Animal to man, fear of the next pandemic
Orangutan’s mysterious death points to threat of diseases that jump to humans
First of three parts
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.
Khan, the zoo’s primary orangutan keeper, was off on medical leave. Yet she’d come in earlier in the day, as soon as she heard something was wrong with Mahal.
Raised on a horse farm in Wisconsin, Khan has a passion for animals, especially primates and most especially orangutans, a great ape found in Asian rainforests and admired for its intelligence.
Even so, her deep affection for Mahal was unique. She had flown to Colorado to pick him up from the Cheyenne Mountain Zoo after the orangutan had been rejected by his mother. Khan had accompanied Mahal to Milwaukee, and when he settled in at the county zoo, she bottle-fed him for the first year.
When Mahal was sick, she would move a mattress into the enclosure and stay with him, allowing him to nest beside her and sleep until morning.
Four years later, 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 sam-
The zoo could not simply mourn the loss of Mahal and dispose of his remains. Other lives were at stake, including those of the zoo’s 45 other primates and the seven employees who cared for them.
ples.
The next morning, 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. In his short life, Mahal had been the subject of a newspaper series and a children’s book.
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?”
The similarities between humans and other primates are well-known. It is the reason monkeys have long been used in medical tests as proxies for humans. It’s also the reason the zoo regularly consults with doctors at Froedtert Hospital on health problems involving its great apes.
But the close biological relationship between the two species takes another form as well. Lethal diseases, including Ebola and HIV, have jumped from apes to humans. Others, such as influenza and polio, have gone the opposite route, passing from humans to apes.
“When you’re dealing with the great apes,” says Khan, “pretty much anything they get, we can get.”
And therein lies the problem. The zoo could not simply mourn the loss of Mahal and dispose of his remains. Other lives were at stake, including those of the zoo’s 45 other primates and the seven employees who cared for them.
Of the 400 or so emerging infectious diseases identified since 1940, more than 60% have been zoonotic, meaning they have passed from animals to humans.
A 2012 report by researchers in Britain, Kenya and Vietnam found that each year zoonotic diseases account for 2.5 billion cases of human illness and about 2.7 million deaths. A separate study published the same year put the direct costs from these diseases at more than $20 billion over the previous decade.
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 search for Mahal’s killer also would illustrate the links between diseases and some of the most powerful forces on the planet: evolution, glacial periods and the Earth’s orbital patterns, known as Milankovitch cycles.
“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.”
*** Like all great apes, orangutans face health challenges in captivity. Males are more susceptible to urinary tract infections than they are in the wild; it’s uncertain why. Many great apes also suffer from heart disease.
Neither illness seemed likely given Mahal’s youth.
The orangutan’s body arrived at the UW lab of Annette Gendron, a veterinary pathologist who’d worked in Kenya for a year and later at the Fresno Zoo before coming to Madison in 1983. In more than 30 years as a pathologist, she’d performed necropsies on everything from great apes and elephants to snakes and giraffes, “almost anything you can think of.”
Following protocol, Gendron and zoo pathology resident Kathleen Deering each dressed in a protective gown, a double set of gloves, a mask and face shield. Necropsies — autopsies performed on animals — take hours and it is all too easy for pathologists to spatter themselves with material from the dead animal.
Once, 40 years ago, Gendron was accidentally exposed to the fungal lung infection Valley fever, while helping veterinarians try to resuscitate an orangutan before it died. On another occasion, one of her gloves leaked while examining the intestines of an antelope and she wound up with an infection under her fingernail.
Although she never became seriously ill, these incidents reinforced her cautious nature.
Gendron began her examination of Mahal by taking measurements, noting the size of the orangutan’s pupils and searching for skin lesions, evidence of trauma and discoloration of the membranes of the mouth.
Then she cut open the orangutan’s body. There was no fluid in the abdomen. Fluid is often a sign of inflammation, which in turn raises a host of possibilities, from tumors to liver or kidney failure.
One by one, Gendron looked at the organs. First the spleen, then the liver, kidneys, adrenal glands, heart, lungs and trachea. She removed and weighed each organ and looked for scarring and abnormalities. She placed tissues from all of the organs in formalin, a preservative that would allow her to view them later under the microscope.
Although the pathologist worked methodically, 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 had also 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.
The necropsy took between four and five hours. When she was finished, Gendron made microscope slides of tissue from the nerves, heart, lungs, brain and other organs.
Over the next few weeks she sent zoo pathologists around the country a digital photo of one of the cysts from Mahal’s liver. 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, who had started out studying hummingbird behavior at Amherst College in Massachusetts, had gone on to focus on primates while earning his PhD at Harvard. He joined the UW faculty in 2008.
Over the last decade, Goldberg had flown to Uganda twice a year for up to a month of fieldwork examining the interactions of people, primates and other animals in and around Kibale National Park.
The fieldwork often reminds him how much the world is changing, and how quickly new health threats can cross from species to species, continent to continent. For much of the world, the Zika virus, named for the forest in Uganda where it was discovered, stands as the prime example.
Spread by the Aedes aegypti mosquito and first discovered in a rhesus macaque in 1947, the virus appeared in humans in Uganda and Tanzania in 1952. However, in the last two years, the virus suddenly spread through large sections of Central and South America. In July, the U.S. recorded its first homegrown cases of the virus in Florida. By December, Zika had been identified in 75 countries and territories.
