Week 10: Emerging and Re- emerging infectious diseases and public health

Emerging infectious disease

An infectious disease that has newly appeared in a population or that has been known for some time but is rapidly increasing in incidence or geographic range.

Re-emerging infectious disease

Diseases that once were major health problems globally or in a particular country, and then declined dramatically, but are again becoming public health problems for a significant proportion of the population.

Infectious diseases

Are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi; these diseases can be spread, directly or indirectly, from one person to another. 

Zoonotic diseases

are infectious diseases of animals that can cause disease when transmitted to humans. 

14^th century - Europe: plague killed _______% of the world’s population

20-45%

1831 - Cairo: __% of population succumbed to cholera

13%

1854-56 - Crimean war: deaths due to dysentery were __ times higher than deaths due to casualties

10x

1899-1902- Boer War: deaths due to dysentery were _ times higher than deaths due to casualties

5x

Why did infectious disease recede in Western countries 20^th century?

• Urban sanitation, improved housing, personal hygiene, antisepsis & vaccination

• Antibiotics further suppressed morbidity & mortality

Since last quarter of 20^th century- New & Resurgent infectious diseases

• Unusually large number- Rotavirus, Cryptosporidiosis, HIV/AIDS, Hantaviraus, Lyme disease, Legionellosis, Hepatitis C

recent emerging diseases

diseases thought to be adequately controlled appear to be making a “comeback”

• In developed countries, public health measures such as sanitation, sewage treatment, vaccination programs, and access to good medical care have virtually eliminated “traditional” diseases such as: 

  • Diptheria, whooping cough, and tuberculosis

  
  

• Many of these diseases are becoming a public health problem once again, as immunization programs and other public standards are enforced less vigorously (until the COVID-19 pandemic) and, as antibiotic resistant pathogens evolve

• Strains of pneumonia-caused by Staphylococcus aureus are ________ to all of the currently available drug treatments

resistant

Among the diseases “reemerging” as a consequence of microbial resistance are: 

• Tuberculosis, and malaria, leading causes of death from infectious diseases worldwide

Major Infectious Disease Epidemics since 1980

COVID-19 Variants

• Summer 2023: EG.5, or, informally, Eris (nicknamed after the Greek goddess of strife and discord)

• As of November 2021, there are four dominant variants of SARS-CoV-2 spreading among global populations: 

  • the Alpha Variant (formerly called the UK Variant and officially referred to as B.1.1.7), first found in London and Kent, 

  • the Beta Variant (formerly called the South Africa Variant and officially referred to as B.1.351), 

  • the Gamma Variant (formerly called the Brazil Variant and officially referred to as P.1)

  • the Delta Variant (formerly called the India Variant and officially referred to as B.1.617.2).

COVID-19: November 2021

South African scientists have detected a new Omicron variant –B.1.1.529 “very unusual constellation” of mutations, which are concerning because they could help it evade the body’s immune response and make it more transmissible

What did these Epidemic Infectious Diseases have in Common?

• All were caused by zoonotic pathogens

  
  

• All  spread by modern transportation

  
  

• Most had Asian origin 

  
  

• Laboratory and clinical diagnoses were problematic

  
  

• Poor communication among countries

  
  

• Major economic impact

Emerging Zoonoses: Human-animal interface

human, environment, vectors, animals relationships

Three Main Factors Contributing To Emergence

• Disease agents

• Human activities resulting in exposure to host

• Environmental factors

Disease agents

• Evolution of pathogenic infectious agents (microbial adaptation & change)

• Microbial evolution and the development of resistance to antibiotics and other antimicrobial drugs

• Changes in ecology and climate

• Modern medicine (e.g. immunosuppression), human susceptible to infection

• Inadequacy of public infrastructure and vaccination programs

• Resistance of vectors to pesticides

Disease Agents: Transmission of Infectious Agent from Animals to Humans

• >2/3^rd emerging infections originate from animals- wild & domestic

  
  

