Editor's note: The following editorial was originally featured in the July-August issue of Bovine Veterinarian, available here.
Our lead feature this month focuses on the Secure Milk Supply program, which intends to protect the continuity of the U.S. dairy business in case of an outbreak of foot-and-mouth disease (FMD). Intertwined with the issue of a secure milk supply, and secure pork and beef supplies, is the question of FMD vaccination and how various vaccination strategies might apply within outbreak scenarios.
James Roth, DVM, PhD, DACVM, director of Iowa State University’s Center for Food Security and Public Health (CFSPH), has defined six types of potential FMD outbreaks, ranging from Type 1, a focal outbreak, to Type 6, a catastrophic North American outbreak, with the type of outbreak influencing the appropriate response strategies. At the lower end of the scale, such as a Type 1 outbreak, the response likely would focus on stamping out, or culling all infected or exposed animals in the affected zone. But as the outbreak spreads to a larger regional or national scale, stamping out becomes unrealistic, and the response would shift toward alternative strategies including vaccination.
Experience from past FMD outbreaks, particularly one in Uruguay in 2001, shows that early response with an emphasis on large-scale vaccination is a viable strategy. During that outbreak, says Pam Hullinger, DVM, MPVM, DACVPM, an epidemiologist at the University of California-Davis, fewer than 7,000 animals were slaughtered, and the direct costs of the outbreak totaled $13 million. In contrast, a similar outbreak in the United Kingdom that same year, where the response focused on stamping out, about 10 million animals were slaughtered and costs reached an estimated $4.6 billion.
However, large-scale vaccination presents numerous challenges. There are seven FMD serotypes and more than 65 strains. Vaccines offer no known cross protection between serotypes and limited cross protection between strains. Hullinger explains that vaccination reduces an animal’s susceptibility to infection and, if infected, the amount of viral shedding and clinical signs, but it does not always prevent infection and does not prevent development of a carrier state in cattle.
Federal law currently prohibits introduction of live FMD virus for any purpose into the mainland of the United States, meaning there is no conventional, killed-virus FMD vaccine production, which requires live FMD virus, in the United States. The North American FMD Vaccine Bank, shared by the United States, Canada and Mexico, serves as an antigen bank, and during an outbreak, vaccines would need to be formulated based on targeted FMD serotypes. USDA also has evaluated commercial vaccines from international sources, and import of these products offers another alternative.