Geographic Spread of Pathogens and Molecular Techniques

Until recently, the only ways to trace the spread of disease have been to 1) identify the pathogen microscopically and classify it on the basis of appearance (phenotypically) or 2) identify the occurrence of resulting disease based upon secondary reports, or upon “syndromic surveillance”–the appearance of signs and symptoms that are characteristic of a particular disease.

A number of molecular epidemiologists and a few geographers have been using molecular techniques and genomic sequencing to trace the spread of pathogens (disease causing microbes) based upon characteristic genomic markers, or upon identification of identical genotypic strains. My team and I are doing this with tuberculosis transmission chains in Ghana. In the January 28th edition of Science,
Croucher and his group report on the use of such techniques to identify the spread and evolution of a particularly virulent strain of one of the major causes of bacterial pneumonia, which causes significant morbidity and mortality. The bacterium, formally called Streptococcus pneuomoniae, and popularly called pneumococcus, is the bacterium covered by the “pneumonia shot” that is recommended for adults >/= 65 years old. Commenting on the article, Enright and Spratt (p. 407) emphasize the importance of using molecular techniques for understanding spatial spread, as well as genomic evolution, particularly in rapidly evolving pathogens.

One might imagine geography departments with labs that have the capability for DNA or RNA sequencing, or increasing collaboration between “epidemiologic geographers,” molecular epidemiologists, and genome scientists, in order to synthesize those with interests in globalization, transportation, settlement patterns, and spread of pathogens.

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