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Transboundary animal diseases are not only a threat to household food security but also represent a barrier to international trade, and hence an impediment to economic and livestock development
Early, accurate warning of new outbreaks of epidemic livestock diseases, and particularly the spread of such diseases to new areas, is an essential prerequisite for the effective containment and control of these diseases. As observed recently, the blame for the global spread of diseases such as foot-and-mouth disease has been put on the weaknesses of disease surveillance systems and the inability to control major diseases at their source, along with the globalization of trade.
In this publication, early warning is identified as all disease initiatives, based predominantly on epidemiological surveillance, targeted to improve the awareness and knowledge of disease or infection distribution, which might also lead to early and accurate forecasting of the evolution of an outbreak.
There have been many instances where outbreaks of serious epidemic livestock disease in new areas eluded the attention of central veterinary authorities for several weeks or months. The diseases were thus allowed to spread unchecked during this period. The consequences have been unnecessary production losses and difficult and more expensive control and disease eradication measures - or, outright, the impossibility of both.
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Rinderpest epidemic in South Africa that caused acute and peracute signs in cattle
PHOTO COURTESY OF G.R. THOMSON |
Failure to report new disease occurrences to neighbouring countries and trading partners either directly or through international organizations such as the Office international des épizooties (OIE) and FAO has meant that other countries have been unable to take the necessary steps to prevent the introduction of the disease. Furthermore, as observed during the Rift Valley fever epizootic in the Horn of Africa and the Arabian Peninsula, the negative impact of transboundary animal diseases (TADs) on trade is also of critical importance to food security matters and human livelihoods. Indeed, many countries are removed from the international livestock market - or were simply never able to enter it - because diseases such as those mentioned above occurred on their soil. This meant that a potential lucrative trade never developed because it was pre-empted from the start by disease occurrence - a quite negative impact, often not fully realized. It then follows that TADs are, therefore, not only a threat to household food security, but also represent a barrier to international trade, and hence an impediment to economic and livestock development. It is widely recognized that to ensure sustained livestock development, the financial return to farmers from livestock trade is necessary.
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THE IMPACT OF TRANSBOUNDARY ANIMAL DISEASES IN THE ABSENCE OF AN EARLY WARNING
SYSTEM
Rinderpest virus disease.
Rinderpest is perhaps the most serious cattle plague because of its high morbidity and high mortality rates. When this virus disease was first introduced into Africa in the late nineteenth century, it spread over almost the whole continent within ten years, killing an estimated 10 million cattle and untold numbers of wildlife - irrevocably changing livestock husbandry and wildlife ecology. Another rinderpest pandemic, in the early 1980s, which saw a resurgence of the disease throughout much of sub-Saharan Africa, was estimated in Nigeria alone to have caused losses to livestock production in the order of US$2 billion. Wildlife populations, including endangered species in Africa, have suffered considerably from rinderpest epidemics passed on to them from cattle. The relatively small and fragmented populations are increasingly at risk from a future resurgence of the disease, as illustrated by the loss of 60 percent of the African buffalo population of the Tsavo National Park in Kenya in 1994/95.
In 1994, rinderpest spread to previously long-time free, mountainous areas of northern Pakistan, killing an estimated 40 000 cattle and yaks and devastating local agriculture. The continuing presence of rinderpest in Pakistan has resulted in trade bans that for many years have denied access of countries to high-quality meat and, perhaps more important, breeding stock of high genetic
value.
Classical swine fever.
Outbreaks in the Netherlands in 1997-98 led to the death or slaughter of some 12 million pigs as part of the eradication campaign. The cost of these outbreaks was estimated to be US$2.5-3 billion, half of which was public money while the other half was about equally shared among farmers and other participants in the livestock production chain. The effects of the epidemic were so severe that the Netherlands Government approved a national pig-restructuring plan, which foresaw a reduction in the national pig herd of about 25 percent within two years.
African swine fever.
