Avian influenza has been found in a second flock of chickens in Delaware, ending hopes that that the first case had been an isolated incident.

State officials said the strain of bird flu virus found in a commercial flock of chickens was the same H7 strain that was found at another farm a few miles away, reported Reuters. It is believed that the H7 strain is not transmissible to humans, and is therefore not as dangerous as the H5N1 strain currently affecting parts of Asia.

As the discovery sent shockwaves through the region's poultry industry, Brazil and China joined the growing list of countries that have banned imports of US poultry. Russia, the largest single foreign market for US poultry, has already moved to ban the import of most poultry products from Delaware, as has Hong Kong.

Delaware officials said a further 72,000 chickens would be culled in order to prevent the spread of the virus.