Emerging infectious disease
An emerging infectious disease is an infectious disease whose incidence has increased recently, and could increase in the near future. Such diseases do not respect national boundaries. 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.
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 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 introductionA widely held opinion among physicians admits the invariability of pathologies. All the illnesses which have existed or which have an outbreak around us are categorized according to arrested and preconceived types, and must enter one way or the other into the frameworks established by the nosologists. History and observation protest wildly against this prejudice, and this is what they teach: Diseases which have disappeared and whose traces are confined to the archives of science, are followed by other diseases, unknown to the contemporary generation, and which come for the first time to assert their rights. In other words, there are extinct and new diseases.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 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
It is this historical existence, this destiny that will be the subject of our talks. I will have to answer, to the extent that our current knowledge allows, questions that you have asked yourself, that every thoughtful or simply curious mind asks: have the infectious diseases that we observe today always existed? Or have some of them appeared in the course of history? Can we assume that new ones will appear? Can we assume that some of these diseases will disappear? Have some of them already disappeared? Finally, what will become of humanity and domestic animals if, as a result of more and more frequent contacts between people, the number of infectious diseases continues to increase?The term emerging disease has been in use in scientific publications since the beginning of the 60s 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
Infectious diseases of man and animals currently emerging as public health problems include some old acquaintances and some that are new in respect to identity or concept.He also notes that some infectious agents are newly considered as diseases because of changing medical technologies
But there are also many familiar organisms formerly considered nonpathogenic that are now associated with nosocomial infections, use of artificial kidneys, and the acceptance or rejection of organ transplants, for example.He concludes the introduction with a word of caution
And so infectious disease, one of man's oldest enemies, survives as an adversary that calls forth our best efforts.However to many people in the 60s and 70s 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
to write about infectious disease is almost to write of something that has passed into historyas well as the epilogue of the 1972 edition
On the basis of what has happened in the last thirty years, can we forecast any likely developments for the 1970s? If for the present we retain a basic optimism and assume no major catastrophes occur the most likely forecast about the future of infectious disease is that it will be very dull. There may be some wholly unexpected emergence of a new and dangerous infectious disease, but nothing of the sort has marked the past fifty years.
The concept gained more interest at the end of the 80s 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
Challenged by the sudden appearance of AIDS as a major public health crisis jointly sponsored the conference "Emerging Viruses: The Evolution of Viruses and Viral Diseases" It was convened to consider the mechanisms of viral emergence and possible strategies for anticipating, detecting, and preventing the emergence of new viral diseases in the future.They further note
Surprisingly, most emergent viruses are zoonotic, with natural animal reservoirs a more frequent source of new viruses than is the sudden evolution of a new entity. The most frequent factor in emergence is human behavior that increases the probability of transfer of viruses from their endogenous animal hosts to man.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
The striking successes achieved with antibiotics, together with widespread application of vaccines for many previously feared viral diseases, made it appear to many physicians and the public that infectious diseases were retreating and would in time be fully conquered. Although this view was disputed by virologists and many specialists in infectious diseases, it had become a commonplace to suggest that infectious diseases were about to become a thing of the past .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.
A well-designed, well-implemented surveillance program can detect unusual clusters of disease, document the geographic and demographic spread of an outbreak, and estimate the magnitude of the problem. It can also help to describe the natural history of a disease, identify factors responsible for emergence, facilitate laboratory and epidemiological research, and assess the success of specific intervention efforts.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 IOM 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".
Contributing factors
The 1992 IOM report distinguished 6 factors contributing to emergence of new diseases which were extended to 13 factors in the 2003 report- 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 |
| Changes in human demographics and travel facilitating rapid global spread | 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 |
| 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. |
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 6 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 |
Major outbreaks
The following table summarizes the major outbreaks since 1998 caused by emerging or re-emerging infectious diseases| Disease | Country or region | Year of start of outbreak |
| Ngari virus | Kenya, Tanzania, Somalia | 1998 |
| Nipah virus | Malaysia | 1998 |
| West Nile virus | USA | 1999 |
| Itaya virus | Peru | 1999 |
| Rift Valley fever | Saudi Arabia and Yemen | 2000 |
| EBLV-2 | Scotland | 2002 |
| SARS-CoV | 2002 | |
| Influenza A virus subtype H7N2 | 2002 | |
| Monkeypox | USA | 2003 |
| Chapare virus | Bolivia | 2003 |
| Plague | Algeria | 2003 |
| HTLV-3, HTLV-4 | Cameroon | 2005 |
| Melaka virus | Malaysia | 2006 |
| LuJo virus | southern Africa | 2008 |
| Multi-drug resistant P. falciparum | South-East Asia | 2008 |
| Candida auris | 2009 | |
| Heartland virus | USA | 2009 |
| Bas-Congo virus | DRC | 2009 |
| Lassa fever | Mali | 2009 |
| Pandemic H1N1/09 virus | 2009 | |
| Huaiyangshan banyangvirus | 2009 | |
| Plague | Libya | 2009 |
| Cholera | Haiti | 2010 |
| Lassa fever | Ghana | 2011 |
| Plasmodium cynomolgi | Malaysia | 2011 |
| H3N2v | 2011 | |
| MERS -CoV | 2012 | |
| Mojiang paramyxovirus | 2012 | |
| H7N9 | 2013 | |
| Sosuga pararubulavirus | 2013 | |
| H10N8 | 2013 | |
| Chikungunya | Caribbean | 2013 |
| 2013 | ||
| Colpodella sp. Heilongjiang | China | 2013 |
| Ebola virus disease | West Africa | 2014 |
| H5N6 | 2014 | |
| Lassa fever | Benin | 2014 |
| Bourbon virus | USA | 2014 |
| Zika virus | Americas | 2015 |
| Crimean–Congo hemorrhagic fever | Spain | 2016 |
| Chikungunya | Pakistan | 2016 |
| Lassa fever | Togo | 2016 |
| Ntwetwe virus | Uganda | 2016 |
| Monkeypox | Nigeria | 2017 |
| Yellow fever | Brazil | 2017 |
| Rat hepatitis E virus | 2017 | |
| Guinea worm | Chad | 2018 |
| Lyme disease | 2018 | |
| H7N4 | 2018 | |
| Monkeypox | Liberia, UK | 2018 |
| Nipah virus | India | 2018 |
| SARS-CoV-2 | Global pandemic | 2019 |