Molecular epidemiology is a branch of

epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evide ...

and

medical science Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care practic ...

that focuses on the contribution of potential genetic and environmental risk factors, identified at the molecular level, to the etiology, distribution and prevention of disease within families and across populations. This field has emerged from the integration of

molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...

into traditional epidemiological research. Molecular

improves our understanding of the

pathogenesis Pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes from Greek πάθος ''pat ...

of disease by identifying specific pathways, molecules and

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

s that influence the risk of developing disease. More broadly, it seeks to establish understanding of how the interactions between genetic traits and environmental exposures result in disease.

History

The term "molecular epidemiology" was first coined by Edwin D. Kilbourne in a 1973 article entitled "The molecular epidemiology of influenza". The term became more formalized with the formulation of the first book on ''Molecular Epidemiology: Principles and Practice'' by Paul A. Schulte and Frederica Perera. At the heart of this book is the impact of advances in molecular research that have given rise to and enabled the measurement and exploitation of the

biomarker In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, p ...

as a vital tool to link traditional molecular and epidemiological research strategies to understand the underlying mechanisms of disease in populations.

Modern use

While most molecular epidemiology studies are using conventional disease designation system for an outcome (with the use of exposures at the molecular level), compelling evidence indicates that disease evolution represents inherently heterogeneous process differing from person to person. Conceptually, each individual has a unique disease process different from any other individual ("the unique disease principle"), considering uniqueness of the

exposome An environmental factor, ecological factor or eco factor is any factor, abiotic or biotic, that influences living organisms. Abiotic factors include ambient temperature, amount of sunlight, and pH of the water soil in which an organism lives. Bi ...

and its unique influence on molecular pathologic process in each individual. Studies to examine the relationship between an exposure and molecular pathologic signature of disease (particularly, cancer) became increasingly common throughout the 2000s. However, the use of molecular pathology in epidemiology posed unique challenges including lack of standardized methodologies and guidelines as well as paucity of interdisciplinary experts and training programs. The use of "molecular epidemiology" for this type of research masked the presence of these challenges, and hindered the development of methods and guidelines. Furthermore, the concept of disease heterogeneity appears to conflict with the premise that individuals with the same disease name have similar etiologies and disease processes.

Analytical methods

The genome of a bacterial species fundamentally determines its identity. Thus, gel electrophoresis techniques like

pulsed-field gel electrophoresis Pulsed field gel electrophoresis is a technique used for the separation of large DNA molecules by applying to a gel matrix an electric field that periodically changes direction. Historical background Standard gel electrophoresis techniques for ...

can be used in molecular epidemiology to comparatively analyze patterns of bacterial chromosomal fragments and to elucidate the genomic content of bacterial cells. Due to its widespread use and ability to analyse epidemiological information about most bacterial pathogens based on their molecular markers, pulsed-field gel electrophoresis is relied upon heavily in molecular epidemiological studies.

Applications

Molecular epidemiology allows for an understanding of the molecular outcomes and implications of diet, lifestyle, and environmental exposure, particularly how these choices and exposures result in acquired genetic mutations and how these mutations are distributed throughout selected populations through the use of biomarkers and genetic information. Molecular epidemiological studies are able to provide additional understanding of previously-identified

risk factor In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection. Due to a lack of harmonization across disciplines, determinant, in its more widely accepted scientific meaning, is often ...

s and disease mechanisms. Specific applications include: * Molecular surveillance of disease risk factors * Measuring the geographical and temporal distribution of disease risk factors * Characterizing the evolution of pathogens and classifying new pathogen species

Criticism

While the use of advanced molecular analysis techniques within the field of molecular epidemiology is providing the larger field of epidemiology with greater means of analysis,

Miquel Porta Miquel Porta (Barcelona, 1957) is a Catalan physician, epidemiologist and scholar. He has promoted the integration of biological, clinical and environmental knowledge and methods in health research and teaching, which he has conducted internationa ...

identified several challenges that the field of molecular epidemiology faces, particularly selecting and incorporating requisite applicable data in an unbiased manner. Limitations of molecular epidemiological studies are similar in nature to those of generic epidemiological studies, that is, samples of convenience - both of the target population and genetic information, small sample sizes, inappropriate statistical methods, poor quality control, and poor definition of target populations.

References