Abstract
1997 has been an eventful year in the area of swine epizootics in several main swine production areas of the globe. Foot and mouth disease swept through Taiwan (Taipei China) in March with immediate ramifications on Pacific rim trade in pork. Taiwan had previously held a major share of the Japanese fresh pork market. In the Netherlands, hog cholera was isolated in February with rapid spread throughout the core swine producing area of Holland. This outbreak has proven difficult to contain and has spread to Spain and Italy. Separate outbreaks of hog cholera have also occurred in central Europe. These events have served to remind pork producers everywhere of the importance of foreign animal disease control to the assurance of access to foreign markets.
Introduction
Risk is a function of the probability of something undesirable happening and the magnitude of the impact of the negative event. A foreign animal disease incursion is a real risk in that it can happen and the consequences can be devastating.
Taiwan
An epizootic of foot-and-mouth disease (FMD) occurred in Taiwan in March 1997 (Shieh, 1997). The FMD virus is very stable in the environment, highly infective, wind borne, and swine produce a large volume of an infective aerosol. Taiwan had been free of FMD for the preceding 67 years and had developed as a major pork producer in the Pacific rim. The first suspected case was reported March 14, 1997. The virus was confirmed as FMD by Taiwan Animal Health Research Institute on March 19. The meat processing industry immediately stopped receiving live hogs, as export markets were immediately restricted. Local live hog prices immediately dropped to less than 20% of the pre outbreak value.
By the end of March, 1,300 pig farms scattered in 15 western prefectures and cities were infected. Taiwan Animal Health Research Institute was overwhelmed by the diagnostic work load. In the field, most of the cases were diagnosed by clinical features. The disease did not immediately spread to the eastern part of Taiwan and offshore islands. The Central Mountain Range, which runs lengthwise through Taiwan may have slowed the spread. All susceptible animals on the infected farms were destroyed and the premises thoroughly disinfected. As the disease was widely disseminated at the time of identification, a policy of nationwide vaccination of all cloven-hoofed farm animals, in addition to the eradication of infected herds, was decided upon. Vaccination is used when it appears that a quarantine and eradication policy will not be successful in containing the outbreak.
The Army was dispatched to help with the disposal of pig carcasses. The means of carcass disposal included burying, rendering, and incineration. Burying was the most common and efficient way. The choice of the disposal method depended on the location of the infected farms. Carcasses were buried on the farm or in landfills, or in public lands close to the infected farms. Farmers were allowed to send their pig carcasses to nearby rendering plans under the supervision of veterinary officers. In water resource protection areas, only incineration using movable incinerators or open field burning was adopted. A disposal capacity of 200,000 pigs per day was reached.
All species of FMD susceptible animals on the eastern side of the island, and elsewhere the dairy cattle and the more valuable breeding pig herds were vaccinated by the end of March. A total of 13 million doses of vaccine was supplied to the producers by the government free of charge.
The route of entry of FMD virus in this incident is suspected to be through the smuggling of live swine via fishing boat. The suspicion was supported when the results of nucleotide sequence analysis of two isolates of the Taiwan virus and comparison with the sequence of reference strains showed that the Taiwan strains were closely related to strains identified as recently circulating in Hong Kong and the Philippines.
Despite animal movement controls and widespread vaccination the whole island was infected by May 4th. By mid-July more than 6,000 farms had been depopulated and four million pigs destroyed.
The Netherlands
Classical swine fever (CSF), also referred to as Hog Cholera, is a contagious viral disease limited to swine. The virus survives in uncooked pork products for 85 days and if frozen up to five years. The European Union (EU) has prohibited vaccination and proceeded with an eradication policy for this virus. CSF was successfully eradicated in Canada in 1963, and in the USA in 1976, but is still present in Mexico. CSF recurs in the EU countries in spite of control programs. Feral swine in Eastern Europe are affected. It is considered endemic in South America, China, the Indian subcontinent and parts of Asia Minor. It is also absent in the UK, Iceland, Australia, New Zealand, Japan, parts of the Caribbean and Scandinavia.
