Chapter 11 : Emerging Foodborne and Agriculture-Related Viruses

Abstract:

An emerging pathogen such as a virus can be defined as a previously unknown agent causing disease or an agent that was once an infrequent cause of illness that has become more common. It can also be defined as an infectious agent introduced into a new geographic area or one that infects a new species ( 1 ). Emergence of a viral pathogen is essentially a two-step process which requires conditions suitable for host introduction and then subsequent conditions that provide the opportunity to disseminate within a new host population ( 2 ). This is evidenced by the fact that emerging viruses and pathogens often arise in specific geographic locations ( 2 ). Numerous factors can be involved in the emergence of viral pathogens. These can include human demographic changes and behavior, travel and commerce, microbial adaptation, development of new technologies and industries, environmental perturbations, and breakdown of public health measures ( 2 ). The latter may be responsible for the re-emergence of poliovirus in parts of sub-Saharan Africa, where vaccine campaigns were suspended as a result of unfounded fears or active warfare. Historically, as human civilization developed as a result of agricultural activities, it is thought that environmental changes and increased human and domestic animal population sizes and densities permitted the introduction and spread of pathogens from wildlife reservoirs ( 3 ). Retrospective evidence suggests that viruses such as measles may have evolved from canine distemper (i.e., dogs) and/or rinderpest virus, a disease of cattle and wild even-toed ungulates such as deer, antelope, and wildebeest. It has been suggested that the variola virus, more commonly known as the smallpox virus, evolved from cowpox or, alternatively, may have evolved from camelpox, a virus of camels which is the closest known relative to the smallpox virus ( 3 ).