In the event of a foreign animal disease (FAD) outbreak in the United States, a rapid and humane method for on-farm swine depopulation will be required to contain the disease and maintain export status. Systems currently used to euthanize swine that rely on the handling and restraint of individual animals (as exists in most on-farm steady-state situations) will likely prove much too slow to stem the spread of disease.

This is a serious challenge. The worst case scenario for the U.S. is an outbreak of Foot-and-Mouth Disease (FMD) in an area with a high population of animals with cloven-hooves. Swine depopulation is especially important; they are known amplifiers of the FMD virus as they can excrete up to 3,000 times more virus than an infected bovine.

To date, the U.S. swine industry has been extremely lucky in that it has not had a foreign animal disease epidemic for decades and has su ccessfully eradicated both Classical Swine Fever (CSF, eradicated in 1978) and FMD (last outbreak in 1929). However, the threats abound. Since 2,000 there have been hundreds of major outbreaks around the world of FADs affecting swine. The U.S. swine industry has benefited from the efforts and experience gained from other countries as they depopulated vast areas in their efforts to control foreign animal diseases in the most devastating outbreaks.

Foot-and-Mouth disease (FMD):

FMD is endemic in parts of Asia, Africa, the Middle East and South America. Since September 2010 there have been reported FMD outbreaks in cloven-footed animals in Israel, Namibia, China, Armenia, Kazakhstan, Georgia, Kuwait, Ecuador, North and South Korea, Vietnam, Mozambique, Iraq, Bahrain, Zimbabwe, Uganda, and most recently Botswana.

Because of its highly infectious nature, FMD-infected animals must be humanely killed and disposed of within 24 hours of diagnosis to limit viral replication and subsequent disease spread, and all susceptible animals on adjacent farms within a specified radius are to be humanely killed and disposed of within 48 hours. However, recent epidemics have been most enlightening in understanding the importance of an early diagnosis and rapid disposal of infected animals. In 2000 and 2010 Japan experienced two FMD epidemics; in marked contrast to the 2000 outbreak where no pigs were destroyed, 200,000 pigs were destroyed in the 2010 outbreak. The high pig fatality in the 2010 outbreak was widely attributed to the slow government response and for this the responsible minister was sacked! South Korea had its most serious epidemic of FMD starting in November 2010. Before it was controlled, about 3 million pigs and 107,000 cattle were destroyed. Subsequently, North Korea experienced an FMD outbreak to which control was haphazard and presumably FMD has spread widely through that country.

Perhaps the most valuable learning experience for U.S. authorities in FMD control came from the 2001-2002 United Kingdom FMD outbreaks, which was first identified in slaughter pigs in February 2001 in Essex and took seven months to eradicate.  The Report from the UK Royal Society stated "that outbreak was the worst experienced by Britain since proper records began and involved 2,030 cases spread across the country. Some 6 million animals were culled (4.9 million sheep, 0.7 million cattle and 0.4 million pigs), which resulted in losses of some £3.1 billion to agriculture and the food chain.”

In the 2001 UK outbreak, animals were euthanized by government-licensed slaughter teams, each of which included at least one veterinarian, using a combination of accepted humane methods, including captive bolt accompanied by pithing rod, gunshot to the brain, and lethal injection. Captive bolt, gunshot, and lethal injection each require that individual animals be handled and restrained, and that operators are properly trained in the correct application of each technique. Given that large U.S. swine operations commonly have 1,000 or more animals in each building and very few animal workers, handling individual animals would greatly slow the euthanasia process and increase the potential for viral replication and spread. Worker safety, as well as emotional trauma, will be significant issues. Clearly, faster, less labor intensive, but similarly humane euthanasia methods would be required f or mass-depopulation if the goals of humane slaughter and timely disposal were to be met in the event of an FMD or other foreign animal disease outbreak in the United States.  This is the most important lesson from the UK outbreak. 

Classical Swine Fever (CSF)

In 1997-1998, the Netherlands experienced a devastating outbreak of CSF. The cost of controlling that outbreak exceeded $1.3 billion U.S. dollars, while the total loss due to the outbreak was estimated to be $2.3 billion U.S. dollars. Eleven million pigs were slaughtered, but only 0.7 million were confirmed as infected. Of those 1.1 million were preemptively slaughtered and 9.2 million were slaughtered for welfare reasons. In response to this emergency the Dutch subsequently developed a conveyor system that could efficiently electrocute swine herds. Although the system is very efficient once it is in place, the units are very expensive to build and cumbersome to move.

Soon afterwards, England experienced a comparatively minor outbreak when CSF was confirmed in East Anglia on August 8, 2000, which lasted until November 3, 2000. In that time, CSF was detected in 16 farms and 74,793 pigs were slaughtered.

Nipah

This virus was first identified in April 1999 on the Malaysian Peninsular. It causes respiratory and central nervous system disease in pigs. That outbreak resulted in the death of 105 humans and about 1,000,000 pigs were culled. The extent of mortalities was attributed to the delay in managing the outbreak because the authorities thought Japanese Encephalitis virus was the responsible pathogen and focused their efforts in a national program to eradicate its vector, the culex mosquito.

Summary

As sobering as these numbers are, the potential situation for the United States in the event of an outbreak of an FAD is much, much worse due to greater numbers of animals, extensive interstate animal movement and continued lack of animal identification and tracking systems. U.S. authorities have made tremendous advances in understanding how to better manage FAD outbreaks; improved systems are now in place to more quickly recognize, diagnose, mass-depopulate, vaccinate stock where appropriate, and appropriately dispose of the carcasses.  Although the Dutch mass-electrocution system has its uses the U.S. will more likely rely on multiple methods, including carbon dioxide for mass-depopulations of swine herds in the future.

Dr. Morgan Morrow is in charge of content for the Swine Health domain on the Pork Information Gateway website.

Dr. Morrow's Extension interests include the application of disease prevention, epidemiologic, and economic techniques to the swine industry. Improving swine profitability through increasing the use of on-farm records and decreasing disease. The correct disposal of mortalities to prevent the spread of disease and the pollution of natural resources. Promoting food safety through research and education.

Source: U.S. Pork Center for Excellence