Understanding the mechanisms that underlie newly emerging and reemerging infectious diseases (EID) is one of the most difficult scientific problems facing society today. EIDs are diseases that have recently increased in incidence or in geographic or host range (e.g., tuberculosis, cholera, malaria, dengue fever, Japanese encephalitis, West Nile fever, and yellow fever), diseases caused by new variants assigned to known pathogens (e.g., HIV, new strains of influenza virus, SARS, drug resistant strains of bacteria, Nipah virus, Ebola virus, hantavirus pulmonary syndrome, and avian influenza virus), and bacteria newly resistant to antibiotics, notably the multiple resistant strains that render the armamentarium of antibiotics useless.
Fundamental questions persist concerning molecular mechanisms and specific cellular processes involved in pathogenesis, as well as transmission dynamics and epidemiology, of pathogens that cause some of the most studied of the reemerging infectious diseases, such as tuberculosis, malaria, and cholera. Newly emerging diseases caused by entirely novel or previously unrecognized pathogens, such as HIV/AIDS, SARS, and hantavirus, or those whose modes of transmission are currently under study, as in the case of Ebola and Nipah, represent yet another significant challenge. Certainly the mechanisms or processes of disease emergence involve factors in addition to those at molecular and cellular levels. These include climate, rainfall, ocean and air circulation patterns, and extreme weather events, as well as the ecology of the pathogens’ reservoirs and vectors, namely those factors associated with larger-scale mechanisms and the dynamic behavior of ecosystems in which parasite (pathogen) and host relationships are embedded. Still other factors are involved, and must be identified, if a truly holistic framework is to be constructed that incorporates factors related to human and societal mechanisms.
Demographic and social changes, along with associated environmental alterations, and even the efforts to control disease, have contributed to the severity of the problem of EIDs. The use of antimicrobials, pesticides, and biological controls predictably are effecting changes in pathogens, hosts, and ecological systems, and often unwittingly facilitating disease emergence or reemergence. Antibiotic resistant Strepococcus A and E. coli 0:157 are prime examples. Pathogens and their hosts, including humans, reproduce, grow, and adapt in an environmental context, devastatingly exemplified by the avian influenza threat (chickens, ducks, pigs, and humans in close confines). This context is most accurately captured using a holistic or systems perspective, considering sub-systems at different levels of organization—those at lower levels embedded within those at successively higher levels—including social as well as physical, chemical, and biological components.
This view, applied to the extraordinary depth and richness of living systems, spanning the scale of microbial genomes to the regional ecosystems populated by humans and reservoir species, evoked the term biocomplexity. Several investigators, including social scientists, conceived and elaborated on similar themes using different terminology. Ecological and social scientists working on ecosystem and natural resources management challenges refer to “social–ecological systems” or “human and natural systems”. The contraction of social–ecological systems, “socioecological systems,” has been used to describe this same systems perspective, stressing coupled human–natural systems and complexity theory, in the context of health and emerging infectious diseases. The hyphenated or contracted terms share with biocomplexity an emphasis on the interaction of humans and nature as a complex system, and arguably embrace what is fundamentally the same paradigm.
Emerging and Reemerging Infectious Diseases: Biocomplexity as an Interdisciplinary Paradigm
by Bruce A. Wilcox and Rita R. Colwell
EcoHealth
https://link.springer.com/article/10.1007/s10393-005-8961-3
Abstract
Understanding factors responsible for reemergence of diseases believed to have been controlled and outbreaks of previously unknown infectious diseases is one of the most difficult scientific problems facing society today. Significant knowledge gaps exist for even the most studied emerging infectious diseases. Coupled with failures in the response to the resurgence of infectious diseases, this lack of information is embedded in a simplistic view of pathogens and disconnected from a social and ecological context, and assumes a linear response of pathogens to environmental change. In fact, the natural reservoirs and transmission rates of most emerging infectious diseases primarily are affected by environmental factors, such as seasonality or meteorological events, typically producing nonlinear responses that are inherently unpredictable. A more realistic view of emerging infectious diseases requires a holistic perspective that incorporates social as well as physical, chemical, and biological dimensions of our planet’s systems. The notion of biocomplexity captures this depth and richness, and most importantly, the interactions of human and natural systems. This article provides a brief review and a synthesis of interdisciplinary approaches and insights employing the biocomplexity paradigm and offers a social–ecological approach for addressing and garnering an improved understanding of emerging infectious diseases. Drawing on findings from studies of cholera and other examples of emerging waterborne, zoonotic, and vectorborne diseases, a “blueprint” for the proposed interdisciplinary research framework is offered which integrates biological processes from the molecular level to that of communities and regional systems, incorporating public health infrastructure and climate aspects.
