By Reneé D. Dewell DVM, MS; Molly J. Lee, DVM Center for Food Security & Public Health, Iowa State University
While not a human (public) health concern, Foot and Mouth Disease (FMD) is the most contagious disease of livestock with cloven hooves, such as cattle, sheep, goats, and pigs. The virus rarely kills adult animals, it causes fever and painful blisters in/on an infected animal’s mouth, muzzle, feet and teats, often resulting in dramatic loss in feed intake, weight gain, body condition, and milk production. Foot and Mouth Disease is the most important disease restricting global trade of animals and animal products, and presents the greatest economic threat to U.S. animal agriculture, with devastating economic impacts extending far beyond animal agriculture. Agriculture is critical infrastructure in the U.S. Cash receipts for livestock and poultry often exceed $100 billion per year. The size, structure, efficiency, and extensive movement within and between states that is inherent in the United States livestock industry will present unprecedented challenges in the event of an FMD outbreak. No country with a livestock industry comparable to that of the U.S. has had to deal with an outbreak of FMD. This article will introduce the potential role of vaccination in a response to an FMD outbreak in the U.S. and will describe some challenges associated with FMD vaccination.
There is no treatment for Foot and Mouth Disease. Historically, control has consisted of quarantining herds, testing animals for disease presence, and killing and disposal of positive herds. This practice, called “depopulation” or “stamping out” is still a useful emergency procedure to control and contain the virus. However, the U.S. has some very large herds including feedlots with greater than 50,000 head of cattle, dairies with greater than 5,000 lactating cows, dairy calf ranches with greater than 70,000 head of calves (between 1 day and 4 months of age), and swine farms with greater than 20,000 sows. These premises are too large to rapidly depopulate to stamp out the disease. If it were possible to depopulate them, carcass disposal would present enormous environmental problems. Stamping out may still be used as part of an FMD outbreak response, especially if the outbreak is a small, localized outbreak. Responding agencies may employ a variety of strategies depending on the circumstances of the outbreak. The use of vaccination against FMD is likely to play a part in a larger FMD outbreak response.
Benefits of Vaccination in an FMD Outbreak
In an FMD outbreak involving a moderate or large number of animals, the rapid use of tens of millions of doses of FMD vaccine will likely be necessary to effectively respond to the outbreak.
Vaccine has been used in other countries to control and eradicate FMD. There can be significant advantages to including FMD vaccination as part of a response. For example, in the 2001 FMD outbreak in Uruguay, a very successful country-wide vaccination program was instrumental in controlling and containing the FMD virus. Cattle are usually considered to be a high priority for emergency FMD vaccine use. If the disease is under control in cattle, most FMD virus strains should not persist in other species.
Vaccination can reduce the number of herds requiring depopulation (thus reducing the costs and environmental impacts associated with disease eradication and carcass disposal) and reduce economic losses to the industry. Foot and Mouth Disease vaccination can reduce, and may eliminate clinical disease and can increase resistance to infection. Finally, because it reduces virus shedding, vaccination may slow the spread of the outbreak and allow responding agencies to stop the spread of the disease more quickly.
Without sufficient FMD vaccine, FMD could rapidly spread across the U.S. and prolong the length of time to eradicate an FMD outbreak. The FMD virus could potentially spread to deer and feral swine and prolong the problem. If an FMD outbreak is not eradicated quickly, it would then require a much more extensive control program and could take many years to eradicate.
There is clear desire on the part of many emergency management personnel to be able to use vaccination as part of the response to FMD. Rapid availability of large amounts of vaccine is very important for controlling an FMD outbreak. In a study designed to estimate vaccination needs for an FMD outbreak in Minnesota, large scale vaccination (1,500 herds per day) reduced the size and duration of the outbreak if initiated within 21 days of the start of the outbreak.1
Challenges of FMD Vaccination
Some stakeholders wonder why the U.S. cattle herd is not routinely vaccinated against FMD to reduce the negative effects if this virus were introduced in our country. After all, if the vaccine is a good tool to use to help control disease outbreaks when they happen, why aren’t we using it before an outbreak occurs? Perhaps like we use calf-hood vaccination to prevent Brucellosis or pre-breeding vaccines in swine? A major challenge of FMD vaccination is the complexity in selecting “which one” of the FMD vaccines should be used. There are more than 65 different strains of the FMD virus in seven different groups or serotypes, with very limited cross-protection between vaccine strains.
Approximately 23 different vaccines would be needed to provide protection against all strains. Vaccine protection is short-lived and vaccination would need to be repeated every 6 to 12 months to be protective. The cost to producers of repeated vaccination for multiple strains would be enormous!
Foot and Mouth Disease vaccination is not permitted by USDA-APHIS as an option for routine, pre-outbreak use, and as a result, the U.S. enjoys “FMD-free without vaccination” status, a highly favored trade status that would be lost with the use of FMD vaccination. The use of FMD vaccine when there is no FMD outbreak in the U.S. would result in significant trade restrictions to U.S. exports, potentially resulting in annual losses of up to $6 billion to the beef industry.
Additionally, while vaccination against FMD increases disease resistance and reduces clinical disease and virus shedding, some vaccinated animals may still become infected with FMD. No vaccine is 100 percent effective in protection against infection. Some vaccinated, but FMD-infected animals may look healthy, and yet still be carrying the virus.
The amount of vaccine needed will depend on the extent of the outbreak, and whether the goal is rapid eradication or implementing a control program. Unfortunately, the amount of vaccine available to the U.S. during an FMD outbreak is far below what would be needed to provide vaccine for even a single livestock dense state. A U.S. outbreak of FMD could quickly outstrip even the world’s supply of emergency FMD vaccine. For example, an FMD outbreak in South Korea depleted the banks of FMD vaccines from around the world in order to vaccinate a population roughly half the size of the livestock population in Iowa. Insufficient vaccination capacity limits the ability of the US to be able to effectively respond with a vaccination strategy should that be the response choice made by USDA.
The U.S. currently has very limited quantities of vaccine that may be available during an outbreak. The USDA has recognized the need for a larger stockpile of FMD vaccine for emergency use. However, development of an adequate FMD vaccine stockpile would be expensive. The USDA lacks the funding to develop an adequate stockpile. It would take many months to obtain the volume of FMD vaccine needed to effectively respond to a large FMD outbreak.
Actions the Beef Community Can Take
The need for additional supplies of FMD vaccine, as well as new vaccine approaches and technologies, to help meet this need has been recognized by USDA and other government entities. USDA APHIS has funded the development of Secure Food Supply Plans that incorporate the use of FMD vaccine as an important control tool. The USDA is collaborating with state officials and all segments of the livestock industries to develop plans to help protect your herds and businesses from foreign animal disease outbreaks such as FMD. As members of the beef community, you should consider benefiting from participation in the voluntary Secure Beef Supply plan, which emphasizes biosecurity—consistently and carefully implemented—as the most effective way to protect your herd before, during, and after an outbreak.