Scaly Mammal Provides Leprosy Link : Armadillos Advancing Search for a Hansen’s Disease Vaccine
Here at the leper colony, Willard Brown was looking after the armadillos.
He was covered from head to toe in surgical garb--gown, hat, gloves and shoe covers. These particular armadillos had leprosy, and one could not be too careful.
The air was pungent from the naturally foul armadillo odor. Being of the nocturnal bent, most of the hard-shelled creatures were burrowed under shredded newspaper in their cubicles.
Brown, who has been overseeing the care and feeding of armadillos for almost 20 years now, led the way through the armadillo quarters, close by the lake and cemetery. Among other things, he was explaining the animals’ diet--of dog food, cat chow, mineral salt and a dash of dirt.
“They eat it in nature, so we feed it to them here,” he said.
Key Research Animals
Armadillos, neither smart nor pretty, have good reason for the care Brown gives them. They are a key element in the search for a vaccine that may someday eradicate leprosy, also known as Hansen’s disease. So here at the isolated Hansen’s Disease Center of the U.S. Public Health Service, as well as at other facilities in the United States and Europe, the lowly armadillo is more than just an ugly face.
In the United States, Hansen’s disease is relatively rare. There are only about 6,000 diagnosed cases, most of which can now be treated on an outpatient basis with drugs that control the disease. (Oddly, thalidomide, notorious for causing congenital defects, is one of them.) At the center here, there are fewer than 250 patients at a time, and many stay only for their initial two weeks of treatment.
But around the world, particularly in developing nations, leprosy still ranks as one of the leading contagious diseases and the means of transmission is still unknown. In its worst form, leprosy can cripple and disfigure. The World Health Organization estimates there are 10 million to 12 million people with leprosy, and that half of them are untreated. The vaccine research, meanwhile, has become more urgent because the drugs most commonly used to treat leprosy are showing signs of being less effective as the disease organism becomes immune to them.
A Shared Susceptibility
Why depend on the armadillo, a mammal who looks like an armored car with claws? The answer is reasonably simple. To produce a vaccine, one must first be able to reproduce the leprosy bacillus, or germ, in large quantities. The bacillus was isolated more than 100 years ago, but it was not until 1971 that scientists in Louisiana discovered the armadillo’s susceptibility to the disease. That made the armadillo not only a source of the bacilli, but also an animal model for studying a human illness.
“This was our gold mine,” said Dr. Richard Truman, one of the researchers at the Hansen’s center.
Now, using bacilli from armadillos exposed to leprosy, vaccination experiments are being conducted in India, Malawi and Venezuela. The armadillo also is essential to production of lepromin, a substance used to determine the severity of leprosy infection.
Scientists at the Louisiana disease center say the armadillo is not the ideal machine for reproducing leprosy bacilli, but for the moment it is the only one they have. Reproduction in a test tube would be purer and could produce greater yields, but even after decades of research, scientists have not been able to unlock that genetic door.
Scourge of Ancients
Leprosy--a name derived from the Greek word lepra , or scaly--goes back centuries. Some of its most revulsive images, such as that of the white-robed outcast ringing a bell to warn of his approach, are rooted in ancient times.
Researchers believe that leprosy was brought from the Middle East to Europe during the Crusades. Because there was no treatment for the disease until the 1940s, lepers were isolated in leprosariums or leper colonies. The Hansen’s center here began that way, a plantation that was designated a leper colony around the turn of the century. The first treatment for leprosy was developed here, and the campaign to rename leprosy Hansen’s disease, after the man who isolated the germ, also began here.
As histories go, the armadillo’s also is a long one--about 55 million years. Armadillos were first prevalent in South America, but 2 1/2 million years ago, when the Panamanian land bridge evolved, they began moving north as far as what is now Kansas and North Carolina. They disappeared from those regions about 5,000 years ago. Scientists say those early models of the armadillo were big, some the size of black bears.
Denizens of the South
The variety common today, the nine-banded armadillo, showed up again in Texas in the mid-1800s and has been thriving ever since. So hardy are armadillos that they number in the millions in the southern United States. Only cold weather and the desert have defined their range. The thousands of armadillos in Florida are direct descendants of two pairs that escaped from a private zoo.
Armadillos can swim by inflating their lungs and floating, or they can rid their dense bodies of almost all oxygen and walk along the bottom of a riverbed. They also have the unhealthful habit of jumping straight up when they sense danger, even when that danger is an approaching car, with the result that large numbers of armadillos never make it to the other side of the road.
In the 1970s, an armadillo craze swept Texas and it became something of an unofficial state animal. Armadillo stew was touted as tasty and county fairs were not complete without armadillo races. Armadillo shells were used to make purses and flower pots. Even today, no Texas airport gift shop is complete without armadillo T-shirts, stuffed toys and ashtrays.
A Link for Research
One who took an interest in the armadillo was Eleanor Storrs, who was then doing research at the University of Texas at Austin into the armadillo’s ability to reproduce four identical offspring.
Over the years, and after she and her husband had moved to Louisiana, Storrs’ interest turned to the study of leprosy. Working at the Gulf South Research Institute, only a few miles from the Hansen’s Disease Center, Storrs came to believe that the armadillo would be an ideal subject for leprosy research. Her primary clue was temperature: leprosy usually begins in the cooler tissues of the body, such as the skin, and the armadillo’s body temperature is about 5 degrees cooler than a human’s.
Working with Waldemar Kirch-heimer from the Hansen’s center, Storrs injected four armadillos with leprosy bacteria. When one of the animals died of leprosy 17 months later, the researchers knew they had made a breakthrough. Sixteen more armadillos were injected with the bacteria and seven of them came down with the disease. But Storrs, now at the Florida Institute of Technology, said that other scientists were reluctant to accept the findings.
“It was amazing to see how they resisted the armadillo,” she said. “What it would do was usurp the research other people were doing with other types of animals.”
Keeps Armadillo Lab
Storrs, who has her own large colony of armadillos at the Florida institute, is hopeful that the vaccine program will meet with success.
“Time will tell,” she said. “I really think most of the scientists intimately involved in it feel it is a viable program.”
But there is also bad news: a number of armadillos in the wild now have leprosy. At some point in the last 20 years, the armadillo became infected with the disease. Truman, of the Hansen’s center, estimates that perhaps 15% of the wild armadillos in Texas and Louisiana have leprosy. He said that, as far as anyone knows, no armadillo injected for an experiment has ever escaped. He believes that, somewhere out there, an armadillo contracted the disease from a human.
Dr. Terry Williams, a Houston dermatologist, believes that human contact with armadillos now also is a factor in the spread of leprosy.
He said that eight of the last nine native Texans he diagnosed as having leprosy had had contact with armadillos over the years, but he emphasized that just touching an armadillo wouldn’t be dangerous. He said that more than 90% of the U.S. population is resistant to the disease anyway. Immigrants from Asia and Mexico, where the disease is more prevalent, account for most new cases, he said.
Armadillo Risk Factor
Of contact with armadillos, Williams said: “A casual exposure isn’t going to do it.”
Dr. Charles K. Job, a pathologist at the Hansen’s center, said it has not yet been established beyond a reasonable doubt that people coming in contact with armadillos risk coming down with the disease.
Still, the armadillo suffers from an image problem now, one that could lead to a marked decline in the popularity of armadillo stew.
“I think it’s a very important message to relay to people,” said Truman.
“They should not eat these animals or handle these animals.”