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

Abstract

A systematic study was performed to investigate the potential of pigs to establish and 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 any of five FMDV strains within serotypes A, O and Asia-1. Furthermore, there was no isolation of live virus from tissue samples harvested at 28-100 days post-infection from convalescent pigs recovered from clinical or subclinical FMD. 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 the 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 provide 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 protein and RNA in lymphoid tissues is common following clinical or subclinical infection.

Differential Persistence of Foot-and-Mouth Disease Virus in African Buffalo Is Related to Virus Virulence

“…Similarly, FMDV has successfully been isolated from lymphoid tissues from carrier sheep and cattle (50,51). Our results, and previously reported data for competent carrier species, are contrary to thorough VI data reported for pigs: no virus could be isolated from 1,140 tissue samples harvested at 28 to 100 dpi despite viral RNA and capsid protein persisting in lymphoid tissue GCs (52). Viral RNA and protein localization after the resolution of viremia in cattle has also been described; similar to the swine data, FMDV RNA and capsid protein were restricted to GCs in animals with negative OPF, and no signal was detected in the epithelium (22).…”

“…Viral RNA and protein localization after the resolution of viremia in cattle has also been described; similar to the swine data, FMDV RNA and capsid protein were restricted to GCs in animals with negative OPF, and no signal was detected in the epithelium (22). FMDV nonstructural proteins were not detectable in lymphoid or oropharyngeal tissue in pigs and noncarrier cattle (22,52). In contrast, during FMDV persistence in cattle, cells containing nonstructural proteins have been detected in pharyngeal tissue within the epithelium and subjacent lymphoid tissue (21).…”

“…The retention of virus on follicular dendritic cells (FDCs) may play a key role in the delayed clearance in vivo. Our data, in addition to data from reported previously for cattle, sheep, and pigs, may represent a juncture in understanding FMDV persistence (22,23,52). Clearly, trapping of viral protein and RNA within lymphoid tissue follicles is a common sequel to infection, even in species, such as pigs, in which the carrier state has not been described.…”

“…Therefore, there is a progressive reduc- tion in virus titers over time, consistent with a delayed clearance despite the induction of high titers of neutralizing antibodies soon after initial infection and antibody titers increasing significantly after 35 dpi, probably due to constant antigenic boost. Similarly, Stenfeldt et al (52) reported declines in FMDV RNA and antigen levels in porcine tissue over time, with clearance being reported by 100 dpi, and in addition, viral RNA was cleared from OPF and tonsil swab samples. The retention of virus on follicular dendritic cells (FDCs) may play a key role in the delayed clearance in vivo.…”

Investigation of foot-and mouth disease outbreak in a pig farm at Kollam district of Kerala, India

“…In other way, it clearly depicts that the virus is inter-transmissible between species; however, the direction of infection / transmission dynamics could not be conclusively traced out. Though pigs are highly susceptible to FMD, they do not become carriers (Kitching et al, 2005;Lubroth et al, 2006;Stenfeldt et al, 2016). However, an infected pig being powerful emitter of airborne FMDV can liberate up to 10 8.6 TCID 50 of virus (about 3000 times as much as cattle) during a 24 hour period Donaldson, 1999;Geering and Lubroth, 2002).…”