ABSTRACT
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1. During the 1970's there was hope that the major epidemic diseases of livestock and humans were being brought under control in many countries and practically eliminated from OECD countries. Most predictions were emphasising the increasing importance of endemic and productivity-limiting non-infectious diseases with a concomitant progressive reduction in the relevance of epidemic diseases to livestock production. With increasing intensive livestock farming in the industrialised world, there was also a notion that at worst infectious diseases could be confined to the least developed parts of the world and therefore would have little impact on development, food security and trade.
2. During the last 15 years, however, infectious and vector-borne animal diseases have become of increasing importance world-wide and disease emergencies are occurring with increasing frequency. Even industrialised nations have been affected. Thus in 1997, the World Health Organisation (WHO) observed, for human health, that:
"Experience has shown that reducing resources to control infectious diseases in favour of other priorities leads to the resurgence of disease and can create problems more widespread and costly than before".
3. This is equally true of animal health and recent examples of outbreaks of either old diseases or newly recognised diseases or re-emerging or evolving diseases bear testimony to this. Some examples are summarised in Table 1.
Table 1. |
Rinderpest is perhaps the most serious cattle plague. The optimism of the 1970s was shattered when during the 1980s rinderpest spread practically throughout South Asia, The Middle East and Tropical Africa, affecting cattle, buffalo and wildlife. The disease has come under control again, thanks to an international partnership through the Global Rinderpest Eradication Programme. Currently (2001), it is confined to only 3 isolated eco-systems: southern Somalia, southern Sudan and parts of southern Pakistan. The success of GREP will depend on whether rinderpest can be eliminated from these foci befere the end of 2003, otherwise there remains a risk that rinderpest could flare up again as it did in 1980s. Foot-and-mouth disease (FMD) is a highly contagious virus disease of cloven-hoofed animals. there are seven distinct types of FMD virus. It is the animal disease with the greatest impact on international trade. Ordinarily the OECD countries are free from this disease while it is endemic in the Least Developed Countries. Roughly, the endemic distribution of the seven types of FMD is as follows: Type O: Asia, Africa, Middle East and South America; Type A: Asia, Africa, Middle East and South America; Type C: Asia, Africa, South America (NB: this type occurs rarely and tends to be sporadic); Type Asia 1: Asia; Types SAT 1, SAT 2, and SAT 3: Africa. In recent years serious epidemics of FMD have occurred outside areas of endemicity causing major economic losses e.g. type O FMD in Taiwan, Province of China in 1997 and again in 2000; type O Pan-Asian topotype which over a period of 10 years spread progressively from South Asia eastward to China, Japan, South Korea, Vietnam, Cambodia and Taiwan Province of China and Westward to the Middle east and Southeast Europe and during 2000-2001 leapt to South Africa and to UK, France, Netherlands and Ireland. Type SAT 2 spread to in Saudi Arabia in 2000, which is the first time this type has been recorded outside Africa. Peste des Petits Ruminants (PPR) PPR was until relatively recently considered to be limited in distribution to West Africa. However, it is now the most evolving epidemic of small ruminants. It has extended throughout sub-Saharan Africa from Mauritania to Somalia and southwards to the coastal belt of the Congo Republic in the west and Sudan, Ethiopia and Somalia in the east. In the Middle East there have been serious epidemics in Jordan, Saudi Arabia and Iraq and now PPR has extended as far west as Turkey, which borders Europe, and Asia it now extends as far eastwards as Bangladesh. It appears that there has been an actual extension of its range as well as increasing aetiological differentiation between PPR and other causes of pneumonic disease in sheep and goats. In India many cases in sheep formerly ascribed to rinderpest are now known to have been caused by PPR. It has been responsible for heavy losses in small ruminants in Nepal, Pakistan, India and Bangladesh. Contagious bovine pleuropneumonia is a serious mycoplasmal