The Research Brief is a short summary of interesting academic work.
The big idea
Years old tissue samples from armadillos in museum collections may accommodate Mycobacterium lepraethe bacteria that causes Hansen’s diseasealso called leprosy, according to recent research by my colleagues and I executed.
Leprosy can cause nerve damage which, without early effective treatment, can lead to paralysis and blindness in the most severe cases. About 140,000 new patients were diagnosed worldwide in 2021, mainly concentrated in India, Brazil and Indonesia. Since 2010, there has been evidence that the nine-banded armadillo, Dasypus novemcinctusis transmitting leprosy to humans in North America and possible elsewhere.
To investigate this connection, we turned to 10 natural history museums in the US These settings offer more than just public exhibitions. They also contain thousands of biological samples collected over many years. Examining these historical specimens can help researchers identify the prevalence and diversity of pathogens across time and space.
Daniel Romero Alvarez
In our study, we used online repositories such as VertNet to identify armadillo specimens held by museums. Next, we physically examined tissue samples from 159 individual animals from 10 armadillo species. Between 1974 and 2017, samples were collected from eight countries in the Americas.
We identified using molecular diagnostic techniques M. leprae bacteria in muscle, spleen and liver tissue in 18 of 122 nine-banded armadillos – a prevalence of 14.8%. All positive samples were collected between 1996 and 2014. Our research allowed us to look into the near past to see that M. leprae circulated in armadillos in previously unknown locations.
Why it matters
How leprosy is transmitted is still under debate. The bacteria can apparently spread in aerosols and droplets released by coughing or sneezing of infected patients. But because some people get sick without being exposed to an infected person or traveling to an area where leprosy is present, researchers think there may be another way it spreads.
Over the past decade, molecular studies of non-human samples, water and soil have suggested that wildlife and the environment have potential sources of leprosy. Our analysis showed that the M. leprae strain identified in the positive museum samples closely resembles a strain that has been circulating in North American armadillos since the 1990s, when leprosy transmission through wildlife was only suggested.
What other research is being done
In animals, researchers have used museum specimens to study snake fungal disease and the chytrid fungus that affects frogs.
Scientists search less often in museum archives pathogens that affect humans. However, researchers have identified Tripanosoma cruzithe agent causing Chagas disease, in wood rats in natural history museum collections, as well hantaviruses in deer mouse copies.
Since about 70% of emerging human infectious diseases originated in the wild, examining museum specimens will likely help identify where and when certain pathogens may have existed. Ultimately, understanding which pathogens show up and where, as we did with leprosy and armadillos, could help scientists anticipate potential outbreaks and perhaps even prevent them.
Daniel Romero Alvarez
What is not yet known
Scientists discovered in 2008 that another pathogen, Mycobacterium lepromatosiscan also cause leprosy. Researchers have yet to unravel the role of this second bacterium in the global incidence of the disease.
All of our 159 armadillo samples were negative for M. lepromatosis. But this bacteria has infected people Mexico, Colombia, Canada and elsewheretogether with red squirrels in the British Isles.
My colleagues and I hope our discovery encourages further research into the role of non-human sources of leprosy transmission in the Americas. Our work is another case study showing that natural history collections can play an important role in research into human infectious diseases.
