Bacteria May Have Caused Dolphin Deaths
Filed under: Discovery,Gulf Oil Spill,News & Resources
A common bacteria known to cause abortions in marine mammals killed some of the hundreds of dolphins — more than 100 of them babies and fetuses — that have washed ashore in the northern Gulf of Mexico since February 2010, dolphin experts say.
(From MSNBC / by JANET McCONNAUGHEY) – What they don’t know is why a germ that has been found in healthy animals and that occasionally killed single animals is now apparently causing an animal epidemic and “abortion storms” like those caused by its land-based cousins.
The deaths are continuing, said Teri Rowles of the National Oceanic and Atmospheric Agency and Stephanie Venn-Watson, head of a group that has been studying the deaths.
The marine Brucella bacteria confirmed earlier this month in two adult dolphins and three fetuses may have become more lethal, or another infection or environmental stress — possibly caused by last year’s oil spill — may have hurt the dolphins’ ability to fight disease, they said.
“We cannot rule in or rule out a role for the Deepwater Horizon oil spill or oil exposure or chemical contaminants or additional infectious diseases,” Rowles said during a teleconference Thursday.
She said scientists are also looking for contaminants from oil and dispersants, though only about 15 percent of the 580 cetaceans that have stranded since February 2010 — three months before the spill began — have been fresh enough for tissue samples.
Those found before the spill were generally too decomposed to test, Venn-Watson said. She thought at least one was tested without finding Brucella, but “I really get the feeling that if we don’t test the right organ we might not know if the dolphin had Brucella.”
The deaths are continuing from Louisiana through the Florida panhandle, Rowles said. Texas has not had unusual numbers of dolphin deaths, said Connie Barclay, spokeswoman for NOAA.
The “unusual mortality event” has killed a few whales and more than 570 dolphins, nearly 520 of them bottlenose dolphins. They included more than 100 pups and fetuses.
More than 20 of the youngest dolphins were among 114 that died before the Deepwater Horizon exploded in flames on April 20, 2010. Another 122 stranded or were reported dead offshore between April 30, 2010, and Nov. 2, 2010. And 344 have stranded since then.
Almost all the stranded animals died, Venn-Watson said.
She said Brucella was found in five of 21 animals tested for it: two adults and three fetuses. It had infected the fetuses’ lungs and the linings around the adults’ brains, and it’s possible that those tissues were not tested in at least some of the 16 in which the germ wasn’t found, she said.
Venn-Watson said the bacteria identified earlier this month as Brucella are now being analyzed to see whether the same strain infected all five dolphins.
“If different strains of Brucella are infecting many different dolphins,” that could indicate that the animals all had compromised immune systems, she said. “If they’re all exactly the same, this could potentially be a new Brucella that is particularly good at causing disease.”
Venn-Watson said the scientists are also checking eight dolphins with lesions matching those of the animals with brucellosis, and have identified another 33 with lesions of the lungs in fetuses and of the brain and central nervous system of adults.
Cows, cattle, dogs and other land mammals tend to be infected by different strains of Brucella, but the germs can make other species ill. Large numbers of abortions, called abortion storms, are a common result of brucellosis in herds of cattle, goats and some other livestock.
Brucellosis has also been diagnosed in seals, sea lions, walruses, dolphins, porpoises, whales and an otter, according to Iowa State University’s Center for Food Security and Public Health. A 2007 paper posted on its website said at least four people had been infected by marine Brucella — a researcher and three people who didn’t work with marine mammals.
Both scientists said people need to be aware that if they see a stranded dolphin or whale in the Gulf of Mexico, they should call the Marine Mammal Stranding Network’s hotline, stay away from the animal and keep their pets away from it.
Rowling said that’s standard advice, because there are several infections that people or pets can get from marine mammals.