disease of cattle. There has been a catastrophic spread of CBPP over the last few years in Africa where it now affects some 27 countries and causes estimated losses of up to US$ 2 billion annually. In 1995 the disease was reintroduced to Botswana for the first time in 46 years. As part of the eradication campaign, all cattle (approximately 320,000) in an area of northern Botswana had to be slaughtered at a direct cost of $100 million; indirect losses were over $400 million. Classical swine fever (CSF) is a generalised virus disease affecting only pigs. It is endemic throughout many of the swine-rearing areas of the world. It is a major and constant constraint to swine production in the countries of Eastern and Southeastern Asia. It is also endemic in some of the Latin American countries and Cuba (since the 1980s). In 1996 it was introduced into Haiti causing major losses and it is now endemic there; it has spread to the Dominican Republic. In 1998 outbreaks were reported in Costa Rica. Classical swine fever is a disease that poses serious threat to the swine industry of the Americas. It is practically absent from the continental part of the Americas. Therefore, the recent epidemic in the Caribbean is seen as a serious threat to North America and South America as well as non-infected Caribbean countries. In Europe, the most serious, recent epidemics have been in Germany, The Netherlands, Spain and the UK. Molecular genetic studies indicated that the causal virus strain was more related to those isolated from Southeast Asia than those circulating in the wild suidae in Europe. African swine fever is another generalised virus disease affecting pigs. It is endemic in southern and eastern Africa where it is maintained an endemic cycle involving soft ticks (Ornthodorus moubata) and wild Suidae (warthogs and bushpigs). Since mid-1990s there have been serious outbreaks in areas, which either had never experienced ASF before or had not had outbreaks for a long time. For example, in 1994 ASF moved from the endemic area in northern Mozambique to Maputo and devastated the pig population killing 80 per cent of the estimated 4,000 pigs in the area. In 1996 it occurred for the first time in Côte d'Ivoire, where it killed 25 per cent of the pig population and, according to various estimates, cost the country between US$ 13 and 32 million in direct and indirect losses and eradication costs. There has since been serious spread of ASF to Togo, Benin, Gambia and Nigeria. In 1999 the disease spread to Ghana where it has since been eradicated. Newcastle disease (ND) is one of the most important viral diseases of poultry. The history of ND is marked by at least three pandemics in domestic birds. The first began with the emergence of the disease in fowl in the middle of the 1920s and spread slowly from Asia throughout the world. The second outbreak appeared to emerge in fowl in the Middle East in the late 1960s, reaching all continents by mid-1970s. A third outbreak in the 1970s, also starting in the Middle East, was associated with a mainly neurotropic and viscerotropic velogenic disease in pigeons. Currently, we are witnessing the forth panzootic. Since 1991, there has been an increase in incidence with series of related outbreaks affecting again poultry in many European countries. Iran, India South East Asia was hit by the worse epidemic ever reported. In 1999, the panzootic reached the American continent and Australia. ND is regarded to be endemic or epidemic almost allover the world. Infectious bursal disease (IBD/Gumboro) emerged in 1957 as a clinical entity responsible for acute morbidity and mortality in broilers in USA. The diseases has now been reported to occur in most parts of the world and is widespread in commercial chicken as well as scavenging chickens. IBD is caused by infectious bursal disease virus (IBDV). Recently, IBDV isolates were described in USA and Europe displaying an antigenic drift. These new "hot" isolates are very virulent for chickens. The disease has an acute stage followed by immunosuppression, resulting in lowered resistance to a variety of infectious agents and poor response to commonly used vaccines. The acute stage of the disease and the immunosuppression that follows are major factors contributing to the economic significance. Nipah Virus: Between late 1998 and mid-1999, a new pig disease characterised by a pronounced respiratory and neurologic syndrome, sometimes with sudden death of sows and boars was noticed to spread among some pig farms