Swimming in dark waters
By Kelley Weir
Researchers study a deadly pathogen’s move to the Pacific
On any given day you can be sure that there are at least a dozen people lined up to see two of the best attractions at any zoo: the sea otters and sea lions. Kids run back and forth in front of the animals’ glass enclosures to encourage the hopelessly cute animals to follow them.
For most travelers to Alaska, wild sea otters and sea lions are also a not-to-be-missed attraction. But with pollution, oil spills and infectious disease significantly affecting some marine populations, that could change. That’s why Morris Animal Foundation is supporting Drs. Tracey Goldstein and Jonna Mazet from the University of California–Davis in their efforts to track a deadly disease that is potentially threatening these animals.
Deadly virus a suspect in recent otter deaths
Phocine distemper virus (PDV) is a pathogen that affects seals and causes lethargy, fever and even death in infected animals. The disease poses no health risk to humans, but the illness is related to canine distemper in dogs.
PDV has caused two epidemics in the Atlantic Ocean; in 1998, the virus killed more than 23,000 harbor seals, and in 2002, 30,000 died. PDV has also been associated with seal deaths on the eastern coast of the United States and Canada, which shows the persistent threat of this virus to marine mammal populations. Many populations in Alaska have declined recently, including Steller sea lions and Northern sea otters. Until Dr. Goldstein’s study, the virus had never been identified in any Pacific Ocean species, but examining the deaths of Northern sea otters in central Alaska led to the discovery of the virus in these animals.
“We were seeing otters die in central Alaska,” says Dr. Goldstein, who is leading the study with Dr. Mazet. “Not the young and old, as we would expect, but prime-aged otters that were dying of bacterial infections.”
To Dr. Goldstein and her team, that was an anomaly. They wondered why animals in their prime were dying. One possibility was a virus that suppressed the immune system in the animals, causing them to become more susceptible to bacterial infection. That’s when, with Morris Animal Foundation funding, the team began to investigate the presence of PDV infections in Northern sea otters.
Putting marine life to the test
Otters and seals often act as sentinel species that indicate issues also affecting other species that may be affected by natural and manmade disasters or emerging viruses. Because these animals live most of their lives in the water and eat smaller creatures, such as urchins and mollusks, that easily absorb contaminants, it is logical that they would be a virtual map of any new viruses like PDV. It made sense to begin testing seals and otters in the Pacific for PDV. Other seal species, such as ice seals (ringed, ribbon and spotted), may also be highly susceptible and share the marine ecosystem with the sea otters. Thus, the current exposure and infection status of those populations needed to be examined.
Dr. Goldstein and her team tested samples from 112 Northern sea otters and more than 400 samples from seven different species of seals for PDV. All of the samples were tested using a new test, developed by researchers at UC-Davis, which specifically screens for PDV.
Sure enough, researchers confirmed, for the first time, that PDV is affecting marine mammals in the Pacific Ocean.
“We found the virus in tissue and nasal swabs” she says. “Now we are trying to see if the virus is actually causing disease in Northern sea otters in Alaska.”
According to Dr. Goldstein, although PDV was first identified in Northern sea otters, as she suspected, the virus is also circulating in other marine mammals like Steller sea lions in Alaska. In addition to further examining the association of PDV with recent sea otter deaths, she and her team will determine the ongoing presence of this pathogen in other species, such as Steller sea lions, harbor seals and ice seals, in Alaska. Evaluating the role of distemper in marine mammal deaths is critical because a new outbreak could devastate the recovery efforts of already declining and vulnerable Arctic marine mammals.
Gathering info to protect populations
Dr. Goldstein cites previous findings that the virus was not circulating in these species during the earlier periods of population declines during the 1970s and 1980s and that PDV was likely introduced to Alaska after 2002. She recommends that other species, like the endangered Hawaiian monk seal, should be closely monitored for evidence of PDV infection as the consequences of exposure to the virus could devastate those populations.
Recently, dead harp seal pups and adults were found over a wide geographic area of shores in Canada, including the St. Lawrence Estuary, northern Newfoundland and Labrador. Confirmed numbers of dead were in the low hundreds and involved mostly adult animals. Because of Dr. Goldstein’s work on PDV in Alaska, Canadian authorities have been alerted to a potential outbreak associated with this viral infection. The presence of an outbreak is now high on the list of possibilities for the cause of death for these animals, though other factors may also be at play.
“Just because the virus is present, it doesn’t mean that it’s causing disease or death,” Dr. Goldstein stresses. “That is what we are trying to find out with this grant from Morris Animal Foundation.”
Dr. Goldstein will continue her work on PDV by growing the virus in culture in a lab in order to have enough material to sequence the entire viral genome. The information gleaned from this study will help make veterinary professionals receiving sick sea otters or seals at marine rehabilitation centers aware of the risk of infection and the need to better quarantine animals to prevent the spread of infection.
Although the deaths of these animals are heartbreaking, some may take solace in the fact that there are dedicated researchers like Dr. Goldstein who are working toward understanding devastating viruses like PDV. Dr. Goldstein’s work is laying the foundation for other researchers to gain more information and develop strategies to protect wild and captive seals, sea lions and sea otters.
Posted by MAFon August 23, 2011.
Categories: Animal studies, Veterinary research , Wildlife health
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