Leprosy (Hansen’s Disease) in the United States — The Role of Armadillos and the Increasing Incidence in Florida
Hansen’s disease is believed to have been introduced into the Western Hemisphere during or shortly after the period of early colonization and became established in areas around the Gulf of Mexico by the middle of the 18th century. In 2010, the last year for which data are available from the National Hansen’s Disease Program, 294 new cases were reported from 34 U.S. jurisdictions (including Puerto Rico), with approximately two-thirds from seven states: California, Florida, Hawaii, Louisiana, Massachusetts, New York, and Texas. The infections were multibacillary in 56.8%.
Florida accounted for 10.2% of U.S. cases in 2010, but this proportion has likely increased since then. During the 10 years from 2004 to 2014, Florida reported a total of 92 cases of Hansen’s disease — an average of fewer than 10 each year. However, starting with five cases in the first 5 weeks of 2015, the total number of confirmed cases for the entire year reached 27 — almost three times the previous annual average. Unfortunately, 2016 has started on a similar upward path, with six confirmed cases from three counties in the first 5 weeks of the year.
While the majority of cases in the United States were acquired in endemic countries, approximately one-third of patients reported that they had not resided in areas of endemicity and, in addition, had no known contact with an individual with Hansen’s disease. Evidence indicates that nine-banded armadillos, which have been epidemiologically associated with Hansen’s disease in the United States and Brazil, may have been the source of infection in at least some of those cases. Armadillos are, to greater or lesser extents, common in the southern United States, and their range extends to Central America and northern Argentina. Beginning in 1975, Mycobacterium leprae infection was identified in armadillos in Texas and Louisiana, but not in Georgia, Alabama, or Florida, although the range of infection appears to have increased.
To further investigate the epidemiology and zoonotic nature of Hansen’s disease, Sharma and colleagues, using serological tests and PCR, found that 106 (15.44%) of 645 armadillos captured in eight separate locations in the southeastern United States not previously known to have enzootic infection were infected. (See Figure.) Animals with evidence of M. leprae infection were detected at all eight of these locations. The armadillos were infected with one of two genotypes (3I-2-v1 and 3I-2-v5) and, of 52 patients evaluated, 22 (42.3%) were infected with one or the other of these. All patients infected with type 3I-2-v1 reported residing in areas of the southern United States where armadillos are present. All 10 patients infected with 3I-2-v15 resided in the only region where armadillos with this same M. leprae genotype strain type also had been found — southern Florida. None of the patients interviewed, however, reported contact with armadillos, but, in addition, none reported contact with known Hansen’s disease cases. All patients harboring type 3I-2-v1 had histories of residence in areas of the southern United States where they may have been exposed to M. leprae through armadillos.
FIGURE. EIGHT LOCATIONS IN 4 STATES IN THE SOUTHEASTERN UNITED STATES WHERE ARMADILLOS WERE SAMPLED AND TESTED FOR INFECTION WITH MYCOBACTERIUM LEPRAE
Armadillos are highly susceptible to infection with Mycobacterium leprae (in contrast to humans, in whom there is a strong genetic component that accounts for the fact that approximately 95% appear resistant to infection), with tissue bacterial loads reaching 1010-1011 organisms per gram. The work of Sharma et al strengthens the link between human infection and armadillos. The fact that infected armadillos had not been detected previously in the southeastern United States suggests that the range of zoonotic Hansen’s disease is expanding and may continue to do so. It can be speculated that the reported increase in human infections in Florida may be a reflection of the expansion of this range.
REFERENCE
- National Hansen’s Disease Program. A Summary of Hansen’s Disease in the United States — 2010. Available at: www.hrsa.gov/hansensdisease/pdfs/hansens2010report.pdf.
The evidence linking armadillos to human Hansen’s disease is increasing and the range of infected armadillos and potentially related human cases has expanded into Florida where the incidence of this infection is increasing.
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