Vesicular exanthema of swine (VES) was rst recognized on ve pig farms in California in April 1932 as a clinical syndrome that was indistinguishable from foot-and-mouth disease (FMD) [1]. Although experimental inoculation of material from these cases failed to reproduce vesicular lesions in either cattle or guinea pigs, the causative agent was presumed to be an atypical FMD virus. However, four novel immunologically distinct viruses were subsequently isolated, which were named VES viruses (VESV) A, B, C, and D, and one of these (VESV type B or 1934B) from 1934 is still available (at the Pirbright Institute, UK). Similar outbreaks (of up to 184 cases/year) were observed every year between 1933 and 1951 (except in 1937-1938). Typically, these outbreaks affected mainly (but not exclusively) garbage-fed pigs in California. Between 1940 and 1942, three immunologically distinct viruses were recovered, but these were subsequently lost or destroyed. A number of pig-passaged tissue samples of another VESV serotype, 101-143 (which was isolated at the Pirbright Institute from a sample collected from pigs in San Francisco stockyards in 1943), are still available, but it has not yet been possible to recover viable virus from these samples. On June 16, 1952, VES appeared at a biological manufacturing plant in Grand Island, Nebraska. The source of this infection was traced to Cheyenne, Wyoming, where pigs had been fed garbage from transcontinental trains that had originated in California. Unfortunately, before the disease was detected in Grand Island, VES-infected pigs had been shipped to Omaha stockyards and sold on. In a little over a month (by July 29), outbreaks had occurred in 19 states, and by September 1953, a total of 42 states and the District of Columbia had

reported cases of VES. Outbreaks continued in California until 1955 and in New Jersey until 1956 [2]. In 1948, a new collection of VESV isolates was started and new serotypes were discovered almost every year. The viruses were named alphabetically and with the year that the serotype was rst isolated as a sufx, namely, A48, B51, C52, D53, and E55. Due to the retrospective nature of this analysis, some of the isolates were named out of chronological sequence (see later text). Subsequently, four unique serotypes were detected on a single farm in San Mateo County, California, in December 1954 (H54) and May (I55), September (F55), and October 1955 (G55). It was speculated that pigs on this farm were persistently infected and that new serotypes evolved by mutation [2]. The VES outbreaks that occurred outside California were initially only caused by B51. However, in 1954 and 1956, two new serotypes (designated K54 and J56) appeared on two farms in Secaucus, New Jersey [3]. As these serotypes were not found elsewhere in the United States, it was postulated that these viruses had evolved from the B51 serotype [4]. On October 22, 1959, the U.S. Secretary of Agriculture announced that VES had been eradicated and subsequently classied as a reportable foreign animal disease [2].