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

Carolina Stenfeldt,Jonathan Arzt,Amy H Delgado,Juan M Pacheco,Barbara P Brito,Matt A Branan,Luis L Rodriguez,Karla I Moreno-Torres

doi:10.3389/fvets.2016.00105

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.

Highlights

Foot-and-mouth disease (FMD) is a highly contagious and economically devastating disease that affects cloven-hoofed animal species
Fifteen pigs were inoculated with foot-and-mouth disease virus (FMDV) A24 Cruzeiro using a simulated-natural system of IOP deposition in order to estimate the parameters of incubation and latency, by determining onset of clinical disease and FMDV shedding
The highly contagious nature of FMDV can be attributed to a combination of factors including broad host range, low infectious dose, and shedding of large quantities of virus by infected animals [3, 4, 42, 43]

Summary

Introduction

Foot-and-mouth disease (FMD) is a highly contagious and economically devastating disease that affects cloven-hoofed animal species. FMD-associated mortality rates among adult animals are generally low, the intensive countermeasures enacted to combat disease outbreaks in FMD-free countries often result in depopulation and destruction of large numbers of infected and susceptible animals [5,6,7]. Large regions of the world, including Europe, Australia, North America, and parts of South America, are kept free of FMD by means of strict regulations on import of animals and agricultural products. Animal populations within these regions where prophylactic vaccination is not practiced are highly vulnerable to potential FMDV incursions due to the lack of herd immunity. There are substantial ethical and environmental concerns associated with depopulation of large numbers of animals for the purpose of controlling potential FMD outbreaks

Methods

Results

Conclusion