大象传媒

Parasites invade our bodies in a variety of ingenious ways - through the food we eat or an insect bite, to boring directly under our skin.

Some, like the beef tapeworm, at several metres in length, can hide harmlessly in our gut for years, while others, like malaria, can kill in a day.

Dr Mark Porter visits the Hospital of Tropical Diseases in London where Professor Peter Chiodini and his colleagues diagnose and treat the patients who have picked up parasites, both here and abroad.

Parasites have complex life cycles requiring them to inhabit one or more hosts to reproduce and ensure their species' survival. Mark discovers how the parasite Toxoplasma has developed an ingenious way to ensure this happens. This parasitic effect could even have implications for the causes and treatment of schizophrenia.

Emerging infections are always a concern for doctors, and parasites are no exception. Mark hears about a parasite threatening to reach our shores, and that man's best friend is the host that's likely to bring it here.