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Seminar Nasional Teknologi Peternakan dan Veteriner 2007 EMERGING DISEASES ASSOCIATED WITH WILDLIFE – A MULTI – DISCIPLINARY CHALLENGE (Timbulnya Beberapa Penyakit yang Berkaitan dengan Hewan Liar Suatu Pendekatan Multidisiplin Ilmu) HUME FIELD1 and JONATHAN H. EPSTEIN2 1 Department of Primary Industries & Fisheries, Queensland, Australia; and the Australian Biosecurity Cooperative Research Centre for Emerging Infectious Diseases 2 The Consortium for Conservation Medicine, Wildlife Trust, 61st 9W, Palisades, New York, USA ABSTRAK Hampir sekitar 75% penyakit infeksius yang timbul dan menjangkiti serta mengancam kesehatan manusia adalah penyakit zoonosis yang ditularkan dari hewan. Sebagian besar dari penyakit tersebut adalah dari hewan liar yang bertindak sebagai reservoir. Timbulnya penyakit tersebut kebanyakan dari faktor predesposisi, misalnya perpindahan penduduk global, perdagangan, perluasan lahan pertanian, penebangan hutan, dan arus urbanisasi. Dari hal tersebut maka penyidikan penyakit tersebut dilakukan dengan pendekatan multidisiplin ilmu yang melibatkan para ahli ilmu kedokteran hewan, kesehatan mayarakat, dan ahli mikrobiologi, ahli yang mendalami ekologi dari spesies hewan liar, ahli yang betul-betul mengerti resiko penularan penyakit dari kebiasaan kehidupan manusia. Penelitian kehidupan hewan liar meliputi populasi hewan yang bersangkutan dan kesulitan yang akan dihadapi pada saat pengambilan sample, bermacam jenis penyakit yang berjangkit pada spesies tersebut yang belum pernah dipelajari sepenuhnya. Hewan liar yang hidup dalam cagar alam (konservasi alam) memerlukan perlakuan yang khusus. Dari hal tersebut maka pertemuan yang membicarakan manajemen resiko terhadap penyakit yang akan timbul memerlukan keahlian yang khusus dari para ahli dalam disiplin tertentu dan kerjasama yang baik untuk mencapai tujuan tersebut. Kata Kunci: Penyakit Baru, Hewan Liar, Pendekatan Multidisiplin ABSTRACT Nearly 75% of all emerging infectious diseases that threaten human health are zoonotic – they have an animal origin. The majority of these have spilled from wildlife reservoirs. Emergence of many can be attributed to predisposing factors such as global travel, trade, agricultural expansion, deforestation/habitat fragmentation, and urbanization. Thus the investigation of emerging diseases associated with wildlife requires a comprehensive multi-disciplinary approach that includes, in addition to the ‘traditional’ veterinary, public health, and microbiological expertise, an understanding of the ecology of the wildlife species, and increasingly, an understanding of human behaviors that increase risk of exposure. However, wildlife studies involve uncontrolled populations, and difficulties are frequently encountered in capturing, sampling, and disease-screening species that may not have been previously studied. Ethical considerations such as conservation status also come into play when working with wildlife populations. Meeting the challenge of managing the risk of emergence of infectious diseases from wildlife requires skills from a range of disciplines working collaboratively towards a common goal. Key Words: Emerging Desease, Wildlife, Multi-Disciplinary Approach INTRODUCTION While the current emphasis on emerging diseases in the scientific literature and in the popular press suggests otherwise, novel diseases have occurred throughout history. By definition, every newly identified disease is novel. The outcome of investigations of cholera epidemics by Dr. John Snow in London in the 1880s illustrated for the first time how the actions of man could precipitate the emergence of disease. At the same time, it also demonstrated the value of an epidemiological approach in the investigation 9 Seminar Nasional Teknologi Peternakan dan Veteriner 2007 of a disease outbreak. As we begin the 2001st century, nearly 75% of all emerging infectious diseases (EIDs) that impact or threaten human health are zoonotic – they have an animal origin (TAYLOR et al., 2001). The majority of these have spilled from wildlife reservoirs into humans either directly or indirectly. Diseases associated with avian influenza virus, SARS coronavirus, Nipah virus, West Nile virus and HIV are examples of emerged zoonoses that have (have had, or may have) a significant impact on human health. THE EMERGENCE ZOONOSES The emergence of many zoonoses can be attributed to predisposing factors such as global travel, trade, agricultural expansion, deforestation/habitat fragmentation, and urbanization; such factors increase the interface and/or the rate of contact between human, domestic animal, and wildlife populations, thereby