African swine fever (ASF) has no vaccine and no treatment, and the mortality rate is usually close to 100 percent. Pig production has become increasingly important and, owing to the changing dietary patterns and growing demand for animal protein, subsistence
peri-urban production systems have turned to short-cycle species, namely poultry and pigs, to meet the increasing market demand. This trend has given rise to many
peri-urban commercial pig-producing units, rearing improved and often pure exotic breeds. Recent outbreaks have caused significant losses and have threatened entire pig populations in some
countries.
ASF is endemic in many parts of East, Central and southern Africa. It occurred for the first time in Côte d'Ivoire in 1996, where it killed 25 percent of the pig population and cost the country, according to various estimates, between US$13 and 32 million in direct and indirect losses and eradication costs. There has since been a serious spread of ASF to Benin, Cameroon, the Gambia, Nigeria and Togo within West Africa. Estimates indicate that in the past five years, the disease has killed almost half of the total standing pig population of the West African region. The disease also seriously constrains swine production development in a number of other countries including Angola, Malawi, Mozambique and
Uganda.
FAO's contribution to various ASF intervention measures in the past five years has amounted to over
US$3 500 000.
In view of the nature of the disease, control and eradication rely on early detection and, where possible, immediate and rapid stamping out should be implemented. This can only be done if there is a system in place to detect any outbreak at its earliest
appearance.
With the increasing speed of global transportation and communication, ASF poses a serious threat to pig-producing areas throughout the world. Preventing and mitigating the serious effects any outbreak might have will strongly rely on an early detection mechanism.
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Some of the common problems that are manifest in early warning systems for serious livestock diseases include:
- lack of farmer awareness programmes on high-threat epidemic livestock diseases and generally inadequate contact between field veterinary staff and farmers;
- disease reporting systems that are based primarily on passive reporting of outbreaks rather than active disease surveillance;
- inadequate training of veterinary and paraveterinary staff in the clinical and gross pathological recognition of epidemic diseases that may be either unusual or exotic for the country, in the implications of delayed action, and the collection and transportation of appropriate diagnostic specimens;
- poor coordination of field and laboratory veterinary services;
- lengthy and overcomplicated routine disease reporting chains and failure to institute an emergency reporting system for serious disease outbreaks;
- failure to establish confirmatory diagnostic capabilities for the target diseases within national laboratories;
- inadequate liaison with international reference laboratories, coupled with the failure to send in new virus strains, sourced from outbreaks, to these laboratories on a regular basis for specialized antigenic, genetic and epidemiological analysis;
- lack of an epidemiology unit and expertise to analyse new disease outbreaks, including traceback and traceforward activities;
- failure to report new disease occurrences to the appropriate international organizations, e.g. OIE, within an acceptable time;
- lack of central contingency planning and other emergency preparedness for epidemic disease.
There is therefore no doubt that early warning, which is a key component of disease surveillance, needs to be strengthened at the national, regional and international levels. The following section illustrates, through concrete examples taken from previous epizootics, the lessons that can be learned from the past.
Understanding early warning with reference to past outbreaks
In cataloguing some of the experiences of early warning given below, several important points should be taken into consideration - the fruit of lessons learned or not learned over the years during TAD outbreaks and efforts for their control. The examples chosen cover a worldwide geographical area and range from smaller outbreaks of foot-and-mouth disease (FMD) to those that developed into epidemic proportions.
FMD epidemics in the United Kingdom
The Executive Committee of the European Commission for the Control of FMD clearly warned member countries about the dramatic deterioration of the FMD situation worldwide. One of the follow-up recommendations of its 65th session was to urge countries to reappraise their strategies and operations to account for these new realities
Background
The most recent major FMD outbreak in the United Kingdom (UK) was recorded in 2001. Before the 1981 Isle of Wight (UK) occurrence, the last major epidemic in the UK was in 1967/68. Many articles and publications were generated on this episode, such as the Report of the Committee of Inquiry on FMD (called the Northumberland Report), which illustrated the importance of early detection of an epidemic. The studies, parameters and policy generated by the 1967/68 outbreak quickly developed into a model. However, with the recent UK 2001 epidemic, new data and parameters have been generated and will be used for further studies on the epidemiology of the disease and to develop new models.
