Web edition: May 22, 2008
Almost as soon as wildlife conservationists learned, 10 days ago, that a magnitude-7.8 earthquake had shaken China's Sichuan Province with devastating intensity, they started asking after the pandas. Those pandas indeed are in trouble. But roundworms are what's sending tremors through cadres of in-the-field panda protectors, not any shaking underfoot.
The vast majority of China's iconic giant pandas dwell in Sichuan's mountainous bamboo forests. More than 30 reserves also dot the region, providing the lumbering bearlike critters special protection. The best known of these: Wolong Reserve. According to the Associated Press, quakes at this facility were so dramatic that Wolong's PandaCam lost the ability to send live online video of the reserve's furry residents.
Although bamboo stands throughout that region may have trembled as the ground shook, area pandas are likely no worse for the quakes, reports Peter Daszak of the Consortium for Conservation Medicine in New York City.
The real stunner, he says, is the accumulating sightings of tiny roundworms littering the internal organs of panda carcasses. These tiny nematodes are emerging as the primary death threat to wild pandas, Daszak and his colleagues report in the latest EcoHealth, a journal that arrived in mailboxes this week.
The first report of the worm in a wild giant panda appeared in 1939. The parasite had taken up residence in the animal’s intestinal tract. Sporadically, since then, evidence of nematode infections has emerged in more of the animals. But the worms don’t seem to find the pandas a good host, explains Daszak, a parasitologist.
When nematodes find their host inhospitable, Daszak says “they cause the exact same disease seen in pandas” – visceral larval migrans. In search of a more welcoming environment, “they begin boring their way through the intestinal cavity.” Ultimately, they can infiltrate liver, brain, heart, even the eyeball. “If they go to the lungs, they can rupture blood vessels and cause an internal hemorrhage,” he notes. “Which is what was seen in these pandas.”
In China, much of the panda-conservation work takes place on reserves, which do a lot of captive breeding. “And this parasite is known from the captive-breeding population,” he says. “But what we’ve got now are data from other pandas that died in the wild.”
What Daszak's team now reports are significant and changing trends in panda mortality over the years. Between 1971 and 1980, most pandas seemed to succumb to old age. Then poaching started to take hold, and by 1986, swelled to account for perhaps 80 percent of deaths in wild pandas. But massive government crackdowns on the slaughter of these animals reduced poaching significantly. Today, it appears to account for fewer than 15 percent of deaths in the wild, just a third the rate of deaths due to old age. However, an estimated half of panda deaths now trace to the nematode Baylisascaris schroederi.
The numbers of affected animals are fairly small – just 10 between 2001 and 2005. “But it’s still a big deal,” Daszak says, “because there are so few pandas left.” The global population in the wild today numbers only about 2,000 animals. Moreover, he notes, in the past 15 years, the proportion of massively infected wild carcasses has been increasing: “That’s the big worrying thing.”
Right now, Daszak concedes, little is known about the parasite – even what animal has typically been its preferred host. “We don’t even know if that [B. schroederi] is the true name of the parasite yet. I’ve got people working on its [shape] and the DNA of this parasite to see if they can determine the proper name for it.” Related species infect other bears and raccoons elsewhere in the world.
The real question, Daszak says, is what has changed in the wild to make this infection more common. “When you get small populations of wildlife, like here, all it takes is a couple things acting together – and you might get extinction.” For China’s giant pandas, which depend on one group of plants for survival, he says, “we now have an earthquake, we have deforestation, we have removal of the bamboo patches, and we have a parasite. With that kind of compound threat, you end up with might constitute a ‘perfect storm’ for panda extinction.”
“But now that we know what a key problem is," the nematode, he says. So there’s a good chance we can do something about it.” Like treat infected animals with parasite-targeting medicines. Or if overcrowding of pandas is helping spread infection, he argues, then "let's expand their territories." Or if an invasive species has ferried the nematodes into panda country, researchers can attempt to rout the aliens.
Overall, Daszak remains optimistic that this infection can be beat.
And that's good news, I told him this afternoon, because everybody loves pandas.
"As conservationists," he reminded me, "we're not supposed to fall for the cute or beautiful animals and give them more attention." The uglies, viperous, stinky, and dangerously predatory species have every bit as much right to protection, he maintains. Then again, he concedes, "a cuddly little panda cub – there's nothing cuter."
Zhang, J.-S., P. Daszak, et al. 2008. Parasite Threat to Panda Conservation. EcoHealth 5(March):6.