(Corrects figure in 12th para for number of refugees in Dadaab to 380,000 from 440,000, after an official correction by UNHCR)
* Outbreak not confined to refugees
* Horn of Africa at risk of disease due drought, movements
* U.N. refugee agency planning airlift of aid and tents
By Stephanie Nebehay
GENEVA, July 15 (Reuters) - Five million people are at risk of cholera in drought-hit Ethiopia, where acute watery diarrhoea has broken out in crowded, unsanitary conditions, the World Health Organisation (WHO) said on Friday.
Cholera, an acute intestinal infection, causes watery diarrhoea that can quickly lead to severe dehydration and death if treatment is not promptly given, according to the United Nations agency.
"Overall, 8.8 million people are at risk of malaria and 5 million of cholera (in Ethiopia)," WHO spokesman Tarik Jasarevic said in a note sent to journalists.
Ethiopian health officials have confirmed cases of acute watery diarrhoea in the Somali, Afar and Oromiya regions of Ethiopia, he told Reuters. "It is not confined to the refugees."
WHO is delivering emergency health kits to Ethiopia and helping train health workers in treating malnutrition and in detecting disease outbreaks, he said.
Drought across the Horn of Africa, now affecting more than 11 million people in Ethiopia, Djibouti, Kenya and Somalia, has increased the risk of the spread of infectious diseases, especially polio, cholera and measles, the WHO says.
"So far WHO has not received any report of polio cases, it really important to help countries to keep their polio-free status," Jasarevic said.
Somalis fleeing severe drought and intensified fighting have been arriving at the rate of more than 1,700 a day in Ethiopia, where 4.5 million people now need assistance, nearly a 50 percent rise since April, he said.
Two million children in Ethiopia are at risk of catching measles, a disease that can be deadly in children, he said.
Ethiopian officials reported 17,584 measles cases and 114 deaths during the first half of the year, UNICEF spokeswoman Marixie Mercado said. The majority of cases were in children.
Measles has also broken out in the sprawling Kenyan Dadaab camps, with 462 cases confirmed including 11 deaths, Jasarevic said.
Dadaab, an overcrowded complex of three camps, now holds some 380,000 refugees, the U.N. refugee agency said on Friday.
UNHCR plans to begin a massive airlift this weekend to bring tents and other aid supplies to the remote border region, spokesman Adrian Edwards told a news briefing.
A Boeing 747 flight carrying 100 tonnes of tents is expected to land in Nairobi on Sunday, he said. Six further flights were planned over the next two weeks.
U.N. High Commissioner for Refugees Antonio Guterres welcomed an announcement by Prime Minister Raila Odinga on Thursday that Kenya is to open an extension to the camps to ease congestion at Dadaab, where 1,300 Somali refugees arrive daily.
"It will prevent congestion increasing further in the short term. Obviously larger needs relate to the need to undertake humanitarian efforts inside Somalia itself," Edwards said.
The United Nations carried out its first airlift of emergency supplies in two years to southern Somalia -- an area controlled by al Shabaab rebels -- on Wednesday, UNICEF said.
"Ten health kits, each sufficient to treat 10,000 people over 3 months are also en route via road," Mercado said.