Weaknesses in the early warning mechanism
A retrospective analysis of the UK epizootic shows that a delayed warning was responsible for the wide spread of the disease in the country. Indeed, the introduction of the FMD virus has been confirmed to have occurred early in February or late January, while clinical detection took place only on 20 February, about three weeks after initial introduction. It has also been advanced that an earlier introduction of a national ban on animal movements (introduced instead officially on 23 February 2001) would have greatly contained the spread of the FMD epidemic - by approximately 43 percent. Indeed, by the time the national ban on livestock movements was implemented, 74 cases were already incubating in other parts of the country.
If the early warning mechanism at national level showed some signs of weakness, it can also be questioned whether or not the introduction of FMD in Europe was somehow predictable, and if the international community could have been more active in alerting national authorities.
During its 65th session in November 2000, the Executive Committee of the European Commission for the Control of FMD (EUFMD) clearly warned member countries about the dramatic deterioration of the FMD situation worldwide. One of the follow-up recommendations of this meeting was to urge countries to reappraise their strategies and operations to account for these new realities. This declaration came as an echo of the recommendations of the meeting of the Research Group, held earlier in September 2000, and from the results of the expert elicitation workshop on the risk of introduction of FMD to Europe.
However, it must be highlighted that, at the time, there was a consensus of experts that the FMD threat to Europe would come mainly from its southeastern region, particularly from Turkey. The results of the above-mentioned workshop also indicated that the first point of introduction of FMD to Europe was more likely to be the Balkans, followed by eastern Europe, southern Europe and, to a lesser extent, western Europe and the "Islands" (UK).
Consequently, although the reintroduction of FMD to Europe was not a complete surprise in the current epidemiological situation worldwide, the pattern of introduction of the disease was fairly different from what had been imagined earlier.
Given the globalization of trade and the wide distribution of FMD in the world, it is likely that FMD-free countries will have to face other incursions of the disease in the future. It is therefore critical to develop emergency preparedness and contingency plans at national and regional levels to prevent the occurrence of other disasters.
FMD in Taiwan Province of China in 1997
Background
In 1997, an epidemic of FMD broke out in Taiwan Province of China and spread throughout the island in less than two months.
An outbreak was first detected in Hsinchu province (western part of the main island) on 14 March 1997, and successive cases were reported in the same prefecture on 17 March. Following these outbreaks, emergency vaccination of pigs and susceptible zoo animals was carried out by the authorities, to control the spread of the disease and particularly to protect the eastern part of the main island.
Nevertheless, the entire island, measuring 380 by 140 km, was infected in approximately 50 days, from the first reported FMD case on 14 March until 3 May 1997. During that period, more than 6 000 farms were infected and 3.8 million pigs were slaughtered, while 13 million doses of vaccine were used during the vaccination exercise.
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FMD spread in Taiwan Province of China |
Weaknesses in the early warning mechanism
It is believed that the FMD infection could have been present on the Taiwanese mainland six weeks before the disease was first detected. How can such a delay in disease recognition be explained?
First, Taiwan Province of China had been free of FMD since 1929, which may explain a lack of awareness with regard to the disease. Furthermore, swine vesicular disease (SVD), which cannot clinically be distinguished from FMD, had been observed in 1997, suggesting that FMD could have been misdiagnosed as SVD. In addition, the disease appeared at the time of the Chinese New Year, a period traditionally known for an increase in animal movements. This association of risk factors certainly fostered the introduction and spread of the disease in the island, and shows the importance of differential diagnosis in disease emergency preparedness.
