A variety of management options exist when local, national, regional or international authorities face decisions on transboundary plant pests and animal diseases. The following sections focus on procedures for choosing the most appropriate action.
Farmers commonly encounter pests around their crops and deal with disease incidence in their livestock. Modern pest management does not attempt to eliminate all pests but tries to create an environment that maintains the pest populations at low densities. On-farm management is different from the control of transboundary pest and disease movements, the goal of which is to prevent the entry of a population that can reproduce and survive in the new location. Migratory pests are usually initially absent from the agricultural environment but arrive suddenly in large numbers and frequently cause destruction before any control methods can be implemented. Likewise, many animal diseases are too virulent or threatening to human health and trade relationships to tolerate, even at a low level. Therefore, prevention is still a key element in the management of migratory pests and animal disease.
Table 46 shows the range of phytosanitary measures used to manage transboundary plant pests and animal diseases. The measures are shown according to where the risk occurs: exclusion measures address the risk before it arrives in the regulating country; safeguards are imposed to reduce the risk in the regulating country (often at borders or first points of entry); and the control of and adaptation to an introduction (entry and establishment) or eradication of the disease occurs in the regulating country.
Quarantine is the first line of defence against transboundary plant pests and animal diseases, and countries allocate considerable resources for implementing effective border and import quarantine policies and programmes to prevent introduction. Quarantine is seen as a public good and government responsibility, since individual farmers and private veterinary services are relatively powerless to avoid or overcome introductions. Countries indicate their quarantine policy through lists of restricted or permitted organisms or articles.
The prevention, control and elimination of transboundary pests and diseases is more than a national public good. Because of cross-border spread, effective protection is only possible through a concerted and coordinated effort among neighbouring countries. The control efforts of individual countries may be continually frustrated by neighbouring countries not taking equivalent action. An international approach also allows better advantage to be taken of natural geographic barriers and broader biological and epidemiological patterns.
PHYTOSANITARY MEASURES FOR MANAGING PLANT PESTS AND ANIMAL DISEASES
Sequence of control measures
Reduce risk of entry
Verification of compliance1
Control or mitigation
Adaptation or acceptance
1. Conditions indicating need to take measures
2. Examples of measures to prevent introduction of pests and diseases
3. Reasons for failure of control measures
4. Problems resulting from reliance on measures listed above
1 Not applicable to migratory pests.
A key aspect of effective exclusion and safeguards is accurately estimating risk. Methods used include modelling to predict the ability of an organism to survive under the conditions of a geographic area that is not yet affected. Tools such as geographic information systems (GIS) make it possible to combine and cross-analyse a large amount of visual and numerical data, such as satellite-retrieved images of the earth's surface, climatological information, disease and livestock population data, and to produce predictions of disease spread. An example of GIS used in this way is the Programme Against African Trypanosomiasis (PAAT) Information System, designed to identify the impact of the tsetse fly and trypanosomiasis on agriculture, to locate areas where control is technically feasible and to determine where animal and human trypanosomiasis occur together.
Satellite data from remote sensing have potential in predicting insect-borne transboundary animal diseases, notably Rift Valley fever. There are major Rift Valley fever outbreaks in parts of Africa at irregular intervals of 15 years or even more, when environmental conditions (including unusually heavy rainfalls with filling of surface ponds, warm and humid weather and increased vegetation cover) in areas at risk favour the emergence and massive multiplication of the mosquito vector of the disease. In the future, the prediction of El Niño phenomena and the determination of normalized difference vegetation indices (an indicator of the amount of rainfall that has fallen in an area) through remote sensing may prove to be cost-effective ways of providing several months' warning of Rift Valley fever outbreaks, although these methods have not yet been applied in practice.