in Peninsular Malaysia. A new virus belonging to the paramyxoviridae family, named `Nipah' was discovered and later confirmed to be the same agent responsible for the human and pig disease. In humans, the virus causes fever, severe headache, myalgia, and signs of encephalitis or meningitis. The case fatality rate has been about 40 per cent. By May 1999 when WHO declared the outbreak to be controlled, a total of viral encephalitis cases with 105 deaths were recorded in human related to pig farming activity. To bring the outbreak under control in the States of Negeri Sembilan, Perak and Selangor a `stamping out' policy was instituted to cull all pigs in the outbreak areas in the first phase. A total of 901, 228 pigs from 896 farms were destroyed in the infected areas from 28 February to 26 April 1999. Rift Valley fever is a mosquito-borne viral zoonotic disease. Until 1977 it was confined to Sub-Saharan Africa. Then it occurred in Egypt in 1977 and again in 1993 caused an estimated 200,000 human cases of the disease with some 600 deaths as well as large numbers of deaths and abortions in sheep and cattle and other livestock species. Following the heavy El Niño rain in 1997/98 a serious outbreak was experienced in Eastern Africa causing not only livestock losses and human deaths but also seriously disrupted the valuable livestock export trade to the Near East. During 2000 an outbreak of Rift Valley fever occurred in Saudi Arabia and Yemen in the wet areas of Gizan and Al-Hudaydah. This is the first time that an outbreak of RVF has been recorded outside Africa. Bovine spongiform encephalopathy (BSE), a prion disease of cattle, was first recognized in the United Kingdom in 1986. Since then, over 170,000 cattle have either died or been slaughtered. The discovery of a probable link between BSE and new variant Creutzfeld-Jakob disease of humans in 1996 led to major disruptions of world beef markets. |
4. Demographic estimates indicate that the world urban population is growing at the rate of 60 million per annum and that by 2010 the urban population will have exceeded that of rural areas. It is also estimated that 26 cities in the world will have populations of 10 million or more and that these will be located mainly in what are now classified as developing countries. This growth in urban population has fuelled the growth of intensification of and peri-urban livestock farming in several developing countries. Inevitably this has led to an increasing importance of endemic diseases in addition to the increased risk of epidemic diseases. The impact of livestock intensification is many-fold:
5. These examples illustrate the dangers that are likely to be associated with livestock development and intensification in developing countries, where the disease burden is greater than in temperate climate, industrialised countries. Therefore, the success of such schemes is bound to depend on the degree of attention given to disease prevention, detection, control and management of animal diseases.
6. The collective geographical location of the diseases of livestock of major economic importance e.g. FMD, rinderpest, contagious bovine pleuropneumonia, classical swine fever, African swine fever, sheep and goat pox, trypanosomosis, tick-borne diseases, Newcastle disease and probably infectious bursal disease extends from Africa across the Middle East and into Asia encompassing many of the poorer countries of the world. The sustained control of these diseases requires socio-political stability and ability to access all livestock by veterinary personnel, apart from the input of resources to supply and deliver vaccines, maintain effective surveillance systems to detect suspected cases at an early stage and provide the trained manpower and resources to implement disease control strategies in the event of outbreaks. Most countries across this sector of the globe do not have resources required to support all of those elements and so they resort to strategic approaches. The national veterinary services in developing countries have, like other departments, to compete for scarce resources but unfortunately they are often politically weak and fare badly when the cake is cut up. Furthermore, economic structural adjustment programmes tended in several cases to weaken the administrative, legal and financial capacity for dealing with major animal diseases. Consequently, progress in the control of animal diseases in many developing countries has become a tediously slow and unpredictable business.
