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SILVER SPRING, Maryland -- Pathology experts contracted by NOAA have identified the bacteria Brucella in five bottlenose dolphins that died in the northern Gulf of Mexico. These five are among the 580 dolphins in higher than expected strandings that began in February 2010 and are continuing. NOAA has declared it an "unusual mortality event," triggering a focused, expert investigation into the cause.
Brucella bacteria are commonly found in populations of marine and terrestrial animals throughout the world, but infection in humans is rare in the U.S., and there are no documented U.S. cases of Brucella in humans originating from marine sources. NOAA advises anyone who sees a stranded dolphin in the Gulf of Mexico region to call 1-877-WHALE HELP (1-877-942-5343). The stranded dolphin should not be touched, and pets should be kept away from the dolphin as well. The public should also avoid touching live dolphins in the wild.
"We believe these five dolphins died from brucellosis. Die-offs from bacterial infections could be occurring because the bacterium has become more lethal, but they could also be occurring, or be more severe, because the dolphins are more susceptible to infection. Severe environmental stress, including from exposure to oil, could have reduced the animals' ability to fight infection," said Teri Rowles, DVM, Ph.D., coordinator of NOAA's National Marine Mammal Health and Stranding Response Program. "Right now, there is insufficient information to distinguish between these possible explanations for the increases in mortality of dolphins in the northern Gulf of Mexico. We continue to investigate the factors causing the die-off, and any possible connection to the BP-Deepwater Horizon oil spill."
Scientists have tested 21 dolphins for Brucella so far, with five testing positive. The two adults and three fetuses with brucellosis died off the Louisiana coast between June 2010 and February 2011. The cause of death for the 16 dolphins that did not test positive for Brucella is still under investigation.Scientists are also looking at additional samples from more dolphins.
NOAA is working with a team of marine mammal health experts, including veterinarians, epidemiologists, biologists and toxicologists, to investigate the cause of death for as many of the 580 dolphins as possible. The working group that advises NOAA on these investigations developed a multi-tiered approach earlier this year. The findings may take years to complete and will be made public when scientifically and legally appropriate. Given the decomposition of some of the carcasses, some analyses cannot be performed.
"As we examine the causes of this unusual mortality event, we are investigating the most common causes of die-offs in dolphins first, including infectious disease and marine biotoxins," said Stephanie Venn-Watson, DVM, MPH, a veterinary epidemiologist and chair of the working group. "With this unusual mortality event including a high number of fetuses, we included Brucella testing due to its known ability to infect dolphins and cause their pregnancies to fail."
On land, Brucella can infect cattle, goats, dogs and pigs and can lead to illness, including failed pregnancies. The Center for Disease Control and Prevention reports that brucellosis in people is rare in the United States, with approximately 100 to 200 people infected with brucellosis per year. NOAA is collaborating with public health officials to protect the health of people working with stranded dolphins. Cooking seafood kills the Brucella bacterium, and as there have been only three cases globally linking Brucella infection to consumption of raw seafood, there is minimal risk of exposure to humans through the consumption of seafood.