Reuters - Between 1.2 and 1.9 million people have been left clinging to survival in Myanmar's cyclone-hit Irrawaddy delta, where delays by the military government in admitting large-scale aid are threatening a massive humanitarian disaster.

Following are the major health threats facing the survivors of Cyclone Nargis, which struck the southeast Asian nation on May 2:

CHOLERA

- Caused by a bacterium that attacks the lining of the small intestine. First signs of infection are chronic "rice water" diarrhoea. Vomiting is also common. Spread by ingesting contaminated food or water.

Victims become dangerously dehydrated within a few hours and can die within 24 hours without oral or intravenous rehydration.

Incubation period is extremely short at between two hours to five days.

If caught early, treatment is relatively simple and mainly involves drinking water and electrolytes. Typically, antibiotics are also administered.

If untreated, as many as one in two victims will die.

DYSENTERY

- Infection of the digestive system, typically caused by drinking dirty water. Symptoms mainly include diarrhoea, often containing blood and mucus, and vomiting.

Risks to sufferers are mainly through dehydration. Intravenous treatment may be necessary if vomiting is too acute. Antibiotics are also used.

DIARRHOEA

- Gastrointestinal infection, spread by ingesting dirty water or food or bad hygiene. The main threat is through dehydration and can be life-threatening, particularly among children.

MALARIA

- Endemic in Myanmar, the mosquito-borne virus kills 3,000 people in the country every year. Symptoms include waves of high fever, aching bones and nausea, eventually resulting in brain damage or death.

A variety of drugs are used to treat malaria, ranging from quinine to artesunate.

DENGUE

- Another mosquito-borne disease, dengue causes severe headache and muscle and joint pains, hence the nicknames breakbone fever or bone-crusher disease.

There is little by way of treatment, other than pain relief and fluid intake to prevent dehydration. Dengue is rarely fatal if patients can remain hydrated, although children are at particular risk.

SNAKE-BITE

- The delta is home to a variety of venomous snakes, most notable of which is the Russell's viper, for which the World Health Organisation is shipping in 3,000 doses of antivenin.