creating increased opportunities for spillover events to occur (DASZAK et al., 2000; 2001). To illustrate, the introduction of a "new" infection into a human or domestic animal population may follow the incursion of humans (accompanied by their domestic animals) into previously remote natural habitats where unknown disease agents exist in harmony with wild reservoir hosts. Upon contact with new species, an agent may jump species barriers, thereby spilling over into humans or livestock. Unlike the natural host, the new host may have no natural immunity or evolved resistance. Additionally, high population densities and management practices may facilitate the rapid spread of pathogens throughout livestock populations. Table 1 provides several examples of disease emergence and the putative factors associated with their emergence. LEDERBERG et al. (1992) describe these changes as providing an ‘epidemiological bridge’ that facilitates contact between the agent and naive population. DASZAK et al. (2000) regard disease emergence as primarily an ecological process, with emergence frequently resulting from a change in the ecology of the host or the agent or both. They argue that most emerging diseases exist within a finely balanced hostagent continuum between wildlife, domestic 10 animal and human populations (Figure 1). The emergence of Nipah virus from fruit bats in northern peninsular Malaysia in 1999 provides a useful example. It is suggested (FIELD et al., 2001; DASZAK et al., 2006) that the emergence of Nipah virus was (in part) associated with the encroachment of commercial pig farms into forested areas of high fruit bat activity. Once the virus ‘spilled over’ into the immunologically naïve pigs, high pig and farm densities then facilitated the rapid dissemination of the infection within the local pig population. The movement of pigs for sale and slaughter in turn led to the rapid spread of infection to southern peninsular Malaysia and Singapore, where the high-density, largely urban pig populations facilitated transmission of the virus to humans. Figure 1. The host-agent ecological continuum1 1 From DASZAK et al. (2006) FACTOR THAT INFLUENCE OF THE DISEASE Thus the epidemiologic investigation of infections associated with wildlife requires a comprehensive multi-disciplinary approach that includes, in addition to the ‘traditional’ veterinary, public health, and microbiological expertise, an understanding of the ecology of Seminar Nasional Teknologi Peternakan dan Veteriner 2007 the wildlife species, and increasingly, an understanding of human behaviors that increase risk of exposure. For example, identifying the factors associated with the emergence of SARS in southern China in 2003 requires an understanding of the ecology of infection both in the natural reservoir and in secondary market reservoir species. Thus, a necessary extension of understanding the ecology of the reservoir is an understanding of the trade, and of the social and cultural context of wildlife consumption. In relation to trade, we know that a wholesale and retail structure exists in the wildlife trade in southern China, with multiple wholesalers providing multiple retailers at a city level. We know that some wildlife are farmed and some wild-caught. What about the marketing structure? Are there dealers who buy and sell from both sources? How much farm-to-farm trading occurs? Do farms periodically augment their stock from the wild? To answer these questions, it is necessary to understand what drives the wildlife trade – a complex mix of economic, social and cultural factors. The demand for, and consumption of, wildlife in southern China has increased in recent years, purportedly associated with improved economic conditions. An increase in legal and illegal wildlife trade has paralleled this demand, with animals reportedly channeled from many and various locations in south-east Asia. A rich cultural heritage underlies wildlife consumption in China - different species and dishes are favoured for a range of social, business and health reasons. And in the markets, wildcaught civets still attract a price premium, because people believe it is more health-giving (and tastes better) than its grain-fed farmed counterpart. Table 1. Putative factors in disease emergence1 Underlying factor Example of factor Changes in water ecosystems Land-use changes Climatic changes Schistosomiasis, Rift Valley fever, hantavirus pulmonary syndrome Human demographic, societal or behavioural changes Population growth and movement High-density habitation Human conflicts Intravenous drug use Sexual behaviour AIDS, SARS, hepatitis C, ebola haemorrhagic fever Ease, extent and frequency of