The most prevalent form of TB as we know it today is TB of the lungs, i.e., pulmonary TB. Even though lung is its most common target, Mycobacterium tuberculosis, the bacterium responsible for TB, can cause disease in practically any part of the body. Earlier eras didn’t understand this so they called TB in different parts of the body by different names. TB of the lungs or pulmonary TB, was called consumption, TB of lymph nodes, scrofula, skin TB, lupus vulgaris, etc. In the early 1800s, famous as the inventor of the stethoscope, first proposed all these various forms were actually the same disease. It took several decades, and and ‘s experimental studies to prove Laennec’s proposal was sound.
When TB’s in the spine, it’s called, after , who wrote the first description of spinal TB, describing it as ‘arthritic TB of the spine‘. Typically, TB in the spine leads to spinal lesions. Contracted like other forms of TB, i.e., through inhalation of TB-laden aerosol droplets, it’s also treated with the same drug regimen.
According to Holloway et al, ‘osteolytic [bone-resorption] lesions on the anterior regions of thoracic and lumbar vertebrae‘ are characteristic of spinal TB (). They say typically only 1 to 4 vertebrae are involved while neural arches and posterior elements are spared. Intervertebral discs and vertebral bodies are damaged. When this damage is severe enough, angular kyphosis and vertebral fusion occur and the spine collapses leading to a characteristic hunchback. This characteristic anatomical feature is used as a signature of possible TB infection in fossil remains ( ).
After all, with lungs the primary target of TB disease, how to construct TB’s, it’s history among ancient humans? Soft tissue like lung degrades so fast, it’s quickly lost to time. Bone TB in general and spinal TB in particular has thus helped map the course of TB through human history since bone, especially spine, TB lesions survive time’s vagaries and have such specific, unique features. Additionally, now molecular technologies can amplify mycobacterial DNA for a more conclusive identification of TB in ancient human remains ( ). For e.g., fossil evidence from the 3rd millennium BCE Italy showed evidence of spinal TB (4). Archeological evidence of spinal TB dates is also found in Egyptian pharaohs since spine and rib lesions resembling those of TB have been observed in their mummies (5, , ). So the practical use for studying bone TB is to help map its course through human history.
On average, bone TB occurs in ~ 3 to 5% of active TB cases, and it can occur in any part of the skeleton, not just spine (8, 9) .
Study of bone TB lesions over time show interesting trends, chief of which is spinal TB was already rare in the past and has been steadily declining in frequency for millenia. A paleopathological study of >10000 skeletons from Europe and the Mediterranean found that ~1% of spines observed had lesions on thoracic or lumbar vertebrae while a similar proportion had rib periostitis (type of inflammation) (10). Holloway’s meta-analysis of paleopathological studies of 1000s of skeletons from Europe to the Mediterranean showed (see figure below from)
- Frequency of bone lesions decreased through time.
- Mainly spinal in earlier times, more recent bone TB involves other skeletal parts such as long bones, joints, hands, feet.
- This change in distribution of TB bone lesions is generalizable, observed not just in Northern Europe but also in the Mediterranean and the New World.
- These changes correspond to when agriculture was introduced to each region, being earliest in the Mediterranean, next in Northern Europe and latest in the New World.
- There were only 25 samples from Asia, too small a sample size which precluded firm conclusions.
In summary, TB has been with us for very long, co-evolving through the twists and turns of our history. This entails reducing prevalence of spinal TB. For evolutionary biologists like, pathogens like M.tb co-evolve towards decreased virulence which would imply spinal TB could represent greater virulence.
1. Holloway, K. L., et al. “Evolution of human tuberculosis: a systematic review and meta-analysis of paleopathological evidence.” HOMO-Journal of Comparative Human Biology 62.6 (2011): 402-458.
2. Donoghue, Helen D., et al. “Tuberculosis: from prehistory to Robert Koch, as revealed by ancient DNA.” The Lancet infectious diseases 4.9 (2004): 584-592.
3. Zink, A. R., et al. “Molecular history of tuberculosis from ancient mummies and skeletons.” International Journal of Osteoarchaeology 17.4 (2007): 380-391.
4. Formicola, Vincenzo, Quinzio Milanesi, and Caterina Scarsini. “Evidence of spinal tuberculosis at the beginning of the fourth millennium BC from Arene Candide cave (Liguria, Italy).” American Journal of Physical Anthropology 72.1 (1987): 1-6.
5. Nerlich, Andreas G., et al. “Molecular evidence for tuberculosis in an ancient Egyptian mummy.” The Lancet 350.9088 (1997): 1404.
6. Zink, Albert R., et al. “Characterization of Mycobacterium tuberculosis complex DNAs from Egyptian mummies by spoligotyping.” Journal of Clinical Microbiology 41.1 (2003): 359-367.
7. Nerlich, Andreas G., and Sandra Lösch. “Paleopathology of human tuberculosis and the potential role of climate.” Interdisciplinary perspectives on infectious diseases 2009 (2009).
8. Steinbock, R. Ted. Paleopathological diagnosis and interpretation: bone diseases in ancient human populations. Charles C Thomas Pub Limited, 1976.
9. Ortner, Donald J. Identification of pathological conditions in human skeletal remains. Academic Press, 2003.
10. Roberts, Charlotte, et al. “Understanding the impact of infectious disease on European populations: contributions from the Global History of Health Project.” Am. J. Phys. Anthropol. (Suppl. 49) (2009): 222-223.