TB in the environment." 

Ivor Yockney — Landcare Research 

"So the prevalence of TB in pigs and the wild pig population is largely just a reflection of what's happening in the environment around them." 

Why survey pigs at all?

Finding an infected pig indicates it has likely picked up the disease from infected wildlife in that area.  

This helps determin

Narrator

e where targeted possum control is needed. 

Ivor Yockney — Landcare Research 

So the areas we're collecting pigs from are areas with a history of cattle testing and possum surveys and they're getting closer to eradication so it's important to have a species such as a pig that's a really good sentinel for disease.  

Narrator

If TB is not found in pigs there is more confidence that disease has been removed from the possum population. Where TB is present in possums, it is highly likely it will also be present in the areas where Pigs are. 

Ivor Yockney — Landcare Research 

In areas where there's been no control and all vector species have been infected, picked prevalence can be as high as eighty-five to ninety percent from year to year to year. That drops away rapidly as soon as possum control is undertaken, until eventually the TB will die out completely from the pig population. So they're a reflection of what's going on and the environment around them. 

Mark Neill — Veterinarian, TBfree 

Pigs are not believed to maintain TB infection in the absence of any other species, they're picking up their infection from the possum population. Once you control the possum population the disease falls out of the pig population. 

Narrator

Wild pig populations are not controlled under the TB free program as the control of the pigs alone has no effect on the persistence of TB. 

Mark Neill — Veterinarian, TBfree 

Because pigs are scavengers, just to give an example one pig could represent the equivalent to a hundred cattle tests. 

Five ferrets or up to a thousand possums depending on the way they're sampled because they scavenge, they're picking up a lot of infection present in the environment if it is present. 

Whereas with possum infection, possums generally die quite quickly after becoming infected so there's very few of them in the environment infected in any one time. 

Ageing pigs

Narrator

For all types of surveys the age on the captured pigs helps identify that earliest state they could have become infected and whether it was born after possum control operations in the area. 

Ivor Yockney — Landcare Research 

The older the pig is the longer it's had to pick up TB in the larger area that it would have been in, in its lifetime. So a younger pig will tell you more about what's happening in more recent times and in a smaller geographical area than an older pig will. Pigs are aged on tooth eruption, so tooth eruption in pigs is quite a quick way to age pigs up to the age of forty-two months. After that you need to section the teeth and you look at the growth rings in the teeth just as you would for a tree with different growth rings for the season. 

Three survey methods 

Narrator

The TB free program uses three types of surveys to collect pigs for sampling. 

Mark Neill — Veterinarian, TBfree 

So we've got several methods of collecting pigs and we try to use the most efficient method based on each specific area. So we can use ground hunters and that's the general pig hunter that live in that area will go collect pigs for us and they need to meet certain requirements and that's around GPS coordinates of the hunting for the day, the location of capture, and they have to use tags to identify the animals and take photos of the location and capture as well. We also have other methods where we use helicopter hunting. In areas where we don't have lots of pigs or the pigs are hard to find we can use slightly more novel approaches such as Sentinel pigs which is where we release the pig into the location, leave it there for a period of six months or so and then come back and recover that pig based on the fact that it is tagged and we can locate it again and see if it's picked up the disease while it was in there. We also can use Judas pigs which is a pig that is released into the area after being captured in the same location and it's tagged and identified and then we go in every month and shoot the pigs that it finds because generally they like to be sort of a group. So then we just keep coming back in and sapling the population. 

What does TB look like?

Narrator

In pigs TB lesions are usually found in the heads below the jaw. 

Ivor Yockney — Landcare Research 

So as soon as a pig is killed at a particular site, it's immediately tagged where it lies. It has a capture location, it has a time of day, it has the date, it has other information. That pig head is then removed off the animal. They then get submitted to a laboratory for post-mortem and then further analysis. Each of the heads are identified and signed out from one contractor and signed into the next contractor. So every single head has paperwork that follows it throughout the process. 

Narrator

Examining a wild pigs lymph nodes gives valuable information about TB and infection in the area where it was caught. Any suspicious samples from surveys are sent straight to laboratories for diagnostic testing. Any positive TB samples are DNA strand typed to assess the likely source of the infection. This is compared with strand types that have been found in the area. 

If the strand type is not one normally identified from the area it might indicate a pig has been shifted into the area or a new strain of TB has been introduced into wildlife. 

Mark Neill — Veterinarian, TBfree 

Compared to other methods, pig surveys are one of the most cost-effective measures of actually finding bovine tuberculosis and positive populations. 

Narrator

Wild pig surveys are another scientific innovation developed in New Zealand and is critical to the goal of achieving TB freedom in wildlife. Ultimately, they'll help achieve the goal or eradicating bovine TB from New Zealand by 2055. 

Find out more about using wild pig surveys for TB research at ospri.co.nz. 

Stay in the loop visit osrpi.co.nz