7. In the immediate post colonial period of the 1960s, the public sector veterinary services of most developing countries were engaged in the delivery of the full spectrum of veterinary activities and services with little or no participation of the private sector. By the mid-1970s many countries were experiencing serious economic difficulties and started seeking financial remedial assistance. It was felt that the rescue lay in structural adjustment of their economies. Changes in fiscal, financial and pricing policy included the elimination of subsidies and removal of tariffs while institutional reforms included privatisation of government-owned enterprises and the introduction of cost-recovery. In seeking to move services from public to private sectors, it was argued that, in most domains, any form of private enterprise is likely to outperform the public sector. This led to a drive for the privatisation of veterinary services, thus aiming at diminishing drastically the role of the state in these activities. Animal health was seen as a private good and veterinary services were seen essentially as providing an animal health care delivery system. So issues like the sale of veterinary medicines and vaccines, provision of clinical services or undertaking vaccinations became uppermost in the implementation the privatisation programme. Surveillance, early warning, laboratory diagnostic services, planning, regulation and management of disease control programmes as well as assurance of the quality and safety of animal products became a secondary consideration. The concepts of control of epidemic (and usually trade-related) diseases and the international obligation to manage and report on these diseases, was lost. As a result of restructuring and decentralisation government veterinary officers were often placed under the control of regional and local authorities within a general agricultural extension system. Thus, the chain of veterinary command that required notification of disease outbreaks enabled a response to disease emergencies and also which managed national disease control programmes was often effectively dismantled.
8. The combination of a poor financial resources and an improperly organised national veterinary service often has led to a deterioration in animal health services with epidemic diseases often spreading unchecked. However, there are examples where greater involvement of the private sector has actually improved the control of epidemic diseases. The most notable example is the case of countries of the Mercosur of South America. Here the private farming and trading sectors became involved in the planning and monitoring of disease control programme and exerted pressure on governments so much so that the efficiency of the supervisory and regulatory roles of the public sector actually improved. As a result, South America has made great strides in FMD control and government services have been able also to react resolutely to disease emergencies. Another example is provided by the Indian National Dairy Development Corporation's involvement in FMD control on farms of members of the co-operative.
9. When political upheaval leads to conflict the consequences for disease control programmes can be catastrophic. For example, following the Gulf War and the military offensive of the Iraq government forces against the rebellious Kurds in the north, there was mass migration into Turkey. The refugees took as many of their animals as possible with them and in doing so introduced rinderpest into Turkey's susceptible livestock population. Turkish farmers in the south-east of the country, rushing to dispose of their sick animals as quickly as possible, spread the disease through the marketing chain to Ankara and as far west as the Sea of Marmara.
10. International political isolation of countries can also lead to a worsening disease situation within the region.
11. Thus there are strong associations between political and social instability and the increased incidence of disease. Attendance to animal health through professionally guided community-based programmes will need to be an increasing component of humanitarian programmes in conflict affected areas to avoid consequential major epizootics.
12. Climatic factors can have a major effect on the rate of transmission of many infectious diseases. Microbial agents and their vector organisms are sensitive to factors such as temperature, humidity, precipitation, surface water, wind and changes in vegetation. This applies particularly to vector-borne diseases (VBDs), such as Rift Valley Fever (RVF) transmitted by mosquitoes; African horse sickness (AHS) and bluetongue (BT) - both transmitted by biting midges (Culicoides spp), African swine fever (ASF), East Coast fever, anaplasmosis, babesiosis and Nairobi sheep disease transmitted by ticks; and trypanosomosis transmitted by tsetse flies. It is projected, therefore, that climate changes and altered weather patterns will affect the range, intensity, and seasonality of many vector-borne and other infectious diseases.
13. Considerable progress has been made in dissecting and defining the climatic and environmental factors that influence vector biology. The data has generally been obtained by a combination of field and laboratory studies. These approaches, combined with satellite remote sensing, geographical information systems (GIS) and biomathematical modelling could be used to develop simulation models to predict when and where disease outbreaks are likely to occur and how things might alter with climate change. Armed with this information control strategies e.g. the use of prophylactic vaccination and vector control, could be used to protect animals in advance of the spread of a disease and thereby reduce its impact.
14. For example, successful attempts have been made to model the abundance and distribution in southern Africa of Culicoides imicola, the vector midge of AHS and BT viruses. The abundance of C. imicola, together with associated climate data have been analysed in combination with certain satellite-derived variables with the aim of developing models of C. imicola abundance to predict the risk of AHS and BT. Similarly for the 1997/98 Rift Valley fever in Eastern Africa, an examination of the satellite remote sensing images could readily identify areas for intensive ground surveillance for RVF and other VBDs.