Directly transmitted transboundary animal diseases are less amenable to remote sensing. Early warning of diseases for which animal movements are a major factor in spread (such as foot-and-mouth disease, CBPP and rinderpest) depend on a good understanding of livestock movement patterns and on-ground intelligence of where disease is active, although there is scope to foresee risk by predicting movement as a result of climatic events. GIS and predictive modelling have been very useful in predicting the wind-borne spread of foot-and- mouth disease in Europe, thereby providing early warning. Several temperate climate countries have, therefore, incorporated such modelling in their contingency planning of response to foot-and-mouth disease. Such systems require good clinical and serological surveillance and diagnostic capacities to confirm cases as well as effective communication, collaboration and information sharing among countries.
Recent information tools have also increased the ability to predict migratory pest invasions. Since outbreaks of migratory pests typically develop in response to rainfall and the greening of uninhabited arid environments, the potential of remote sensing as a supplementary tool to ground monitoring has been recognized for some time. In many affected countries and at regional and international organizations, vegetation indices are now regularly available from remote sensing sources and assist teams surveying for migratory pest outbreaks.
Crop and animal protection is the immediate objective for controlling pests and diseases that enter a country. In these cases, farmers play a key role in implementing control operations but frequently need the support of plant and animal protection services or regional organizations for technical advice, equipment and supplies. Support includes surveillance, reporting and emergency actions. These steps continue until a decision is be made to accept an introduction and abandon control activities.
The control of animal diseases may involve vaccination, movement control - at times achieved through the construction of major fences - chemoprophylaxis and therapy, slaughter of infected and possibly in-contact animals, disinfection and vector control in the case of vector-borne diseases. The latter can be achieved through the application of chemicals, by biological means and by changing the natural habitat.
Preventive vaccination can routinely be applied on a national scale, as was the case with foot-and-mouth disease in the EC prior to 1991 and in Uruguay before the country managed to eradicate the disease, or to certain areas with an elevated risk of disease introduction, often termed "buffer zones". Preventive vaccination may reduce export opportunities. Disease-free countries are normally reluctant to import livestock and livestock products from countries allowing the use of corresponding vaccines. In addition, the application of vaccination will considerably prolong the time required before official recognition of disease freedom can be obtained or re-obtained in the case of a declared disease outbreak.
Interregional and international reporting systems serve to inform officials of the entry and spread of pests and diseases of concern. This is done internationally through the FAO Emergency Prevention System for Transboundary Animal and Plant Pests and Diseases (EMPRES), described in Box 7.
In 1994, the Director-General of FAO was authorized to establish the Emergency Prevention System for Transboundary Animal and Plant Pests and Diseases as a priority programme.
The livestock diseases component of the programme aims to strengthen FAO's role in the prevention of and immediate response to emergencies caused by major epizootic diseases that cross boundaries. The plant pests component focuses on preventive control of the desert locust, leading to a reduced risk of catastrophic plagues.
The major thrust of the animal disease component of EMPRES has been to eradicate rinderpest. Progress on this goal has been rapid and effective. It emphasizes proactive efforts to prevent emergencies by increasing early warning and early research, and through the application of research. EMPRES also aims to provide a catalyst for cooperation among countries in the fight against transboundary pests and diseases.
The desert locust component of EMPRES has emphasized the strengthening of national capacities for early identification of locust outbreaks through efficient surveying, followed by rapid reaction to control any outbreaks. Importance has also been given to reducing the amount of pesticides used and investigating environmentally safer technologies.
The socio-economic effects of transboundary pests and diseases are lessened through biologically based measures aimed at control, containment, eradication or disinfestation. The economic impacts may also be lessened through risk management, which might include insurance schemes, increased agricultural production or improved infrastructure. Alternative sources of income and employment through rural development or financial aid can also help. Any combination of these measures might produce a more stable and/or higher income stream for a farmer than relying solely on biological methods.
Insurance protection. Risk can be shared among a large group of people through insurance. When the group includes people who face non-covariant risks, the averaging of risk can reduce the overall risk to the group and provide opportunities to manage risks. Private insurance schemes have been considered for crops subject to specific pest risks but the insurance companies have not yet accepted this approach, primarily because farmers face covariant risks of poor weather, pests and economic forces. However, government agencies have provided crop disaster insurance in many countries through subsidized programmes.
