Whale Beachings Linked to Mysterious Heart Defect
John Pickrell in England
for National Geographic News
|August 6, 2003|
Typically known for suddenly killing otherwise healthy, young human
athletes, a deadly heart condition with mysterious causes is affecting
populations of two whales species found in both U.S. Atlantic waters and
the Gulf of Mexico. Already this year more than three times the typical
number of diseased whales found in an entire year have beached in the
The increase in the number of stranded dwarf sperm whales, Kogia simus, and pygmy sperm whales, Kogia breviceps, with the heart defect is "disturbing, worrisome, and something we want to investigate," said marine mammal veterinarian and pathologist Gregory Bossart, director of Harbor Branch Oceanographic Institution's Marine Mammal Research and Conservation Division, in Fort Pierce, Florida.
A workshop on the disease, dilated cardiomyopathy, was held at Harbor Branch last month. The meeting united both human and marine mammal researchers and medics, hoping to better understand the heart defect with the help of medical techniques usually used by physicians on humans.
The disease has been found in more than three-quarters of stranded dwarf and pygmy sperm whales beached so far in the Southeast this year, said Bossart, and has been known as one cause of beaching since the 1980s.
On average over the last five years just 12 diseased whales beached and died in the region annually, said Blair Mase, the Southeast Marine Mammal Stranding Coordinator, based at the National Oceanic and Atmospheric Administration (NOAA) Southeast Fisheries Science Center in Miami. However, already this year, 38 diseased whales have washed up on to Southeast beaches. The figures should be treated with caution, however, warned Dann Odell, stranding expert with the Hubbs-Seaworld Research institute in Orlando, Florida. Stranding figures can show great variation from year to year, he said. Several more years' data may be required to prove an increase in stranding frequencies due to the heart defect.
Dilated cardiomyopathy was first documented in both species by Bossart and colleagues in 1985, after 29 beached whales were found to have a heart defect. Little research into causes and treatments has been carried out since then, but this year's mysterious increase in stranding has spurred Bossart's team into action.
Cardiomyopathy is characterized by enlargement and ensuing weakening of the heart. The dilated form is due to the expansion of the lower chambers of the heart (the right side alone in both Kogia species). A thickening of the walls of these chambers causes hypertrophic cardiomyopathy, the more common disease in humans. Both diseases can cause the heart to deteriorate until it is unable to function.
The human version of the diseasenearly always due to inherited genetic defectsis thought to be responsible in many cases where young footballers, basketball players, and other athletes drop dead unexpectedly, said George Hensley, a retired human pathologist formerly of the University of Miami Jackson Memorial Hospital. Hensley is aiding in applying knowledge of the related human heart defect to recognizing and studying the whale disease. According to a recent news article in the journal Science, cardiomyopathies may claim more than 27,000 human lives each year in the U.S.
Deep Ocean "Extra-Terrestrials"
In addition to limited knowledge of the heart defect, very little is known about these species of whale. They've never been kept in captivity, and were deemed too small for commercial whaling purposes, said Bossart. "They're like little extra-terrestrials."
And little they are, compared to their giant sibling species the sperm whale, Physeter catadon, made famous as Moby Dick in Herman Melville's classic novel. The sperm whale can reach over 60 feet (18.2 meters) in length and has a heart "large enough to walk inside of," said Bossart.
In contrast the two smaller species reach 12 to 15 feet (3.65 to 4.55 meters) in length, weigh 1,000 to 1,500 pounds (450 to 680 kilograms), and have a heart about three times larger than a human. All three species are found in deep oceans worldwide, where they hunt for squid.
The first step in understanding more about the pathology and causes of the disease affecting these elusive animals will be to systematically examine the hearts of stranded whales.
To this end Bossart's team are preparing a dissection manual, using techniques typically applied to human hearts. Harbor Branch is one of few facilities to house a necropsy (animal autopsy) facility large enough to rigorously examine 15-foot-long marine mammals weighing thousands of pounds.
Bossart plans to distribute the manual to members of the Southeast Regional Marine Mammal Stranding Network. The network's members include volunteers, universities, government agencies, and others who respond to, and keep records of, strandings.
Marine mammal pathologists have until now used inconsistent methods to sample and study whale hearts, which has slowed progress in understanding the condition. The dissection methods agreed upon at the recent workshop should remedy that problem.
It's important to know what parts of the heart are typically damaged, and when during an animal's life the disease strikes, said Ruth Ewing also of the NOAA Southeast Fisheries Science Center in Miami. Though stranded cardiomyopathy victims are usually adults, it's not known whether the illness strikes young animals and becomes progressively serious, or if it mainly appears in older individuals. Though they have no record of it so far, marine mammal researchers also want to know if the disease is turning up in other parts of the world.
"We want to determine what's causing the cardiomopathy because right now we only have a list of possibilities," said Bossart. These include genetic defects as in the majority of human cases, but nutritional deficiencies, toxic pollutants, and viral infections could all also be responsible.
There have been increases in many illnesses found to harm marine mammals over recent decades, said Bossart. These include new infectious diseases, viral and bacterial, and also cancerpreviously very rare in whales and dolphins.
"We may be seeing the effects of man's poor stewardship of the ocean," said Bossart. "The seas have been used as man's toilet for centuries, and now it's starting to catch up with us."
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