The spiky monotreme now holds the title as the world's only echidna to be allergic to ants - her sole food source.

She first arrived at Melbourne's Healesville Sanctuary as a baby after her burrow was accidentally dug up at a nearby property.

So when vets noticed eye and skin changes almost two years later they set to find out what was wrong and the results surprised even the most seasoned campaigners.

Sanctuary vet Claire Madden said the allergy was bizarre and the first of its kind recorded in the world.

"Ants make up 100 per cent of their diet, with some dirt," she said.

"So understandably we were in a bit of shock at the finding."

Without an option of an alternative diet, veterinary dermatologists at the Melbourne Veterinary Specialist Centre developed two vaccines to train Matilda's immune system to tolerate the creepy crawlies.

Without treatment, Matilda was at risk of getting a deadly infection or losing her sight.

The three-year-old has responded well to the treatment and has been vaccine-free for six months, but will be closely monitored by vets for the rest of her life.

Australian Associated Press