Armadillos and Leprosy (Conclusion)

Dead Armadillos
Not that they meant it this way:
mostly mammal, mostly blind,
bellies up, stinking of leprosy.

The way Rasputin’s mystical voice
led Annushka into his eyes
is how headlights lull armadillos.

They came to know the roar of full-lit ecstasy.

They fill our roadsides with their heaven.

--J. Rodney Karr*

Beginning of this story

Besides armadillos and mice, several other mammals had proved, or soon would prove, susceptible to injections of M. leprae—rats, hedgehogs, ground squirrels.  But scientists had always believed people were the only natural host for the microbe.  That’s why they were shocked by a 1975 report of leprosy in wild armadillos.

Several factors combined to make the situation seem like a horror story.  The wild leprous armadillos had turned up in Louisiana, not too far from the site of experiments by Storrs, Kirchheimer, and others.  The obvious inference was that experimental animals might have escaped, or at least that the carcasses of lab animals might have been cannibalized by wild armadillos.  If leprosy was new to the armadillo population, there was no way to know how fast it might spread between armadillos—or even into the human population.

At roughly the same time, the armadillo’s conquest of the United States was fast becoming familiar to the average American.  Newspapers reported the leprosy connection, creating the latest version of the deadly animal invasion story that seems to crop up with a different cast of characters every few years (black widow spiders, killer bees, and fire ants have all figured in similar scare-stories).  Finger-pointing among a few biologists didn’t help matters.

Armadillos dig for insects and carrion compulsively, and that trait had already given them a folkloric reputation as grave-robbers in parts of the south.  The possibility of armadillos having contracted leprosy from human corpses was an alternative to blaming the scientists—though not an attractive one, since either scenario left open the possibility that people might be in for a wave of disease.  Of course, scientists who worked with leprosy realized that its threat was minor.  Not only does the disease progress slowly, but it is frequently re-introduced to the United States by human immigrants without spreading widely.  These points were not always mentioned in the press.

Other developments complicated the story.  Chimpanzees came down with leprosy in 1977, as did sooty mangabey monkeys in 1981.  In both cases, the primates were lab animals, but not the subjects of leprosy experiments.  These discoveries, which suggested that leprosy might occur naturally in any number of nonhuman species, lent credence to the idea that armadillos might have carried the disease long before the species was used in leprosy research.  Whether wild primates get the disease outside labs is still hotly debated; skeptics think humans infected a few chimps and mangabeys somewhere in the process of capture or lab work. To add another layer of mystery, no one has yet observed leprosy transmitted between armadillos in captivity, but cage-mates of infected primates have come down with the disease.

In 1983, researchers reported leprosy in five people in Texas who had frequently handled armadillos.  It was impossible to prove that armadillos were the source of the infection, since even now no one is certain of the disease’s route of transmission, but the implication couldn’t be ignored.   Since then, armadillos have been implicated in a number of other human cases.  Why so many people would be handling armadillos puzzled me, since my only hands-on experience had been the ridiculous armadillo race. Truman resolved my confusion: “People do eat quite a lot of armadillo.”

Truman and his colleagues finally put the question of scientific culpability to rest in 1986.  They tested blood samples which had been drawn from armadillos in the early 1960s and kept frozen in a wildlife sera collection at Louisiana State ever since.  Truman’s group found some of these samples contained definitive evidence of M. leprae.  Since the samples predated the 1968 clinical work, Storrs and Kirchheimer and later leprosy researchers were off the hook.  They couldn’t have provided the first contact between M. leprae and wild armadillos.

But if scientists weren’t to blame, who was?  Leprosy is un-American; even today, Native Americans don’t seem to get it.  Truman and company looked into the distribution of the disease in the U.S. In both armadillos and people, the disease occurs most frequently in moist, low-lying areas.  So far, this generalization has held true for people on several continents. So perhaps M. leprae is hiding in some natural reservoir that occurs in such moist areas.  It’s already been established that the microbe can survive for several weeks in soil, but no one knows whether it typically does so.

Truman’s survey could hypothetically have revealed an origin point from which the disease was spreading.  In fact, leprosy turned out not to follow such a pattern.  No point of origin showed up.  The even distribution led Truman’s group to deduce that leprosy has been here a long time, in both humans and armadillos—maybe centuries. We’ll probably never knw when M. leprae arrived in America. Columbus’s invasion marks the earliest possible date. And after the disease arrived, it was only a matter of time until a cold and hungry mammal raided the wrong grave.

Hastily, all alone,
a glistening armadillo left the scene,
rose-flecked, head down, tail down.
--Elizabeth Bishop

A shorter version of this story originally appeared in Discover.

*J. Rodney Karr dedicates his poem to "all the little critters who have met their maker along America's highways and roads."



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