Transmission of Foot-and-Mouth Disease Virus during the Incubation Period in Pigs

Abstract

Understanding the quantitative characteristics of a pathogen’s capability to transmit during distinct phases of infection is important to enable accurate predictions of the spread and impact of a disease outbreak. In the current investigation, the potential for transmission of foot-and-mouth disease virus (FMDV) during the incubation (preclinical) period of infection was investigated in seven groups of pigs that were sequentially exposed to a group of donor pigs that were infected by simulated-natural inoculation. Contact-exposed pigs were comingled with infected donors through successive 8-h time slots spanning from 8 to 64 h post-inoculation (hpi) of the donor pigs. The transition from latent to infectious periods in the donor pigs was clearly defined by successful transmission of foot-and-mouth disease (FMD) to all contact pigs that were exposed to the donors from 24 hpi and later. This onset of infectiousness occurred concurrent with detection of viremia, but approximately 24 h prior to the first appearance of clinical signs of FMD in the donors. Thus, the latent period of infection ended approximately 24 h before the end of the incubation period. There were significant differences between contact-exposed groups in the time elapsed from virus exposure to the first detection of FMDV shedding, viremia, and clinical lesions. Specifically, the onset and progression of clinical FMD were more rapid in pigs that had been exposed to the donor pigs during more advanced phases of disease, suggesting that these animals had received a higher effective challenge dose. These results demonstrate transmission and dissemination of FMD within groups of pigs during the incubation period of infection. Furthermore, these findings suggest that under current conditions, shedding of FMDV in oropharyngeal fluids is a more precise proxy for FMDV infectiousness than clinical signs of infection. These findings may impact modeling of the propagation of FMD outbreaks that initiate in pig holdings and should be considered when designing FMD control strategies.

Foot-and-Mouth Disease Infection Dynamics in Contact-Exposed Pigs Are Determined by the Estimated Exposure Dose

“…The analyses presented herein are based on data derived from a series of three complementary experimental studies, defined herein as Study A, B, and C (Table 1 ) ( 8 , 23 , 24 ). These studies were originally designed for the purpose of investigating FMDV pathogenesis and transmission in pigs, with minor variation in study design across experiments.…”

“…Study C (Table 1 ) was designed to determine the transition from latent to infectious phases in IOP inoculated pigs ( 23 ). A previous publication based on this study provided descriptive analyses of FMDV infection dynamics following contact-exposure, and demonstrated that transmission of FMDV occurred prior to the onset of clinical signs.…”

“…The progression of clinical FMD was monitored through clinical examinations during which a standardized cumulative scoring system was used to assess appearance and dissemination of characteristic (vesicular) FMD lesions ( 23 ).…”

Review of Seneca Valley Virus: A Call for Increased Surveillance and Research

“…Whether cattle, wild cloven-hoofed animals or mice are directly infected by SVV or not, is still unknown. FMDV, another picornavirus that also affects pigs and causes similar vesicular disease, spreads by direct contact or exposure to aerosolized virus, and it also affects various wild cloven-hoofed animals ( Rweyemamu et al, 2008 ; Stenfeldt et al, 2016 ). However, many aspects of SVV infection characteristics, host range, and epidemiology remain unknown.…”

Horizontal transmission of foot‐and‐mouth disease virus O/JPN/2010 among different animal species by direct contact

“…Infectiousness in FMDV‐inoculated pigs starts 24 hr after inoculation but before the first clinical signs of viremia appear (Stenfeldt, Pacheco, et al, ). In contrast, FMDV‐inoculated cattle are not infectious until on average 0.5 days after clinical signs appear (Charleston et al, ) although virus shedding also occurs during pre‐clinical and early recovery stages (Nelson et al, ; Orsel et al, ).…”