LITMIR.BIZ

      Viruses reside in Earth’s vast oceans and everywhere else on our planet. Courtesy of NASA’s Earth Observatory, Suomi NPP satellite image courtesy of NASA/GSFC.

Figure 1.1 The human virome. Our knowledge of the diversity of viruses that can be present in or on a normal human (including some potential pathogens) has increased greatly with the development of high-throughput sequencing techniques and new bioinformatic tools. Current estimates of the numbers of distinct viral families with DNA or RNA genomes in various sites are in parentheses; the > symbol signifies the presence of additional viruses not yet assigned to known families. The numbers may increase as diagnostic tools improve and new viral families are identified. Data from Popgeorgiev N et al. 2013. Intervirology 56:395-412; see also http://www.virology.ws/2017/03/23/the-viruses-in-your-blood/.

BOX 1.2

      DISCUSSION

       The first animal virus discovered remains a scourge today

      Foot-and-mouth disease virus infects domestic cattle, pigs, and sheep, as well as many species of wild animals. Although mortality is low, morbidity (illness) is high and infected farm animals lose their commercial value. The virus is highly contagious, and the most common and effective method of control is by the slaughter of entire herds in affected areas.

      Outbreaks of foot-and-mouth disease were widely reported in Europe, Asia, Africa, and South and North America in the 1800s. The largest epidemic ever recorded in the United States occurred in 1914. After entry into the Chicago stockyards, the virus spread to more than 3,500 herds in 22 states. This calamity accelerated epidemiological and disease control programs, eventually leading to the field- and laboratory-based systems maintained by the U.S. Department of Agriculture to protect domestic livestock from foreign animal and plant diseases. Similar control systems have been established in other Western countries, but this virus still presents a formidable challenge throughout the world. A 1997 outbreak of foot-and-mouth disease among pigs in Taiwan resulted in economic losses of greater than $10 billion.

      In 2001, an epidemic outbreak in the United Kingdom spread to other countries in Europe and led to the slaughter of more than 6 million infected and uninfected farm animals. The associated economic, societal, and political costs jolted the British government. Images of mass graves and horrific pyres consuming the corpses of dead animals (see figure) sensitized the public as never before. Minor outbreaks that occurred later in the United Kingdom and parts of Asia were also controlled by culling. But in 2011, South Korea was reported to have destroyed 1.5 million pigs, roughly 12% of its population, to curb a more serious outbreak spread of the virus.