Bacteria causing catfish deaths in US traced to China

Since 2009, catfish farming in Alabama, Mississippi and Arkansas in the US has been seriously impacted by an emerging strain of Aeromonas hydrophila bacteria that causes serious infection - leading to death in as little as 12 hours.

Researchers have found that the bacterium causing the epidemic is closely related to organisms found in diseased grass carp in China.

A hydrophila, which can be found in both fresh and brackish water, only affects fish that are stressed or injured.

"But the newer strain has affected even apparently healthy fish with no obvious signs of duress," said Mark Liles, an associate professor in the department of biological sciences at the Alabama-based Auburn University.

Disease outbreaks have been responsible for an estimated loss of more than $12 million (Rs.71 crore) in catfish aquaculture operations in the US.

The researchers studied the molecular epidemiology of the epidemic-causing hydrophila to try to trace its evolution.

They compared samples of the bacteria to 264 known Aeromonas strains in an international database.

Only one virulent strain came close to matching the one sampled from Alabama: ZC1, isolated from a diseased grass carp in China's Guangdong Province.

A common ancestor is responsible for the virulent hydrophila strains causing fish disease in both China and the US, the researchers found.

The findings appeared in the journal mBio.