The two countries, so far free of Ebola, produce 60 per cent of the world's cocoa. Experts say if an outbreak occurs, bean prices will surge beyond the 3.5-year high reached in September and affect retail chocolate prices.

"If prices rise at a greater rate, chocolate manufacturers will pass the increase onto consumers," said Andrew Rolle of Juremont, a major Australian importer of chocolate ingredients.

"It's a fragile market there at the best of times. There will be labour issues with the cocoa farmers in the fields, political issues, transport issues with accessing stock through ports."

Australian chocolate makers typically have six to 12 months' of cocoa supply in storage, so any price rises after an outbreak won't be immediately seen, he added.

The commodity price was heading for a sixth straight monthly gain, the longest streak in 12 years, the International Cocoa Organisation said.

Boutique chocolatier Haigh's raised prices by 3 per cent earlier this year, expecting bean prices to remain rising because of the growing popularity of dark chocolate and Asia's booming middle class.

Chief executive Alister Haigh said the outbreak was at the forefront of his mind, as a third of Haigh's cocoa was sourced from Ghana.

"The prices we've set will suffice for the near future. That's not to say there's been a huge increase, but we're well covered for the next six months."

Nearly two-thirds of the 3000 deaths have occurred in Guinea and Liberia, which share a porous and poorly policed border with the Ivory Coast, a vital source for chocolate giants Cadbury and Nestle.

"It's a long border. It's vulnerable and hard to control. It's a serious threat," an exporter in the port city of Abidjan told Reuters.

The US health authorities have predicted another 1.4 million people could be infected in West Africa by January without extra intervention. If the virus spreads into the Ivory Coast, transport restrictions may be enforced, swaths of farming land quarantined, and migrant workers stopped in their tracks.

The economy-sustaining cocoa industry could be brought to its knees, hitting the incomes of millions of farmers, buyers and exporters.

"What we fear is that under a quarantine nothing will move, that farmers will flee, that trucks won't go in and that the cocoa will rot on the trees," an exporter told Reuters. Another market strategist said that would be "pandemonium".

Both Mondelez, owner of Cadbury, and Nestle did not respond to questions about possible impacts on retail prices.

Mondelez said it was monitoring the epidemic closely and none of its supply was under any immediate threat. A spokesman said: "However, as a matter of normal practice we do have contingency plans in place to address potential supply risks."

Nestle, maker of KitKat and Milo, said: "It is too early for predictions on the possible effects on our business."

Higher prices, though, are unlikely to suppress Australia's insatiable appetite for chocolate, with IBISWorld figures showing we are on track to spend $1.98 billion on the mood-lifter this financial year.

THE COCOA PRODUCTION LINE

• There are up to 2 million small-scale cocoa farms in the Ivory Coast and Ghana, producing 60 per cent of the world's cocoa.
• Cocoa bean prices reached a 3.5-year high of $US3221 per tonne in September, soaring 15 per cent this year alone.
• The increase is being labelled the "Ebola premium" by traders and investors in the US.
• The record price of $US3826 per tonne for cocoa on the US market was set in 2011 when the Ivory Coast's post-election civil war disrupted supply.
• If the Ivory Coast's cocoa supply halts, investors fear prices could double