• Emerging Influenza infections in Humans associated with Geese, Chickens & Pigs

  
  

• Animal displacement in search of food after deforestation/ climate change (Lassa fever)

  
  

• Humans themselves penetrate/ modify unpopulated regions- come closer to animal reservoirs/ vectors (Yellow fever, Malaria)

Host

• Human demographic change (inhabiting new areas)

• Unprecedented worldwide population growth, urbanization

• Increased international travel

• Human behaviour (sexual & drug use)

• Human susceptibility to infection (Immunosuppression)

• Poverty & social inequality

• Changes in human behaviour, technology and industry

• Human encroachment on wilderness habitats that are reservoirs for insects and animals that harbour infectious agents

• Social unrest and civil wars

• Bioterrorism

Host: Poverty, Neglect & Weakening of  Health Infrastructure

• Poor populations- major reservoir & source of continued transmission

• Poverty- Malnutrition- Severe infectious disease cycle

• Lack of funding, poor prioritization of health funds, misplaced in curative rather than preventive infrastructure, 

• Failure to develop adequate health delivery systems

Host: Human Behaviour

• Unsafe sexual practices (HIV, Gonorrhoea, Syphilis)

  
  

• Changes in agricultural & food production patterns- food-borne infectious agents (E. coli)

  
  

• Increased international travel (Influenza)

  
  

• Outdoor activity 

Host: Uncontrolled Urbanization & Population Displacement

• Growth of densely populated cities- substandard housing, unsafe water, poor sanitation, overcrowding, indoor air pollution (>10% preventable ill health)

  
  

• Problem of refugees & displaced persons

  
  

• Diarrhoeal & Intestinal parasitic diseases, ARI

Lyme disease (B. burgdorferi)- Changes in ecology, increasing deer populations, suburban migration of population

Host: Policy and knowledge limitations

• Deterioration in surveillance systems for infectious diseases, including laboratory support, to detect new or emerging disease problems at an early stage  (e.g. Indonesian resistance to “scientific colonialism”)

  
  

• Illiteracy limits knowledge and implementation of prevention strategies

  
  

• Lack of political will – corruption, other priorities

Host: Bioterrorism

• Biowarfare/bioterrorism: An unfortunate potential source of new or emerging disease threats (e.g. anthrax and letters)

• Possible deliberate release of infectious agents by dissident individuals or terrorist groups

• Biological agents are attractive instruments of terror- easy to produce, mass casualties, difficult to detect, widespread panic & civil disruption

Highest potential of bioterrorism:

• Bacillus anthracis – causes anthrax

• Clostridium botulinum toxin - cause paralysis and even death through respiratory failure.

• Francisella tularensis - causes pneumonia

• Yersinia pestis – plagues – e.g., bubonic plague.

• Variola virus - smallpox

• Viral haemorrhagic fever viruses

• Likeliest route- aerosol dissemination  

Environment

• Climate & changing ecosystems

• Economic development & Land use (urbanization, deforestation)

• Technology & industry (food processing & handling)

• Changes in food processing, handling, and agricultural practices

• International travel & commerce 

• Increased worldwide transport, migration, and relocation of animals and food products

• Breakdown of public health measure (war, unrest, overcrowding)

• Deterioration in surveillance systems (lack of political will)

Environment: Climate & Environmental Changes

• Deforestation forces animals into closer human contact- increased possibility for agents to breach species barrier between animals & humans

  
  

• El Nino- Triggers natural disasters & related outbreaks of infectious diseases (Malaria, Cholera)

  
  

• Global warming- spread of Malaria, Dengue, Leishmaniasis, Filariasis  

Antimicrobial Drug Resistance by Disease Agents

• Antibiotic resistance is one of the biggest threats to global health, food security, and development today.

• Antibiotic resistance can affect anyone, of any age, in any country.

