Thesavannas of Tanzania are home to as many as half of the world's lions.University of Minnesota ecology professor Craig Packer has beenstudying lions in Tanzania's Serengeti National Park for the past 30years. He was there in 1994, when inexplicably, the animals starteddying.
He estimates that about 1,000 lions died over arelatively short period of time. Packer says it was unprecedented."Over the previous 30 years nothing had been seen anything like it."
Then,in 2001, it happened again. "In the nearby Ngorogoro crater we sawanother die-off," says Packer, "just like the one in the Serengetiseven years earlier."
By analyzing the lions' blood, Packer andhis colleagues found that the two die-offs seemed to be triggered byoutbreaks of canine distemper virus, a disease that usually affectsdomestic dogs.
Packer describes distemper as the "carnivoreequivalent of measles." When a person gets measles, their body producesan immunological response to the virus, so that if the same person isinfected again, the disease will not develop.
"Distemper has thesame effect in the bodies of carnivores," Packer explains. "Whenever ananimal is exposed to distemper, the animal if it survives theinfection has antibodies and is therefore immune to further cases."
Accordingto Packer, it's relatively common for lions to get the disease. In theSerengeti, he has seen distemper outbreaks about every six or sevenyears, usually with no symptoms. "Most of the time it's harmless, youjust find out that the animals were exposed because you see theirantibodies in their blood."
But in 1994 and 2001, about a thirdof the animals that got infected, died. What had turned a normallybenign outbreak into a devastating epidemic?
Packer says that in1993, in the Serengeti, "we had the first in a series of pretty seriousdroughts that we've been having out in East Africa."
The droughtwas especially brutal for a common prey of lions, the Cape buffalo. Forthe lions, the drought-weakened buffalo made an easy catch: they atealmost nothing else. But the unexpected feast came at a high price."The buffalo," Packer explains, "were infested with ticks."
Andwith them, came a tick-borne parasite, called . Animals in theSerengeti are always exposed to ticks and , which at its worstcan cause malaria-like symptoms, anemia, and hemorrhaging. In a normalyear, Packer says, lions can tolerate the parasite. "But [?] thedrought of 1993 led to an unprecedented increase in the lions' exposureto ."
And then, as soon as the drought ended, distemperstruck the -ridden lions. The combination proved fatal. AsPacker puts it, "getting canine distemper is like having a short sharpbout of AIDS."
Like AIDS, the distemper virus attacks theimmune system, weakening the body's defense against other infections."So the virus kind of liberated the tick-borne disease so that it couldbe far more destructive than it would have otherwise been," explainsPacker.
Although the lion populations were able to recover fromthe die-offs within a few years, Packer thinks deadly epidemics willbecome more frequent if climate change continues.
"What we'reseeing now is much greater variability in the weather than we'd everseen in the past." Packer says that most climate change models predicta greater variance in weather, with a greater chance of flood ordrought in any given year. "That's definitely been the experience in my36 years in working out here."
Packer adds that extreme droughtsand floods are likely to continue unleashing new, potentiallysynergistic combinations of diseases, which could be more deadlytogether than they would be on their own. His research is published inthe journal .