History of smallpox centuries, the WHO certified the global eradication of smallpox in December 1979. Smallpox is one of two infectious diseases to have been eradicated, the other being rinderpest, which was declared eradicated in 2011. It has been suggested that smallpox was a major component of the Plague of Athens that occurred in 430 BCE, during the Peloponnesian Wars, and was described by Thucydides. Galen's description of the Antonine Plague, which swept through the Roman Empire in 165–180, indicates that it was probably caused by smallpox. Returning soldiers brought the disease home with them to Syria and Italy, where it raged for
Human disease modifier gene and shifting from clinical reliance on epidemiological data to patient-specific genetic and biological data. Ultimately, developing therapeutics for human disease informed by an understanding of its molecular mechanisms is challenging. In the case where multi-gene interactions give rise to disease, a series of thorough methodological steps must be taken to determine these mechanisms. For the common case in which a major locus is causally associated with disease, but there exists considerable, unexplained phenotypic variation, this process of discovery typically begins with establishing heritability of the disease phenotype, and the reasonable likelihood that modifier genes contribute to the observed phenotypic variation.