Home > Animal deaths, disease and pestilence, Gulf of Mexico > Dolphin deaths in Alabama, Mississippi may be caused by measles-related illness

Dolphin deaths in Alabama, Mississippi may be caused by measles-related illness

March 2, 2011



MOBILE, Ala. — With six new dolphin carcasses discovered in Mississippi and Alabama since Saturday, a review of the scientific literature associated with similar mass die-offs of marine mammals around the world suggests a common culprit: a morbillivirus.

In the same family as the viruses that cause measles in humans and canine distemper in dogs, there are well-documented outbreaks of fatal morbillivirus infections in dolphins, whales and seals around the world since the 1980s.

Jerry Saliki, a University of Georgia researcher and veterinarian who has published a number of scientific papers on morbillivirus infections in dolphins, said the virus could be responsible for the current mass die off.

“It is certainly possible. In the past, there have been significant die offs in the Gulf with dolphins that were attributed to morbillivirus,” Saliki said Monday. “But, there are so many possible causes of mass mortality. Unless a laboratory test confirms, you cannot pin it to morbillivirus.”

Saliki said it takes a few days to confirm the presence of morbillivirus in a dead animal, provided viable samples can be collected. He speculated that no one had so far tested the Gulf animals for the disease, adding, “you can only find things you actually look for.”

Federal officials said Monday that tests for morbillivirus are “pending.”

44 dolphins found dead this year

The new carcasses found over the weekend included five calves and one adult. In Alabama, two were found on West Point Island, next to Dauphin Island, and another was found near Fowl River. In Mississippi, calves were found in Gulfport, Pass Christian and on Cat Island. The total for the two states so far this year is 44 dolphins, with 36 of those being calves, according to records kept by the Institute for Marine Mammal Studies in Gulfport.

Between 2002 and 2007, an average of three dead dolphins washed up between Apalachicola, Fla., and the Texas/Louisiana border in January and February, according to federal records. This year, 77 animals have been found during the same time period.

“This has become quite a significant event,” said Kim Amendola, with the National Marine Fisheries Service. “You look at the numbers from previous years and you can see the difference.”

In 1987 and 1988, 740 dolphins washed up dead on beaches along the Atlantic Coast, including many calves, due to an outbreak of morbillivirus. Scientists estimated that thousands of dolphins died during the episode. Some scientists have speculated that as many as half of all dolphins on the East Coast may have died during the epidemic.

As is the case with the current episode in the Gulf, the carcasses of many dolphins may have disappeared in the ocean before they could be counted. Other morbillivirus outbreaks have been documented in the Mediterranean, the Irish Sea and Russia.

Morbillivirus outbreak has struck before

Several spates of dolphin deaths in the Gulf since the 1980s have been attributed to morbillivirus outbreaks. Scientific papers about those outbreaks noted that the virus moved slowly along the coast from east to west, much like flu outbreaks spread through the human population. A more recent scientific paper described the Gulf’s dolphin population as “immunologically naive,” meaning they did not have antibodies to these viruses.

“Mass mortality only occurs in an immunologically naive population. Once the virus goes through, the survivors are probably protected. That’s why you don’t see mass mortality occurring year after year,” Saliki said. Given that dolphins live an average of about 20 years, Saliki said it was possible there are many dolphins in the Gulf that have never been exposed to morbillivirus.

Most of the animals discovered in Alabama and Mississippi have been stillborn or aborted calves. Saliki said morbillivirus itself is not known for causing infected animals to abort.

“But, any animal that is really sick, it might abort, even though the infection might not be the actual cause,” Saliki said. “We could be seeing something like that.”

Saliki said he was unaware of any research that addressed the possibility that exposure to oil or other contaminants, such as occurred during the summer’s oil spill in the Gulf, might increase a dolphin’s susceptibility to morbilliviruses.

Ultimately, the ongoing dolphin die off in the Gulf is unusual and distressing, but not unprecedented. While the number of dead dolphins found this year is much higher than normal, the 77 dead animals that have been found represent just a small percentage of the Gulf’s population of 45,000, according to the National Marine Fisheries Service.

Federal scientists say some other marine mammals, such as pygmy sperm whales, have also died unexpectedly during what they describe as “an unusual mortality event” that began more than a year ago.

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