Chapter 30 Supplement One Health
Interdependence of People, Other Species, and the Planet
The One Health approach can provide integrated and collaborative solutions to a number of important global health and sustainability challenges. As an example of its widespread applicability, we highlight the Millennium Development Goals (MDGs, www.un.org/millenniumgoals), one of the most globally accepted development metric paradigms. The United Nations spearheaded the MDGs to address poverty, education, equity, mortality, sustainability, and health. The eight targets for the MDGs address wide-reaching and complex global issues, and as such, they require multisectoral, integrated approaches. Adopting a One Health approach could help in achieving the MDGs by strengthening cross-sectoral collaboration and approaching problems with a preventive focus.1–3 In fact, six of the eight MDGs could benefit from a strategic application of the One Health approach (Table S30-1).
|Millennium Development Goals||Potential Benefits of One Health Approach|
|Goal 1: Eradicate extreme poverty and hunger.*||Improved crop agriculture and livestock production; better understanding of how climate change will affect food security.|
|Goal 2: Achieve universal primary education.||Indirect relevance.|
|Goal 3: Promote gender equality and empower women.||Indirect relevance.|
|Goal 4: Reduce child mortality.*||Reduce diarrheal infections, one of the biggest killers of children, by improving water quality and food safety.|
|Goal 5: Improve maternal health.*||Improve water quality and food safety; reduce use of biomass for fuel and promote use of alternative, cleaner stoves.|
|Goal 6: Combat HIV/AIDS, malaria, and other diseases.*||Understand the environmental and behavioral drivers of disease emergence; approaches to vector control; and relevance of animal reservoirs of disease.|
|Goal 7: Ensure environmental sustainability.*||Reduce the rate of environmental degradation; incorporate more efficient, less costly, and less environmentally damaging agricultural and industrial methods; recognize the importance of addressing climate change.|
|Goal 8: Develop a global partnership for development.*||Integrate health, environmental stewardship, energy, trade, business, and public infrastructure systems to improve health.|
ONE HEALTH CASE STUDY 1 Deforestation, Intensive Livestock Production, and Nipah Virus Emergence4
An outbreak of a novel paramyxovirus, the Nipah virus, struck Malaysia in late September of 1998. Although the virus is native to fruit bats (Pteropodidae family),5 unusually close contact between bats and swine during 1998 allowed the virus to jump species. Those in contact with infected swine quickly became ill, and the virus rapidly spread across peninsular Malaysia and into Singapore through the transport of infected pigs (Fig. S30-1). By the time the outbreak was contained in May 1999, 105 individuals had died, most of whom were directly involved with swine farming. Additionally, more than 1.1 million pigs had been slaughtered at a cost of $97 million, effectively devastating Malaysia’s swine industry.
(Modified from Nadimpalli M, Akoroda U, Williams JT: Nipah virus in Malaysia, 1998-99: a One Health perspective. In Barrett MA, Sackey-Harris M, Stroud C, editors. Applications of the One Health approach to current health and sustainability challenges: an educational resource, vol 1, Durham, NC, Duke University, University of North Carolina, North Carolina State University [In press].)
Retrospectively, it was determined that ineffective control measures and poor disease surveillance greatly exacerbated the spread and severity of disease. The novel exposure of humans to Nipah virus was caused by a unique combination of environmental, animal, and human factors: deforestation, forest fires, and a drought in 1998 are thought to have forced fruit bats to concentrate in fruit orchards in northern Malaysia.6,7 The proximity of these orchards to pig nurseries allowed for the spillover of Nipah virus from bats to pigs,8 and unprotected physical contact between pigs and pig farmers allowed the virus to rapidly infect humans. Unfortunately, the disconnect among Malaysia’s human, animal, and environmental health entities made recognizing Nipah virus as the causative agent of the outbreak particularly complicated for the Malaysian government. A One Health approach involving interdisciplinary collaborations among these entities could have resulted in more rapid identification of the outbreak and implementation of more suitable control measures, saving lives.
Fruit bats are native to several countries in or proximal to Southeast Asia, including Indonesia, Madagascar, India, Bangladesh, China, Thailand, Cambodia, Papua New Guinea, and Australia. Bats in all these countries have tested seropositive for either Nipah virus or Hendra virus, a closely related paramyxovirus also capable of infecting humans.9 There is potential for overlap in distribution of Hendra and Nipah viruses and for pteropid bats to act as vectors for long-distance transmission to humans or animals.10 Although the 1998-99 Nipah virus outbreak affected only Malaysia and Singapore, future outbreaks of Nipah virus could occur in any country within the geographic range of these bats. Pteropid bats migrate in response to available food sources, and their movements do not recognize national boundaries. Human outbreaks have recently occurred in both India and Bangladesh, for example, from the consumption of contaminated fruit and fruit products.9 A One Health approach could be invaluable to any country dealing with or hoping to prevent an outbreak of Nipah virus in the future.
Note: The text in this case study was modified with permission from Nadimpalli M, Akoroda U, Williams JT: Nipah virus in Malaysia, 1998-99: a One Health perspective. In Barrett MA, Sackey-Harris M, Stroud C, editors: Applications of the One Health approach to current health and sustainability challenges: an educational resource, vol 1, Durham, NC, Duke University, University of North Carolina, North Carolina State University [In press].
ONE HEALTH CASE STUDY 2 Biodiversity Loss, Land Use, and Lyme Disease11
Lyme disease is the most prevalent vector-borne disease in the temperate zone. It is a zoonosis caused by the bacterium Borrelia burgdorferi. The bacteria are maintained in transmission cycles involving tick vectors and wild animal hosts (rodents, birds, and other wild mammals).
