VOA for students09-09-20 environmentd007 严重干旱引发疾病,狮子相继死亡

Severe Droughts Trigger Disease, Lion Die-Offs
Wild lion populations can generally tolerate a certain level of parasites and disease. But new research shows that extreme climate conditions — such as severe droughts — can cause infection rates to skyrocket, resulting in mass die-offs.
The savannas of Tanzania are home to as many as half of the world's lions. University of Minnesota ecology professor Craig Packer has been studying lions in Tanzania's Serengeti National Park for the past 30 years. He was there in 1994, when inexplicably, the animals started dying.
CRAIG PACKER: We estimate that about 1,000 lions died over a relatively short period of time. It was unprecedented over the previous 30 years nothing had been seen anything like it.
Then, in 2001, it happened again.
CRAIG PACKER: In the nearby Ngorogoro crater we saw another die-off, just like the one in the Serengeti seven years earlier.
By analyzing the lions' blood, Packer and his colleagues found that the two die-offs seemed to be triggered by outbreaks of canine distemper virus, a disease that usually affects domestic dogs.
CRAIG PACKER: The distemper is a kind of "equivalent of measles." The nice feeling for us about measles visit our body produces an immunological response to the virus, so that we can only be infected once. The distemper has the same effect in the bodies of carnivores. So in any age, whenever an animal is exposed, the animal — if it survives the infection — has antibodies and is therefore immune to further cases to distemper.
According to Packer, it's relatively common for lions to get the disease. In the Serengeti, he has seen distemper outbreaks about every six or seven years, usually with no symptoms.
CRAIG PACKER: Most of the time it's harmless, you just find out that the animals were exposed because you see their antibodies in their blood.
But in 1994 and 2001, about a third of the animals that got infected, died. What had turned a normally benign outbreak into a devastating epidemic?
CRAIG PACKER: In 1993, in the Serengeti we had the first in a series of pretty
serious droughts that we've been having out in East Africa.
The drought was especially brutal for a common prey of lions, the Cape buffalo. For the lions, the drought-weakened buffalo made an easy catch: they ate almost nothing else. But the unexpected feast came at a high price.
CRAIG PACKER: The buffalo were infested with ticks.
And with them, came a tick-borne parasite, called babesia. Animals in the Serengeti are always exposed to ticks and babesia, which at its worst can cause malaria-like symptoms, anemia, and hemorrhaging. In a normal year, Packer says, lions can tolerate the parasite.
CRAIG PACKER: But the drought of 1993 led to an unprecedented increase in the lions' exposure to babesia.
And then, as soon as the drought ended, distemper struck the babesia-ridden lions. The combination proved fatal.
CRAIG PACKER: Getting canine distemper is like having a short sharp bout of AIDS.
Like AIDS, the distemper virus attacks the immune system, weakening the body's defense against other infections.
CRAIG PACKER: So the virus kind of liberated the tick-borne disease so that it could be far more destructive than it would have otherwise been.
Although the lion populations were able to recover from the die-offs within a few years, Packer thinks deadly epidemics will become more frequent if climate change continues.
CRAIG PACKER: What we're seeing now is much greater variability in the weather than we'd ever seen in the past. Most climate change models predict
a greater variance in weather. And that’s definitely been the experience in my
36 years in working out here.
Packer adds that extreme droughts and floods are likely to continue unleashing new, potentially synergistic combinations of diseases, which could be more deadly together than they would be on their own. His research is published in the journal PLoS ONE.
I’m V eronique LaCapra.。