A new species of bacterium that causes leprosy has been identified through intensive genetic analysis of a pair of lethal infections, a research team reports in the December issue of the American Journal of Clinical Pathology.
All cases of leprosy, an ancient disease that still causes much disfigurement, disability and social ostracism in the developing world, previously had been thought to be caused by a single species of mycobacterium. However, a new discovery by researchers at Colorado State University and the University of Texas M. D. Anderson Cancer Center Laboratory Medicine confirm a new, second species that causes a rare, severe form of the disease.
The second species of leprosy mycobacterium was recently identified and determined to cause diffuse lepromatous leprosy, or DLL. DLL occurs mainly in Mexico, the Caribbean and countries in South America.
Colorado State University researcher John Spencer became involved in the discovery in 2007 when a man showed up in a Phoenix health clinic covered with lesions and experiencing sensory loss in his feet. His doctors were mystified as to whether his condition might be caused by a bacterial infection, an autoimmune disease, or a type of cancer. His tissues began to break down, his organs began to fail and, after two weeks in the intensive care unit, the man died. His doctors suspected the man, who was originally from Mexico, died of complications from an aggressive, and often fatal, rare form of leprosy called diffuse lepromatous leprosy with Lucio’s phenomenon.
"We received serum and biopsy specimens from a clinician at the clinic who wanted confirmation of their suspicions of leprosy," said Spencer, an assistant professor in the Department of Microbiology, Immunology and Pathology and researcher with the Mycobacteria Research Laboratories in the College of Veterinary Medicine and Biomedical Sciences. "Through serologic antigen recognition profiling and sequencing analysis of the DNA from this isolate at CSU and by Dr. Xiang Han, head of the Diagnostic Laboratory at the M. D. Anderson Cancer Center in Houston, it was determined that this mycobacterium was different. It showed a 2.1 percent difference in the 16S ribosomal gene from the bacterium known to cause leprosy, indicating a possible difference in species. It was a mycobacterium, but it wasn’t M. leprae – the bacterium previously known to cause this disease."
Across a group of bacteria called mycobacteria, the 16S rRNA gene is 93 to 100 percent identical. There are more than 110 species of mycobacteria, with those causing tuberculosis and leprosy the best known.
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, mostly among immigrants. Leprosy initially attacks skin and nerve cells. It can be successfully treated with antibiotics in its early and intermediate stages.
Mexican researchers Lucio and Alvarado first described the pathology and symptoms of this second form of leprosy found primarily in the Jalisco, Sinaloa and Michoacan provinces in 1852. The disease largely went unnoticed by outside scientists for more than 150 years, though rarely similar cases appeared in other parts of the world. When more than a dozen genes were sequenced last year, none of these sequences matched up to the any of the 110 known mycobacterial species but they were most closely related to M. leprae.
This summer, Spencer and three students traveled to the provinces of Jalisco and Sinaloa to share their findings.
Though not officially approved yet, Dr. Han named the new species Mycobacterium lepromatosis, and the paper written about the discovery recently appeared in the American Journal of Clinical Pathology. They have since confirmed M. lepromatosis as the cause of two lethal cases of DLL in Singapore.
Han and M. D. Anderson colleagues diagnose infections in cancer patients. Han developed in 2002 a way to identify unusual bacteria by analyzing small but significant differences in the 16S ribosomal RNA gene.
"This is like a fingerprint analysis to solve crimes," Han said. He has discovered and named several new bacterial species that cause unusual infections.
Sequencing the 16S rRNA gene is a fast and accurate way to identify mycobacteria, which usually grow slowly. Accurate identification improves patient care decisions.
The team is working to better understand the bacterium and how it causes DLL. They are attempting to sequence the entire M. lepromatosis genome and looking for ways to grow the organism in the lab. Neither leprosy mycobacteria can be cultured because over millions of years they lost genes necessary to survive outside their hosts, a process called reductive evolution.
One of the puzzles of leprosy is that M. leprae strains collected worldwide are virtually identical, while the clinical features of the disease and its severity vary greatly both geographically and from person to person. Evidence suggests that individual host immune factors play the key role in determining how the disease progresses.
The authors conclude that the new species M. lepromatosis could account for some of this geographical and individual variation.
Funding for the project came from private philanthropy at M. D. Anderson Cancer Center, a National Cancer Institute grant to M. D. Anderson’s DNA Core Facility, a National Institute of Allergy and Infectious Disease grant to Colorado State University and a College Research Council Award from Colorado State University.
Han and Dr. R. Geetha Nair a physician with Maricopa Integrated Health System in Phoenix, are co-authors of the research along with Dr. Yiel-Hea Seo, Dr. Kurt Sizer, Taylor Schoberle and Gregory May all of M. D. Anderson’s Department of Laboratory Medicine; and Spencer and Wei Li of the Mycobacterial Research Laboratories, Department of Microbiology, Immunology and Pathology at Colorado State University.