A disease from a nasty fungal family that kills bats, snakes and bearded dragons has been found in New Zealand’s threatened tuatara, but it turns out they might have had for aeons without anyone realising.
No-one knows whether the ancient reptiles harboured Paranannizziopsis australasiensis before human settlement, or caught it from exotic creatures imported before the advent of tight biosecurity controls. It may even have arrived via a natural invasion, such as a turtle washing up in New Zealand.
Conservationists feared the worst when lab tests revealed a previously-unknown fungus infesting the sores of at least five tuatara and a bearded dragon at Auckland Zoo.
Because the zoo didn’t know its creatures were infested, it had been rearing endangered northern tuatara for the Department of Conservation. Rangers had been taking the reptiles to supposedly-safe sanctuary islands.
The fungus is from the same family of diseases that has wiped out colonies of bats and killed otherwise-healthy snakes in the United States. Wildlife rangers feared that their well-meaning efforts to increase tuatara babies’ survival rates had accidentally sickened the species.
But it seems that tuatara have been living with their particular strain of fungus for ages, and it doesn’t seem to bother them much.
Richard Gibson, Auckland Zoo’s curator of Ectotherms and Birds, says investigators are now almost certain that its presence has nothing to do with the breed-for-release programme, since the disease has been discovered on at least one island where captive animals have never been taken.
“I don’t think we’ll ever be able to say if it’s endemic to New Zealand or whether it was brought here by people or animals…but we’re almost certain it was not through the breeding programme. There’s no reason to worry about it in the wild now,” says Gibson.
It seems Paranannizziopsis australasiensis is just one of countless, non-deadly diseases that people didn’t know about, but animals have lived with for ages.
Rangers went looking for it in the wild after the zoo found it in captivity. They saw no evidence that it was hurting wild animals.
“The fact they don’t get really sick with it suggests they’ve been living with it for a long time, it’s when you have a novel fungus you can have problems,” says Gibson.
“With snakes [which are affected by a different strain] it is a new strain and environmental stresses are also getting to them and [it’s similar] with white nose fungus in bats. If their environment is changing, if they are hungrier or more stressed, it affects animals and diseases may become more or less virulent.”
Outside zoos, a tuatara wouldn’t find itself being inspected for sores, let alone submitted to swabbing and testing for novel organisms. That’s why the disease went unnoticed for so long, says Gibson.
“The funny thing is, there are countless diseases we know about and even more we don’t. We find it in captivity and we worry about it, but we don’t know if it’s in the wild until we look.”
Native disease?
It was 25 years ago when the Department of Conservation asked the zoo to help breed baby tuatara for DOC to release on island sanctuaries.
The zoo reared young ones, and DOC released them on Stanley and Cuvier islands for years, not suspecting they carried anything dangerous.
The two islands near the Coromandel are among only a handful of islands that host northern tuatara, a more threatened sub-species than the Cook Strait tuatara that people may see at Zealandia wildlife sanctuary near Wellington.
“Little brown lesions had been observed ever since tuatara had been in captivity but no one ever took them seriously because they cleared up, or if they got bad we might treat them with a bit of iodine,” says Gibson. “Even in the wild tuatara are at mercy of their environment and if they’re in shallow burrow that gets flooded.. they might get lesions.”
One captive tuatara was found to have the fungus after it died, but there’s no evidence the fungus was what killed the creature, says Gibson.
In 2011 and 2012 Auckland Zoo’s vet decided to get to the bottom of the spots and sores and found some of the tuatara harboured a fungus in their lesions.
All the New Zealand investigators could tell was that the fungus was from a family of diseases that had killed otherwise healthy wild snakes and pet bearded dragons in the United States. It was also related to the ‘white nose’ fungus associated with millions of North American bat deaths. But the strain of disease was a mystery.
Keepers sent swabs from infected reptiles to a specialist lab in Canada, which declared the culprit to be a previously-unknown disease, now named Paranannizziopsis australasiensis.
So far, the only animal outside New Zealand known to have caught it is an aquatic snake at Melbourne Zoo.
While the fungus’ existence is news to humans, Gibson suspects it doesn’t hurt tuatara unless they get stressed or sick by other means. Traces have been found on healthy skin and in soil from tuatara burrows, as well as in sores and grazes.
Still, the breeding programme was in limbo for years while researchers tried to figure out if captive creatures might have spread the disease to the wild.
After it was identified, the release phase of the breed-and-release programme was halted while wildlife rangers from the Department of Conservation caught and swabbed wild tuatara from islands including Cuvier and Stanley, North Brothers, Lady Alice, Coppermine and Taranga, as well as from Cape Kidnappers and Zealandia.
If the disease was found only on Stanley and Cuvier or in places like Zealandia, hosting hordes of human visitors, researchers would have suspected that zoos – or at least, people – were the culprits.
But researchers received welcome news: the fungus was found on at least one wild island where no captive tuatara had been released.
Tuatara handlers now think it’s unlikely that conservation efforts infected wild creatures, clearing the way for the zoo’s remaining 29 captive northern tuatara to be released last month.
DOC set free the last few dozen animals on Stanley and Cuvier islands in March, marking the end of the captive breeding project.
Tuatara as old as 10 – very youthful, in tuatara terms — scuttled into the forest to begin what their breeders hope will be century-long lives of impeccable health and breeding in the wild.
Conservation efforts will now switch to transferring animals between islands to increase genetic diversity. Some islands began with only a handful of animals, so northern tuatara from nearby islands will be transferred to bolster the gene pool.
Not fatal
Since the fungus isn’t fatal, zookeepers may be thankful it appears to be endemic to New Zealand.
Gibson, the curator, told Newsroom last year clearing the fungus from wild tuatara would have been nearly impossible. Even after working hard to cure captive creatures, zoo staff managed a temporary fix that required an intensive six-week-long drug treatment under a vet’s supervision.
“The minute you treat an animal and put it back in an environment that’s not sterile they can catch it again,” said Gibson. “We don’t know if it’s on leaves or in the soil or on the crickets we feed them…In terms of doing it in the wild, there’s absolutely no chance whatsoever.”
If wild reptiles have had the fungus forever, it wouldn’t be surprising if it was found more often in zoos, said Gibson.
Young captive tuataras’ artificially-close proximity means infections can spread more easily, just as viruses and bacteria do in human daycare centres.
Plus, captive reptiles are inspected every month, increasing the chances of seeing spots. “A tuatara in the wild might go six months without seeing another tuatara,” he said.
Any impact of Paranannizziopsis australasiensis in the future might turn on whether it breeds best in hotter or colder temperatures, and whether animals it infects are already stressed by other environmental pressures.
“Maybe the fungus only causes lesions if they are a bit under the weather or maybe it doesn’t cause the lesions, it just infects them,” Gibson told Newsroom last year.
“Animals on the edge of their comfort zone may be more stressed and so more susceptible to disease,” he said.
“If it prefers a hot tuatara, then climate change making tuatara warmer will help it thrive. We just don’t know.”
Slow-moving, slow-breeding tuatara are the sole remnants of an ancient branch of reptiles called Sphenodontia. They evolve slowly and haven’t changed much since they co-existed with dinosaurs. Wild ones survive on a few dozen pest-controlled islands and mainland sanctuaries.
Even in sanctuaries, some populations may find themselves under pressure from climate change.
Researchers at Victoria University found males at North Brothers Island were surviving at higher rates than females, because more males hatch at higher temperatures.
The news is not all dire, though — transplants from the biggest wild population at Stephens Island/Takapourewa are thriving at Zealandia.
