Submitted to: The Veterinary Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2012
Publication Date: 8/1/2012
Citation: Pacheco Tobin, J., Tucker, M.T., Hartwig, E.J., Bishop, E.A., Arzt, J., Rodriguez, L.L. 2012. Direct contact transmission of three different foot-and-mouth disease virus strains in swine demonstrates important strain-specific differences. The Veterinary Journal. 193(2):456-463.
Interpretive Summary: Foot-and-mouth disease (FMD) is a highly contagious viral disease affecting domestic and wild cloven-hoofed animals. Pigs are excellent viral amplifiers of foot-and-mouth disease virus (FMDV) and play an important role in the airborne transmission and spread of FMDV to other species and among different premises. Thus, protection of pigs either by vaccination or antiviral therapy could be essential to control FMD outbreaks. Currently the international standard challenge method for pigs consists of direct virus inoculation in the foot. This method results in clinical disease in most cases, but it bypasses many of the important defense mechanisms during the viral infection and could also overwhelm vaccine-induced immune responses. A direct contact transmission method would be a more natural way of FMD transmission to pigs. However, vaccine trials using direct contact often fail due to either overwhelming or not enough exposure to challenge virus. In this study, we have established a consistent contact exposure methodology in pigs for two different strains of FMDV. Each strain required a different exposure time, but an 18 hour exposure time was sufficient for both strains. This controlled virus challenge methodology will help in the development of better vaccines, antiviral therapies, and other control measures in pigs.
Technical Abstract: A novel direct contact transmission model for the study of foot-and-mouth disease virus (FMDV) infection of swine was utilized to investigate transmission characteristics of three FMDV strains belonging to serotypes A, O and Asia1. Each strain demonstrated distinct transmission characteristics and required different exposure times to achieve successful contact transmission. While a 4 h exposure was sufficient for strain A24 Cruzeiro (A24Cru), both O1 Manisa and Asia1 Shamir transmission required 18 h or more. Viral excretion levels from donors (for all three strains) and virus present in room air (for A24Cru and O1 Manisa) were evaluated and associated with clinical signs and observed transmission pattern. Although all directly inoculated donor animals showed acute FMD, A24Cru had the highest levels of viral shedding in saliva and nasal swabs followed by O1 Manisa and Asia1 Shamir. Virus levels in room air were higher and were detected longer for A24Cru than for O1 Manisa. These results provide direct evidence for important strain-specific variation in transmission characteristics and emphasize the need for thorough evaluation of different FMDV viral strains using a well defined contact transmission methodology. This information is critical for vaccine and biotherapeutic efficacy testing, pathogenesis and disease modeling of FMDV transmission.