• Antibiotic resistance occurs naturally, but misuse of antibiotics in humans and animals is accelerating the process.

• A growing number of infections – such as pneumonia, tuberculosis, gonorrhoea, and salmonellosis – are becoming harder to treat as the antibiotics used to treat them become less effective.

• Antibiotic resistance leads to longer hospital stays, higher medical costs and increased mortality.

Antimicrobial Drug Resistance

• AMR threatens all countries in recent decades, AMR has become widespread, irrespective of countries’ level of income. 

• In Europe, it has been estimated that 25,000 people die every year from antibiotic-resistant bacteria. 

• A recent report by the US Centers for Disease Control and Prevention (CDC) conservatively estimated that at least 2 million illnesses and 23,000 deaths a year in the USA could be attributed to antibiotic resistance.

• Such estimates are useful for giving an indication of the scale of the problem, yet it is difficult to determine whether resistance is the cause of death or it is a correlate of long antibiotic treatment, hospitalization and underlying sickness.

AMR Causes

• Wrong prescribing practices

• Non-adherence by patients

• Counterfeit drugs

• Use of anti-infective drugs in animals & plants

AMR Loss of effectiveness:

• Community-acquired (TB, Pneumococcal) & Hospital-acquired (Enterococcal, Staphylococcal

• Antiviral (HIV), Antiprotozoal (Malaria), Antifungal  

AMR Consequences

• Prolonged hospital admissions

• Higher death rates from infections

• Requires more expensive, more toxic drugs

• Higher health care costs

AMR Prevention and control

• Antibiotic resistance is accelerated by the misuse and overuse of antibiotics, as well as poor infection prevention and control. 

• Steps can be taken at all levels of society to reduce the impact and limit the spread of resistance.

• Individual level

• Policy makers level

• Health professionals

• Healthcare industry

• Agriculture sector

To prevent and control the spread of antibiotic resistance, individuals can:

• Only use antibiotics when prescribed by a certified health professional.

• Never demand antibiotics if your health worker says you don’t need them.

• Always follow instructions when using antibiotics.

• Never share or use leftover antibiotics.

AMR prevention and control: Individuals

• Prevent infections by regularly washing hands, preparing food hygienically, avoiding close contact with sick people, practising safer sex, and keeping vaccinations up to date.

  
  

• Prepare food hygienically, following the WHO Five Keys to Safer Food (keep clean, separate raw and cooked, cook thoroughly, keep food at safe temperatures, use safe water and raw materials) and 

  
  

• Choose foods that have been produced without the use of antibiotics for growth promotion or disease prevention in healthy animals.

AMR prevention and control: Policy makers

• To prevent and control the spread of antibiotic resistance, policy makers can:

  • Ensure a robust national action plan to tackle antibiotic resistance is in place.

  • Improve surveillance of antibiotic-resistant infections.

  • Strengthen policies, program, and implementation of infection prevention and control measures.

  • Regulate and promote the appropriate use and disposal of quality medicines.

  • Make information available on the impact of antibiotic resistance.

AMR prevention and control: Health Professionals

• To prevent and control the spread of antibiotic resistance, health professionals can:

  • Prevent infections by ensuring hands, instruments, and environment are clean.

  • Only prescribe and dispense antibiotics when they are needed, according to current guidelines.

  • Report antibiotic-resistant infections to surveillance teams.

  • Talk to patients about how to take antibiotics correctly, antibiotic resistance and the dangers of misuse.

  • Talk to patients about preventing infections (for example, vaccination, hand washing, safer sex, and covering nose and mouth when sneezing).

AMR prevention and control: Healthcare industry

• To prevent and control the spread of antibiotic resistance, the health industry can:

  
  

• Invest in research and development of new antibiotics, vaccines, diagnostics and other tools.

AMR prevention and control: Agriculture sector

• To prevent and control the spread of antibiotic resistance, the agriculture sector can:

  • Only give antibiotics to animals under veterinary supervision.

