Aspects of the persistence of foot-and-mouth disease virus in animals--the carrier problem.

Foot-and-mouth disease virus (FMDV) is a member of the Aphthovirus genus in the Picornaviridae family. Seven distinct serotypes, each including a wide range of variants, have been defined. FMD, affects wild and domesticated ruminants and pigs, is difficult to control and is the major constraint to international trade in livestock and animal products. After the acute stage of infection, FMDV may cause a prolonged, asymptomatic but persistent infection in ruminants. Also, vaccinated or naturally immune animals subsequently exposed to live virus may become persistently infected (the so-called carriers), a situation which can result in export embargoes if vaccination is included in a country's control policy.