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Title: Detection of Foot-and-Mouth Disease Virus RNA and capsid protein in lymphoid tissues of convalescent pigs does not indicate existence of a carrier state

Author
item STENFELDT, CAROLINA - Oak Ridge Institute For Science And Education (ORISE)
item Pacheco Tobin, Juan
item Smoliga, George
item Bishop, Elizabeth
item Pauszek, Steven
item Hartwig, Ethan
item Rodriguez, Luis
item Arzt, Jonathan

Submitted to: Transboundary and Emerging Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2014
Publication Date: 6/18/2014
Citation: Stenfeldt, C., Pacheco Tobin, J., Smoliga, G.R., Bishop, E.A., Pauszek, S.J., Hartwig, E.J., Rodriguez, L.L., Arzt, J. 2014. Detection of Foot-and-Mouth Disease Virus RNA and capsid protein in lymphoid tissues of convalescent pigs does not indicate existence of a carrier state. Transboundary and Emerging Diseases. DOI: 10.1111/tbed.12235.

Interpretive Summary: A systematic study was performed to investigate if pigs could function as long-term carriers of Foot-and-Mouth Disease Virus (FMDV). After examination of 51 pigs infected with 1 of 5 strains of FMDV, infectious virus could not be detected in serum or oral or nasal secretions after the clinical signs of disease had disappeared. Furthermore, live virus was not detected in tissue samples obtained at 35-100 days after infection from pigs that had recovered from the disease. Despite lack of detection of live virus, viral degradation products consisting of genome fragments (RNA) and structural proteins could be detected in select lymph nodes harvested at 35 days after infection. This detection of viral remnants declined markedly by 60 days after infection, and was completely absent at 100 days post infection. The data obtained from this study provides the most extensive investigation of FMDV persistence in pigs. The overall conclusion is that domestic pigs are unlikely to carry infectious FMDV for prolonged periods after recovery from clinical disease. It is, however, possible to detect certain viral degradation products in lymph nodes during a limited period of time in pigs that have recovered from FMD.

Technical Abstract: A systematic study was performed to investigate the potential of pigs to maintain persistent Foot-and-Mouth Disease Virus (FMDV) infection. Infectious virus could not be recovered from sera, oral, nasal- or oropharyngeal fluids obtained after resolution of clinical infection with FMDV serotypes A, O or Asia-1. Furthermore, there was no isolation of live virus from tissue samples harvested at 35-100 days post infection from convalescent pigs recovered from clinical FMD, or from pigs that had been subclinically infected following vaccination and challenge. Despite lack of detection of infectious FMDV, there was a high prevalence of FMDV RNA detection in lymph nodes draining lesion sites harvested at 35 days post infection, with the most frequent detection recorded in popliteal lymph nodes (positive detection in 88% of samples obtained from non-vaccinated pigs). Likewise, at 35 dpi, FMDV capsid antigen was localized within follicles of draining lymph nodes, but without concurrent detection of FMDV non-structural protein. There was a marked decline in detection of FMDV RNA and antigen in tissue samples by 60 dpi, and no antigen or viral RNA could be detected in samples obtained at 100 dpi. The data presented herein provides the most extensive investigation of FMDV persistence in pigs. The overall conclusion is that domestic pigs are unlikely to be competent long term carriers of infectious FMDV; however, transient persistence of FMDV degradation products in lymphoid tissues is common following clinical infection.