Leptospirosis, also known as Weil's disease, is a bacterial disease that is usually caught from contact with water contaminated by urine from infected rats.

Health officials have warned of the risk of the disease from the floodwaters that have inundated Jakarta for the past week.

Sarnata, 61, was admitted to hospital on Thursday morning in the acute stage of leptospirosis. His kidneys were damaged and he was losing consciousness because part of his brain had been damaged, the official Antara news agency said.

"Sarnata has entered the third stage of the disease, he cannot speak because his brain is damaged," said Nazir, a doctor at Jakarta Tarakan hospital.

"There are three stages of leptospirosis, with early stages showing high fever, muscle pains, red eyes ... the worst will damage the brain and can be irreversible," he said.

Leptospirosis, which causes high fever and painful joints, is treated with antibiotics. It is rarely fatal, although kidney or liver failure or meningitis can result.

"The risk of acquiring leptospirosis can be greatly reduced by not swimming or wading in water that might be contaminated with animal urine," according to the US Centres for Disease Control.

But many in the city have little option but to wade through the flood waters while children also regularly swim in them.

The floods in Jakarta, the worst in at least five years, have claimed 50 lives and displaced about 500,000 people in the capital and surrounding towns, according to the national disaster crisis centre.

"Fifty people died in Jakarta, Bekasi, Karawang and Tangerang," Linda, an official at the centre, told AFP.

Environment Minister Rachmat Witoelar has blamed the floods on excessive construction on natural drainage areas, but city governor Sutiyoso said it was a "cyclical natural phenomenon."

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