It was a typical lazy weekend getaway in Indonesia for primary school teacher Debbie Downes: sunbathing on the beach and swimming in Bintan's warm, tropical waters. But unfortunately for Downes, she came home with more than just a tan.
'A couple of days after I got back,' she says, 'my foot started to itch. My friend said it was probably athlete's foot, so I went to the pharmacy and bought some powder. Days later it was still itching so badly I couldn't sleep, I was feeling lethargic and off colour, and then I noticed there was a network of red lines beginning to snake their way up my foot to the ankle.'
Downes had caught a parasitic disease called schistosomiasis or bilharzia, commonly known as swimmer's itch. It's caused by a species of flatworm that burrows through the skin in the feet, via a cut or sore. 'The red lines were actually track marks where the worm was burrowing under my skin and crawling around.'
The vast majority of these nasties don't originate in Hong Kong, but, say medical experts, are picked up on the mainland, in Southeast Asia, or in developing countries. Hong Kong then becomes the 'get to know you' point for the parasites and the travellers who are carrying them.
'The most common means of infection is by ingestion,' says family GP Michael Cheng. 'The food or water is contaminated with the parasites or their eggs. They attach themselves to the intestinal wall, and sometimes migrate to other internal organs.'
'Based on our clinical experience,' says KH Kung from the Surveillance and Epidemiology Branch at the Centre for Health Protection in Kowloon, 'common parasites include roundworms, pinworms, hookworms, tapeworms and liver flukes.'