An explosion of 10 primary infected farms occurred in southeast Netherlands in the first week of February 1997 (de Leeuw, 1997 personal communication). CSF was first suspected by a practitioner who was treating a herd in Venhorst for three weeks. CSF suspect samples had been sent to Lelystad on January 31 and February 1, but were inconclusive. On Monday, February 3, the farmer sent meat pigs to a slaughterhouse near Eindhoven. The plant vet-in-charge saw typical CSF pathology and closed the plant as per EU Directive (Council Directive, 1991). The closing of the slaughter plant meant that suspicion of CSF (and impending movement restrictions) became public knowledge prior to official declaration of national health status. The EU Directive on control of CSF requires isolation of the virus prior to initiation of movement controls. The virus was isolated on February 4 and the standstill order published.
Epidemiological modelling suggests viral introduction occurred in late December or early January and a point source was common to the 10 index herds. A CSF virus was isolated in Paderborn, Germany, in the first week of January related to swill feeding. There have been more than 42 herds infected in this area of Germany so far this year. The Paderborn strain of CSF is genetically similar to the Netherlands strain. It is suspected that truckers located in east Netherlands transported pigs in Germany. Experiencing an unusually cold winter of -150C, the truckers did minimal or no cleaning and disinfection of the trucks between shipments of German and Dutch pigs.
Epidemiologic evidence also suggests the industry responded with widespread moving of pigs both within Holland and to major trading partners in anticipation of a standstill order. Preemptive slaughter (depopulation without disease identification) of 24 herds in the immediate area was not successful in containing the outbreak.
The area under movement restriction peaked in the first week of September and further spread in the Netherlands has been curtailed (Figure 1). There were 420 herds identified as infected as of October 21. This is similar in size to the last major CSF outbreak in the Netherlands in 1983-85 where 218 of 17,038 feeder herds and 223 of 19,141 multiplier herds were infected (Terpstra, 1987). The infected herd data represents a small component of the impact of this outbreak. More than one million swine have been destroyed due to herd depopulation; however, movement restrictions have caused a further five million swine to exceed market weight and be destroyed due to overcrowding on the farm of origin.
Disease Status and International Trade
In the world economy, the unimpeded flow of international trade in animals and animal products requires veterinary regulations designed to prevent the spread of transmissible diseases to animals. The Sanitary and Phytosanitary Agreement of the World Trade Organization explicitly recommends the use of standards, guidelines and recommendations developed under the auspices of the Office International des Epizooties (OIE). A Code, prepared by the International Animal Health Code Commission of the OIE, provides standards for international trade. There is a list of animal diseases which have significant economic impact and are the basis for trade restrictions. Trade restrictions based on differing disease status are justified trade barriers.
Animal Health Risks and Hazards
A series of events must occur in an unbroken chain to experience harm or damage from a biologic risk factor or infectious agent. That is; the agent must survive transport and enter the disease free area, it must find and infect a susceptible host, that host must develop the disease to a sufficient extent and infect at least two other susceptible animals prior to dying or recovering from the disease. If each of these events does not occur, a disease cannot be introduced and propagated.
If all the links in the chain are intact then the hazard has met the first half of the "disease risk-impact" equation that is, an undesirable incident has occurred. The magnitude of the negative impact of the event can still be minimized by appropriate response. On July 2 CSF (from the Netherlands) was identified in a herd in Limburg Province of Belgium. Five additional farms were identified as infected in the next week comprising 9,000 total pigs. Preemptive slaughter was initiated on 56 'high-risk' farms and 37,780 pigs were destroyed (Pig Disease Information Centre, 1997). Belgium was declared CSF free on September 9. This incident was tragic for certain producers, but it was not a disaster.
The national animal health program addresses both parts of the risk-impact equation. Risk of an incursion is minimized by import restrictions on live animals and products. Foreign animal disease response preparedness minimizes the impact of an incursion.
Import
There is a small continual risk of introduction of foreign animal disease (FAD) to Canada. In order of likelihood for swine, the top three disease risks are, pseudorabies from the USA, foot and mouth disease virus from Asia/Africa, and CSF virus from Mexico, Europe, or Asia.
All animals or products which enter Canada do so under a quality hazard analysis and control system. Low risk products are tested free of contamination and higher risk animals or products come in under a permit describing conditions which further reduce risk. Animals and products imported are certified free of disease and import inspection procedures at the points of entry further minimize introduction. In handling live swine from a pseudorabies infected country, post import quarantine and testing further minimizes the hazard. There are some products in which the risk of carrying a FAD cannot be suitably reduced (meat and live animals from Asia/Africa) and their import is prohibited.
