Sydney  -   Hundreds of endangered Australian Green and Golden Bell frogs huddle inside a sauna, shielded from Sydney’s winter chill. The sauna -- a small greenhouse containing black-painted bricks warmed by the sun -- may be pleasant, but it also protects the frogs from a deadly chytrid fungus that would otherwise drive them to extinction. Macquarie University biologist Anthony Waddle holds one frog -- no bigger than a credit card -- in his hand as its green and gold colours become more vibrant in the heat. “Chytrid is the worst pathogen ever”, he told AFP. It is a water-borne disease that burrows into the frogs’ skin, attacking their bodies and eventually killing them. Waddle said that globally, the disease has caused the decline of 500 amphibian species and driven 90 to extinction -- six in Australia. “Nothing has ever caused this much devastation,” he told AFP. “In Australia, we have frogs that only live in glass boxes now. This is a huge, ongoing problem.” But Waddle’s dollhouse-sized saunas could change that. In their warm interiors, the deadly chytrid fungus cannot grow on the frogs, allowing them to fight off the infection and survive.