Featured Research

from universities, journals, and other organizations

Some ancient mysteries of leprosy uncovered

Date:
February 20, 2014
Source:
University of Texas M. D. Anderson Cancer Center
Summary:
Research is finally unearthing some of the ancient mysteries behind leprosy, also known as Hansen’s disease, which has plagued humankind throughout history. The new research findings suggest that the disease might be the oldest human-specific infection, with roots that likely stem back millions of years. There are still hundreds of thousands of new cases of leprosy worldwide each year, but the disease is rare in the United States, with 100-200 new cases annually. Leprosy is known for attacking a patient's skin and nerves. Effective antimicrobial treatments exist today. However, when misdiagnosed or untreated, the disease can lead to extensive skin lesions, deformities in the patient's face and extremities, disabilities, and even death. Leprosy carries a social stigma and diagnosis is frequently and notoriously delayed.

Research at The University of Texas MD Anderson Cancer Center is finally unearthing some of the ancient mysteries behind leprosy, also known as Hansen's disease, which has plagued mankind throughout history. The new research findings appear in the current edition of journal PLOS Neglected Tropical Diseases. According to this new hypothesis, the disease might be the oldest human-specific infection, with roots that likely stem back millions of years.

Related Articles


There are hundreds of thousands of new cases of leprosy worldwide each year, but the disease is rare in the United States, with 100-200 new cases annually. Leprosy is known for attacking a patient's skin and nerves. Effective antimicrobial treatments exist today. However, when misdiagnosed or untreated, the disease can lead to extensive skin lesions, deformities in the patient's face and extremities, disabilities, and even death. Leprosy carries a social stigma and diagnosis is frequently and notoriously delayed.

An incidental yet important discovery

Work led by MD Anderson pathologist Xiang-Yang Han, M.D., Ph.D., a professor in laboratory medicine, resulted in the discovery in 2008 of a new leprosy-causing species, called Mycobacterium lepromatosis. Before that time, only one species of bacteria, called Mycobacterium leprae, was known to cause leprosy.

In the past several years, Han and other researchers have found the new leprosy agent in patients from Mexico, Canada, Brazil, Singapore, and Myanmar. Han's team, in collaboration with Francisco Silva, an evolutionary geneticist from Spain, analyzed 20 genes of Mycobacterium lepromatosis and compared them with those of Mycobacterium leprae.

They found the two leprosy bacteria came from a last common ancestor around 10 million years ago. Before the divergence, the common bacteria ancestor had undergone a massive reductive evolution that resulted in inactivation of approximately 40 percent of all the genes in its genome. Those genes went on to become non-functioning pseudogenes or were even lost. This reductive evolution, unique among all pathogenic bacteria known so far, was unearthed from genome sequencing of Mycobacterium leprae several years ago before the discovery of Mycobacterium lepromatosis, by another research team.

A unifying theory

In the newly published study, Han and Silva came to the hypothesis that leprosy has existed for millions of years. This theory was built by connecting the dots from several known facts and published studies.

One piece of evidence is the fact that leprosy is a strict human disease without other hosts or reservoirs. Once outside of the human body, leprosy bacteria are unable to grow in artificial media. One caveat is that Mycobacterium leprae is found in wild armadillos, but only in North America and South America. It's believed the animals likely first acquired the infection from early American explorers a few hundred years ago.

A second piece of evidence suggesting a long history of leprosy lies within the bacterial genome. All worldwide Mycobacterium leprae strains analyzed so far, more than 400 in total, have been found to have essentially identical genomes, or be clonal. This suggests human beings carried the leprosy bacteria when departing Africa around 100,000 years ago to populate the rest of the world. It also means that leprosy bacteria are extraordinarily stable within their human hosts, a sign of mature parasitic life far older than 100,000 years.

A third piece of evidence relates to the last common ancestor of the two known leprosy bacteria, which completed reductive evolution around 10 million years ago, resulting in a lean genome and the loss of free-living ability. A well-adapted lean parasite is confined to its specific host species and is unlikely to switch to other host species.

