Abstract
Foot-and-mouth disease virus (FMVD), one of the most contagious viruses of cloven-hoofed animals, may cause a prolonged, asymptomatic but persistent infection in ruminants, named the "carrier state". However, it remains an open question whether this carrier state occurs in pigs. Here we present quantitative analyses of the duration of FMDV RNA and infectivity in lymphoid and epithelial tissues in experimentally infected pigs with FMDV C-S8c1. The data indicated that although FMDV RNA remained in blood until day 14 post-infection (pi), viremia was cleared by day 7 pi. However, all tissues tested were positive for FMDV until day 14-17 pi. Interestingly, the specific infectivity of FMDV in these tissues was in some cases even higher than the FMDV C-S8c1. We therefore propose that a "pseudopersistent state" may occur in pigs in which virus replicates in lymphoid tissues for a prolonged period of time, thereby representing a potential source of virus.
Highlights
Foot-and-mouth disease (FMD) is one of the most contagious and economically devastating viral diseases of cloven-hoofed livestock
Evolution of FMD virus (FMDV) lesions in the coronary band epithelium Twenty pigs were infected with 105 PFU of FMDV C-S8c1 in the coronary band and four pigs were used as uninfected controls
Other tissues did not show infectious virus by plaque assay but high amount of viral RNA could be detected. This might indicate that the amount of FMDV particles was very low Discussion Two critical determinants of FMD pathogenesis are the ability of the virus infection to spread through the different tissues and, the clearance rate by the host immune response
Summary
Foot-and-mouth disease (FMD) is one of the most contagious and economically devastating viral diseases of cloven-hoofed livestock (reviewed in [1,2,3]). The disease is characterized by the formation of vesicles on the feet, mouth, tongue, and snout, with most of the animals developing viremia, that results in high morbidity but low mortality in adult animals [4]. The infectious agent, FMD virus (FMDV), is a member of the Aphtovirus genus of the Picornaviridae family, and contains a single-stranded positive-sense RNA genome of about 8 500 nucleotides [5]. FMDV shows high genetic and antigenic variability, which is reflected in the seven serotypes and multiple subtypes reported to date [6]. In the field, this heterogeneity is reflected by the lack of cross-protection even between intraserotype variants [7]. Disease control is achieved by vaccination with chemically inactivated whole-virus vaccine that only provides short-
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