Donald Rumsfeld has made a killing out of bird flu. The US Defence Secretary has made more than $5m (£2.9m) in capital gains from selling shares in the biotechnology firm that discovered and developed Tamiflu, the drug being bought in massive amounts by Governments to treat a possible human pandemic of the disease.

More than 60 countries have so far ordered large stocks of the antiviral medication - the only oral medicine believed to be effective against the deadly H5N1 strain of the disease - to try to protect their people. The United Nations estimates that a pandemic could kill 150 million people worldwide.

Britain is about halfway through receiving an order of 14.6 million courses of the drug, which the Government hopes will avert some of the 700,000 deaths that might be expected. Tamiflu does not cure the disease, but if taken soon after symptoms appear it can reduce its severity.

The drug was developed by a Californian biotech company, Gilead Sciences. It is now made and sold by the giant chemical company Roche, which pays it a royalty on every tablet sold, currently about a fifth of its price.

Mr Rumsfeld was on the board of Gilead from 1988 to 2001, and was its chairman from 1997. He then left to join the Bush administration, but retained a huge shareholding .

The firm made a loss in 2003, the year before concern about bird flu started. Then revenues from Tamiflu almost quadrupled, to $44.6m, helping put the company well into the black. Sales almost quadrupled again, to $161.6m last year. During this time the share price trebled.