INTRODUCTION
Understanding the mechanisms that underlie newly emerging and reemerging infectious diseases (EID) is one of the most difficult scientific problems facing society today. EIDs are diseases that have recently increased in incidence or in geographic or host range (e.g., tuberculosis, cholera, malaria, dengue fever, Japanese encephalitis, West Nile fever, and yellow fever), diseases caused by new variants assigned to known pathogens (e.g., HIV, new strains of influenza virus, SARS, drug resistant strains of bacteria, Nipah virus, Ebola virus, hantavirus pulmonary syndrome, and avian influenza virus), and bacteria newly resistant to antibiotics, notably the multiple resistant strains that render the armamentarium of antibiotics useless (Smolinski et al., 2003).
Fundamental questions persist concerning molecular mechanisms and specific cellular processes involved in pathogenesis, as well as transmission dynamics and epidemiology, of pathogens that cause some of the most studied of the reemerging infectious diseases, such as tuberculosis, malaria, and cholera. Newly emerging diseases caused by entirely novel or previously unrecognized pathogens, such as HIV/AIDS, SARS, and hantavirus, or those whose modes of transmission are currently under study, as in the case of Ebola and Nipah, represent yet another significant challenge. Certainly the mechanisms or processes of disease emergence involve factors in addition to those at molecular and cellular levels. These include climate, rainfall, ocean and air circulation patterns, and extreme weather events, as well as the ecology of the pathogens’ reservoirs and vectors, namely those factors associated with larger-scale mechanisms and the dynamic behavior of ecosystems in which parasite (pathogen) and host relationships are embedded (Horwitz and Wilcox, 2005). Still other factors are involved, and must be identified, if a truly holistic framework is to be constructed that incorporates factors related to human and societal mechanisms.
Demographic and social changes, along with associated environmental alterations, and even the efforts to control disease, have contributed to the severity of the problem of EIDs (Wilcox and Gubler, 2005). The use of antimicrobials, pesticides, and biological controls predictably are effecting changes in pathogens, hosts, and ecological systems, and often unwittingly facilitating disease emergence or reemergence (Lederberg et al., 1992; Gubler, 1998; Burroughs et al., 2003; Knobler et al., 2003; Smolinski et al., 2003). Antibiotic resistant Strepococcus A and E. coli 0:157 are prime examples. Pathogens and their hosts, including humans, reproduce, grow, and adapt in an environmental context, devastatingly exemplified by the avian influenza threat (chickens, ducks, pigs, and humans in close confines). This context is most accurately captured using a holistic or systems perspective, considering sub-systems at different levels of organization—those at lower levels embedded within those at successively higher levels—including social as well as physical, chemical, and biological components.
This view, applied to the extraordinary depth and richness of living systems, spanning the scale of microbial genomes to the regional ecosystems populated by humans and reservoir species, evoked the term biocomplexity (Colwell, 1998). Several investigators, including social scientists, conceived and elaborated on similar themes using different terminology. Ecological and social scientists working on ecosystem and natural resources management challenges refer to “social–ecological systems” (Berkes and Folke, 1998; Berkes et al., 2003) or “human and natural systems” (Gunderson and Holling, 2002). The contraction of social–ecological systems, “socioecological systems,” has been used to describe this same systems perspective, stressing coupled human–natural systems and complexity theory, in the context of health and emerging infectious diseases (Waltner-Toews, 2001). The hyphenated or contracted terms share with biocomplexity an emphasis on the interaction of humans and nature as a complex system, and arguably embrace what is fundamentally the same paradigm. For convenience in this article, we will refer to “human–natural systems perspective” as synonymous with “biocomplexity.” We also note these ideas, including those associated with “eco-epidemiology” expressing the need for a broadened concept of causality in epidemiology (Kaufman and Poole, 2000), are part of a larger emerging paradigm called “post-normal science” by some investigators (Ravetz, 1999).
In this article, we draw from our own research and the results of a recent meeting entitled Social–Ecological Systems and Emerging Infectious Diseases, that was part of the National Institutes of Health Roadmap initiative, Research Teams of the Future, the purpose of which was to examine EIDs through the lens of this new paradigm. The objective of this meeting was to facilitate interdisciplinary research on the problem of emerging and reemerging infectious diseases. Our aim here is to provide a short review and synthesis of these interdisciplinary approaches and insights emerging from the meeting and reported in the recent literature. We use the case of cholera, the current scientific understanding of which currently provides a basis for the most complete human–natural systems model of any EID, and a complementary model based on zoonotic and vectorborne EIDs in general. Together, with two published EID case studies from this meeting, a framework is developing that has significant potential for explaining the phenomenon of global infectious disease emergence. We believe the approach has significant bearing on the interdisciplinary methodology of emerging infectious disease research, and suggests future research directions, as well as prospects for managing infectious disease emergence.
