Infectious diseases emerging from Chinese wet-markets: zoonotic origins of severe respiratory viral infections

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Abstract
In China, close contacts between humans and food animals have resulted in the transmission of many microbes from animals to humans. The two most notable infectious diseases in recent years are severe acute respiratory syndrome and avian influenza. In this review, these two severe zoonotic viral infections transmitted by the respiratory route, with pandemic potential, are used as models to illustrate the role of Chinese wet-markets in their emergence, amplification and dissemination. Two research groups independently discovered the presence of severe acute respiratory syndrome coronavirus-like viruses in horseshoe bats. An astonishing diversity of coronaviruses was also discovered in different species of bats. For the recent and still ongoing avian influenza H5N1 outbreak that originated in Southeast Asia, from 2003 to 21 April 2006, 204 humans have been infected, with 113 deaths. Most patients had recent direct contacts with poultry. In Chinese wet-markets, unique epicenters for transmission of potential viral pathogens, new genes may be acquired or existing genes modified through various mechanisms such as genetic reassortment, recombination and mutation. The wet-markets, at closer proximity to humans, with high viral burden or strains of higher transmission efficiency, facilitate transmission of the viruses to humans.