In October 2013, Jeremy Farrar was appointed Director of the Wellcome Trust - UK's largest medical research funding charity. The Trust funded �750 million's worth of health-related research - about the same as the government's Medical Research Council. This means Jeremy Farrar is a major figure in British science.

Since 1996, the doctor and clinical scientist had run the Wellcome-funded Oxford University Clinical Research Unit in Ho Chi Minh City in Vietnam - a British-Vietnamese collaboration specialising in infectious diseases such as malaria, HIV, TB and avian flu. He lost close friends and colleagues when the SARS pandemic took off in East Asia in 2003, and dealt with the first cases of the dangerous H5N1 bird flu when it arrived in Vietnam the following here.

In conversation with Jim Al-Khalili, Dr Farrar talks about the personal and professional impact of those experiences and of his feelings of impotence as a doctor treating HIV/AIDS patients as a junior doctor in London in 1980s.

With his international perspective and his hands-on experience of the deadly potential of infectious diseases, he talks to Jim about the great health challenges faced by the world in the coming decades.