The feasibility of insurance schemes to compensate farmers or communities for crop losses as a result of migratory pests has undergone little study. Belhaj43 found that insurance compensation to farmers for losses from desert locust outbreaks would be approximately equal to the costs paid for control, if outbreaks occurred every year. He concluded that, since desert locust outbreaks occur less frequently, cost-benefit analysis argues for an insurance programme against desert locust.
Increased or adaptation of agricultural production. Farmers are well aware of the potential for pests and diseases to harm their activities. In various ways, they select strategies that will mitigate any damage. Among their options are choices of where to locate, especially if they are pastoralists. Farmers can also choose production techniques and crops that are more resistant to infestations and other risks. This is one reason why pearl millet is a primary crop in the Sahel, where poor soils, variable rains and high evapotranspiration make other grains risky to grow.44 Another approach is to diversify output so that periodic damage to one product can be buffered by the production of other products that are not afflicted by the same problems. Thus, farmers in certain areas engage in mixed farming systems of crops and livestock to spread the risk of infrequent and uncertain pest and disease infestations.
Another alternative for farmers to reduce the impact of transboundary pests and diseases is to increase their production to allow for storage of stockpiles and diminish the impact of pre-harvest losses. Farm management strategies are likely to incorporate some additional production when possible to serve as a buffer against losses.
ERADICATION OF THE ORIENTAL FRUIT FLY IN MAURITIUS
In 1991, the Ministry of Agriculture in Mauritius established a network of quarantine traps for exotic fruit flies. In June 1996, one oriental fruit fly (Bactrocera dorsalis) was found in a trap near the airport in
Mauritius. The trap in which the flies were found was not one of the quarantine network traps, but a trap being used for a research project unrelated to quarantine. Because of the close links between research and quarantine operations in the country, the fly was reported and a major quarantine and eradication programme was initiated immediately.
Consideration of how to respond to the introduction included both economic and political issues. There are several other important species of fruit fly present in Mauritius (e.g. Ceratitis capita, C. rosa and Bactrocera zonata), and the country currently has very few fruit exports. Crop losses from the oriental fruit fly were unlikely to add significantly either to the crop losses or to control costs within Mauritius.
The only immediate economic impact was the curtailment of fresh capsicum exports to Réunion, which amount to some hundreds of kilograms per year. However, it was politically important for Mauritius to take responsibility to prevent the further spread of the oriental fruit fly into other islands in the Indian Ocean and on to the mainland of Africa, where losses would be enormous. Fruit exports of $200 million from South Africa to Europe and the United States would be jeopardized. It was recognized that Mauritius benefits from quarantine actions taken by other countries in the region and that it must act in this case.
The quarantine trap grid was immediately extended in the area surrounding the airport, and fruit in the area was inspected for larval infestations. Larvae were reared from infested fruit found near the airport and it was clear that the oriental fruit fly had established in Mauritius. Morphological examination indicated
Since that time, a trapping grid has been maintained so that any new entry can be controlled. In late 2000, the programme was to convert from a European-supported regional effort to a locally funded country programme.
Improved infrastructure. Crop losses and other increases in costs of production are often attributable to poor infrastructure and support services. In some countries, deteriorated or non-existent transportation infrastructure causes up to 30 percent post-harvest losses when products are taken to market. A lack of extension services to farmers reduces productivity in multiple ways, including an inability to respond to pest and disease problems when they arise.
Public provision of infrastructure is justified by the public good nature of infrastructure services such as roads, marketing information, credit systems, extension and education and irrigation canals. Investment in infrastructure has historically provided high returns and is virtually essential if countries are to raise their agricultural productivity. Improvements in such systems can reduce costs dramatically at the farm level, thereby compensating for losses from pests and disease.
