Animals as Sentinels
Tufts Veterinary Medicine — V6, No.2
Cover story by Cynthia B. Hanson
Wildlife can act as a barometer for human and environmental health by helping us gauge levels of risk from toxins, emerging diseases, or bioterrorism.
FIVE PAIRS OF BINOCULARS PIVOT IN UNISON AS THEY TRACK TWO juvenile semipalmated plovers riding the crisp ocean breezes that waft over Gooseberry Neck Beach in southern Massachusetts. But suddenly their focus shifts to a great black-backed gull posed on the beach like a sentinel soldier as it eyes them from a distance.
Despite its regal appearance, there’s something off-kilter about its contour—the soft down of feathers on its underbelly looking oddly distorted. As it takes flight, the little group of birders follow its path, concurring on what is becoming startlingly apparent: A large mass is dangling from its abdomen like an omen in the wind.
“Right there you see a bird that could end up [dead] on the beach, and that’s data,” says Jamie Bogart, a research assistant at the Lloyd Center for the Environment in South Dartmouth, Mass., a nonprofit organization involved in environmental education and research focusing on marine biology and coastal ecology.
Bogart is leading this sneaker-clad group on a three-mile bird identification walk along the rocky beaches of Gooseberry Neck as part of the Seabird Ecological Assessment Network (SEANET) project. In 2002, Tufts Veterinary School started the program in conjunction with the Lloyd Center to instruct volunteers on how to collect information for a database on coastal birds. Equipped with satchels containing data sheets, rubber gloves, rulers, calipers, scissors, cameras and plastic sacks, citizen scientists are instructed on how to identify live birds and gather information from bird carcasses. The information is then entered into a database that researchers at the Tufts Wildlife Clinic can use as indicators for human and environmental health.
Photograph by Kathleen Dooher
“Seabirds are very good sentinels because they’re high up on the food chain,” explains Tufts’ Dr. George Saperstein
“Seabirds are very good sentinels because they’re high up on the food chain,” explains Tufts’ Dr. George Saperstein, department chair for Environmental and Population Health. “Since the seabirds are eating the fish, over time they’re potentially bioaccumulating toxins. Or if there was an [infectious disease such as West Nile or a bioterrorist] event, we might see a die-off in the seabirds,” he adds.
“Fish-eating birds are exposed to the same contaminants that we are through the fish that they eat. So you may get similar levels of bioaccumulation, which makes them good sentinels for human health in terms of seafood consumption,” says Rebecca Harris, Ph.D., G01, a biologist at the clinic and the SEANET coordinator. “If you’re interested in shellfish, you would monitor eiders [sea ducks], for example. Other species like gannets and terns are exclusively fish eaters,” she notes.
“They also provide valuable geographic data on where contaminants are located. And there also are a lot of health risks and pathogens that we share in common, including those resulting from marine biotoxins [red tides],’ she says.
After their successful launch with the Lloyd Center, Tufts started a second SEANET collaboration on Cape Cod in 2003 with the Mass Audubon/Wellfleet Bay Wildlife Sanctuary [Funders for the SEANET project include the Geraldine R. Dodge Foundation, NOAA Coastal Services Center, GIS Integration and Development Grant, National Fish and Wildlife Foundation, International Fund for Animal Welfare, Gulf of Maine Council on the Marine Environment, Fuller Foundation, Davis Conservation Foundation, Tufts Institute of the Environment, Lynn Trayser Mitchell Memorial Bird Fund, and Massachusetts Environmental Trust]. From there, SEANET quickly proliferated into a network of 300 volunteers working with various environmental groups along the Atlantic from New Jersey to Canada. Tufts has started to talk with groups in Florida as well in an effort to extend the project down the entire east coast.
In addition to monitoring the impact of oil spills on coastal marine life, SEANET is acquiring data on the effects of oil-laced bilge waste and ballast water from boats. Some 70 percent of the birds collected from Atlantic Canadian beaches had oil on their feathers and died from oil pollution, Harris says. “We thought it would be a good idea to use the same methods and extend that kind of monitoring down the east coast of the US because it hasn’t regularly been done here.”
Although she hopes the project will involve long-term monitoring, which is dependent on continuing grant money, the information obtained over the last few years has already proved useful. For example, researchers were able to determine from the data that so far there appears to be less chronic oiling of birds on the east coast of the US than in Canada, probably due to stricter laws and larger fines, Harris says. Additionally, the project has provided “base-line data on what sort of background levels of mortality you can expect to see in different species.”
Photograph by Kathleen Dooher
What’s unique about this is the recruitment of citizens as scientists.
As our group hikes over miles of uninhabited shoreline while scanning mounds of seaweed for clumps of feathers, Sally Hand recalls a recent oil spill in Buzzards Bay that left hundreds of birds dead on the beaches. She points to a shadow of black residue still clinging to some of the larger boulders.
