Emerging Animal Diseases: Global Markets, Global Safety: Workshop Summary (2002)

In the last two decades, two major animal disease outbreaks have emerged in the United Kingdom. The outbreak of BSE, or “mad cow disease,” which began in the United Kingdom in 1986, has infected about 200 thousand cattle and has led to the preemptive slaughter and destruction of 4.5 million. The foot-and-mouth disease (FMD) epidemic in the United Kingdom last year led to the eradication of 4 million livestock. While FMD is extremely contagious and harmful to livestock, there is little risk to human health. However, exposure to BSE has been linked to a growing number of cases of variant Creutzfeldt-Jakob Disease (vCJD) in humans (See Box 2-1 for a description of FMD and BSE).

Given the global nature of animal disease and food safety in the twentyfirst century, Professor David King, the Chief Scientific Adviser to the British Government and Head of the Office of Science and Technology, was called upon to share insights gained from the recent British FMD outbreak. King began by describing foot-and-mouth disease as a highly infectious, viral disease that causes fever and vesicles around the mouth and the feet in cloven-hoofed animals. It is an unpleasant and painful disease, can be sometimes fatal to young animals, and has serious impact on productivity. Although it is possible to keep foot-and-mouth disease out of a country with tight import controls, King noted

that 35 countries have declared outbreaks of foot-and-mouth disease around the world over the last couple of years. An outbreak can have significant impact on international trade for up to two years after the country is declared disease free, based on the disease-free standards set by the Office of International Epizootics (OIE), the “World Health Organization” of animal diseases.

By the time the first case of FMD was reported to British public officials

on February 20, 2001, the disease had already had more than three weeks to spread. This time lapse was crucial because, as King noted, each affected farm was a “viral factory,” and the disease was spreading rapidly and would soon be out of control. Contributing to this was the incubation period, during which the infected animals can transmit the disease but do not display signs and symptoms.

Based on the results of mathematical models used to simulate the outbreak, officials estimated that the number of new cases was doubling every nine days. These models, created by four independent modeling teams, incorporated available biological evidence and played an important role in fighting the outbreak. This highlighted the need for good scientific information to feed into models on animal transport and trade; epidemiology through surveillance and reporting; the mechanisms for transmittal and establishment of the disease; and a good, current animal census. Both stochastic models, which are both time-and resource-consumptive, and deterministic models, which are less detailed but more efficient, were used. Once there was agreement between the two stochastic models on a particular scenario, the deterministic models could then run several different intervention scenarios much more quickly.

Multiple scenarios for different intervention strategies were created using the models, attempting to balance the fastest possible resolution of the outbreak, with the minimization of the number of culled animals. Because the models were so precise and vivid, they were comprehensible by both policymakers and the public and helped garner support for the intervention strategies to which the models pointed. King credited the modelers with the ultimate success of the eradication program, by producing what turned out to be very accurate models predicting the impact of various intervention strategies in a very short period of time (See Figure 1). Given the crucial role of the models in battling the epidemic, King suggested that epidemiological modeling should be included as part of veterinary training, so that veterinarians have “a full understanding of what these models can do and what they incorporate.”

Through an emergency interagency advisory group and with the input of scientists, veterinarians, and modelers, U.K. officials decided that an aggressive approach to controlling the disease was the required intervention strategy: the destruction of all livestock on infected farms within 24 hours of detection by veterinarians, followed by the culling of livestock on all adjacent properties within 48 hours. Since rapid action was paramount, officials “slaughtered on suspicion”—taking action immediately following the diagnosis by two veterinarians knowledgeable about the disease, rather than waiting for the more definitive results of lab tests. Officials also imposed tight restrictions on the movement of people, animals, and farm equipment after determining that the virus (Type O of FMD) was being spread primarily by such movements, rather than through aerosol transmission.

Although, in the end, the culling strategy led to the destruction of 4 million

cattle and sheep, the models predicted that the toll would have been far greater with a less aggressive strategy. The models also predicted that the toll could have been cut in half if the outbreak had been recognized a few weeks earlier. This highlighted the importance of early reporting and quick response in stamping out the disease very rapidly. King recommended to policymakers dealing with future outbreaks, “There should be a strategy in place so that, as soon as this happens, you know what you are going to do.”