Rural development. Both private and public action to improve opportunities in rural areas can help overcome losses from pests and disease. The public sector can take action to develop
rural areas by encouraging alternative industries, locating public facilities in vulnerable rural areas and expanding adult education opportunities, such as job training and skills improvement.
Farmers can also engage in income diversification strategies in order to reduce the impact of pest and disease outbreaks on their household income. Reardon45 has demonstrated that increases in non-farm employment and income have occurred in rural areas across all regions. Among the factors cited by Reardon for encouraging households to undertake non-farm employment is a low level of food production owing to temporary or long-term constraints, including the loss of output from periodic pest and disease outbreaks.
Food and financial aid. National governments and international agencies rely on emergency safety nets when disaster strikes farming communities. These are mainly donations of food or financial aid intended to carry the victims through temporary shortages. While, in theory, such a response to emergency may be the most direct and low-cost way to prevent localized famine or hunger from developing from a pest or disease outbreak, in practice it is less effective because emergency safety nets are often underfunded or non-existent in the places they are most needed.
Global prevention of transboundary pest and disease spread is being challenged by economic and ecological change. New technology is increasingly seen as the way to meet these challenges.
The most dramatic change comes from the increase in trade and movement of passengers and the new trade routes that have opened. The globalization of commodity trade is understandable considering that the unit costs of sea freight have dropped by almost 70 percent in real terms in the past 10 to 15 years while air freight unit costs have decreased by 3 to 4 percent over the same period.46 Biological and ecological transformations are increasing the virulence of some existing pests and diseases, while also exposing animals and humans to previously contained emerging diseases. Consumers have grown increasingly concerned about food safety and are demanding more information and more stringent regulation of food supplies. Demands on public authorities are growing without a commensurate increase in resources.
Simultaneously, new technologies, new attitudes concerning risk and new trading principles may guide countries towards a more rational and comprehensive world system of plant and animal protection.
Air freight, which delivers fresh products more rapidly, has enabled pests and diseases to survive the transit more readily. In addition, totally new trade routes have led to new pathways for introduction and increased trade in livestock and livestock products also puts larger numbers of animal and people at risk of disease. These new trade routes highlight the greater susceptibility of crops or native plants, or even fish, to exotic pests when they have not co-evolved or when the parasites and predators of the pests are not present in the new environment.
The last 30 years or so have been remarkable for the emergence of apparently new infectious human diseases. This includes the appearance of diseases such as AIDS, Lassa fever and Ebola virus disease. The same has occurred with animal diseases. New zoonotic diseases have been emerging at a rate of at least one per year, including avian flu, Nipah virus, BSE (see Box 9) and equine morbillivirus disease. Not only do new infections emerge, but also new biotypes or antigenic types of existing infectious diseases. A notable example has been the hypervirulent form of infectious bursal disease, which has swept across much of Europe and Asia in recent years, causing devastating losses to poultry industries. Vector-borne pathogens (e.g. West Nile fever) have expanded beyond their traditional range. Other examples include bluetongue disease in Europe and cases of Rift Valley fever in Saudi Arabia for the first time.
THE TRANSBOUNDARY SPREAD OF BSE
FAO has urged countries around the world to take action to reduce the risk of bovine spongiform encephalopahy (BSE).
Cattle in Britain were probably first affected by BSE - commonly known as mad cow disease - in the early 1980s, but the new disease, caused by a novel infectious agent called a prion, was only recognized in 1986. The disease has a long incubation period (more than three years), and therefore the epidemic in the United Kingdom expanded despite official control measures. BSE has since spread to other European countries, while several other countries outside Europe have reported BSE in imported cattle.
BSE was apparently transmitted in cattle in feed supplements that contained meat and bone meal (MBM). It is believed that a new variant of Creutzfeldt-Jakob disease (vCJD), a progressive, fatal neurological disease in humans, may be related to the consumption of BSE infected tissues. There is currently no method for diagnosis in early stages of infection and no cure for the disease, either in animals or in humans.
