ADVENTURE sport enthusiasts have been warned of serious health risks after a disease transmitted by rodent urine struck down at least 18 Hong Kong 'iron men' who took part in a competition in the Philippines. The victims have been diagnosed with the tropical disease leptospirosis, which causes high fever, muscular pain and kidney and liver failure. With a similar adventure-sport competition to be held here later this year, doctors have warned competitors to take preventive medicine or vaccines before taking part. More than 300 people took part in the Action Asia Philippines Challenges in May last year in Subic Bay. Competitors were required to jump off waterfalls, scale rock faces, cross rivers and climb a series of steep jungle hills. Athletes spent six hours running through the jungle before they trawled through swamps and crawled through 'foul-smelling' mud. Only 20 people were able to complete the course. A fortnight after the games ended some athletes started to have fever, chills, muscle pain and, in some cases, rigors. Microbiologists at the University of Hong Kong, who handled two cases, found the infections had affected most of the patients' liver and kidney functions. Doctors estimate up to 30 competitors could have caught the disease. One German competitor was seriously ill with short-term kidney failure after returning to Berlin and needed dialysis. The disease is caused by infections of coil-shape bacteria, leptospira. The bacteria are usually transmitted by the urine of rodents, cats and dogs. Leptospirosis is prevalent in China, Southeast Asia, Africa, and South and Central America. Epidemics have been reported after heavy rainfall. Subic Bay had its first big monsoonal fall of the season an hour into the challenge. After penetrating the skin, the bacteria can invade organs including the liver, kidneys and the brain, although the mortality rate is less than 10 per cent. Dr John Simon, a private specialist in tropical diseases who took care of most of the Hong Kong patients, all expatriates, said they had run a high fever up to 41 degrees Celsius and experienced severe muscular pains. 'Some of them had red eyes, almost all of them had some degree of renal [kidney] impairment shown on the blood tests. 'One patient had fluid around his heart because of the renal problems. 'In some stages, they had to crawl through the mud. I think at this stage that they got infected.' The patients were treated with the antibiotic doxycycline and all recovered. 'Everyone who travels, whether they go on ordinary holidays or for adventure trips, should be aware of the danger,' Dr Simon said. He said the outbreak could have been prevented if the competitors had taken preventive medicine. Diagnosis of the disease was difficult and it was much less common than malaria, hepatitis and typhoid, he said. University of Hong Kong microbiologist Professor Yuen Kwok-yung said: 'The lesson is, everyone has to be careful while travelling. It is a good practice to consult doctors before going to developing countries.' Professor Yuen said the disease was rare in Hong Kong and people infected in the past were mostly street sleepers. Action Asia race director Ryan Blair said adequate precautions had been taken in each event and his organisation had also sought help from the Centres for Disease Control in the United States. 'Our Action Asia Challenge events are not walks in the park for the family; they are challenging, tough adventure races only undertaken by fit adventure-seekers. 'The incidents in the Philippines were surprising to us since we had event staff travelling in and out of the jungle in the exact location as competitors raced for a five-month period prior to the event and they never contracted any virus or other disease,' he said. Racers and staff are all covered by insurance. Mr Blair said 63 people caught the same disease in 1998 after an adventure race in Springfield, Illinois, in the United States. Three other games will be held in Thailand, Malaysia and Taiwan in the next 18 months.