Past human health and migration : the analysis of microbial DNA associated with human remains recovered from a glacier in Canada
In paleopathology, the assessment of disease occurs through macroscopic observation, which is dependent on the preservation of the sample and the experience of the observer. Many disease events do not leave any visible signatures and therefore go undetected. The relatively new field of paleomicrobiology incorporates molecular techniques where microbial DNA, if present, is amplified from an archaeological sample. The identification of genetic material from micro-organisms, including bacteria and viruses, can confirm a diagnosis that was originally based on visible osteological or mummified tissue changes. Even more promising is the capability of molecular technology to detect microbial DNA evidence of disease processes that were not visibly evident. Based on phylogenetic analyses of modern isolates, scientists have concluded that micro-organisms such as Mycobacterium tuberculosis and Helicobacter pylori have been associated with humans for thousands of years. M. tuberculosis is the causative agent of the disease tuberculosis, and H. pylori is known for its role in gastritis and peptic ulcers. Both are pathogenic bacteria that still impact the health of modern populations. Through the analysis of microbial DNA from these two bacteria in skeletal and mummified tissue, data can be accumulated regarding the spatial and temporal impact of these infections. Interestingly, due to the lengthy association between these bacteria and humans, phylogenetic studies on modern strains have shown that strain characterizations of both M. tuberculosis and H. pylori bacteria reveal connections with past human migrations. In 1999, human remains were discovered eroding out of a glacier in northern British Columbia, Canada on the traditional territory of the Champagne and Aishihik First Nations. The Aboriginal elders named the site Kwäday Dän Ts’ìnchi, which means ‘long ago person found.’ Radiocarbon testing of bone collagen and artifacts from the site suggested a time-frame of approximately AD 1670 to 1850, which is either pre-European contact or early post-contact for that area. I analyzed the tissues of the ancient individual specifically for genetic evidence of M. tuberculosis and H. pylori to identify partial health status and determine if a connection could be made to strains associated with European populations to clarify whether the site was pre or post-European contact. Through polymerase chain reaction (PCR) testing of the individual’s tissues with primers specific for the IS6100 insertion sequence, TbD1, and Rv3479, katG and gyrB genes, I identified evidence of a possible latent tuberculosis infection. Genetic characterization of the katG gene associated with the ancient M. tuberculosis strain revealed a potential connection with European strains. Amplification and sequencing of the gyrB gene fragment indicated the presence of two alleles that may have been the result of a selective pressure. PCR testing of the individual’s stomach tissue with specific primers for regions with the vacA gene resulted in a positive identification of H. pylori DNA. Genetic characterization of this virulence-associated gene indicated that the strain contained a vacA signal (s) region s2 allele. This allele is more commonly identified in Western strains that do not cause disease, which suggests that the individual had no gastric symptoms and that European strains were present in northwestern Canada at that time. The vacA middle (m) region contained a hybrid m2a/m1d sequence. Modern hybrids are rare but they have been identified in Asian strains. Studies have shown that the m2a allele is more common in Western strains. A phylogenetic analysis identified that the m1d region clusters with previously published novel strains associated with Aboriginal individuals that are closely related to Asian strains. This indicates a past connection between the ancient individual and his ancestors who arrived in the New World from Asia thousands of years ago.
Kwäday Dän Ts'Ìnchi, Helicobacter pylori, ancient DNA, microbial, Mycobacterium tuberculosis
Doctor of Philosophy (Ph.D.)