“We found a dead loon on the point,” she says, while waving to a stony spit of land protruding into the bay. “Every bit of him was covered. It was like somebody held him by the bill and dipped him in oil.”
Hand walks Gooseberry Neck monthly with another volunteer with data sheets and binoculars in hand. If the seniors find a bird carcass, they mark it by clipping the wing, and then they photograph, measure, and bag it if it isn’t too decayed. The carcass is then popped into a freezer at the Lloyd Center, and eventually it’s sent to Tufts Wildlife Clinic for necropsy to determine the cause of death and levels of toxins. The information is entered into the Tufts database and also ends up in a collection of data from around the United States at the National Wildlife Health Center in Madison, Wis., a government-run agency.
“What’s unique about this is the recruitment of citizens as scientists,” says Saper-stein.
It’s an indispensable ingredient to its success, agrees Harris. “SEANET gets the public involved in the monitoring, which I think is a very key piece of this because it’s got the educational component as well.”
“And it’s a great opportunity for our veterinary students,” adds Tufts’ Dr. Flo Tseng, assistant professor in the Department of Environmental and Population Health. “Other beached-bird projects don’t have the same level of analysis—they’re only doing visual examinations. We’re taking that one step further and doing x-rays and gross necropsies [internal exams], as well as saving tissue samples for other kinds of testing.”
Photograph by Kathleen Dooher
AMONG THOSE FISHING and other beachgoers on this warm September morning is a man in green swim trunks launching a canary-yellow kayak into the bay. He asks what our little band of beachcombers is doing and then points to a cluster of islands on the horizon where he says he found beaches so strewn with bird carcasses several years ago that he had to step gingerly among them.
Massive die-offs are not uncommon among seabirds, but researchers are paying closer attention to such incidents these days because they can involve large numbers of endangered species and can be indicators of an emerging disease, toxic algal blooms or even a bioterrorist attack. Harris cites an example last summer when a large group of Common Terns suddenly died on Monomoy Island off of Cape Cod.
“At a certain fledgling stage, right when they were ready to fly and migrate with their parents, the fledglings were all dying. Tufts has been involved in doing necropsies and sampling for a lot of the birds,” she explains. “What turned up in most of the cases was a salmonella culture—bacteria that can cause fatal disease in young birds.
“It’s been documented many times that [beached birds] may be immune compromised [from bioaccumulated toxins], and maybe that’s the case with these terns,” she adds. “We’re going to do contaminant testing on them, too. Maybe they could have handled the salmonella load if they hadn’t had other issues.”
It’s still unknown where the birds picked up the bacteria. “It’s something we’re working on with the Massachusetts Department of Public Health. The key to this project is collaboration—working with the Environmental Protection Agency, state agencies, US Fish and Wildlife Service, National Oceanic and Atmospheric Administration, and United States Geological Survey, to name just a few,” she adds.
Tufts is increasing its alliance with state and federal agencies on several fronts to create databases and coordinate information on public health issues. For example, Tufts Wildlife Clinic will soon be monitoring wildlife populations for emerging diseases in a joint program with the Massachusetts Department of Public Health. The clinic also is developing a system to necropsy animals and transport them to state biosecure labs that can handle select agents in the event of a bioterrorist attack that shows up first in wildlife.
“What we are trying to do is get a handle on the background rate of zoonotic diseases in Massachusetts and identify any potential early-warning signs of changes that could affect human health,” says Dr. Fredric Cantor, V84, the state public health veterinarian for the Massachusetts Department of Public Health. “We’re looking at the frequency of appearance and also the geographical hot spots, when it occurs and how often it occurs” with emerging diseases such as West Nile virus, Eastern equine encephalomyelitis, tularemia, and tick-borne illnesses, he adds.
In addition to working with the state, Tufts received 523 million in grant money and contracts several years ago from a range of federal government agencies to do research on emerging diseases. And last year, the National Institutes of Health awarded Tufts $25 million for a seven-year research program on food- and water-borne pathogens and to create a Botulinum Therapies Research and Development Center, the first of its kind in the United States. The CDC has identified the botulinum toxin as the second most serious potential bioterrorist agent, next to smallpox.
Of the emerging infectious diseases in the world, 75 percent are zoonotic, meaning that humans can contract them from animals. And 90 percent of the agents most likely to be used by bioterrorists are animal diseases, Saperstein says. “It’s only smallpox that’s strictly human. So the human and public health infrastructure needs to be working closely with veterinarians, and in particular veterinary schools. Because most of these diseases are zoonotic, we may be the ones that detect it first,” he adds.
“What better place to work on these diseases than at the veterinary school—a school whose faculty, staff and students have a deep and sincere collective respect for animals. Since most of these diseases occur naturally in animals, we understand them and are used to working with their causative agents,” he points out.