Lyme disease is transmitted to humans and domesticated animals by certain species of ticks from wildlife. Although the geographic range of the bacterium causing Lyme disease has expanded and contracted for millennia with environmental change (i.e., interglacials) in Eurasia and North America, the Lyme epidemic in the United States was likely caused by human-induced changes in land use. One example includes farmland reverted to woodland as the result of changing economics and policy in agriculture. This caused increased deer and tick populations and a culture of outdoor recreational activity in these woodlands, which enabled greater interaction of people with infected ticks. As development increased forest fragmentation, exposure of humans to infected ticks also increased (Fig. S30-2). Evolution of B. burgdorferi for different reservoir hosts has resulted in genetic variants that cause different disease entities in humans.11a
(Modified from Veterinarians Without Borders: One Health for One World: a compendium of case studies, 2010. Courtesy Nicolle Rager-Fuller, National Science Foundation.)
Changes to biodiversity are likely to have impacts on Lyme disease risk by affecting the abundance and range of reservoir hosts in any given locality. Although this has become a paradigm for exploring conservation and infection disease risk relationships, the direction of effect is as yet not completely predictable. Emergence of Lyme disease risk in North America is being driven by a warming climate, which enhances the survival of the tick vector.
Understanding the environmental determinants of Lyme disease helps to predict the risk of exposure and assists public health professionals in making decisions. For instance, communication among managers of parklands, the general public, hunters, dog owners, and public health officials allows disease awareness to be raised, decreasing chances of an epidemic in humans. Understanding links between ecological processes and disease entities allows for more precise understanding of the links among animal, environmental, and human health.
Recent rapid changes in climates, landscapes, and how people interact with their environment have been associated with the emergence of more severe diseases. Thus, populations who live near changes in land use (urbanization, encroachment into wilderness, abandonment of farms, intensification of agriculture) need to be monitored for changes in health outcomes. By involving local people in surveillance and response and investigating their concerns seriously, policy makers are less likely to be surprised by new diseases and will be more able to respond quickly and effectively.
ONE HEALTH CASE STUDY 3 Rift Valley Fever at the Interface of Humans, Domestic Animals, and the Environment11
Rift Valley Fever (RVF) is a zoonotic disease affecting mainly sheep and cattle in the Rift Valley in Africa, and more recently the Middle East. It is caused by a mosquito-borne virus. The severity and degree of clinical signs may vary according to age or breeds of the animals affected, with infections usually inapparent or mild in adults but with high mortality rates in newborn animals and abortions in pregnant animals. The majority of animal infections result from infected mosquito bites, whereas most human infections are caused by direct or indirect contact with the blood or organs of infected animals. RVF in humans is usually asymptomatic or characterized by an acute fever. However, although 99% of infections are subclinical, the numbers of deaths can be high because of the sheer numbers of people infected. The virus infects the vector at every stage of its life cycle, and infected mosquito eggs can lie dormant in the ground for long periods in semi-arid areas. Hatching is stimulated by wet weather, and the local flooding that follows allows water to accumulate in pools that provide an ideal mosquito breeding ground. Most species of the Aedes mosquito rarely feed on humans, but when large numbers of animals become infected through mosquito bites, this can lead to direct transmission to humans by infected blood and tissue (e.g., during butchering) and also mass transmission by secondary mosquito vectors that become infected by biting livestock.
Identified in the 1930s in Kenya, RVF virus now circulates in many other African countries, as well as on the Arabian Peninsula, where epizootics and associated human cases have been reported. Larger epidemics appear to occur about every decade. Climate change could have a major impact on the occurrence and distribution of the disease due to more frequent extreme weather events and the impact of these events on the biology and geographic distribution of arthropod vectors. Additionally, it is argued that the international trade of livestock and large-scale human movements, which have both expanded during the past 40 years, are important contributory factors. RVF, being a transboundary zoonotic infection associated with human health impacts and large losses of livestock assets, is complicated by climatic changes commonly affecting vulnerable African communities. Poor pastoralists, already facing increased climate-related hazards such as droughts and floods and lacking adequate support policies, may be most seriously affected.
Prediction of outbreaks of RVF can be made using satellite imaging because vegetation responds to increased rainfall, and variations in vegetation can be easily measured by satellite. In East Africa, vegetation index maps have been used together with ground data to monitor vector populations and RVF viral activity, and a correlation between these two parameters has been established. Vegetation measurements can be used in a more proactive way to forecast RVF before cases reach epidemic proportions. Such predictions can improve the timeliness of action to identify, prevent, and/or control the disease by implementing vector control. Steps that can be taken to prevent amplification of the virus in livestock include vector control and targeted, hygienic mass vaccination of animals. Strengthening global, regional, and national early-warning systems and coordinating subsequent prevention and intervention measures will be crucial.
ONE HEALTH CASE STUDY 4 Origins of Human Immunodeficiency Virus
Two types of human immunodeficiency virus (HIV) can infect humans: HIV-1, which causes the majority of HIV infections worldwide, and HIV-2, which is largely geographically confined to West Africa.12,13 HIV-1 has infected more than 60 million people worldwide and has resulted in more than 25 million deaths.14 Both types have been traced back to simian immunodeficiency viruses (SIVs) endemic in more than 26 different species of nonhuman primates15 (Fig. S30-3). The pandemic strain of HIV-1 (group M) is most closely related to SIV documented in chimpanzees and originated from one distinct cross-species transmission event. HIV-2 is most closely related to SIV from wild sooty mangabeys. Based on banked human blood, tissue samples and estimates of viral mutation rates, scientists have calculated that the HIV-1 (group M) jump from chimpanzees to humans occurred in central Africa during the late 19th or early 20th century, a time of rapid urbanization and social change in the region.
(Modified from Sharp PM, Hahn BH: Origins of HIV and the AIDS pandemic. Cold Spring Harbor Perspect Med 1(1), 2011.)