FMD in North Africa in 1999
The FMD outbreak in the Maghreb is an excellent illustration of disease spread through new routes of introduction. Increase in trade exchanges, improvement of means of communication and transportation create opportunities for TADs to enter new populations and areas
Background
FMD infection has been cyclic in the Maghreb region for several decades. The infection has been regularly introduced into the region from the east and west. Its main routes of introduction have been from Egypt and the Libyan Arab Jamahiriya in the east (the Tunisian FMD virus infections of 1969, 1975, 1979, 1982 and 1989) or from the west through either South America (1977) or Spain (1983). Throughout this period, the Sahara desert has played the role of a protective barrier, preventing disease infection and spread from the infected countries of West Africa.
Algeria.
In 1999, FMD was detected in beef cattle near the capital city, Algiers. A limited spread eastward and westward to different localities was also reported (see map). In total, 165 farms and 139 communes were infected, while 1 605 animals were destroyed, 2 153 slaughtered and 1 270 685 vaccinated.
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FMD spread in North Africa - 1999 |
Morocco and Tunisia.
FMD occurrences were reported in Morocco on 25 February 1999, in the province of Oujda near the Algerian border. Only two outbreaks were reported in Tunisia: one on 2 March in Grombalia (Nabeul Governorate) and the other on 11 March in Jendouba, on the border with Algeria.
Weaknesses in the early warning mechanism
The 1999 FMD occurrence in Algeria registered a complete change in the epidemiological feature of FMD in the Maghreb region. The close relationship recognized between the Algerian FMD strain and strains found in West Africa showed the emergence of a new route of virus introduction into the Maghreb region, represented by the Sahara.
However, the disease spread in Algeria and neighbouring countries was limited for two main reasons:
- The local population was partly protected by the blanket vaccination implemented earlier (following the 1997 and 1998 FMD occurrences in Morocco and Tunisia, respectively).
- While it is true that the Islamic festivities, which took place during the epidemic, increased animal movements, it also led to the slaughter of several million susceptible animals.
As observed in the FMD epidemic in the United Kingdom, the FMD outbreak in the Maghreb is an excellent illustration of disease spread through new routes of introduction. Increase in trade exchanges, improvement of means of communication and transportation create opportunities for TADs to enter new populations and areas. Hence known traditional patterns may need to be reassessed frequently as changes occur throughout the world.
African swine fever outbreak in the United Republic of Tanzania in 2001
The absence of laboratory diagnostic capacity for ASF, the lack of disease awareness at national and regional levels, and the delay in disease reporting are the main shortcomings of the disease surveillance and early warning system with regard to the ASF epizootic in the United Republic of Tanzania
Background
The presence of African swine fever (ASF) has previously been reported in the United Republic of Tanzania, with the most recent and serious outbreaks affecting the Mbeya and Kilimanjaro regions in the 1980s.
The 2001 ASF outbreak in the capital city, Dar-es-Salaam, was confirmed at Onderstepoort Veterinary Institute, South Africa, in May 2001, and occurred principally among pig units of pig meat traders receiving pigs from the northern regions of Mbeya, Morogoro, Dodoma, Tanga, Arusha and Kilimanjaro.
The virus was described to have no relation with the warthog related strains and closely resembled the Mozambique/Malawian strains, suggesting that the disease might have originated from these known endemic foci in the northern region of Malawi and eastern parts of Zambia, both of which border with Tanzania.
Control strategies
FAO assisted the Tanzanian Government in implementing an ASF emergency control programme, through the technical cooperation project "Emergency surveillance for rinderpest and other transboundary animal diseases" (TCP/URT/0067). Since a stamping-out policy was not adopted, alternative control measures were taken, such as the identification of affected pigs through epidemiological investigation, the implementation of quarantine measures and dissemination of information through the media on the main features of the disease to avoid further spreading.