NEW EID RESEARCH PARADIGM
Two complementary views or general models of emerging infectious disease have developed, based on the human–natural systems perspective: one centered on and illustrated by the case of cholera and the other which builds on the accumulating cases of mainly reemerging zoonotic and vectorborne diseases. Cholera is historically the most studied infectious disease, since the discovery of its etiology established the theory of communicable diseases and the field of epidemiology (Snow, 1855). The relatively recent discovery (Huq et al., 1983; Colwell, 1996) of the connection of cholera with the natural environment and ecological processes has dramatically broadened the scope of cholera research. With a few exceptions, zoonotic and vectorborne diseases are, in general, readily understood as having links with the natural environment. However, the connection between their epidemiology and ecosystem dynamics or processes, not to mention coupled human–natural system behavior, is only now beginning to be appreciated. Some EIDs like SARS, Ebola, even HIV/AIDS, and the more recent and disturbingly potentially disastrous avian influenza (Aldhous and Tomlin, 2005; Osterholm, 2005) are diseases that effectively originate as zoonotic parasites or pathogens whose transmission cycles can become completely uncoupled from their animal reservoirs.
新興・再興感染症（EID）の根底にあるメカニズムを理解することは、今日社会が直面している最も困難な科学的問題の 1 つです。 EID とは、最近発生率が増加した病気、地理的または宿主範囲が増加した病気（結核、コレラ、マラリア、デング熱、日本脳炎、西ナイル熱、黄熱病など）、既知の病原体に割り当てられた新しい変異型によって引き起こされる病気（例: 感染症）です。 、HIV、新型インフルエンザウイルス株、SARS、細菌の薬剤耐性株、ニパウイルス、エボラウイルス、ハンタウイルス肺症候群、鳥インフルエンザウイルス）、および抗生物質に対して新たに耐性となった細菌、特に抗生物質の兵器を提供する複数の耐性株 抗生物質は役に立たない。
結核、マラリア、コレラなど、最も研究されている再興感染症のいくつかを引き起こす病原体の、発病に関与する分子機構や特定の細胞プロセス、さらには伝播動態や疫学に関して、基本的な疑問が依然として残っている。 HIV/AIDS、SARS、ハンタウイルスなど、まったく新規の病原体やこれまで認識されていなかった病原体によって引き起こされる新たに出現した疾患や、エボラ出血熱やニパの場合のようにその感染経路が現在研究中の疾患は、さらに大きな課題となっています。 確かに、病気の出現のメカニズムやプロセスには、分子および細胞レベルの要因以外の要因も関与しています。 これらには、気候、降雨量、海洋と空気の循環パターン、異常気象現象に加えて、病原体の保有場所と媒介生物の生態学、すなわち、寄生虫（病原体）が生息する生態系のより大規模なメカニズムと動的な挙動に関連する要因が含まれます。 ) とホスト関係が埋め込まれています。 人間および社会のメカニズムに関連する要素を組み込んだ真に全体的な枠組みを構築するには、さらに他の要素も関与しており、特定する必要があります。
人口動態や社会の変化、それに伴う環境の変化、さらには病気を制御する取り組みも、EIDs の問題の深刻化に貢献しています。 抗菌剤、殺虫剤、生物学的防除の使用は、予想通り、病原体、宿主、生態系に変化をもたらし、知らず知らずのうちに病気の発生や再発を促進していることがよくあります。 抗生物質耐性のある Strepococcus A および E. coli 0:157 がその代表的な例です。 病原体と人間を含むその宿主は、環境状況の中で繁殖、成長、適応します。鳥インフルエンザの脅威がその壊滅的な例です（狭い範囲内のニワトリ、アヒル、豚、人間）。 このコンテキストは、組織のさまざまなレベルのサブシステム（社会的要素だけでなく、物理的、化学的、生物学的要素を含む、より高いレベルのサブシステム内に埋め込まれた下位レベルのサブシステム）を考慮した、総合的またはシステムの観点を使用することで最も正確に捉えられます。
この見解は、微生物ゲノムの規模から人間や貯水池種が生息する地域生態系にまで及ぶ、生命システムの並外れた深さと豊かさに適用され、生物複雑性という用語を呼び起こしました。 社会科学者を含む数人の研究者が、異なる用語を使用して同様のテーマを考案し、詳しく説明しました。 生態系および天然資源管理の課題に取り組む生態学および社会科学者は、「社会生態系」または「人間と自然のシステム」を指します。 社会生態学的システムの短縮形である「社会生態学的システム」は、これと同じシステムの観点を説明するために使用され、健康と新興感染症の文脈において、人間と自然のシステムの結合と複雑性理論を強調しています。 ハイフンでつながれたまたは短縮された用語は、複雑なシステムとしての人間と自然の相互作用に重点を置く生物複雑性と共通しており、おそらく基本的に同じパラダイムを包含しています。