by Sally Colby
When a serious disease breaks in a foreign country, people tend to think “That won’t happen here.” But when COVID-19 emerged and threatened the U.S., that thinking quickly changed. During the 2001 foot and mouth disease (FMD) outbreak in the UK, images of livestock being tossed into pits drew U.S. farmers closer to the reality of dealing with a highly contagious viral livestock disease.
“Foot and mouth disease is considered the most highly contagious viral disease of cloven-hooved livestock and wildlife throughout the word,” said Dr. Danelle Bickett-Weddle, Iowa State University College of Veterinary Medicine. “It’s the disease, above all, that limits world trade among countries of animals and animal products.” Although FMD is a serious issue for livestock, the disease is not considered a public health or food safety concern.
FMD is currently active in about two-thirds of the world’s countries. Bickett-Weddle said 66 countries are free of FMD, but many have never been free of the disease. Canada dealt with FMD in 1952, and it was discovered in Mexico in 1954.
“The U.S. has not had an outbreak since 1929,” said Bickett-Weddle. “That’s a long time ago, but it’s the consequences, if it were to ever come to the United States, that we’re concerned about.” To that end, the USDA has initiated rigid strategies to prevent the disease from entering the country and a clear plan of action if it does.
Any cloven-hooved animal can be affected by FMD, including sheep, goats, swine and cattle. Deer, elk, wild pigs and other cloven-hooved wild animals are also susceptible, but Bickett-Weddle said foot lesions cause pain and reluctance to move, thus controlling the spread.
FMD doesn’t cause death in adult animals, but causes severe lameness, mouth sores and teat lesions. However, mortality is high in young animals, especially with certain viral strains.
Sheep are considered the maintenance host for FMD. “They can spread it silently because they don’t show obvious clinical signs,” said Bickett-Weddle. “Swine are amplifying hosts – they’re viral factories – so once the virus gets in the swine population, they can produce millions of infective doses every day.”
Cattle are the most seriously and visibly affected, and are often the first species to exhibit clinical signs. Bickett-Weddle said if cattle and sheep are comingled, cattle would show clinical signs while sheep would not. Cattle carry the virus for up to six months, and some may remain infected for up to 3.5 years. Sheep can carry the virus for up to 12 months.
FMD spreads in several ways, including aerosol, direct contact, fomites and oral contact. Animals shed the virus in bodily excretions such as milk, saliva, feces and urine. FMD infects an uninfected animal through direct contact with fluid from ruptured vesicles – the blisters on the feet and mouth.
The USDA’s goal in managing any foreign animal disease is to detect, control and contain the disease as quickly as possible, with the ultimate goal of eradication. Since FMD is so highly contagious and has serious consequences for several livestock species, the U.S. has a plan of action if the disease is detected here. The plan is outlined in USDA’s Red Book, available on the USDA website, which includes steps to facilitate continuity of business for non-infected animals and products.
Part of the plan includes “stop movement” and the 72-hour National Movement Standstill that was initiated in previous North American outbreaks. Bickett-Weddle compared stopping animal movement to stopping human movement in the early days of COVID-19 – a challenge that’s close to impossible to achieve. “The goal is no new movement of livestock for a period of time,” she said. “Right now, the proposal is 72 hours.” During that time, officials locate new infections and conduct early traceability to detect, control and contain.
Once FMD is verified, movement in or out of the area is by permit only. Permits are issued on a risk basis, with live animals considered higher risk. The USDA’s Secure Food Supply Plan guides business continuity for affected (not infected) premises. Business continuity planning minimizes the unintended negative effects of disease and disease response during control and eradication efforts.
“Traceability is huge,” said Bickett-Weddle. “We need to keep track for our trading partners because we are FMD-free without vaccination, which is the highest category possible from a trade perspective. Once vaccinated, animals are traced until death.”
Biosecurity is critical when dealing with FMD, from initial suspicion to waiting for test results and initiating control measures. “Trace back and trace forward becomes important in foreign animal diseases,” said Bickett-Weddle. “The OIE [Office International des Epizooties, the world organization for animal health] states that the incubation period for FMD is 14 days. When we talk about tracing, we look at two incubation periods – 28 days. Where were animals, where were people, where was movement happening? We need to go back that far in time to figure out the epidemiology – how the disease is spreading.”
Plans for handling a foreign animal disease should be included in every farm’s management plan. Bickett-Weddle suggested resources such as a contingency planning document that outlines inventory and movements, financial planning, enhanced biosecurity, communication, sheep health and managing inputs (feed) and outputs (products).
Routine biosecurity is insufficient with such a highly contagious disease, so Bickett-Weddle suggested appointing a biosecurity manager to develop a written, operation-specific enhanced biosecurity plan – even for small operations. The plan should include designating lines of separation – borders that cannot be crossed. Outline biosecurity steps for equipment, people and vehicles. Be mindful that farm trucks, ATVs, herding dogs and livestock guardian dogs can complicate biosecurity on pasture-based operations.
Secure Sheep and Wool, developed in 2019-2020, is one segment of the FMD response plan and is built on the risk assessment and guidelines in other species’ plans. The plan was funded by the American Sheep Industry Association (ASI).
Killed vaccines play a role in managing FMD. Bickett-Weddle said six of the seven FMD serotypes are currently active in the world. Vaccines are not cross-protective, so a vaccine must be specific to the serotype in the outbreak. With 65 additional virus subtypes, nailing down the exact vaccine can be challenging. Cattle are the most vaccinated species worldwide, followed by pigs. Sheep are not commonly vaccinated – if the disease is controlled in the cattle population, sheep don’t need it.
While the FMD vaccine is the most used vaccine worldwide, Bickett-Weddle said it isn’t currently available or used in the U.S. “We’d have to isolate the virus, identify the serotype then select the correct vaccine,” she said. “It’s for strategic use if we were to get FMD in the U.S., and USDA decides how and if it will be used. Biosecurity and movement control are essential in an outbreak because it will take a while to get vaccine to where it’s needed.”
Bickett-Weddle said producers make risk management decisions regarding disease prevention and are responsible for keeping animals free from infection. “What changes in an FMD outbreak is that state and federal officials are responsible for protecting the health of animals,” she said. “Their goal is to prevent spread.”
Secure Sheep and Wool Supply information is available at securesheepwool.org.