Weaknesses in the early warning mechanism
On 20 February 2002, a workshop was held in Dar-es-Salaam, attended by Tanzania's senior animal health staff and a FAO consultant, to review the 2001 ASF outbreaks and the lessons learned. Delay in disease reporting and ineffective disease investigation seem to have been the main factors responsible for the spread of the disease
Although ASF was diagnosed in peri-urban areas of Dar-es-Salaam towards the end of May 2001, it is now known that there were high pig mortalities, suggestive of acute ASF, in the Mbeya area as early as February. These outbreaks were not properly investigated and the information was not communicated to the Central Epidemiology Unit of the Veterinary Services in the capital. There were further delays when the disease reached Dar-es-Salaam, as the first cases were seen and treated by a private veterinary practitioner and not reported to government veterinarians for at least two weeks. In addition, the laboratory diagnosis for ASF was not in place in Tanzania in 2001 and specimens had to be sent to Onderstepoort Veterinary Institute in South Africa for confirmation.
Furthermore, in late 2000, it was known that ASF was very active across the border in Malawi and this could have raised "alarm bells" since movement of pigs from this country into Tanzania is known to occur. Also, the local government authorities (LGAs) failed to strengthen the initial response actions of the municipal veterinary services with their own emergency response. The LGAs' negligence was attributed to lack of financial resources. Moreover, at the LGA level, no one was assigned to follow up and document all the outbreak cases until the Zoosanitary Unit intervened at the ministerial level. The emergency disease response mechanism was also not implemented at the national level, which could probably be attributed to the low disease priority status accorded earlier to ASF.
However, it is now realized that threats of ASF to Tanzania are increasing because of the recent upsurge of the disease in many parts of Africa, improved means of transport and expansion of the pig industry in the country.
In conclusion, the absence of laboratory diagnostic capacity for ASF, the lack of disease awareness at national and regional levels, and the delay in disease reporting are the main shortcomings of the disease surveillance and early warning system with regard to the ASF epizootic in Tanzania.
Eradication of ASF in Côte d'Ivoire
Background
During the last six years, ASF has leapt to prominence in Africa as a re-emerging disease. In 1996, a devastating ASF epizootic occurred in Côte d'Ivoire, destroying a flourishing pig industry around Abidjan and also in the central and western parts of the country. The epidemic, which was introduced in April 1996 in Abidjan and rapidly spread in July to the central and western regions of the country, resulted in the loss of 80 percent of the commercial pig herd. The extension zones for ASF have followed illegal movements of pigs and pork products from the infected areas.
The disease was eradicated within a year, but at a very high cost, and the industry is only now showing signs of recovery.
Occurrence of the disease
The first case was recorded on 16 April 1996 among 43 pigs in a backyard piggery of Abidjan. At first, the farmer slaughtered some of the diseased pigs, but sold some others to farmers in Abidjan, fostering the spread of the disease. Two weeks later, on 1 May, one of the farmers whose pigs were affected by the disease decided to contact a veterinarian, who alerted the Direction of Veterinary Services and the Central Veterinary Laboratory. Lesions of acute ASF were apparent from clinical observations and the necropsy that was performed. The laboratory confirmation was carried out at the ASF reference laboratory in France on 21 May 1996. A preliminary epidemiological investigation revealed that the source of infection was likely to be product wastes that had been brought in from an ASF-infected country to feed the pigs.
Weaknesses in the early warning mechanism
In spite of early efforts to stamp out the epizootic, the disease spread to village pigs in various parts of the country, and can be related to:
- delayed communication resulting from the lack of farmers' disease awareness (veterinary attention was sought on 1 May, two weeks after probable infection);
- lack of knowledge of animal movements, especially illegal movements from infected areas;
- late disease diagnosis owing to inadequate laboratory facilities (the Laboratoire central de pathologie animale had excellent facilities but lacked the capability to perform ASF confirmatory diagnostic tests).
Although ASF eradication in Côte d'Ivoire can be seen as a successful example of disease control as the disease was in fact eradicated, it should not be forgotten that this epidemic ruined all the efforts by the government and professionals for the development of the pig industry in the country. The economic loss was estimated at around 10 539 million CFA francs (US$14 000), and more than 25 percent of the national herd was lost.
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