By Peter Apps

LONDON, March 1 (Reuters) - Floods, insecurity and war-damaged infrastructure have combined to raise the risk of cholera in Africa this year and experts say new methods are needed to fight its spread among the poorest of the poor.

A bacterial disease that spreads mainly through contaminated water and causes vomiting, diarrhoea and sometimes death, cholera has infected some 12,000 people already in 2007, mainly in a belt spreading through Angola to Congo.

"The last three years have been particularly bad," Claire-Lise Chaignat, head of cholera prevention for the World Health Organisation (WHO), told Reuters from Geneva.

"And this year, with all the rains, we are very much concerned about what is going to happen. We are only in February. Last year in February we did not have so many cases."

The 2007 cholera death toll already stands at around 320 and WHO officials fear this year could be worse than 2006, which saw 160,000 cases centring on Angola and Sudan, both countries weakened by decades of fighting.

The Sudan outbreak spread first from the south into the rest of the country and into neighbours in the Horn of Africa.

Much of it now appears to have burnt itself out but worries persist about Somalia -- where violence makes surveillance difficult -- and also Ethiopia, where health officials worry widespread diarrhoea might really be cholera.

"You can definitely draw a direct link between the recent floods in Somalia and the increased threat of cholera," said CARE International spokeswoman Amber Meikle in Nairobi.

"Until we have proper humanitarian access it is very difficult to gauge the extent," she added.

But the real concern for WHO and other agencies remains the ongoing outbreak in Angola.

HUGE COUNTRY OVERWHELMED

Normally, cholera outbreaks die out after around a year as the immunity of affected populations increases.

But in Angola -- where two decades of civil war have left the infrastructure shattered and where sewage and water systems in many towns have been out of action for years -- it is still reaching previously unaffected communities.

Aid agencies fear heavy rains might make controlling the outbreak more difficult still. Already it has crossed the border into parts of Namibia, the Democratic Republic of Congo and the smaller Republic of Congo.

"It is such a huge country and you get it spreading from province to province," said Chaignat of Angola. "I think they were overwhelmed by what happened."

In contrast, aid workers say they have been impressed by Mozambique's response to the latest floods, which have displaced tens of thousands of people and raised the risk of disease.

"It is something they have been very aware of. They are trying to get people out of the camps as soon as possible," said Michael Huggins, U.N. World Food Programme spokesman for southern Africa.

Quick and well-funded responses have often meant success in reducing or preventing cholera outbreaks. Experts say it is the creeping outbreaks that attract fewer resources.

QUARANTINE, EDUCATION

"You need a multidisciplinary approach so you deal with the water sector, the education sector, the health sector and the media," said WHO's Chaignat.

"They need to practice quarantine and proper health education so people know where is contaminated and where they can go to get uncontaminated water.

Health officials should pay more attention to preventing outbreaks occurring in the first place, she said, possibly using oral vaccines to immunise populations in areas where it was not immediately possible to improve sanitation.

But with vaccines costing around $3 a dose and cholera no risk to richer developing countries, Chaignat said funding is hard to find.

"The sad thing about cholera is that with few means we could make a big difference," she said. "This affects the poorest of the poor populations." (Additional reporting by Jeremy Clarke in Nairobi)

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