15. Some VBDs are zoonotic diseases and cause serious illness and death in humans. Climate change is likely to increase the prevalence and incidence of many such diseases (geographically or from season to year-round). For example, global warming and resulting rising sea level would displace some human populations, perhaps resulting in migration into wilderness areas where zoonotic infectious agents are being transmitted in silent life cycles.
16. It is predicted that global warming will be characterised by more frequent storms and flooding in certain areas. Higher temperature, increased humidity and more extensive surface water might result in increased insect populations and a higher incidence of VBD. On the other hand, periods of drought will cause the extensive migration of pastoral herds in search of water and grazing and favour the spread of disease by vectors and by contact between animals. These conditions would increase the likelihood of livestock mingling with wildlife populations and the transmission of pathogens. Support for these predictions is provided by the strong association shown between the major epidemics of AHS in South Africa which occur every 10 to 15 years and the warm (El Niño) phase of the El Niño/Southern Oscillation (ENSO) which is mediated by the combination of rainfall and drought brought to South Africa by ENSO. Warm-phase ENSOs bring both rainfall and drought to southern Africa. Populations of C. imicola can increase 200-fold in years of heavy rain. However, heavy rainfall occurs for other reasons in many non-ENSO years but epidemics of AHS do not result. It seems that a combination of heavy rainfall followed by drought is the critical combination, which leads to epidemics. It has been proposed that this is because the high temperatures during droughts increases vector population growth rates and the coincidence of this with the congregation of horses with the virus reservoir (zebra) at the few remaining sources of water creates the conditions favourable for the vector to transmit AHS virus.
17. In Asia the impact of floods, droughts and cyclones has has not been a sufficiently analysed in term of animal health. Yet these climatic changes are taking place with increasing veracity on the continent. For example in Bangladesh only six years between 1960 and 1992 were free of climate induced disasters. It has been estimated that droughts occurred on average every 2.3 years and floods and cyclones every 1.8 years. It can be expected that both established diseases and newly introduced diseases are likely to be of increasing intensity. This has already been evidenced in Bangladesh by the pattern of Peste des Petits Ruminants, a disease, which was first recognised in the country in 1993.
18. Increased road construction across Central and South America, Africa and Asia aimed primarily at responding to expanding industrial needs has also made it easier and cheaper to transport animals over long distances on land. Similarly, the growth of sea and airfreight systems facilitates the transport of animals around the world. The most common mechanism for the transmission of infectious organisms is contact between infected and susceptible hosts. Modern animal transport systems are ideally suited for spreading disease. The animals commonly originate from different herds or flocks, they are often confined together for long periods in a poorly ventilated stressful environment - all of which will favour the transmission within the group of infectious disease should one or more sick animals be present. If not destined for slaughter, the animals will be introduced into new herds or flocks where they will be subjected to social and dietary stress and an exchange of microorganisms with the resident population.
19. A spectacular inter-continental trade transfer of a pest was exemplified by the New World Screwworm (Cochliomyia hominivorax) in Libya in 1988. This was the first time this pest became established outside its natural range in the Americas. Recent years have seen some spectacular examples of the consequences of extended trade links. The outbreaks of FMD type SAT 2 in dairy herds in Saudi Arabia and in sheep in Kuwait during 2000 probably resulted from the importation into the Arabian Peninsula of cattle or sheep from Eastern Africa. While FMD type SAT 2 virus is endemic in many parts of Africa this is the first occasion that the SAT 2 sero-type has been recorded outside Africa.
20. The dynamics of FMD between Myanmar, Thailand and Malaysia is often a direct result of movement of trade cattle. Similarly the vast movement of pigs in eastern Asia has been associated with the spread of foot-and-mouth disease.
21. The movement of infected animals is the most common mechanism by which infectious diseases such as FMD and ND are transmitted. However, spread can also result from the feeding to animals of contaminated foodstuffs such as hay and contaminated unheated waste food of animal origin. The transport of contaminated meat and fodder around the world is a mechanism by which FMD can be spread over long distances and by which exotic strains can be introduced into new territories.
