Foot-and-mouth disease (FMD) virus spreads much more aggressively in pigs than previous research suggests, according to new USDA research published in Scientific Reports. Pigs infected with the FMD virus were highly contagious to other pigs just 24 hours after infection and before showing any clinical signs of infection, such as fever or blisters.
Although African swine fever may be stealing the headlines right now, foot-and-mouth disease continues to be the most important foreign disease of livestock worldwide.
Prior to this research, people believed that transmission of FMD occurred after visible signs of sickness. This research is a game-changer for infectious disease experts, who use this information to provide the right data and guide the resources to protect livestock against foreign animal diseases (FADs) if there is an outbreak.
Recently, a variety of disease-dynamics models have helped identify critical targets for control efforts, predict impacts and estimate resource requirements for specific outbreak scenarios for FMD, says Jonathan Arzt, lead investigator and veterinary medical officer with USDA’s Agricultural Research Service. However, none of these models included the impact of preclinical transmission.
Using a mathematical modeling approach, Artz’s team worked with scientists at the Center for Epidemiology and Animal Health in USDA’s Animal and Plant Health Inspection Service, to estimate the occurrence of FMD preclinical transmission. They discovered that disease transmission occurred approximately one day prior to development of visible signs of disease.
FMD’s Potential Impact on the U.S.
They took this information and incorporated it into a second model that simulates disease spread. The results showed that simulation of FMD outbreaks in the U.S. pig production sector, including a preclinical infectious period of one day, would result in a 40% increase in the number of farms affected.
Artz explains this equates to 166 additional farms and more than 664,000 pigs euthanized compared to the existing scenario of no preclinical transmission.
Although the U.S. has not had an FMD outbreak since 1929, this highly contagious, sometimes fatal, viral disease is still considered a serious threat to U.S. agriculture, Artz says. If FMD is introduced into FMD-free countries like the U.S., it could cost billions of dollars in losses to the economy from trade bans and eradication, which often includes euthanasia of a huge number of affected animals.
Arzt, who works in ARS’s Foreign Animal Disease Research Unit at the Plum Island Animal Disease Center in Orient Point, N.Y., says infectious disease modeling is a critical part of preparedness and protection of U.S. livestock.