A bacterium causing an epidemic among catfish farms in the southeastern United States is closely related to organisms found in diseased grass carp in China, according to researchers at Auburn University in Alabama and three other institutions. The study, published this week in mBio®, the online open-access journal of the American Society for Microbiology, suggests that the virulent U.S. fish epidemic emerged from an Asian source.
Since 2009, catfish farming in Alabama, Mississippi and Arkansas has been seriously impacted by an emerging strain of Aeromonas hydrophila, which causes Aeromonas septicemia in catfish. A serious infection that can cause death in as little as 12 hours, Aeromonas septicemia's clinical signs include skin lesions and blood loss.
Normally 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, says senior study author Mark Liles, PhD, an associate professor in the Department of Biological Sciences at Auburn.
When initial tests of the diseased fish showed A. hydrophila was responsible, says Liles, scientists "didn't believe it at first, because the signs didn't match the more typical opportunistic infections in stressed fish that we associate with A. hydrophila." To date, disease outbreaks have been responsible for an estimated loss of more than $12 million in catfish aquaculture operations in the southeastern United States, he says.
Liles and colleagues studied the molecular epidemiology of the epidemic-causing A. 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. ZC1 was isolated from fish that had experienced an epidemic outbreak atypical of Aeromonas infections.
Researchers also identified a less aggressive related A. hydrophila strain called S04-690, taken in 2004 from a diseased catfish in a commercial aquaculture pond in Mississippi. That strain caused a serious Aeromonas septicemia outbreak that killed thousands of catfish but did not result in an epidemic on neighboring farms.
Next, the scientists evaluated the evolutionary relationships of additional Chinese carp bacteria samples from epidemics in the Hubei Province in China. This revealed that all of the Chinese carp bacteria samples, including ZC1, group together with the recent U.S. epidemic samples of bacteria in catfish, suggesting that a common ancestor is responsible for the virulent A. hydrophila strains causing fish disease in both China and the United States.
S04-690, from the Mississippi fish, also was found to be in the same group, related to both the U.S. catfish and Asian carp bacteria. However, it was genetically distinct from the other two strains. By contrast, A. hydrophila strains that do not cause epidemics are more heterogeneous.
Additional experiments found that isolated bacteria from diseased catfish in America and diseased carp in China shared alternate forms of 10 key 'housekeeping' genes required for basic cellular function.
It's not clear how the bacterium was introduced in America, Liles says. It could be from importing Asian carp to America for aquatic weed control, or from transporting ornamental fish or contaminated processed seafood products from Asia. The spread of disease among farms also is not fully understood but could result from birds that move from pond to pond eating catfish, or from harvesting equipment that may be insufficiently sanitized between uses.
Liles and other researchers are investigating means to control the spread of illness, including developing vaccines against the bacteria, and using medicated feed and/or probiotics. Meanwhile, he says, U.S. farmed catfish are safe to eat and pose no disease threat to humans due to strict standards regarding harvesting and processing of sick animals.
The study was funded by Auburn University and the Alabama Agricultural Experiment Station.
mBio® is an open access online journal published by the American Society for Microbiology to make microbiology research broadly accessible. The focus of the journal is on rapid publication of cutting-edge research spanning the entire spectrum of microbiology and related fields. It can be found online at http://mbio.asm.org.
The American Society for Microbiology is the largest single life science society, composed of over 39,000 scientists and health professionals. ASM's mission is to advance the microbiological sciences as a vehicle for understanding life processes and to apply and communicate this knowledge for the improvement of health and environmental and economic well-being worldwide.
Jim Sliwa | Eurek Alert!
Researchers master gene editing technique in mosquito that transmits deadly diseases
27.03.2015 | Rockefeller University
Honey bees use multiple genetic pathways to fight infections
27.03.2015 | Penn State
In an experiment at the Department of Energy's SLAC National Accelerator Laboratory, scientists precisely measured the temperature and structure of aluminum as...
The IPH presents a solution at HANNOVER MESSE 2015 to make ship traffic more reliable while decreasing the maintenance costs at the same time. In cooperation with project partners, the research institute from Hannover, Germany, has developed a sensor system which continuously monitors the condition of the marine gearbox, thus preventing breakdowns. Special feature: the monitoring system works wirelessly and energy-autonomously. The required electrical power is generated where it is needed – directly at the sensor.
As well as cars need to be certified regularly (in Germany by the TÜV – Technical Inspection Association), ships need to be inspected – if the powertrain stops...
When an earthquake hits, the faster first responders can get to an impacted area, the more likely infrastructure--and lives--can be saved.
The Atlantic overturning is one of Earth’s most important heat transport systems, pumping warm water northwards and cold water southwards. Also known as the Gulf Stream system, it is responsible for the mild climate in northwestern Europe.
Scientists now found evidence for a slowdown of the overturning – multiple lines of observation suggest that in recent decades, the current system has been...
Because they are regularly subjected to heavy vehicle traffic, emissions, moisture and salt, above- and underground parking garages, as well as bridges, frequently experience large areas of corrosion. Most inspection systems to date have only been capable of inspecting smaller surface areas.
From April 13 to April 17 at the Hannover Messe (hall 2, exhibit booth C16), engineers from the Fraunhofer Institute for Nondestructive Testing IZFP will be...
25.03.2015 | Event News
19.03.2015 | Event News
17.03.2015 | Event News
27.03.2015 | Trade Fair News
27.03.2015 | Physics and Astronomy
27.03.2015 | Life Sciences