Pete Bethune's venomous snake bite: Kiwi faces ghastly new medical problem

Conservationist Pete Bethune's left leg has doubled in size since being bitten by a poisionous snake in Costa Rica. Photo / Supplied

Injured conservationist Pete Bethune continues to improve after surviving a deadly viper attack, but has detailed squeamish side effects which he says are baffling doctors.

In his latest update on social media, an alert-looking Bethune has revealed treatment for the venomous snake bite is working, and his swollen leg is starting to shrink.

But he has revealed some nasty impacts, saying his groin is the subject of concern as the area has changed colour, is swelling and has become "black, soft and mushy".

"The doctors had a look at that - they're a bit perplexed by it - they're saying it's not normal with a catheter - and they've just gone away to have a pow wow about what they're going to do.

"I do worry about things going black down there."

Bethune, who was bitten by a Fer-de-lance viper in the Costa Rican jungle on Boxing Day, said he was now able to left his injured leg slightly, describing it as a small victory.

"The swelling has reduced quite a bit and I no longer have those sharp pains that were running through my leg."

He also revealed he was close to being transferred to a different hospital to undergo surgery.

"They were going to open up the leg to the relieve the pressure but thankfully just in time the swelling stabilised and now it's definitely coming down and on the mend."

As well as painful swelling, there was a tight ball where the viper sank its fangs into his calf.

"The doctors have said there may be permanent muscular damage. They said they won't know for a week or two but I'll settle for that after what's happened."

Bethune had just walked past a pile of leaves when he felt a sudden jab to the back of one of his legs.

The 55-year-old founder of non-profit organisation Earthrace, was with several crew members when the incident happened on December 26.

Conservationist Pete Bethune in hospital in Costa Rica. Photo / Supplied

Crew members attempted to carry Bethune through the jungle but because the terrain was so steep, he was forced to drag himself through rugged jungle terrain and waterfalls to get to safety.

He ended up being piggybacked to a vessel waiting to get them to the mainland.

His infected leg doubled in size, the poison reached his groin and his health got progressively worse.