Orangutan’s mysterious death reveals threats
Diseases like one that killed Mahal could jump to humans
MILWAUKEE — On a frigid night a few days after Christmas 2012, Trish Khan drove back to the Milwaukee County Zoo to check on the star attraction, a playful, wildly popular 5-year-old orangutan named Mahal. It was almost 11 p.m.
As she examined the orangutan on that winter evening, Khan noted how much he resembled a sick human child: no energy, no appetite. After an unsuccessful attempt to administer antibiotics, Khan and one of the zoo veterinarians decided to move the orangutan into a smaller room and wait until morning to anesthetize him and take blood samples.
The next day, a zookeeper found Mahal lying motionless on the floor. He was dead at just 5 years of age; the typical orangutan lives 35 or 40 years in the wild and sometimes more than 50 in captivity.
Stunned as they were by the loss, Khan and her colleagues now faced a mystery with implications for both animals and humans: What killed Mahal?
“Is it something that could affect our other orangutans or other animals?” Khan remembers wondering. “Is it something that could affect our keepers?”
Zoo officials in Milwaukee were not taking any chances. Within hours of his death, Mahal’s body lay in a cooler packed in ice, bound for a pathologist’s lab at the University of Wisconsin-Madison.
So began an investigation that would span more than three years and lead to the discovery of a new species of pathogen.
“The fact that we share so many diseases with primates tells us about evolution,” explains Tony Goldberg, the UW professor of epidemiology who led the investigation into Mahal’s death. “There are an awful lot of primate pathogens that don’t really care whether they’re in a human or a chimpanzee or an orangutan.” ‘Never seen anything like this’
The orangutan’s body arrived at the University of Wisconsin lab of Annette Gendron, a veterinary pathologist.
Gendron began her examination of Mahal by removing organs and looking for scarring and abnormalities. She had noticed something strange from the very beginning. Mahal had an enlarged spleen and liver. Both organs were overrun with cysts, small gray bubbles.
“There were enormous numbers inside the liver,” Gendron says. “We’d never seen anything like this.”
Whatever it was, the pathogen also had clogged Mahal’s lungs. The official cause of death was acute respiratory distress syndrome; what it meant was that the orangutan had essentially drowned in his own blood.
Over the next few weeks she sent zoo pathologists around the country a digital photo of one of the cysts. She hoped specialists who’d examined great apes might have run into something similar. No one had.
One of the colleagues Gendron contacted was Goldberg, a fellow member of UW’s faculty of veterinary medicine.
Goldberg collected samples of Mahal’s liver, lungs and spleen. A few weeks of genetic testing provided Goldberg with an answer — of sorts. The killer’s DNA appeared to be that of a cestode, or tapeworm. Except the sequence didn’t match any known tapeworm.
It was something new.
In Mahal’s case, the tapeworms were still in the larval stage; that explained the little gray bubbles. But what species of tapeworm did the larvae come from? How did they get inside an orangutan? And how did they survive the antiworming medication the Milwaukee zoo administers to its orangutans every three weeks? Different species, same group
One answer emerged quickly, though it raised new questions.
On the very day Goldberg received the sequencing information from the machine, a scientific paper appeared in The International Journal for Parasitology naming a new genus, or group, of tapeworms. Scientists discovered the new group inside the bodies of weasels in Japan and Finland.
What linked the new group, Versteria, to the larvae inside Mahal was a similar genetic signature. Although the two were not an exact match, they appeared to be different species within the same group.
Goldberg had an idea how the tapeworm larvae had wound up inside Mahal.
Some orangutans like to eat dirt. Coincidentally, tapeworm eggs spend part of their life cycle in the soil waiting to become dinner for a passing vole or mouse. Perhaps Mahal had been eating dirt and accidentally ingested a mouthful of tapeworm eggs.
Once inside Mahal, the eggs would have developed into the gray, larval cysts. These thick walls of tissue could have shielded them from the zoo’s regular deworming treatment.
The theory still left open the question of how Mahal had picked up a genus of tapeworm previously found only in Finland and Japan. The orangutan had never been to those countries. The only homes he’d known were the zoos in Colorado Springs and Milwaukee.
About 10 months after the tapeworm paper was published, Goldberg came to Colorado State University to give a talk on the Mahal investigation. Afterward, he was approached by a veterinary student, Margot Stuchin.
Stuchin had been performing animal dissections and was scheduled to work on a group of deceased ermines, weasel-like creatures.
She asked if Goldberg would be interested in any tapeworms she happened to find.
In the coming months, Goldberg went through the guts of a mink, five long-tailed weasels and 11 ermines. Unmasking Mahal’s killer
When his team scoured the genetic scripts of the tapeworms found in Wisconsin and Colorado, they discovered that the tapeworms found only 30 miles from the Milwaukee County Zoo were just 90 percent similar to those found inside the orangutan. The tapeworms found in Colorado were much closer to those taken from Mahal — 99.5 percent similar.
The DNA findings suggest the orangutan likely ingested the tapeworm eggs in Colorado, which would mean that when Mahal arrived in Milwaukee, he already carried the infection that would kill him.
The science of DNA had unmasked Mahal’s killer and pointed to its origin. But the tapeworm took some secrets to its grave.
For one thing, zoo staffs do not remember ever seeing Mahal eat dirt. And if Mahal had come to Milwaukee with the tapeworm larvae already inside him, why had the infection waited four years before multiplying explosively through his body and killing him?
“My gut tells me,” Goldberg says, “we will never know for sure.”