Emerging infectious disease

History of the concept of emerging infectious diseases

The French doctor Charles Anglada (1809–1878) wrote a book in 1869 on extinct and new diseases. He did not distinguish infectious diseases from others (he uses the terms reactive and affective diseases, to mean diseases with an external or internal cause, more or less meaning diseases with or without an observable external cause). 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 (Birth, Life and Death of Infectious Diseases), and later in Destin des maladies infectieuses (Fate of Infectious Diseases) 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:[[File:Trends in Infectious Diseases Mortality, 1900-1996.png|thumb|Throughout the 20th century until 1980, with the exception of the 1918 Spanish flu pandemic, the death rate from infectious diseases in the United States was steadily decreasing. However, because of the AIDS epidemic, the death rate from infectious diseases increased by 58% between 1980 and 1992.]] 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 (of which the public became aware through the AIDS epidemic) 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 (ProMED) was formed by a group of scientists as a follow-up in 1994 and the Centres for Disease Control (CDC) 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 (COVID-19) 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 (due to drug resistance, measles (due to declining vaccination rates), and cholera (due to climate-related factors)
• 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

The 1992 report distinguished six factors contributing to emergence of new diseases (Microbial adaptation and change; Economic development and land use; Human demographics and behavior; International travel and commerce; Technology and industry; Breakdown of public health measures) which were extended to 13 factors in the 2003 report (Chapter 3 of the report detailing each of them):

• 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

Their classification serves as a basis for many others. The following table gives examples for different factors:

Zoonotic diseases

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 (NIAID) 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.

Newly recognized (since the 1980s):

• Acanthamebiasis
• Australian bat lyssavirus
• Babesia, atypical
• Bartonella henselae
• Coronaviruses, including SARS coronavirus
• Ehrlichiosis
• Encephalitozoon cuniculi
• Encephalitozoon hellem
• Enterocytozoon bieneusi
• Helicobacter pylori
• Hendra virus (equine morbilli virus)
• Hepatitis C
• Hepatitis E
• Human herpesvirus 8
• Human herpesvirus 6
• Lyme borreliosis
• Microsporidia
• Parvovirus B19

Re-emerging:

• Coccidioides immitis
• Enterovirus 71
• Prion diseases
• Streptococcus, group A
• Staphylococcus aureus

Diseases with bioterrorism potential, CDC category A (most dangerous):

• Anthrax
• Clostridium botulinum
• Tularemia
• Smallpox and other pox viruses
• Viral hemorrhagic fevers
  • Arenaviruses: Lymphocytic choriomeningitis (LCM), Junin virus, Machupo virus, Guanarito virus, Lassa fever
  • Bunyaviruses: Hantaviruses, Rift Valley Fever, Crimean-Congo hemorrhagic fever virus
  • Flaviviruses: Dengue
  • Filoviruses: Ebola, Marburg
• Yersinia pestis

Diseases with bioterrorism potential, CDC category B:

• Brucella species (brucellosis)
• Burkholderia pseudomallei (melioidosis)
• Burkholderia mallei (glanders)
• Coxiella burnetii (Q fever)
• Epsilon toxin of Clostridium perfringens
• Food-borne and Water-borne Pathogens
  • Bacteria
    • Campylobacter jejuni
    • Diarrheagenic E. coli
    • Listeria monocytogenes
    • Pathogenic vibrios
    • Salmonella
    • Shigella species
    • Yersinia enterocolitica
  • Protozoa
    • Cryptosporidium parvum
    • Cyclospora cayetanensis
    • Entamoeba histolytica
    • Giardia lamblia
    • Toxoplasma
  • Fungi
    • Microsporidia
  • Viruses:
    • Caliciviruses
    • Hepatitis A
• Mosquito-borne encephalitis viruses
  • California encephalitis
  • Eastern equine encephalitis (EEE)
  • Japanese encephalitis virus (JE)
  • Kyasanur Forest virus
  • LaCrosse virus (LACV)
  • Venezuelan equine encephalitis (VEE)
  • Western equine encephalitis (WEE)
  • West Nile virus (WNV)
  • Yellow fever
• Ricin toxin (from Ricinus communis)
• Staphylococcal enterotoxin B
• Typhus fever (Rickettsia prowazekii)

Diseases with bioterrorism potential, CDC category C (least dangerous):

• Influenza
• Multidrug-resistant tuberculosis (MDR-TB)
• Nipah virus
• Rabies
• SARS coronavirus
• Tick-borne encephalitis virus
• Tick-borne hemorrhagic fever viruses
• Other hantaviruses
• Other rickettsias

Since 2004, NIAID has added to its biodefense emerging pathogen list:

