That wonderful tropical holiday can be bad for your health. GEOFF CUMMING reports

Kristina Strode Penny's finely tuned body has survived the world's toughest multi-sport endurance tests, from muddy swamps in Borneo to the Patagonian desert. None of that could prepare her for a battle 18 months ago against a parasite which wormed its way into her stomach after an event in Fiji.

She was in Queenstown preparing for the Southern Traverse when the symptoms appeared, three weeks after her team won the 2002 Fiji Eco-Challenge.

"It was a Tuesday - I remember it quite vividly. I woke up with a rash all over my abdomen. It was very hot and fiery and I started to get a stiff neck, stomach pains and joint pain. My head was not in a normal space, I was not quite conscious of what was going on."

She drove immediately to Christchurch to see her doctor - a journey she believes she would not have survived without her endurance background. "It was my ability to focus that got me to Christchurch."

After five days in hospital, asleep most of the time, she was well enough to go home but it was four months before she could resume training.

Memories of her ordeal have prompted Strode Penny to take more than passing interest in the fight for life in Auckland Hospital of television presenter Lana Coc-Kroft, who collapsed in Fiji last week. Although Coc-Kroft is thought to be suffering from a severe viral infection, the Fiji connection reminds us of our vulnerability to mysterious illnesses while visiting tropical climes.

The resurgence of diseases such as malaria and dengue fever - and the continued uncertainties surrounding parasitic and airborne illnesses - show medical science still has some way to go to create a world free of infectious disease. Something as apparently innocuous as a mosquito bite can still kill. Yet travellers are complacent about taking precautions against malaria and dengue fever - and there are some illnesses that no amount of planning can thwart.

The strongyloides parasite which afflicted Strode Penny was picked up from soil contaminated with animal faeces - an occupational hazard for international multisporters. "Once it touches your skin it gets into your blood stream, burrows into your lungs, passes into your throat then into your stomach where it starts nesting." In her case, doctors found a treatment by inquiring overseas and the human equivalent of sheep drench did the trick.

But most of us have heard of someone who has diced with death, or at least diarrhoea, in India, Ecuador or Upper Volta - and the cause and cure are never identified. Seven years after a bout of stomach cramps and diarrhoea in Egypt, a Herald colleague remains unable to tolerate fatty foods and alcohol. Despite visits to Auckland Hospital for more than a year after his return, doctors never found out what it was. "Somehow it had damaged my digestive system - at one point they discovered my pancreas wasn't functioning properly."

From a public health point of view, infectious diseases pose a greater threat than individual episodes of Delhi belly, however dire. But even with publicly notifiable tropical viruses which have volumes of medical case histories behind them, an aura of mystery remains.

The virulence with which tropical viruses can attack foreigners is easily explained, says Mark Thomas, associate professor of infectious diseases at the Auckland Medical School. "We go to these countries with no prior exposure to them and no immunity. People that live in malaria areas are the ones who haven't died from malaria in childhood. With typhoid, children have often been exposed as infants. Then we turn up not having been exposed to it."

He draws a parallel with the devastation inflicted on tropical cultures by "European" diseases such as influenza and measles. It's a wonder more visitors to the Third World don't get sick, says Thomas, particularly now that tourists are more likely to venture off the beaten track.

The small number who are admitted to hospital find that tropical illnesses are not easily beaten. For a start, diagnosis can be uncertain. "It depends a little bit on where you've come from what we think you might have.

"There's no malaria east of Vanuatu, so malaria is ruled out for anybody coming from Samoa, Tonga or Fiji. But there's plenty of dengue in those islands and quite a bit of typhoid."

While a good laboratory can identify malaria and typhoid within a few days, other diseases, such as dengue and leptospirosis are harder to pinpoint. "There are some illnesses where you are relying on detecting antibodies in the blood and these may not show up for three or four weeks after infection."

And identification doesn't necessarily mean the illness will quickly be cured. "With dengue fever, we just don't have drugs that work against that particular family of viruses. There are relatively few drugs that do work against viral infections.

"We do have extremely effective treatments for malaria and we can prevent recurrences. Everybody who gets malaria gets cured - although some may die while we are curing the malaria."

But Thomas says the notion that the Third World is alive with mysterious diseases for which there is no cure is overplayed.

"There's no big mystery about dengue. We know it's a virus, we don't know quite how it does some of the things it does to people, but there are things we can do to alleviate it.

"Even with rare diseases like Ebola, it's amazing how much information there is about them. With Sars, within months of it appearing, we knew what it was very quickly.

"If you come back with a disease from a Third World country and it's severe enough for you to go to hospital, by and large we will find out what it is.

"That doesn't mean we can treat it."

Yet 40 years ago, scientists were ready to close the books on infectious diseases. Smallpox had been eradicated and it was thought polio would go the same way. Treatments had been developed for malaria and typhoid while historic killers like the plague, TB and cholera seemed containable with antibiotics.

The emergence of new killers such as Aids and Sars shattered delusions of invincibility. More humbling is the resurgence of malaria, dengue and cholera - diseases considered conquered 30 years ago.

Duane Gubler, the US Department of Health director of vector-borne infectious disease, puts their resurgence down to the combination of spreading urbanisation, more rapid movement of people and animals, and complacency. It was assumed that new wonder drugs and antibiotics would effectively control tropical diseases and research into them waned. So did preventive programmes. There's also little incentive for major pharmaceutical companies to find cures and treatments which poor countries can't afford to pay for.

But there's every incentive for well-off Western countries to undertake research and to provide aid to Third World neighbours for prevention programmes.

As for Strode Penny, she's leaving nothing to chance. Before leaving for an event in Borneo last year, she took every vaccine and prophylactic drug she could think of. "I came away clean, which was more of a cause for celebration than winning the race."

High-profile casualties

Endurance athlete Steve Gurney almost died when he contracted leptospirosis from bat dung in an adventure race in Malaysia in 1994. He lay in intensive care in a Malaysian hospital before being transferred to Singapore with lung and kidney failure. He battled depression for months afterwards and it was two years before his body fully recovered.

The cricketing career of Martin Crowe, New Zealand's finest modern-day batsman, was dogged by the lingering effects of viruses picked up on tours to Asian countries, starting with food poisoning on a tour of Sri Lanka. Late in his career, playing on a dodgy knee, he missed the first leg of a twin tour of India and South Africa to lessen the risk of illness.

Sports Cafe presenter Lana Coc-Krofthad completed filming for Celebrity Treasure Island in Fiji when she became delirious with a mysterious fever and low blood pressure. She was sedated and flown to Auckland Hospital where she slipped in and out of consciousness and needed a respirator.

Commonwealth Games team doctor Nick Chamberlain was bitten by a mosquito in Kuala Lumpur in 1998. He ended up in intensive care with severe dengue fever.