In industrialized nations, CSF has been frequently transmitted by the feeding of uncooked table scraps to hogs. In Canada the practice of "swill feeding" is stringently regulated and also a very small industry. As of March 1995 there were a total of 35 waste feeding premises in Canada; New Brunswick: 2, Nova Scotia: 13, Ontario: 18, and Québec: 2.
Passenger travel by air has increased in the past few decades. Although some products or infected material may come in undetected with airline passengers, there is a natural protection against the second link in the biological chain being fulfilled (exposure to a susceptible animal). The current animal husbandry industry in Canada is highly concentrated and isolated from the human population. Most swine farms have a infectious disease control protocol. Farm managers restrict human access to farms to minimize the risk of endemic disease transmission such as transmissible gastroenteritis virus. It is very unlikely that a FAD virus could stray onto the average swine farm in Canada.
In the swine industry, Canada also benefits from an environment which precludes the presence of feral swine. Feral swine have been a focus of residual CSF virus infection in Germany and central Europe. In Sardinia CSF is well established in the feral swine population; however, African swine fever (ASF), a viral disease with a similar mode of transmission and clinical picture, is not sustainable in this region's feral swine (Laddomada et al., 1994). This absence of feral swine in the Canadian ecosystem decreases both the risk of the domestic stock being infected from wild animals and the impact of an incursion of a swine specific FAD (CSF, swine vesicular disease, ASF). In the event of a swine specific FAD, the duration of trade restrictions against Canadian pork products would be reduced as there would be no requirement to demonstrate to our trading partners that the virus had also been eliminated from the wild population.
Response
In management of natural and man made disasters it has been demonstrated that planning and preparation can minimize the harm done. In the current political and social reality of the animal industry, no response would be successful without the full support of the industry involved.
Contingency planning can be viewed as having four major components: resources (authority, personnel and facilities), intelligence, strategic planning, and rapid response (Buchanan, 1997).
The lead agency for the control of a FAD incursion in Canada has been delegated via the federal minister of agriculture to the Canadian Food Inspection Agency (CFIA). The legal authority to respond is largely contained in the Health of Animals Act, but there is the ability to access the resources of Emergency Preparedness Canada, the military, and provincial and local authorities. The scientific support in logistics and diagnostics is located in the new high security virus laboratory located in Winnipeg. The CFIA maintains a network of District Veterinary Offices and employs more than 2,000 people in Canada.
Intelligence is the maintenance of an early warning system to identify an exotic disease early in the outbreak. Early identification is a key to minimizing the impact of an undesirable event. Intelligence is also related to the identification of hazards, and risk analysis.
FAD incursions into previously free areas have been detected either on the farm of origin, at the abattoir, or at a regional diagnostic laboratory. The Canadian Veterinary infrastructure has deep penetration into all of these critical early detection points. More than 95% of animals slaughtered in Canada are killed at Federally registered abattoirs. Federal regulations directed at wholesome food require antemortem inspection of animals and post mortem inspection of animal carcasses. Most Canadian farms have regular service by a veterinarian. Most food animal practitioners in Canada are accredited by the CFIA to provide export inspection and certification services to the USA and Mexico. This relationship fosters close contact between food animal practitioners and federal veterinarians responsible for foreign animal disease control. In addition the Health of Animal Act places a legal obligation on practising veterinarians to report suspected cases of foreign animal disease.
In addition to the front line intelligence of veterinarians on farms and in food establishments, Canadian farmers have good access to provincial diagnostic laboratories. Provincial and private diagnostic laboratories in Canada have a working relationship with the CFIA and are likewise obligated to report suspicion of foreign diseases.
Strategic planning is chronologically the first of the four parts of disaster response. Within the CFIA there is a Science Advisory and Management Division (SAMD) and a FAD Policy Group in the Animal Health Division. The SAMD group provides detailed risk assessment information on the status of trading countries and the risk of imported products based on each disease of concern. The Animal Health-FAD Group provides the contingency planning protocol in the form of Manual of Procedures and ongoing policy development. The Virus Laboratory in Winnipeg provides both the technical facilities to identify a foreign pathogen and a core group of research scientists to maintain national expertise in this area.
The final component of disaster impact containment is rapid response. The mobilization of resources to respond to an incursion of foreign animal disease must be appropriate to the severity of the hazard. Overreacting reduces the credibility of the system, while under reacting increases the final economic impact. The quality of this part of the control equation is difficult to verify in the absence of an actual threat; however, recent Canadian events would suggest that the response would be appropriate.
