A ProMED-mail post
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International Society for Infectious Diseases
Date: 4 Mar 2010
Source: The New York Times [edited]
Cancer Kills Many Sea Lions, and Its Cause Remains a Mystery
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For 14 years, since they 1st reported that a disturbing proportion of
deaths among rescued California sea lions was caused by metastatic
cancer, researchers have been trying to pinpoint the source of the illness.
In 1996, Dr. Frances Gulland, the director of veterinary science at
the Marine Mammal Center in Sausalito, and colleagues at the
University of California, Davis, found that a striking 18 percent of
deaths in stranded adult sea lions were the result of tumors in the
reproductive and urinary tracts.
"It's such an aggressive cancer, and it's so unusual to see such a
high prevalence of cancer in a wild population," Dr. Gulland said.
"That suggests that there's some carcinogen in the ocean that could
be affecting these animals."
The center has not observed the same syndrome in other seals. Years
of study have led researchers to think the answer lies not with any
one culprit, but with several. Their research has added to a body of
evidence concerning industrial contaminants in the ocean and their
effects on the health of its inhabitants.
Sea lions have had to cope with a variety of challenges lately. There
was the animals' mass exit from Pier 39 in San Francisco late last
year, which experts suspect was driven by a hunt for a better food
supply. Also in 2009, the Sausalito mammal center had an unusually
busy year. It took in a record 1370 sick and injured California sea
lions, and doctors found major problems in many, including
malnutrition, parasitic diseases and bacterial kidney infections.
Some had brain seizures from a toxic algae poisoning.
But the cancers are what Dr. Gulland found most worrisome. One day
last month, a volunteer rescue crew netted an ailing sea lion
stranded on Stinson Beach and drove back to the hospital, which was
newly rebuilt and reopened last summer. The thin, lethargic 200-pound
young adult male had paralysis in its genital area and in its swollen
hind flippers, clear signs of cancer.
"It's pretty distressing to see," Dr. Gulland said.
The veterinary team had to euthanize the animal. A post-mortem
examination revealed not only cancer in the penis, but also tumors
riddling the lymph nodes, lower spine, kidneys, liver and lungs. The
disease typically starts around the penis in males and the cervix in
females, then spreads. In an average year, the Marine Mammal Center
sees 15 to 20 California sea lions with cancer.
The center always performs a post-mortem dissection. That work is
"really what tells us about health trends in the ocean," Dr. Gulland said.
The nonprofit center is one of the 2 biggest marine mammal
rescue-and-rehabilitation facilities in the world -- the other is in
the Netherlands -- dedicated to researching the health troubles of
the animals it finds, said Dr. Sylvain De Guise, a veterinary
scientist at the University of Connecticut.
Members of the medical staff in Sausalito, Dr. De Guise said, "have
been pioneers at going beyond treating one individual at a time and
releasing it, and have tried to understand the bigger picture, the
causes and consequences."
Ordinarily, veterinary experts do not see much cancer in wild
animals, but there has been little monitoring for the disease.
Recently, however, cancer has emerged as a key concern for some
endangered species, including green sea turtles, Attwater's prairie
chickens and Tasmanian devils, said Denise McAloose, a veterinary
pathologist at the Wildlife Conservation Society in New York City.
In addition, about 18 percent of dead, stranded beluga whales in the
St. Lawrence River estuary in Canada were found to have intestinal
tumors or other cancers, which have been linked to industrial pollutants.
No one knows how much of the general California sea lion population
has tumors, or if the current rate is higher than before. No
diagnostic test for the disease exists, said Dr. Robert DeLong, a
research biologist at the National Marine Mammal Laboratory in
Seattle who has participated in the cancer studies.
In his field observations among a colony of 100 000 animals in the
Channel Islands -- the birthplace for most California sea lions that
travel the state's coast -- Dr. DeLong said he saw 2 to 5 sea lions a
year with huge advanced tumors.