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22. The most dramatic example, however, is the evolution of the spread of FMD sero-type O that is now referred as the Pan-Asian topotype, which over a 10-year period has spread through most of Asia, has affected parts of Europe and South Africa. This virus was first identified in northern India in 1990 and spread westwards into Saudi Arabia during 1994 and, subsequently, throughout the Near East and into Europe (Turkish Thrace, Bulgaria and Greece) in 1996. In 1993 it was found in Nepal and later in Bangladesh (1996) and Bhutan (1998). In 1999, it was reported from Mainland China (Tibet, Fujian and Hainan) and then detected in Taiwan Province of China. In late 1999 and in 2000 it reached most of Southeast Asia. Most recently it has been introduced into the Republic of Korea, Japan, the Primorsky Territory of the Russian Federation and Mongolia (areas free from FMD since 1934, 1908, 1964 and 1973, respectively). The virus has been isolated from a wide variety of host species (cattle, water buffaloes, pigs, sheep, goats, camels, deer and antelope). In September 2000, the FMD Pan-Asian topotype was identified on a pig farm in Kwa Zulu, South Africa. It is believed that infection was introduced there through swill collected from a ship originating from South Asia. In February 2001 the same strain was identified in England, again probably introduced through swill feeding. This virus has now (early April 2001) already resulted in over 1,000 outbreaks in the UK and a small numbers of outbreaks in Ireland, France and the Netherlands.
23. Animal diseases are increasingly been accepted as natural disasters both in their own right and as consequences of other disasters. In view of the increasing frequency of disease emergencies, it is necessary to develop systems for their prediction, early detection, and structured risk-based surveillance leading to early warning. This in turn should be able to lead to an organised and structured response in order to contain a disease outbreak and prevent it from evolving into a major epidemic. It is equally important to address disease at source where it is ordinarily endemic in order to reduce its impact on food security, on the vulnerability of poor communities and to reduce the risk of spread from endemic areas to free areas causing serious disasters. This is the basic principle which underlines the EMPRES-Livestock programme, whose vision is stated as: "To promote the effective containment and control of the most serious epidemic livestock diseases as well as newly emerging diseases by progressive elimination on a regional and global basis through international co-operation involving early warning, early/rapid reaction, enabling research and co-ordination".
24. Therefore, in addressing animal disease as a natural emergency EMPRES has developed a Code of Conduct to guide Member Countries to establish a structured approach to disease emergencies. This is referred to Good Emergency management practice (GEMP) in animal health which is defined as the sum total of organised procedures, structures and resource management that lead to early detection of disease or infection in an animal population, prediction of the likely spread, prompt limitation, targeted control and elimination with subsequent re-establishment of verifiable freedom from infection in accordance with the International Animal Health Code.
http://www.fao.org/WAICENT/FAOINFO/AGRICULT/AGA/AGAH/EMPRES/GEMP.htm
25. The programme is also available on CD. It approaches disease emergencies in four main segments:
26. The programme is underpinned by a set of resource materials as videos, manuals, photo-library, model contingency plans and has links to major internet sites dealing with disease emergency management.
27. Finally, it should be noted that faced with the dilemma of the need for sustained agricultural production coupled with the desire for increased and liberalised trade on the one hand and the threat of infectious diseases on the other, the World Food Summit in Rome 1996 committed the world governments and the civil society to: - «Seek to ensure effective prevention and progressive control of plant and animal pests and diseases, including especially those which are of transboundary nature, such as rinderpest, cattle tick, foot and mouth disease and desert locust, where outbreaks can cause major food shortages, destabilise markets and trigger trade measures; and promote concurrently, regional collaboration in plant pests and animal disease control and the widespread development and use of integrated pest management practices».
* Prepared by Mark M. Rweyemamu, Senior Officer, Infectious Diseases-EMPRES Group; and D. Hoffmann, RAP Senior Animal Production and Health Officer.