  • Not use antibiotics for growth promotion or to prevent diseases in healthy animals.

  • Vaccinate animals to reduce the need for antibiotics and use alternatives to antibiotics when available.

  • Promote and apply good practices at all steps of production and processing of foods from animal and plant sources.

  • Improve biosecurity on farms and prevent infections through improved hygiene and animal welfare.

No infectious disease had spread so fast and far as ____ did in 2003

SARS

Lesson learned from SARS

• An infectious disease in one country is a threat to all

• Important role of air travel in international spread 

• Tremendous negative economic impact on trade, travel and tourism, estimated loss of $ 30 to $150 billion 

• High level commitment is crucial for rapid containment 

• WHO can play a critical role in catalyzing international cooperation and support

• Global partnerships & rapid sharing of data/information enhances preparedness and response

Highly Pathogenic Avian Influenza (H5N1)

• Since Nov 2003, avian influenza H5N1 in birds affected 60 countries across Asia, Europe, Middle-East & Africa

• >220 million birds killed by AI virus or culled to prevent further spread

• Majority of human H5N1 infection due to direct contact with birds infected with virus

Swine Influenza A (H1N1)

• Swine flu causes respiratory disease in pigs – high level of illness, low death rates

• Pigs can get infected by human, avian and swine influenza virus

• Occasional human swine infection reported

• In US from December 2005 to February 2009, 12 cases of human infection with swine flu reported

Swine Influenza Outbreaks

• March 18 2009 – H1N1 outbreak reported in Mexico

• April 15^th CDC identifies H1N1 (swine flu)

• April 25^th WHO declares public health emergency

• April 27^th Pandemic alert raised to phase 4

• April 29^th Pandemic alert raised to phase 5

Swine Influenza - late stage outbreak

• By May 5^th more than 1000 cases confirmed in 21 countries

• Screening at airports for flu like symptoms (especially passengers coming from affected area)

• Schools closed in many states in USA

• May 16^th India reports first confirmed case

• Stockpiling of antiviral drugs and preparations to make a new effective vaccine 

Swine Influenza: Worldwide

• 162,380 cases

• 1154 deaths

Swine Influenza: India

• 558 cases

• 1 death 

Coronavirus Disease 2019 (COVID-19)

• The SARS CoV 2 virus that causes COVID 19 is an emerging zoonotic pathogen

• Ribonucleic acid (RNA) Viruses Cause respiratory disease, often severe 

How did COVID-19 start?

• Wuhan, China is a city with population of more than 11 million people.

• SARS-CoV-2 first isolated from BAL samples obtained on December 30, 2019

• Initial cases linked to the Huanan Wholesale Seafood Market

Evidence about the origin

• 27 of original 41 patients had contact with Wuhan seafood market (Huang et al., Lancet 2020)

• But the first case (symptom onset Dec 1) had no link to the market!

• Early evidence of person to person transmission

• Samples from market Jan 1 and Jan 12

  • 33/585 positive, 31 from western market where live animals sold

• Global statistics: 58.7 million infections; 37.5 million recovered; 1.4million deaths (Nov 23, 2020)

Possible Explanations

• Market was source of original spillover to humans, but first cases not detected, 

  OR

• Spillover event occurred elsewhere, and then transmission happened by an infected person coming to market and contacting multiple people there

COVID timeline

How Zoonotic Viruses “Spillover”

“Spillover” and “Amplification”

Intermediate Hosts for Novel Coronaviruses

Confirmed COVID-19 cases

COVID-19 in Canada

COVID 19 and the capacity of the healthcare system

The role of mitigation strategies

Bottom Line for Prevention of Future Zoonotic Disease Outbreaks

• Many other coronaviruses and other pathogens circulating in natural animal reservoirs.

• Just as we are “social distancing” to control COVID 19, we need to maintain a “distance” between human populations and animal pathogens that could spillover to humans!