international travel Worldwide movement of goods and people ‘Airport’ malaria, dissemination of mosquito vectors, rat-borne hantaviruses Technology and industry Changes in food processing and packaging Globalisation of food industries Increased frequency of medical/surgical transplants Increased use of immunosuppressant drugs. BSE, E. coli haemolytic uraemic syndrome, SARS, transfusionassociated AIDS and hepatitis, opportunistic infections in immunosuppressed patients Microbial adaptation and change Microbial evolution. ‘Antigenic drift’ in influenza viruses, multiple antibiotic resistant bacterial diseases Inadequate public health measures Inadequate water quality, sanitation, and vector control Response to environmental selection pressures Reduction of disease prevention programs 1 Example of disease Ecological changes Tuberculosis resurgence in USA, diptheria resurgence in former USSR, cholera in refugee camps in Africa Adapted from LONGBOTTOM (1997); MORSE (1995) 11 Seminar Nasional Teknologi Peternakan dan Veteriner 2007 Wildlife studies involve uncontrolled populations, and many of the complexities that arise from surveying wildlife are related to the inherent difficulties of capturing, re-capturing, sampling, and running diagnostic tests on species that may not have been previously studied. Working in remote locations also makes the collection, storage, and transport of biological samples difficult, especially when optimal diagnostic results depend on maintaining a cold chain. Identifying appropriate diagnostic tests and facilities to enable the effective screening of samples represents another challenge, especially when laboratory facilities are limited, or when agents require the highest level of biosecurity. Serologic tests specifically developed for diseases of wildlife are limited, and those used in wildlife studies are commonly transposed from domestic species. The validity of such tests and the meaningful interpretation of test results can therefore be problematic. For example, even where a test has been validated in domestic species, test characteristics should not be assumed to be the same in wildlife species, given possible differences in pathogen strains, host responses, and exposure to crossreacting infections in the wildlife species (GARDNER et al., 1996). Finally, ethical considerations must come into play when working with wildlife populations, and issues such as the conservation status of the target species may influence the appropriate study design. Meeting the challenges and complexities of understanding and managing the risk of emergence of infectious diseases from wildlife requires skills from a range of disciplines (both ‘hard’ and ‘soft’ sciences) working collaboratively towards a common goal. ACKNOWLEDGEMENTS This work is supported in part by an NIH/NSF “Ecology of Infectious Diseases” award from the John E. Fogarty International Center R01-TW05869, and is published in collaboration with the Australian Biosecurity 12 Cooperative Research Center for Emerging Infectious Diseases (AB-CRC). REFERENCES DASZAK, P., A.A. CUNNINGHAM and A.D. HYATT. 2000. Emerging Infectious Diseases of Wildlife- threats to biodiversity and human health. Science. 287: 443 – 448. DASZAK, P., A. CUNNINGHAM and A. HYATT. 2001. Anthropogenic environmental change and the emergence of infectious diseases in wildlife. Acta Tropica. 78: 103 – 116. DASZAK, P., R. PLOWRIGHT, J.H. EPSTEIN, J. PULLIAM, S. ABDUL RAHMAN, H.E. FIELD, A. JAMALUDDIN, S.H. SHARIFAH, C.S. SMITH, K.J. OLIVAL, S. LUBY, K. HALPIN, A.D. HYATT, A.D., A.A. CUNNINGHAM and THE HENIPAVIRUS ECOLOGY RESEARCH GROUP (HERG). 2006. The emergence of Nipah and Hendra virus: Pathogen dynamics across a wildlife-livestock-human continuum. In: Disease Ecology: Community Structure and Pathogen Dynamics. COLLINGE, S.K. and C. RAY (Eds.). Oxford University Press. pp. 186 – 201. FIELD, H., P. YOUNG, JOHARA MOHD YOB, J. MILLS, L. HALL and J. MACKENZIE. 2001. The natural history of Hendra and Nipah viruses. Microbes and Infection. 3: 315 – 322. GARDNER, I., S. HIETALA and W. BOYCE. 1996. Validity of using serological tests for diagnosis of diseases in wild animals. Rev. Sci. Tech. Off. Int. Epiz. 15: 323 – 335. LEDERBERG, J., R.E. SHOPE and S.C. OAKS. 1992. Emerging infections: microbial threats to health in the United States. Washington: National Academy Press. LONGBOTTOM, H. 1997. Emerging Infectious Diseases. Communicable Disease Intelligence. 21: 89 – 93. MORSE, S.S. 1995. Factors in the emergence of infectious diseases. Emerg. Infect. Dis. 1: 7 – 15. TAYLOR, L., S. LATHAM and M. WOOLHOUSE. 2001. Risk factors for human disease emergence. Phil. Trans. R. Soc. Lond. 356: 983 – 989.