ONE OF THE MOST daunting zoonotic diseases is tularemia, a rare bacterium that recently resurfaced on the island of Martha’s Vineyard off the coast of Massachusetts. Nicknamed “rabbit fever,” tularemia is highly infectious and may be environmentally stable. It has been shown to naturally contaminate water and soil, but the bacteria also can become aerosolized. The disease, carried in animal excrement and by ticks and fleas, infects landscapers on the Vineyard after they kick it into the air during mowing and leaf blowing.
Tularemia is easy to produce and spread around. The CDC lists it as a Category-A disease, meaning it’s a serious potential bioterrorist agent.
Tularemia was included in military bioweapons research from the 1940s to the 1960s, mainly by the Soviet Union and the US, explains Sam Telford, Ph.D., a researcher and associate professor in the veterinary school’s Division of Infectious Diseases in the Department of Biomedical Sciences. But in 1969, President Richard Nixon signed legislation banning biowarfare research in the US. However, the US government still supports research on bioterrorist agents for biodefensive purposes, which means the research is acceptable if done to protect US citizens in the event of a biological attack.
Because most of the bioterrorist agents on the CDC’s list are zoonotic, Tufts recently built a specialized laboratory for working with tularemia and other highly infectious agents. This is what in part lured Telford to Tufts two years ago from Harvard University’s School of Public Health, where he specialized in tick-borne diseases. Among other things, he is trying to determine the factors that allow tularemia to persist in the environment year after year.
Photograph by Kathleen Dooher
Shrimp may be more susceptible to viruses today because of chemical pollutants, declining immunity, climate change, salinity, or lower levels of genetic immunity
“Raccoons and skunks are very heavily exposed to tularemia. So maybe we can use them as sentinels because who among us doesn’t have a skunk or raccoon visiting our yard every night?” says the intense, but affable, researcher with circular glasses and an eccentric bow tie. “They’re scavengers—nosing around in people’s trash, picking up ticks in people’s yards. They have lots of opportunity to serve as little detectives and get exposed. If we had a program where we assayed them for exposure—people do that for example with rabies—then maybe we’d have a warning when an outbreak starts to happen,” he adds. “So animals do play a really important role in telling us what’s out there in nature.”
Maxene Armour, bioterrorism education coordinator for Massachusetts, agrees that animals are important indicators for disease. Armour offers workshops to the public “to help animal caregivers recognize when something is out of the ordinary with their animal. We ask them to look at a group of clinical signs that may alert us that a bioterrorist agent or pathogen has been released,” she says.
Cats can show signs of plague; dogs can be indicators of tick-borne diseases that are spreading in an area. And chickens are excellent sentinels for emerging diseases such as West Nile virus and Eastern equine encephalomyelitis.
Public-health officials received early warning signs of West Nile virus when exotic birds started dying at a New York City zoo, Telford points out. “Emerging diseases and biodefense really should be one and the same. They’re identical, and in fact anyone who has followed the West Nile epidemic can see the lessons that it has for biodefense,” he says.
“We were completely unprepared for an introduction of a foreign virus which swept through [the US] like wildfire. We’re lucky that it was West Nile virus, essentially because there are far worse agents,” he notes. “For example, Rift Valley fever—not only does it have human public-health implications, but it would devastate our agricultural industry because it affects sheep and cattle and goats.”
Carried by the same mosquitoes that transmit West Nile virus, Rift Valley fever appears to be following in the footsteps of its predecessor—it’s creeping up from central Africa into the Middle East and Mediterranean. Scientists can only speculate on how West Nile virus leapt across the Atlantic—perhaps intentionally, or more likely accidentally, via hitchhiking mosquitoes in an airplane cargo bay.
“The issue with diseases like Ebola and West Nile and Rift Valley fever has to do with how were moving plants and animals around the globe—more and more and faster and faster,” says Dr. Mark Pokras, director of the Tufts Wildlife Clinic and Tufts Center for Conservation Medicine. “In the olden days of horseback and ship travel, somebody got on a ship to sail to the new world and if they were sick, they either got better or they died before they got here. It was relatively unlikely that they’d be carrying the disease across with them.
“But now with instantaneous transport you can get on a plane in South Africa in the morning and get off the plane anywhere in the world in the evening. And transporting any of these diseases—and I’m not even talking about bioterrorism, I’m talking about accidental transport – is a real serious possibility,” he says.
Pokras then offers a startling example: The US recently introduced equine infectious anemia from North America to South Africa, “a serious horse disease that never was on the African continent before. We just introduced it by shipping racehorses over there,” he says emphatically.