• One Health approach: humans, animals, environments

The Best Defense (Multi-factorial)

• Coordinated, well-prepared, well-equipped Public Health systems

• Partnerships- clinicians, laboritarians & Public Health agencies

• Improved methods for detection & surveillance

• Effective preventive & therapeutic technologies

• Strengthened response capacity

• Political commitment & adequate resources to address underlying socio-economic factors

• International collaboration & communication

Strategies to Reduce Threats of Emerging Diseases

• Improved methods of detection and surveillance – national, regional and global

• Use and Development of vaccines

• Improve zoonotic control

• Better health education

• Development of predictive models

• Reducing the potential of rapid spread

• Feasible Control Strategies

• Investigation and early control measures

• Implement prevention measures

  • behavioural, political, environmental

• Monitoring, evaluation

Surveillance at national, regional, global level:

• epidemiological, 

• laboratory

• ecological

• anthropological

National surveillance: current challenges

• Independent vertical control programmes

• Surveillance gaps for important diseases

• Limited capacity in field epidemiology, laboratory diagnostic testing, rapid field investigations

• Inappropriate case definitions

• Delays in reporting, poor analysis of data and information at all levels 

• No feedback to periphery

• Insufficient preparedness to control epidemics

• No evaluation

Improving global surveillance

• Improve global surveillance (continued)

  • Utilize geographical information systems

  • Utilize global positioning systems

  • Utilize the Global Atlas of Infectious Diseases (WHO)

  • Increase and improve laboratory capacity

  • Coordinate human and animal surveillance

What does GOARN stand for?

Global Outbreak Alert & Response Network 

Global Outbreak Alert & Response Network (GOARN)

• Coordinated by WHO

• Mechanism for combating international disease outbreaks

• Ensure rapid deployment of technical assistance, contribute to long-term epidemic preparedness & capacity building

Which organisations will improve global early response capacity

• WHO

• National Disease Control Units (e.g. USCDC, CCDC)

• Training programs

Use and Development of vaccines

• Increase coverage and acceptability (e.g., oral)

• New strategies for delivery (e.g., nasal spray administration)

• Develop new vaccines

• Decrease cost

• Decrease dependency on “cold chain”

• NEW DRUG DEVELOPMENT 

Decrease inappropriate drug use

• Improve education of clinicians and public

• Decrease antimicrobial use in agriculture and food production

Improve vector and zoonotic control

• Develop new safe insecticides

• Develop more non-chemical strategies e.g. organic strategies

Better and more widespread health education

(e.g., west Nile virus; bed nets, mosquito repellent)

Development of predictive models based on:

• Epidemiologic data

• Climate change surveillance

• Human behavior

Establish priorities 

• The risk of disease

• The magnitude of disease burden

  • Morbidity/disability

  • Mortality; Economic cost

• Reduce potential for rapid spread

• Develop more feasible  control strategies

Main Strategies to Reduce Threats of Emerging Diseases

• Develop new strategies requiring low-cost technology

• Social and political mobilization of communities

• Greater support for research

• Reduce poverty and inequality

Essential factors for disease eradication

• Knowledge of its epidemiology and transmission patterns/mode

• Availability of effective  tools for diagnosis, treatment and prevention

• Knowledge of local cultural and political characteristics

• Community acceptance and mobilization

• Political will and leadership

• Adequate and sustained funding

Global Threat of Epidemic Infectious Diseases Challenge to Reverse the Trend

• Prevent movement of pathogens and vectors via modern transportation

• Improve international cooperation and data sharing

• Improve effective laboratory-based surveillance

• Rebuild public health infrastructure to prevent & control vector-borne and zoonotic diseases

  • Trained personnel

  • Laboratory and epidemiologic capacity

  • Tools (vaccines, drugs, insecticides, mosquito control, etc)

  • Understanding disease ecology

• Political will

  • Economic support

  • Regional prevention and control programs