Lastly, the oldest age of the leprosy bacteria's pseudogenes suggest that gene inactivation began approximately 20 million years ago. This is likely the point when the ancestor of leprosy bacteria jumped to our early human ancestors and transitioned from free-living to strictly parasitic. In essence, the theory unifies the reductive evolution of the leprosy bacteria and their strict parasitic lifestyle in humans into a single continuous, long process.

Insights into the pathogenesis of leprosy

Han and Silva also brought human evolution, host genetic diversity, and host immunity into the complex picture of leprosy. Their hypothesis that leprosy existed for millions of years offers new insights into disease pathogenesis.

For example, the parasitic adaptation of the leprosy bacteria inside hominid-human hosts is similar to a very long hide-and-seek game. In this scenario, the parasite hides by mutating or removing harmful molecules while retaining protective ones. In the end, this leads to evasion from host immunity, a phenomenon commonly seen in leprosy. Finally, Han and Silva concluded that leprosy can be viewed as a natural consequence of a long parasitism.

Han, a clinical microbiologist, routinely diagnoses secondary infections caused by various kinds of microbes in patients with cancer. "Many patients who come to MD Anderson suspected of having cancer turn out to have infections instead and we make such game-changing diagnoses nearly every day" said Dr. Han.

"Discovering the new leprosy agent Mycobacterium lepromatosis was incidental. However, locating this additional leprosy cause significantly adds to our understanding of the ancient disease. In particular, tracing the ultimate origin of leprosy through the parasitic adaptive evolution of the leprosy bacteria is rather insightful, not only for this single disease but also for our better understanding of the mechanism behind other human infections. Medical historians and anthropologists may appreciate this also." Han's team is currently focused on the decoded genome of Mycobacterium lepromatosis and its assembly.


Story Source:

The above story is based on materials provided by University of Texas M. D. Anderson Cancer Center. Note: Materials may be edited for content and length.


Journal Reference:

  1. Xiang Y. Han, Francisco J. Silva. On the Age of Leprosy. PLoS Neglected Tropical Diseases, 2014; 8 (2): e2544 DOI: 10.1371/journal.pntd.0002544

Cite This Page:

University of Texas M. D. Anderson Cancer Center. "Some ancient mysteries of leprosy uncovered." ScienceDaily. ScienceDaily, 20 February 2014. <www.sciencedaily.com/releases/2014/02/140220132000.htm>.
University of Texas M. D. Anderson Cancer Center. (2014, February 20). Some ancient mysteries of leprosy uncovered. ScienceDaily. Retrieved December 18, 2014 from www.sciencedaily.com/releases/2014/02/140220132000.htm
University of Texas M. D. Anderson Cancer Center. "Some ancient mysteries of leprosy uncovered." ScienceDaily. www.sciencedaily.com/releases/2014/02/140220132000.htm (accessed December 18, 2014).

Share This


More From ScienceDaily



More Plants & Animals News

Thursday, December 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

When You Lose Weight, This Is Where The Fat Goes

When You Lose Weight, This Is Where The Fat Goes

Newsy (Dec. 17, 2014) Can fat disappear into thin air? New research finds that during weight loss, over 80 percent of a person's fat molecules escape through the lungs. Video provided by Newsy
Powered by NewsLook.com
The Hottest Food Trends for 2015

The Hottest Food Trends for 2015

Buzz60 (Dec. 17, 2014) Urbanspoon predicts whicg food trends will dominate the culinary scene in 2015. Mara Montalbano (@maramontalbano) has the story. Video provided by Buzz60
Powered by NewsLook.com
Rover Finds More Clues About Possible Life On Mars

Rover Finds More Clues About Possible Life On Mars

Newsy (Dec. 17, 2014) NASA's Curiosity rover detected methane on Mars and organic compounds on the surface, but it doesn't quite prove there was life ... yet. Video provided by Newsy
Powered by NewsLook.com
Ivory Trade Boom Swamps Law Efforts

Ivory Trade Boom Swamps Law Efforts

Reuters - Business Video Online (Dec. 17, 2014) Demand for ivory has claimed the lives of tens of thousands of African elephants and now a conservation report says the illegal trade is overwhelming efforts to enforce the law. Amy Pollock reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins