Emerging infectious disease
An emerging infectious disease refer to infectious diseases that have either newly appeared in a population or have existed but are rapidly increasing in incidence, geographic range, or severity due to factors such as environmental changes, antimicrobial resistance, and human-animal interactions. The minority that are capable of developing efficient transmission between humans can become major public and global concerns as potential causes of epidemics or pandemics. Their many impacts can be economic and societal, as well as clinical. EIDs have been increasing steadily since at least 1940.
For every decade since 1940, there has been a consistent increase in the number of EID events from wildlife-related zoonosis. Human activity is the primary driver of this increase, with loss of biodiversity a leading mechanism.
Emerging infections account for at least 12% of all human pathogens. EIDs can be caused by newly identified microbes, including novel species or strains of virus. Some EIDs evolve from a known pathogen, as occurs with new strains of influenza. EIDs may also result from spread of an existing disease to a new population in a different geographic region, as occurs with West Nile virus outbreaks|West Nile fever outbreaks]. Some known diseases can also emerge in areas undergoing ecologic transformation. Others can experience a resurgence as a re-emerging infectious disease, like tuberculosis or measles. Nosocomial infections, such as methicillin-resistant Staphylococcus aureus are emerging in hospitals, and are extremely problematic in that they are resistant to many antibiotics. Of growing concern are adverse synergistic interactions between emerging diseases and other infectious and non-infectious conditions leading to the development of novel syndemics.
Many EID are zoonotic, deriving from pathogens present in animals, with only occasional cross-species transmission into human populations. For instance, most emergent viruses are zoonotic.
History of the concept of emerging infectious diseases
The French doctor Charles Anglada wrote a book in 1869 on extinct and new diseases. He did not distinguish infectious diseases from others. He writes in the introduction:Charles Nicolle, laureate of the Nobel Prize in Physiology or Medicine elaborated the concept of emergence of diseases in his 1930 book Naissance, vie et mort des maladies infectieuses, and later in Destin des maladies infectieuses published in 1933 which served as lecture notes for his teaching of a second year course at the Collège de France. In the introduction of the book he sets out the program of the lectures:The term emerging disease has been in use in scientific publications since the beginning of the 1960s at least and is used in the modern sense by David Sencer in his 1971 article "Emerging Diseases of Man and Animals" where in the first sentence of the introduction he implicitly defines emerging diseases as "infectious diseases of man and animals currently emerging as public health problems" and as a consequence also includes re-emerging diseases:He also notes that some infectious agents are newly considered as diseases because of changing medical technologies:He concludes the introduction with a word of caution:However, to many people in the 1960s and 1970s the emergence of new diseases appeared as a marginal problem, as illustrated by the introduction to the 1962 edition of Natural History of Infectious Disease by Macfarlane Burnet:as well as the epilogue of the 1972 edition:The concept gained more interest at the end of the 1980s as a reaction to the AIDS epidemic. On the side of epistemology, Mirko Grmek worked on the concept of emerging diseases while writing his book on the history of AIDS and later in 1993 published an article about the concept of emerging disease as a more precise notion than the term "new disease" that was mostly used in France at that time to qualify AIDS among others.
Also under the shock of the emergence of AIDS, epidemiologists wanted to take a more active approach to anticipate and prevent the emergence of new diseases. Stephen S. Morse from The Rockefeller University in New York was chair and principal organizer of the NIAID/NIH Conference "Emerging Viruses: The Evolution of Viruses and Viral Diseases" held 1–3 May 1989 in Washington, DC. In the article summarizing the conference the authors write:They further note:In a 1991 paper Morse underlines how the emergence of new infectious diseases is the opposite of the then generally expected retreat of these diseases:As a direct consequence of the 1989 conference on emerging viruses, the Institute Of Medicine convened in February 1991 the 19-member multidisciplinary Committee on Emerging Microbial Threats to Health, co-chaired by Joshua Lederberg and Robert Shope, to conduct an 18-month study. According to the report produced by the committee in 1992, its charge "was to identify significant emerging infectious diseases, determine what might be done to deal with them, and recommend how similar future threats might be confronted to lessen their impact on public health." The report recommended setting up a surveillance program to recognize emerging diseases and proposed methods of intervention in case an emergent disease was discovered.The proposed interventions were based on the following: the U.S. public health system, research and training, vaccine and drug development, vector control, public education and behavioral change. A few years after the 1989 Emerging Viruses conference and the 1992 report, the Program for Monitoring Emerging Diseases was formed by a group of scientists as a follow-up in 1994 and the Centres for Disease Control launched the Emerging Infectious Diseases journal in 1995.
A decade later the IOM convened the Committee on Emerging Microbial Threats to Health in the 21st Century which published its conclusions in 2003.
In April 2000 the WHO organized a meeting on Global Outbreak Alert and Response, which was the founding act of the Global Outbreak Alert and Response Network.
In 2014, the Western African Ebola [virus epidemic] demonstrated how ill-prepared the world was to handle such an epidemic. In response, the Coalition for Epidemic Preparedness Innovation was launched at the World Economic Forum in 2017 with the objective of accelerating the development of vaccines against emerging infectious diseases to be able to offer them to affected populations during outbreaks. CEPI promotes the idea that a proactive approach is required to "create a world in which epidemics are no longer a threat to humanity".
Classification
One way to classify emerging infections diseases is by time and how humans were involved in the emergence:- Newly emerging infectious diseases – diseases that were not previously described in humans, such as SARS-CoV-2 and MERS
- Re-emerging infectious diseases – diseases that have spread to new places or which previous treatments no longer control, such as methicillin-resistant Staphylococcus aureus, tuberculosis, and cholera
- Deliberately emerging infectious diseases – diseases created by humans for bioterrorism, such as bioterrorism-related agents like anthrax and smallpox
- Accidentally emerging infectious diseases – diseases created or spread unintentionally by humans, such as vaccine-derived poliovirus
Contributing factors
- Microbial adaptation and change
- Human susceptibility to infection
- Climate and weather
- Changing ecosystems
- Human demographics and behavior
- Economic development and land use
- International travel and commerce
- Technology and industry
- Breakdown of public health measures
- Poverty and social inequality
- War and famine
- Lack of political will
- Intent to harm
| Factor of emergence | Example |
| Microbial adaption | genetic drift and genetic shift in Influenza A |
| Changing human susceptibility | mass immunocompromisation with HIV/AIDS |
| Climate change | diseases transmitted by animal vectors such as mosquitoes are moving further from the tropics as the climate warms. By increasing the range of these animal vectors, the diseases are appearing in previously unaffected regions. |
| Changes in human demographics and travel facilitating rapid global spread | Globalization and travel facilitates the rapid spread of pathogens, ex SARS-related coronaviruses |
| Economic development | use of antibiotics to increase meat yield of farmed cows leads to antibiotic resistance |
| War and famine | Clearing of animal habitats that increase the range of diseases such as ebola |
| Inadequate public health services | |
| Poverty and social inequality | tuberculosis is primarily a problem in low-income areas |
| Bioterrorism | 2001 Anthrax attacks |
| Land use | Dam construction and irrigation systems can encourage malaria and other mosquito-borne diseases Use of indiscriminate pesticides in industrial farming reduces/eliminates biological controls of known disease vectors. Deforestation and habitat destruction increase human exposure to zoonotic pathogens, Nipah virus which is linked to bat-to-human transmission. |
| Anti-vaccination or Vaccine hesitancy | Re-emergence of measles |
| Wildlife trade | Has been linked to zoonotic emergence and spread of new infectious diseases in humans, including Nipah virus and COVID-19. Crowded and unhygienic wet markets and wildlife farms have been implicated in animal-human transmission of emergent viruses, including novel coronaviruses and influenza viruses Complex issues surrounding the commerce and consumption of bushmeat are also of particular concern. |
Zoonotic diseases
, originating from animal sources, pose a significant threat to human health. Proximity to wildlife, and climate change have created favorable conditions for the transmission of zoonotic diseases, leading to outbreaks such as Zika, Ebola, and COVID-19. Up to 75% of emerging infectious diseases are zoonotic, originating from viruses and other pathogens that are transmitted from animals to humans. Understanding the mechanisms of transmission, the role of wildlife trade, and the importance of surveillance and early detection is crucial for mitigating the impact of zoonotic diseases on human health. Surveillance efforts involving wastewater have been identified as valuable tools for detecting early warning signs of disease emergence and providing timely interventions.List
NIAID list of Biodefense and Emerging Infectious Diseases
The U.S. National Institute of Allergy and Infectious Diseases maintains a list of Biodefense and Emerging Infectious Diseases. The list is categorized by biodefense risk, which is mostly based on biological warfare and bioterrorism considerations. As of 2004, it recognized the following emerging and re-emerging diseases.WHO list of most important emerging infectious diseases
In December 2015, the World Health Organization held a workshop on prioritization of pathogens "for accelerated R&D for severe emerging diseases with potential to generate a public health emergency, and for which no, or insufficient, preventive and curative solutions exist." The result was a list containing the following six diseases:- Crimean–Congo hemorrhagic fever
- Filovirus diseases
- Highly pathogenic emerging Coronaviruses relevant to humans
- Lassa fever
- Nipah virus infection
- Rift Valley fever
- Human transmissibility
- Severity or case fatality rate
- Spillover potential
- Evolutionary potential
- Available countermeasures
- Difficulty of detection or control
- Public health context of the affected area
- Potential scope of outbreak
- Potential societal impacts
Newly reported infectious diseases
| Number of species known in 2005 | Number of species reported from 1980 to 2005 | |
| TOTAL | 1399 | 87 |
| Bacteria | 541 | 11 |
| Fungi | 325 | 13 |
| Helminths | 285 | 1 |
| Prions | 2 | 1 |
| Protozoa | 57 | 3 |
| Viruses | 189 | 58 |
| DNA viruses | 36 | 9 |
| RNA viruses | 153 | 49 |