When Dr. Gulland and Dr. Linda Lowenstine, a veterinary pathologist
at the University of California, Davis, began investigating the
cancer mystery, the obvious suspect was environmental contaminants.
The Channel Islands lie off the Southern California Bight, where,
from the late 1940s until the early 1970s, manufacturing companies
discharged millions of pounds of DDTs and PCBs into the sea. Cleanup
continues, but the chemicals linger.
But if those chemicals are solely to blame, the researchers asked,
why was cancer originating mainly in the uro-genital tract, and not
in the kidney or liver, as one would expect?
"That didn't really fit," Dr. Lowenstine said.
But, in examining sea lion tumor cells with an electron microscope,
Dr. Lowenstine noticed what looked like viral particles. And indeed,
in a major discovery in 2000, a different team of researchers in
Washington, D.C., identified a herpesvirus in the sea lions, a close
relative of the human herpesvirus that fosters Kaposi's skin cancer
lesions in AIDS patients. Recent studies by the California
researchers have shown that the sea lion virus likes to live in the
reproductive tract and, among adults, is twice as common in males --
infecting 45 percent of them -- as in females.
But environmental contaminants are not off the hook. Because it takes
several "hits" of environmental or genetic damage to turn a healthy
cell into cancerous one, the researchers speculated that the virus
and chemicals could be interacting to trigger tumors.
Sea lions accumulate high concentrations of PCBs and DDTs in their
blubber from eating contaminated fish; mothers also pass the
compounds to babies. An analysis by the California researchers and
experts at the Northwest Fisheries Science Center in Seattle found
that animals with higher blubber PCB concentrations were more likely
to have died of cancer.
"PCBs are notorious for 2 different things," Dr. Lowenstine said.
They can suppress the immune system, which may increase a sea lion's
vulnerability to the herpesvirus infection, but they also have
estrogen-like hormonal effects.
[Byline: Ingfei Chen]
--
Communicated by:
ProMED-mail
[It might be an understatement to say this was an interesting
article. If the sea lions and some sea turtles are having problems,
it might be a logical next step to think perhaps a similar situation
may be occurring in some of the whales and dolphins that beach themselves?
Certainly, as this article points out, there are other situations,
such as the Tasmanian devil that has virus related tumors. Canine
venereal tumors are also virus related. In the dogs and in the
Tasmanian devil, they are deemed transmissible tumors. It may be
possible that since this a tumor, suspected to be caused by a virus,
and the uro-genital area of the sea lions, that it too is a
transmissible tumor. Perhaps it is spread through copulation?
This article also mentioned seizures in these animals. In 1998, there
were several problems in California with undiagnosed sea lion
seizures, as related in ProMED-mail posts 19980704.123901 and
19980601.1055. Perhaps the seizures then were related early stages of
this virus? Or cancer? Other areas of the world have had sea lion
die-offs. Perhaps some of them were this same sort of occurrence?
Pictures of California Sea Lions may be found at:
- Mod.TG]
[see also:
1998
----
Sea lions, seizures, undiagnosed - USA (California) (02) 19980704.1239
Sea lions, seizures, undiagnosed - USA (California) 19980601.1055
Sea lion die-off - New Zealand (03) 19980503.0864
Sea lion die-off - New Zealand (02) 19980310.0457
Sea lion die-off - New Zealand 19980308.0441
Sea lion die-off - Sub-Antarctica (08) 19980218.0313
Sea lion die-off - Sub-Antarctica (07) 19980211.0273
Sea lion die-off - Sub-Antarctica (06) 19980207.0237
Sea lion die-off - Sub-Antarctica (05) 19980205.0226
Sea lion die-off - Sub-Antarctica (04) 19980205.0223
Sea lion die-off - Sub-Antarctica (02) 19980203.0215
Sea lion die-off - Sub-Antarctica 19980201.0207]
....................sb/tg/ejp/mpp
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