WWF Learning has produced a fascinating article on the problem of pathogen pollution - where diseases pass from wildlife to humans or vice versa.

This problem threatens the survival of several endangered species, including the great apes and Asian lions, and also increases the risk of large-scale epidemics among human populations, who are increasingly eating or encountering wild animals.

There is even a possibility that the recent SARS outbreak was the result of a civet cat disease being transferred to vulnerable human populations which have never encountered this disease before - and consequently have no innate or acquired immunity to it - with both economically and socially dire consequences.

In this age of mass, inter-continental transport and trade there are therefore serious threats of new diseases emerging and continuing to cause global epidemics.