• Yersinia pestis (plague, category A)
• Chapare virus (category A areanavirus)
• Lujo (category A arenavirus)
• Chlamydia psittaci (category B)
• Naegleria fowleri (category B)
• Balamuthia mandrillaris (category B)
• St. Louis encephalitis virus (SLEV, category B)
• Tick-borne hemorrhagic fever viruses (category C)
  • Bunyaviruses: Severe Fever with Thrombocytopenia Syndrome virus (SFTSV), Heartland virus
  • Flaviviruses: Omsk Hemorrhagic Fever virus, Alkhurma virus, Kyasanur Forest virus (reclassified from B to C)
• Powassan virus (Deer Tick virus, category C)
• Chikungunya virus (category B)
• Coccidioides species (category C)
• Human coronavirus HKU1 (category C)
• Middle East respiratory syndrome coronavirus (category C)
• Anaplasmosis
• Aspergillus
• BK virus
• Bordetella pertussis
• Borrelia miyamotoi
• Clostridioides difficile
• Cryptococcus gattii
• Enterococcus faecium
• Enterococcus faecalis
• Enterovirus 68
• JC virus
• Leptospirosis
• Measles
• Mucormycosis
• Mumps virus
• Poliovirus
• Zika virus (category B)

NIAID also monitors antibiotic resistance, which can become an emerging threat for many pathogens.

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 (Ebola virus disease and Marburg virus disease)
• Highly pathogenic emerging Coronaviruses relevant to humans (MERS and SARS)
• Lassa fever
• Nipah virus infection
• Rift Valley fever

These were selected based on the following measures:

1. Human transmissibility (including population immunity, behavioural factors, etc.)
2. Severity or case fatality rate
3. Spillover potential
4. Evolutionary potential
5. Available countermeasures
6. Difficulty of detection or control
7. Public health context of the affected area(s)
8. Potential scope of outbreak (risk of international spread)
9. Potential societal impacts

Newly reported infectious diseases

In 2007 Mark Woolhouse and Eleanor Gaunt established a list of 87 human pathogens first reported in the period between 1980 and 2005. These were classified according to their types.

Major outbreaks

The following table summarizes the major outbreaks since 1998 caused by emerging or re-emerging infectious diseases.

Methicillin-resistant ''Staphylococcus aureus''

Methicillin-resistant Staphylococcus aureus (MRSA) evolved from methicillin-susceptible Staphylococcus aureus (MSSA), otherwise known as common S. aureus. Many people are natural carriers of S. aureus, without being affected in any way. Infections occur in healthcare settings (Healthcare acquired-MRSA) and in the community (Community acquired-MRSA), often leading to severe skin infections, pneumonia, and bloodstream infections. Community-acquired MRSA, is increasingly found in healthy individuals such as athletes, prisoners, and schoolchildren outside of hospital settings. MSSA was treatable with the antibiotic methicillin until it acquired the gene for antibiotic resistance. MRSA is a major public health threat due to its resistance to antibiotics. Through genetic mapping of various strains of MRSA, scientists have found that MSSA acquired the mecA gene in the 1960s, which accounts for its pathogenicity, before this it had a predominantly commensal relationship with humans. It is theorized that when this S. aureus strain that had acquired the mecA gene was introduced into hospitals, it came into contact with other hospital bacteria that had already been exposed to high levels of antibiotics. When exposed to such high levels of antibiotics, the hospital bacteria suddenly found themselves in an environment that had a high level of selection for antibiotic resistance, and thus resistance to multiple antibiotics formed within these hospital populations. When S. aureus came into contact with these populations, the multiple genes that code for antibiotic resistance to different drugs were then acquired by MRSA, making it nearly impossible to control. It is thought that MSSA acquired the resistance gene through the horizontal gene transfer, a method in which genetic information can be passed within a generation, and spread rapidly through its own population as was illustrated in multiple studies. Horizontal gene transfer speeds the process of genetic transfer since there is no need to wait an entire generation time for gene to be passed on. enhanced hospital hygiene protocols to reduce healthcare-associated infections, and development of new antimicrobial agents and alternative therapies, such as bacteriophage therapy. However, prevention is the most preferred method of avoiding antibiotic resistance.

Scientific Advisory Group for Origins of Novel Pathogens

On 16 July 2021, the Director-General of WHO announced the formation of the Scientific Advisory Group for Origins of Novel Pathogens (SAGO), which is to be a permanent advisory body of the organisation. The Group was formed with a broad objective to examine emerging infectious diseases, including COVID-19. The group's primary objective is to provide scientific guidance on identifying the origins of emerging pathogens, including SARS-CoV-2. The group has also recommended enhanced global surveillance systems. According to the WHO Director-General, "SAGO will play a vital role in the next phase of studies into the origins of SARS-CoV-2, as well as the origins of future new pathogens."

• https://www.bloomberg.com/news/articles/2021-08-25/embattled-who-virus-origins-team-says-window-closing-for-probe
• https://www.scmp.com/news/china/politics/article/3146730/political-rows-hamper-covid-19-origins-hunt-more-china-research
• https://www.statnews.com/2021/08/25/the-who-seeks-experts-to-investigate-the-origins-of-pathogens/
• https://www.telegraph.co.uk/global-health/science-and-disease/proposes-new-pandemic-origins-inquiry-team-amid-mounting-criticism/
• https://www.wsj.com/articles/covid-19-origin-researchers-warn-time-is-running-out-to-find-answers-11629903950
• https://www.wsj.com/articles/who-seeks-to-revive-stalled-inquiry-into-origins-of-covid-19-with-new-team-11632657603
• https://news.yahoo.com/window-rapidly-closing-gather-evidence-121852213.html

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