Foot and mouth

  • Published 2001 in Nature Immunology

Abstract

It has been a difficult year for the British Ministry of Agriculture, Fisheries and Food (MAFF). The foot and mouth disease (FMD) virus has been but the latest infectious agent to wreak havoc with Britain’s livestock industry (BSE was pushed out of the headlines as this new crisis developed). Over 3.3 million animals have been slated for disposal so far in the attempt to eradicate the infectious agent. Because of national and European Union laws designed to ensure a virus-free zone (although there have also been outbreaks in France, the Netherlands and Ireland), outbreaks are dealt with by killing susceptible livestock on the same farm as well as neighboring herds, so called “ring” culling, after an infected animal is detected. Many more animals than those infected must be culled to prevent fast viral spread. The economic costs go beyond the woes of individual farmers—if losses to the tourism industry in the UK are factored in, the current outbreak is estimated to have cost over £12 billion ($16.5 billion). An immunologist’s first question was probably why haven’t susceptible animals been vaccinated as a prophylactic measure against such a menace? Scientific, political and economic reasons lie behind this. Current vaccines are limited in scope and the FMD virus has seven types and more than 60 subtypes. Most infections this Spring were from a virulent O, or Pan-Asian, serotype that is especially prevalent in sheep—animals that can be infected without noticeable signs. Immunization with the current vaccine of chemically inactivated O-serotype virus protects most, but not all, exposed livestock and it is not equally effective in all species. Ensuring that no animal carries the virus would entail an expensive biannual vaccination program that correctly anticipates the subtype threat (unless a subunit vaccine were developed that included epitopes from multiple types and subtypes and that didn’t select for antigenic variants). The virus infects ungulates, including those in the wild such as deer, so no country can effectively vaccinate all suitable hosts. With current vaccines, some immunized animals exposed to the virus can still act as carriers, without ever exhibiting signs of the disease. In reality, improved vaccines and immunization protocols would prevent this suspected carrier state from being a major factor in disease transmission, but this takes large investments in veterinary immunology and vaccine development. Countries like Germany and others cancelled their vaccination programs in the early 1970s when the enormous costs were calculated. A major concern with vaccination is the difficulty in differentiating between vaccinated and virus-exposed animals. In other livestock diseases, such as pseudorabies, “marker” vaccines are available with incomplete gene sets, making them easily discernable from the natural infection. FMD infection, however, is initially detected by the presence of antibodies to viral proteins, with newer ELISAs able to detect nonstructural proteins, which are not present in vaccines. At this time, the Agricultural Research Service of the US Department of Agriculture (USDA) is also developing portable PCR technology, for on-site detection of viral nucleic acids that could differentiate between the FMD serotypes and viruses such as swine vesicular disease virus and vesicular stomatitis virus. This Internet-enabled system would provide accurate diagnoses in less than two hours and eliminate confusion over vaccine versus infection. However, the timetables for availability and acceptance as an assay for virus-free status are not clear. “Virus-free” status cannot be accorded to a country that vaccinates all of its livestock prophylactically. And without virus-free status, import to international markets that are themselves FMD-free is denied. With most governments making it clear that they will not prophylactically vaccinate for fear of then being unable to reconfirm their FMD-free status, the market for improved vaccines is small and the pharmaceutical industry has little incentive to invest in the necessary research to improve them. Of course, given the current system of regulations, it is far more likely that vaccination be used as a “firebreak”, as was recently done in the Netherlands, in an attempt to prevent their outbreak from spreading. However, the vaccine takes about 8–14 days to provide protection and, if not administered at the first sign of infection, its ability to contain the outbreak lessens. Its use in conjunction with ring culling is a combination that should become standard in future outbreaks. The current vaccination and control procedures for maintaining livestock health reflect the low priority of animal health on national agendas. Funding for veterinary research lags far behind that for biomedical research. In Germany, for instance, the funding of medical institutes in Berlin alone exceeds that of all veterinary faculties. In the US, only about 15% of USDAfunded research focuses on livestock. Developed nations have grown complacent with their abundant and seemingly safe food supply over the past three decades. As the present situation indicates, however, increased research funding devoted to the immunology and health of our animals is necessary to better detect, protect and defend them from emerging and re-emerging microbial threats. EDITORIAL

DOI: 10.1038/89700

Cite this paper

@article{2001FootAM, title={Foot and mouth}, author={}, journal={Nature Immunology}, year={2001}, volume={2}, pages={565-565} }