The goal of this study was to characterize the properties and duration of the foot-and-mouth disease (FMD) carrier state and associated serological responses subsequent to vaccination and naturally occurring infection at two farms in northern India. Despite previous vaccination of cattle in these herds, clinical signs of FMD occurred in October 2013 within a subset of animals at the farms containing juvenile-yearling heifers and steers (Farm A) and adult dairy cattle (Farm B). Subsequent to the outbreak, FMD virus (FMDV) asymptomatic carriers were identified in both herds by seroreactivity to FMDV non-structural proteins and detection of FMDV genomic RNA in oropharyngeal fluid. Carriers’ seroreactivity and FMDV genome detection status were subsequently monitored monthly for 23 months. The mean extinction time of the carrier state was 13.1 ± 0.2 months, with extinction having occurred significantly faster amongst adult dairy cattle at Farm B compared to younger animals at Farm A. The rate of decrease in the proportion of carrier animals was calculated to be 0.07 per month. Seroprevalence against FMDV non-structural proteins decreased over the course of the study period, but was found to increase transiently following repeated vaccinations. These data provide novel insights into viral and host factors associated with the FMDV carrier state under natural conditions. The findings reported herein may be relevant to field veterinarians and governmental regulatory entities engaged in FMD response and control measures.
Bibliographical noteFunding Information:
This work was funded by the Indian Council of Agricultural Research, New Delhi. Additional funding was provided by the United States Department of Agriculture (USDA) Agricultural Research Service (ARS) Project 1940-32000-057-00D, the United States Department of State’s Biosecurity Engagement Program through the USDA-ARS Office of International Research Programs and a specific collaborative agreement between USDA-ARS and University of Minnesota. CS is a recipient of Plum Island Animal Disease Center Research Participation Program fellowship, administered by the Oak Ridge Institute for Science and Education through an inter-agency agreement with the US Department of Energy. The funding sources had no role in study design, data collection and analysis or the decision to publish the work.
United States Department of State, Biosecu-rity Engagement Program through the USDA-ARS Office of International Research Programs; Indian Council of Agricultural Research; United States Department of Agriculture (USDA); Agricultural Research Service, Grant/Award Number: 1940-32000-057-00D; University of Minnesota.