Kiwi conservationist Pete Bethune is about to defy the odds and walk out of a Costa Rican hospital cured of a deadly snake bite that almost claimed his life a fortnight ago.

The intrepid environmentalist is just hours away from being discharged after a 14-day stint in hospital, after falling victim to one of the deadliest snakes on the planet deep in a South American jungle.

Initially fearing he wouldn't make it out alive, Bethune managed a difficult three-hour trek, clambering and dragging himself through unforgiving terrain to reach his boat.

By the time he had reached hospital, his left leg had swollen to at least double the size of his right after the Fer De Lance viper sank its fangs into his lower calf.

But now, after nearly a fortnight of treatment with a few medical challenges, a buoyant Bethune is celebrating a remarkable milestone.

"I'm getting close to leaving," he said in his latest Facebook update.

"I've got final tests today. Just waiting for results of those. If they are all good then I'm heading back to the ship. So hopefully back on the ship tomorrow. "

Pete Bethune struggles down streams in the Costa Rican jungle after being bitten by a poisonous snake. Photo / Supplied

He said he was "super looking forward" to getting back to the ship and waiting crew.

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"It's going to be amazing."

At this stage the only thing that would prevent him from leaving would be if something untoward turned up in the tests.

He said his body was well and truly on the mend, though his ankle was still not flexible enough to rotate normally. However, it was improving every day.

Bethune, who is in Costa Rica to help stop wildlife poaching and illegal gold mining, described the first days of his stay in hospital as a blur.

"When I first came in here they put me on morphine. You are lucid in a sense of what's going on but it's very dream-like."

He said the doctor treating him told him he had been given the greatest level of antivenom of any snake-bite victim he had ever treated.

Bethune is marvelling at his remarkable survival, after being certain he would not make it out of the jungle alive.

The Fer-de-lance viper that struck Pete Bethune on his lower leg. Photo / Supplied

He described the journey out as one of the most extraordinary three hours in his life.

"When that snake first got me I thought I was gone.

"We were so far up the jungle and the only quick way out of there was down through these waterfalls."

He said the doctors were surprised how far the venom had progressed through his body, not realising he had spent harrowing hours scrambling down steep rock faces in order to reach help.

A GoFundMe page to pay for the conservationist's medical bills stands at $19,005, about $11,000 shy of the goal.