On the Trail of Tuberculosis

Tuberculosis is one of the most infectious and fatal diseases worldwide. The spread of tuberculosis has been associated with social and biological factors, therefore determining its roots and tracing its history is important. Studies of historical cases of tuberculosis can help to understand the spread of the disease in modern populations. By looking at the mechanisms that caused the spread in history we can better prevent spread in the future. Numerous studies have attempted to discover how the disease was first contracted and spread, but detecting its origins is difficult. A new study by Nicklisch et al. (2012) examines the presence of indicators of tuberculosis (TB) in Neolithic populations in Germany.

Fig. 3 Grade 4 Rib Lesions, via Nicklisch et al. (2012)

TB is from the genus Mycobacterium, and has a number of species that can infect humans and animals.  The disease that most infects humans is caused by M. tuberculosis, and is primarily transmitted by droplet infection between humans. First the pathogen infects the lung tissue and then the lymph system, followed by spreading to the other organs. The second most common to humans is M. bovis. The pathogen spreads through the consumption of infected milk, dairy products, and meat. TB only affects the bones in 2-5% of cases where virulence is highest. Changes in the joints can be indicators of TB, although these also mimic other diseases. TB can also be diagnosed in ancient populations through the use of DNA when analysis of bone is not conclusive enough.

Nicklisch et al. (2012) propose to study the presence of lesions on the pleural (lung side) of ribs, which in the past haven’t been used due to difficulty in identification. The sample includes skeletal remains from three sites in Germany dating to the Neolithic (5450–4780 cal BCE). The assemblage includes 57 individuals with varying ages and both sexes represented. The lesions found on the skeletons were scored from 0-4, with 0 indicating no lesions, 1 with minor periostitis, 2-3 with distinct lesions and 4 with major lytic lesions. Molecular analysis was also conducted on all the remains, in addition to the microscopic analysis. The analysis showed that 36% of the individuals had lesions on the ribs, with 21% of them being more severe. Molecular analysis found that 8 individuals (of a random subset of 21) were positive for TB.

Fig 6 Collapse of vertebral bodies due to TB, via Nicklisch et al (2012)

There are problems with using only rib lesions to diagnose TB. The lesions aren’t specific to TB, they can also be caused by other lung diseases and pleural infections. Trauma to the lungs may also cause them to appear. Further, diagnosis of TB by lesions alone requires the presence of other indicators such as bony reactions in the joints, specifically the vertebrae. Analysis of the complete skeletons from this German sample show that a number have other indicators of the bacterium such as destruction of bone in the spine and lesions in the joints. However, the molecular evidence shows that TB was definitely present at all three sites. Since the disease only leaves bony traces on a small number of individuals it is highly likely that a number of people from these sites died from the disease before it had a change to change their skeleton.

Comparison of the sites shows that there was a difference in prevalence. The virulence of a disease is related to the environment, both natural and cultural, and the health and nutritional status of the individuals at the site. At all sites there was a high prevalence of nutritional and stress related pathologies. Immune systems are further compromised, especially when facing TB, if the individual has a low protein and low iron diet. Stable isotope analysis of the three populations found that the site associated with the lowest intake of meat had the highest prevalence of rib  and joint lesions relating to TB.

The importance of studying TB in the Neolithic is to determine why the disease started in this period, and the mechanisms that caused it to spread. This was the period when agriculture and animal husbandry became a pivotal part of human life and drastically changed the way we interacted with the environment. Major cultural changes in social structure and burial patterns are also associated with this period. Often health declines as well when people are switching to a more grain rich, rather than protein heavy, diet. The increased interaction with domesticated animals also introduced new diseases to humans. Theories about how TB started posit that it was found in animals and transferred through infected milk. It is still unknown which TB started first, but we do know it began during this interaction. By finding early Neolithic sites with TB, and then looking at their agricultural and animal practices, we can better understand the disease itself. While Nicklisch et al. (2012) are able to reveal the presence of TB at these sites using a range of evidence, it is the connection to culture that we are missing. My only criticism is that I wish I knew more about the early culture who was experiencing the disease so I could better interpret how it was introduced and spread.

Works Cited

ResearchBlogging.orgNicklisch, N., Maixner, F., Ganslmeier, R., Friederich, S., Dresely, V., Meller, H., Zink, A., & Alt, K. (2012). Rib lesions in skeletons from early neolithic sites in Central Germany: On the trail of tuberculosis at the onset of agriculture American Journal of Physical Anthropology, 149 (3), 391-404 DOI: 10.1002/ajpa.22137

3 responses to “On the Trail of Tuberculosis

  1. Pingback: On Giants Shoulders #54: A Sleigh Load of History « Contagions·

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