In this concluding programme Lionel Kelleway looks at the battle to control and eliminate parasites. Far from being simple hitchhikers, they are remarkably sophisticated and successful organisms, able to outwit immune systems and overcome the body's defence mechanisms. Even if eradication of all parasites were possible, it may not be desirable, as some scientists suggest that we may need them just as much as they need us.
Producer Sarah Blunt. E-MAIL: nature@bbc.co.uk
WEBSITE: www.bbc.co.uk/nature/programmes/radio