All countries that have imported cattle or MBM from Western Europe, especially the United Kingdom, during and since the 1980s, can be considered to be at risk from the disease. FAO data show that MBM from Europe has been exported to many countries since the 1980s, when BSE was identified. Some countries also re-exported MBM to third countries. An initial risk assessment of BSE for selected countries not belonging to the EC has been carried out by the European Commission. It is based on whether countries have imported MBM or live cattle during the risk period (1980s onwards), as well as the measures in place for risk management in the livestock, meat and feed industries and the nature and structure of those industries.
Concern has spread among consumers, and the economic impacts of the BSE outbreaks in the EC will be felt for years. Beef prices in the EC dropped by 17 percent in the last months of 2000 (and are expected to continue a downward trend). By the end of 2000, the disease had cost the United Kingdom more than 5 billion euros through slaughter of cattle and calves, loss of jobs and markets. Finally, it is impossible to put a price on the cost of the loss in public confidence in the livestock industry.
Although Britain has been fighting the disease for years, it was only recently that a multilateral response to the disease was developed. Pressure on governments to respond to the human health risk of BSE grew dramatically after it appeared beyond the borders of the United Kingdom in countries that were believed to have adequate safeguards. EC farm ministers met in late 2000 to implement strict control responses including the following:
An EC transmissible spongiform encephalopathies (TSE) regulation, which may include full herd and cohort slaughter, is intended to come into force in July 2001.
Among the important lessons of relevance for transboundary pest and disease response is the need to recognize when collective action is needed. Current actions by the EC, national governments and the international agencies involved (FAO, WHO and OIE) are aimed at improving understanding of the disease characteristics and risks (much remains unknown about the disease and the infective agent) and assisting countries in protecting their animal and public health. Emphasis is being placed on better diagnostics, identifying risks to other animal species and the transmission of risks, both up and down the production and food chain.
Experts are currently recommending that countries at risk should implement effective surveillance for BSE in cattle as well as controls on the animal feed and meat industries. At present, this means: reporting signs of disease, laboratory testing of samples from slaughtered cattle, the correct disposal of fallen stock and improved processing of offal and by-products.
However, all countries should take precautionary measures, including general improvements to their food and feed safety systems. Attention should be paid to slaughtering procedures (cease slaughter or rendering practices that could spread contamination that endanger human and animal health), and to the processing and use of offal and by-product parts. The rendering industry should be scrutinized and appropriate procedures adopted everywhere; appropriate risk analysis on their production and trading systems should also be conducted.
It should be stressed that the epidemic of BSE was the result of recycling animal protein and the subsequent amplification of the problem in the food chain. The banning of MBM and regulation of the feed industry should arrest the spread of the disease in all countries.
In many countries, there is a trend towards increased intensification and commercialization of livestock production, particularly in peri-urban areas. The higher concentration of animals that results, often under suboptimal husbandry conditions, provides greater opportunity for transboundary animal diseases and other infections (e.g. Nipah virus) to move rapidly and cause economic losses.
In some regions of the world, tropical rain forests and other wilderness areas are being converted to livestock farming. This brings human communities and their farm animals into close contact with a completely new range of infectious diseases and vectors that may have previously only circulated in wildlife reservoirs and may be completely unknown. Some of these diseases may be transmittable to humans and/or livestock, and they may spread very rapidly in the new, fully susceptible hosts.
One reason for the increasing concern about transboundary pests is the increasing susceptibility of agricultural and natural resources to infestation and damage. Plantation agriculture has increased the vulnerability to pests and diseases for years, with pesticide application and veterinary control the primary solutions. The genetic variability of the world's principal crops is now becoming more limited with the greater concentration of breeding stock in the hands of a few private companies. Resistance in insects and diseases is taking hold with the increased use of genetically modified crops. The genetic manipulation of these crops may keep them safe from infestation for a time, but the result may be more invasive or damaging pests that evolve in conjunction with these super plants.