One important aspect of managing the outbreak was keeping the media and the general public informed. “It was quite clear that since we had a massive logistical problem and a very large media interest, apparently not only in the United Kingdom, that we would have to present what we were doing openly and transparently to the media, and from the 24th of March onwards, I went on television and radio on a regular basis to inform the country as to how things were proceeding and why we were doing what we were doing,” King said.

Since the disease was, for the most part, not fatal to livestock and presented no harm to human health, the aggressive culling policy and the related decision not to use vaccination as a control method were significant concerns of the public. King explained that there were enormous economic incentives behind the policies: Under the guidelines of the OIE, a country has to be completely free of FMD for a year in order to resume trade in livestock, beef, and related products. Since “there is no internationally recognized test to distinguish between infected and vaccinated animals,” the OIE imposes additional trade restrictions on vaccinating countries. If the United Kingdom had decided to eradicate the disease by using vaccination, it would be necessary to wait an additional year before resuming trade, resulting in a two-year trade ban. In addition, all vaccinated animals would ultimately have to be culled if the United Kingdom were to have its FMD-free status restored because they could not be differentiated from infected animals, and, therefore, could not be traded. This would result in the slaughter of a greater number of animals than required by the non-vaccination strategy and was therefore not pursued. In addition, vaccination gives immunity to an animal within four to ten days. If, however, an animal is incubating the disease when it is vaccinated, it will continue to develop the disease and will become infectious. King said that a faster, smarter vaccine, one that could stop the disease in its tracks and produce a marker protein enabling diagnosticians to tell whether an animal has been infected or vaccinated, would have been invaluable. “If we had had those available, I believe the situation would have been very different,” he said. Scientists are working to meet this challenge, but one “was not available to us,” he said.

Diagnostic tests, however, could also have been very valuable during herd screening and case identification, if there were a fast and reliable protocol such as a polymerase chain reaction-based technique that could be used in the field. Because of the time required to obtain results, serology (testing the blood samples to determine whether animals were infected with the pathogen) did not

play a large role during the “slaughter on suspicion” phase of the outbreak control policy, which instead relied on two veterinarians’ professional diagnosis. It was, however, a component to successfully resolving the FMD outbreak, used in combination with the declaration of infected areas as FMD zones, where full FMD controls were applied. All animal movement throughout the country was restricted, and then serologic testing of animals was used to determine when a region, and ultimately the country, could be declared FMD free. This would then allow the country to move towards applying to the OIE for FMD-free status.

Within three weeks of implementation of the strategy, the outbreak was leveling out, and by mid-May, the disease was under control, slightly ahead of the schedule the models predicted. On January 14, 2002, the United Kingdom was declared FMD-free.

Thomas McManus, an Irish cattle farmer, described the personal devastation that resulted from the BSE and FMD outbreaks. The first case of BSE was diagnosed in Ireland in 1989 and, by 1996, the disease in the United Kingdom and Ireland had spiraled out of control. In March 1996, the government announced that there was a link between BSE and vCJD, which led to the collapse of the beef market. McManus said his cattle fell from a value of £600 a head to zero, since they could no longer be sold on the market. The government bought all his cattle over the age of 30 months “to take them out of the food chain,” but at a price that was only two-thirds of the previous market value.

McManus said his losses were further compounded in February 2001, when the first case of FMD was reported in the United Kingdom. The FMD outbreak led to a ban on beef exports and stringent restrictions on the movement of people, animals, and farm equipment. McManus said he and other Irish farmers suffered large financial losses that they never recouped because the loss of their export market has kept the price of beef about 30 percent below pre-BSE levels. He said his farm has not been profitable for the past six years. “The farm wasn’t fit to support me, so I had to find an alternative job.”

McManus noted that his father and grandfather were also farmers, and, prior to the epidemics, he was able to make a good living from the farm. His sons, however, have declined to take over the farm because “there is no money in it.” He said many other Irish farmers have found themselves in the same predicament. Many have left farming or have suffered bouts of depression, some resulting in suicide. “I had never seen a case of BSE, and yet I have suffered severe losses,” McManus said, noting that he and other farmers have watched their businesses of many years fail through no fault of their own. He highlighted the importance of rapid response by the government to prevent disasters of

epidemic proportions. “I don’t think you can put the blame anywhere but on the government for not being fast enough and not doing things in time,” he said. “And a word of caution I would say to you that are going to make a report to the government: A stitch in time saves nine.”