THE POSSIBILITY OF disease being spread by the movement of species around the globe is something Tufts’ Dr. Acacia Alcivar-Warren thinks about daily. For several months the molecular geneticist and associate professor of Environmental and Population Health has been trying to determine the cause of an outbreak of taura syndrome virus on Texas shrimp farms. The disease is of great concern in the shrimp industry because it can cause cumulative mortalities ranging from 40 to 90 percent in shrimp culture populations.
“We don’t know how this outbreak occurred because the shrimp came from current stocks produced in the US that were supposed to be virus-free,” she says. “The US has an excellent breeding program in Hawaii with taura syndrome virus-resistant and virus-free animals. Similar breeding programs have been used by private industry.”
While she hasn’t ruled out the possibility that the virus was spread intentionally, she suspects the real culprit may have been frozen shrimp imported from other countries. “Gulls are vectors for these viruses. They could be transferring it from water, the garbage or from farm to farm,” she points out.
Alcivar-Warren believes the Texas outbreak highlights a much bigger problem: “Shrimp are exported all over the world without veterinarian-mandated quarantine regulations. Some experts believe that the US Department of Agriculture should have an inspection program for all of the shrimp coming to the US the same way it inspects beef, chickens and pork chops.”
Seafood imports generate the second-largest trade deficit in the US, after oil. And shrimp is a significant slice of that market—it recently topped tuna as America’s favorite seafood. Most shrimp imported into the US comes from Asia and Latin America, and US shrimp farms produce less than 10 percent of that market.
The white spot syndrome virus presents an even greater threat than taura syndrome to the shrimp industry because it can cause 100 percent mortality, she adds. Researchers recently found the virus in imported frozen shrimp in Massachusetts supermarkets, and it has been found in other crustaceans as well. While shrimp viruses don’t present a threat to human health, Warren says she’s concerned that they could spread to native crustacean populations in the US, especially with the impact of climate change.
Gulls are vectors for these viruses. They could be transferring it from water, the garbage or from farm to farm.
In addition to a USDA-funded grant to identify the genes responsible for susceptibility and resistance to taura syndrome virus, Alcivar-Warren started a database in 1998 to document genetic diversity, viruses and levels of chemical pollutants in wild shrimp. Eventually she plans to create a computer model that integrates these factors with the status of mangrove forests, intensity of shrimp farming, water temperature and salinity data gathered from shrimp-producing countries. In addition to conserving and protecting wild shrimp populations, she hopes the database will provide the shrimp industry with information that can help them select animals for breeding based on high levels of genetic diversity and low prevalence of disease and pollutants.
Alcivar-Warren collects shrimp and sea-water samples around the world to have them tested in an EPA-approved laboratory. “The heavy metal I find of most concern in shrimp is cadmium,” a cancer-inducing pollutant, she says. “Cadmium may affect the development and survival of animals … Chronic exposure leads to kidney dysfunction in humans,” she adds.
Global emissions of cadmium compounds arise principally from point industrial sources including combustion of fossil fuels, waste slag, phosphate fertilizers and sewage sludge. The sources for human exposure are air, water and food, with shellfish representing the major route of uptake for the general public.
“Shrimp may have been dealing with viruses for centuries” but may be more susceptible to them today because of chemical pollutants, declining immunity from toxic exposure, climate change, salinity, or lower levels of genetic immunity, she states.
“So what is the potential effect of these levels of pollutants? … We don’t know,” she says with intensity. But she hopes to find out with the help of this tiny ocean sentinel that could provide valuable information for human and environmental health.
Getting the Mercury and Lead Out
When the Massachusetts Division of Fisheries and Wildlife started to reintroduce bald eagles and peregrine falcons into the state in 1983, Dr. Mark Pokras, V84, was among a group of wildlife specialists who met the birds at the airport to examine them and take blood samples before they were released into the wild.
The specialists resampled the birds two month later and found their mercury levels had skyrocketed by nearly 500 times. Those tests offered the first evidence that New England had a mercury problem, says Pokras, director of the Wildlife Clinic at Tufts Veterinary School.
“Since that discovery, Tufts Wildlife Clinic has done a lot of work specifically on heavy metals. We focus mostly on mercury and lead because there’s a lot of regional and national concern with them,” he adds.
“The mercury is airborne. It comes from factories, coal-fired power plants, municipal incinerators and the tailpipes of cars” and is turned into an organic form in lakes and streams by microorganisms in the sediments, he explains. The microorganisms get eaten by plankton, which get eaten by fish, and eventually the toxins end up in the bellies of birds. “It’s a classic case of bio-magnification,” he says.
“I can’t show you a single animal that’s died from mercury. But I know a lot of them are being affected subtly, sub-lethally, with behavior changes, immune suppression or as endocrine disruption. But I can show you two freezers full of animals that died from lead,” he adds wistfully, while referring to a study he started in 1988 on mercury and lead levels in common loons.The resulting 16-year-old database has served as a model for the Seabird Ecological Assessment Network (SEANET) project.
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