Global warming trends may change rainfall and weather patterns in a number of regions, affecting in particular the global distribution of insect vectors, for example mosquitoes and Culicoides midges and the important transboundary animal diseases that they transmit (Rift Valley fever, bluetongue, African horse sickness). Climate change is also a source of increasing susceptibility to pests in many parts of the world.
The "tool kit" for combating pests is shrinking faster than new technologies for control can be developed and proven. Likewise, pesticide spraying campaigns against migratory pests in Africa have come under attack. A global concern for the environment has driven much of this change. At the same time, consumers are demanding lower pesticide residue limits in the belief that human health is affected by these residues. Technology for pesticide residue testing is less expensive and becoming more readily available so that enforcement of these lower limits is more likely.
The same trend in public attitudes has caused a greater awareness of potential environmental impacts of the introduction of exotic pests. As this concern comes from an environmental perspective, tools and ideas from environmental science, law and policy are entering into the discussion on animal and plant health. Alien invasive species are seen as a primary threat to native species, possibly as serious as habitat reduction. Different interests are entering the discussion of plant and animal health and broadening them beyond purely technical control issues.
A vast array of molecular biotechnology applications is available and emerging in animal production and health, involving both on-farm and off-farm activities. Use of DNA biotechnology in animal health may contribute significantly to improved disease control. Advanced diagnostic tests make it possible to identify the disease-causing agent(s) and to monitor the impact of disease control programmes, to a degree of diagnostic precision (subspecies, strain, biotype level) not previously possible. For instance, newly developed diagnostic tests are revealing an incidence of BSE that was previously undetected. Enzyme immunoassay tests have the advantage of being relatively easily automated and have been developed for a wide range of parasites and microbes. Their availability in developing countries is still low, however.
Molecular epidemiology is being used to trace the origin of pathogens better than ever before. This is particularly useful for epidemic diseases that can be better controlled by the early pinpointing of their source. The development of genetic techniques that allow the detection of pathogen DNA/RNA (rather than antibodies) in livestock also enhances animal health efforts.
Finally, recombinant vaccines can offer greater safety and specificity, more stability and distinctions between vaccinated and naturally infected animals. They may also offer possibilities for vaccines to be developed against parasites where conventional methods have failed.
An innovation that supports pathway analysis and could be used for liability actions in the future is the use of genetic "fingerprinting" to reveal the source of entry of a population of quarantined pests, as is already used extensively for foot-and-mouth disease and rinderpest through world reference laboratories. This has been demonstrated with fruit flies entering Florida and citrus canker in the same state. By establishing the source of the entry, measures can be taken to close down the pathway or improve its compliance. This may also be used to indicate if the population is a new introduction or a resurgence of an earlier introduction that was thought to have been eradicated.
An operational tool of great interest is the systems approach to compliance. A systems approach to quarantine security is much more complex than a single treatment, yet it will facilitate trade and reduce the environmental and social impact of unnecessary fumigation. These agreements are based on research showing the critical points of possible infestation and demonstrating compliance with measures that, when carried out in total, reduce the risk of the product introducing a quarantine pest to a level acceptable to the importing country.
Other new tools and technologies that show promise or are already proving successful include:
At the same time, challenges that new technologies may impose are:
Emerging issues that will affect future regulatory approaches include:
The pressure to include environmental considerations more fully will force many nations to evaluate the relative advantages of creating a biosecurity approach across ministries and agencies that maintains their areas of expertise, or to continue with separate policy divisions and to cooperate ad hoc on operational programmes.
In recent years, locust and grasshopper research has focused more on applied aspects, and considerable attention is now being paid to the task of translating promising research results into operational practice. The following points indicate particular areas where progress is being made:
On the other hand, there have also been important gaps in the research efforts. Field trials with desert locusts have been difficult because of the unpredictable and fast-changing nature of infestations. Research on some important migratory pests, such as the red locust, has been neglected. There has not generally been sufficient attention paid to research on the population dynamics of locusts or to the use of integrated pest management approaches in other migratory pests. Furthermore, the research institutes of locust-affected countries have not participated sufficiently.