In 1994, bovine spongiform encephalopathy (BSE) was identified in a single purebred beef cow in Alberta. The federal FAD control staff analyzed the situation and recommended to the industry that the herd from which this cow originated should be depopulated and further, all British cattle imports should be traced to their current Canadian residence and removed from Canada or destroyed. At the time, BSE was not linked to any human health risk. In a remarkably efficient consultation with their constituents, the Canadian Cattlemen's Association agreed with the recommendations and an eradication policy was adopted. What may have appeared to be an excessive response at the time, has in retrospect proven to be a prudent decision. BSE has recently been strongly linked to Variant-CJD in humans (Hill et al., 1997).
In 1996 chronic wasting disease (CWD), a prion encephalopathy of elk and mule deer was identified in a captive farmed elk in Saskatchewan by the provincial veterinary laboratory. CWD is not a named disease or a disease with international trade implications. It is only known to occur in a small area of the United States. After consultation with the Canadian game farming industry it was decided to eradicate this herd of animals and institute a national surveillance program for CWD.
In both of these recent incidents the federal regulators, in conjunction with the industries, have cooperated in developing a prompt appropriate response to minimize the risk of foreign disease affecting our animal industries. Future performance is generally well predicted by past performance.
Non-obvious Risk Factors
Contingency planning and risk analysis are effective in mitigating the damage of hazards which can be identified and quantified by scientific means. Some hazards are difficult to identify or quantify.
An emerging disease by definition is a previously unknown disease, or, a significant variant of a previously nonpathogenic pest. In the fall of 1992 an epizootic of unusually severe acute bovine viral diarrhea (BVD) occurred in feedlots in Ontario (Alves et al., 1996). The outbreak continued for several years with considerable economic impact. BVD is not a named disease in Canada and has no significant trade implications. During this outbreak no unified disease control program emerged. On the international scene, porcine reproductive and respiratory syndrome virus emerged about ten years ago and has spread worldwide (Albina, 1997).
Biological terrorism, which is the malicious introduction of a foreign disease to domesticated animals, has not been considered seriously in the past as a significant hazard. In late August 1997 the New Zealand Ministry of Agriculture and Food was faced with the reality that rabbit calicivirus disease (RCD) was present in feral rabbits in the South Island. It appeared the disease had been deliberately and illegally introduced by people, farmers specifically, wanting to use it as a biocontrol tool for feral rabbits. The NZ-MAF had well-prepared contingency plans in place to deal with just such an event. Heavy penalties exist under the NZ Biosecurity Act for anyone found guilty of deliberately introducing an unwanted organism, including the possibility of making the guilty party contribute to the cost of control.
Despite the best laid plans, by September 10 the NZ Government moved to legalize the ongoing spread and use of this previous foreign animal disease as a biocontrol. It was quickly apparent in this situation that control of the disease in the wild rabbit was not possible and vaccination of domestic rabbits would be the mode of protection in the future (New Zealand Rabbit Information Centre, 1997).
Another non-obvious risk factor in disease introduction relates to the changing relations between industry, government and individual producers. In April 1997 the Food Production and Inspection Branch of Agriculture Canada was replaced by an agency (CFIA). This significant change in management reflects the reality that the nature of regulation has changed from a top down police approach to a consultive service approach, with a greater industry responsibility and partnership. The positive side of this arrangement is that the end user of government services, the Canadian citizen, should be able to access more appropriate and economical services. A potential down side is that successful "rapid response" requires a more authoritarian approach to operations. In our recent incidents with prion diseases (BSE, CWD) which are not highly transmissible, the consultative approach was clearly effective and appropriate. The introduction of a highly infectious agent to an area of significant animal population density may result in a different outcome.
The final non-obvious risk factor is any risk factor not yet mentioned or that no one has yet thought of. There is a temptation for government regulators and industry in their scientific risk assessment mode to assume that all the risks have been considered and controlled.
Conclusion
Foreign animal disease introduction is a persistent small risk to our animal industries. Producer associations should be familiar with and supportive of national FAD control plans and be prepared to participate should a foreign animal disease be identified in Canada. At the producer level, biosecurity is the key to preventing personal tragedy in the event of a FAD incursion.
References
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