First, he analysed the samples to find their viral load (the number of virus particles per cubic centimetre) and the subtype of virus involved.

ECONOMIST: In one part of Europe, HIV may be getting less virulent

Professor John Oxford, a virologist at Queen Mary University of London, believes the bioterrorism threat is "a load of old tosh" but still argues in favour of keeping the virus.

BBC: Should the US and Russia destroy their smallpox stocks?