But Goldberg can point to a more personal example of today’s rapid-transit pathogens. In the summer of 2012, just six months before Mahal died, Goldberg had returned to Madison after working in western Uganda. He’d been home only three days when the dull ache he’d detected in his nose flared into a searing pain, impossible to ignore.
By angling a mirror and contorting his body, the scientist was able to peer inside his nostrils. There it was, just as he’d suspected: the pale, fat back end of a fully engorged tick.
“It took all of my willpower not to claw off my face,” he would recall.
Instead, Goldberg gently extended a pair of forceps until they surrounded the tick’s mouth, then he pulled firmly, but carefully. Out came a creature about the “diameter of a pencil eraser,” he recalls, “really nothing more than a distended stomach.”
DNA testing revealed it was a new species of tick, a discovery that, in the scientist’s view, far outweighed his discomfort. Somehow the tick had crawled onto Goldberg’s body in the Ugandan forest and stowed away inside his nostril through the plane trip to the U.S. The scientist’s reward was a paper he coauthored entitled, “Coincident Tick Infestations in the Nostrils of Wild Chimpanzees and a Human in Uganda,” published in the American Journal of Tropical Medicine and Hygiene.
But it wasn’t Goldberg’s tick discovery that made Gendron think of him for the Mahal investigation. She recalled his recent paper on hepatocystis, a single-cell parasite transmitted by midges.
Could the cysts inside Mahal be hepatocystis?
*** There’s just no love for the lowly parasite.
The shark is more frightening, the naked mole rat uglier, the black mamba snake deadlier. Yet few creatures provoke a more visceral shudder of disgust than lice, tapeworms, mites and the various other organisms known as parasites.
After his close encounter with the tick, Goldberg understood why.
Still, years of research had tempered his reaction. “You wind up having a lot of respect for parasites,” he says. “They are very clever.”
They have to be. To keep living, parasites must depend upon another organism, or host. They employ finely-tuned machinery to infect and stay in the host without being detected and killed off by the host’s immune system.
Parasites are master survivors. They have been around much longer than humans, likely as long as there have been living organisms, according to Eric Hoberg, former curator of the 120year-old U.S. National Parasite Collection, among the world’s largest repositories of different parasites.
Although it’s not known how many parasites share the earth with us,
Stunned as they were by the loss, Trish 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?” “The fact that we share so many diseases with primates tells us about evolution. 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.” TONY GOLDBERG, UW PROFESSOR OF EPIDEMIOLOGY WHO LED THE INVESTIGATION INTO MAHAL’S DEATH
one estimate puts the number of different helminths, or intestinal worms, at between 75,000 and 300,000. All told, more than half of the organisms on the planet are parasites, from the microscopic bacterial cell to the multicellular tapeworm.
Many have evolved clever tricks to find the right host, survive and spread.
Take the wiley Toxoplasma gondii, a singlecell parasite that starts by infecting a mouse but must enter a cat in order to reproduce. To go from mouse to cat, Toxoplasma gondii disables the rodent’s ability to smell cat urine, essentially leading the mouse into the jaws of its enemy.
Of greater concern to humans is the Guinea worm. The worm’s larvae develop after being consumed by water fleas; they then infect humans who drink the flea-infested water.
Once inside the human body, the worms grow to two or three feet in length, until the female worm causes a burning sensation so extreme it drives the human to seek relief by submerging the infected area in water. The worm’s offspring are then released from a skin blister into the water to continue their life cycle.
The sheer number of parasites can make identifying them difficult, and as Mahal’s death would show, there is still much we don’t know.
*** Goldberg crossed busy Campus Drive and proceeded to Gendron’s UW lab to collect samples of Mahal’s liver, lungs and spleen. All were securely stored inside biosafety bags. Goldberg then spent the afternoon performing a series of molecular tests on the tissue samples. He found no sign of hepatocystis.
He spent the rest of the week conducting more tests, checking whether something might be interfering with the chemistry and skewing his results. Still negative.
In his black lab notebook, he noted that ahead of him lay “a huge task.”
Not that the challenge displeased him. He loved a good mystery.
Goldberg and David O’Connor, a colleague at UW’s Primate Center, compared Mahal’s genetic sequence with that of another orangutan, obtained from a massive DNA repository known as GenBank.
The scientists took Mahal’s sequence, then subtracted the other orangutan’s. What remained, Goldberg reasoned, would contain the killer’s genetic signature.
They performed the analysis using a technique known as shotgun sequencing. Long strands of DNA are broken into millions of smaller, easier-to-read pieces and then reassembled by computer into the longer sequence. They felt compelled to work quickly.
“We really rushed it,” Goldberg recalls. “We were really curious and we were afraid there would be an outbreak at the zoo.”
He kept thinking about the story of Tracey McNamara, then head pathologist at the Bronx Zoo. In 1999, McNamara noticed that a disturbing number of crows near the zoo were becoming ill and dying. Around the same time, New York City health officials discovered that a small number of people had become deathly ill with what appeared to be St. Louis encephalitis. Mosquitoes pick up the virus from birds, then pass it to humans.
Tests showed, however, that the virus making the crows and humans sick wasn’t St. Louis encephalitis. It was West Nile virus. The virus had been discovered in Uganda in 1937, but the sick crows at the Bronx Zoo marked its first appearance in the U.S.
By the time Goldberg began working on the Mahal case, West Nile had spread across the continental U.S., sickening almost 2,500 people and causing 119 deaths in 2013 alone. Early on in his investigation of the orangutan’s death, he had no way to know whether he might be dealing with another West Nile virus.
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.