BIOL334 Lecture 6- Emerging and Re emerging Diseases Flashcards
Define Emerging Infectious Diseases
Infectious diseases that have newly appeared in a population (Global or Regional).
Define Re-Emerging Diseases
Re-emergence is the reappearance of a known disease after a significant decline in incidence
- Global or regional
How many pathogens are known to effect humans?
1415 pathogens
- 61% zoonotic
70% of newly recognised pathogens are zoonoses
Emerging infections since 1973
1973- Rotavirus 1977- Ebola virus 1977- Legionella 1982- E.coli O157:H7 1982- Borrelia burgdoferi 1992- Vibrio cholera O139 2019-COVID
Factors contributing to the emergence of diseases (AGENT)
AGENT (pathogen)
- Evolution of pathogenic infectious agents (microbial adaptation and change)
- Increasing virulence of microbes- Influenza A virus exhibits frequent change in antigenic structure- new strains.
- Development of resistance to drugs
- Resistance of vectors to pesticides
Factors contributing to the emergence of diseases (HOST)
HOST
- Human demographic change (inhabiting new areas)
- Mass migration of people (natural and man-made disasters) with rehabilitation of displaced people in temporary human settlements- bad hygiene.
- International travel as a result of trade and tourism contributes to global dispersion of disease agents, reservoirs and vectors.
- Human susceptibility to infection (immune suppression)
- Poverty an social inequality (poor housing, sanitation, infrastructure, water)
- Unsafe sex (HIV, Gonorrhoea)
- Changes in agricultural and food productions patterns- food borne infectious agents (pathogenic E.coli-meat).
- Increased travel (influenza, COVID)
- Out door activity- pick up diseases such as Lyme disease
Factors contributing to the emergence of diseases (Environment)
- Climate change and changing ecosystems (deers- carry ticks, ticks reproduce better in warmer temp, animals close to us- impact water systems etc).
- Economic development and land use (urbanisation, deforestation)- changes habitats of animals that carry pathogens and we come into contact with them.
- Technology and industry (food processing and handling- e.g., irrigation of veg with river water- contamination)
- International travel and commerce
- Breakdown of public health measures (war, unrest, overcrowing- refugee camps)
- Deterioration in surveillance systems (lack of political will- outbreaks aren’t tracked and prevented)
What percentage of emerging infections originate from animals?
66%
What infection is associated with humans in close proximity with chickens, pigs and geese?
Influenza
What disease is associated with animal displacement in search for food after deforestation/climate change?
Lassa fever
Lassa fever is an acute viral haemorrhagic fever illness that is primarily transmitted to humans via contact with food or household items contaminated with infected Mastomys rats’ urine or faeces
What diseases are associated with humans modifying unpopulated regions and coming closer to animal reservoirs/vectors?
Malaria
Yellow fever
Deforestation impact on disease spread
Deforestation forces animals into closer human contact, increased possibility for agents to breach species barrier between animals and humans
How does climate change influence the spread of disease?
Climate change influences the spread of malaria, Leishmaniasis and Dengue
- Natural disasters and related outbreak of infectious diseases (Malaria, Cholera).
- Changes in the habitat of disease vectors
- Greater rainfall
- High temperatures
- Changes in the direction of bird migration
How does poverty, neglect and weakening of health infrastructure impact disease spread?
Poor populations- major reservoir and source of continued transmission. Poor health= susceptible
Poverty- malnutrition- severe infectious disease cycle
Lack of funding- poor prioritisation of health funds, failure to develop adequate healthy delivery systems
How does uncontrolled urbanisation and population displacement affect the spread of pathogens?
Growth of densely populated cities
- Informal settlements, substandard housing, unsafe water, poor sanitation, indoor air pollution
- Uninhibited and reckless industrialisation leading to migration of labour population from rural to urban areas in unhygienic squatter settlements.
Problem of refugees and displaced persons- diahorreal and intestinal parasitic diseases
Changes in ecology, increasing deer populations- Lyme disease (borrelia)
Urban areas in unhygienic settlements- Ghana, Accra
Causes of antimicrobial drug resistance
- Incorrect prescribing practices
- Non adherence by patients
- Counterfeit drugs
- Use of anti-infective drugs in animals and plants- spread
- Community acquired resistances- resistant Tb spread
- Hospital acquired (MRSA).
Consequences of antimicrobial drug resistance
- Prolonged hospital admissions
- Higher death rates from infection
- Requires more expensive more toxins drugs
- Higher health care costs
Economic impact of selected infectious disease
- Mad cow diseases massive costs 10-13 billion
- COVID- monitoring, vaccines etc.
Why is correlation vs causation dangerous, when determining the causation of new diseases
It can tamper with management and treatment processes.
Kochs Postulates
A way to determine the cause or etiologic agent of infectious disease:
- Find evidence of a particular microbe in every case of a disease
- Isolate that microbe from an infected subject and cultivate it artificially in the lab
- Inoculate a susceptible healthy subject with the laboratory isolate and observe the result disease- difficult to do in humans, ethical issues
- Re-isolate the agent from this subject.
Bradford-Hill Framework
Determining causation:
Strength- large effects makes causal relationship more likely. Strong relationships allow co-variable to be identified
Consistency: is there evidence for the same findings from more than one study in also different settings?
Temporality: is absolute- exposure must precede outcome
Biological gradient: dose response? Exposure threshold below which no effect is seen?
Plausibility: Does the exposure effect make sense?
Coherence: does it all hold together in light of similar effects caused by something else?
Experiment: Animal/human experiments/ does removing exposure reduce the effect
Analogy: Are there analogous situations that support the relationship? Similar pathogen/chemical?
Precautionary Principle
Exposure A is cause of outcome B- reduce A and it will reduce B at an individual of population level
Exposure A is likely to cause outcome B-
PP says waiting for clear information of exposure A to outcome B is unacceptable and should reduce A now
- Complication by how to achieve reduction
- Hysteria in the media
- Separating genetic and environmental factors
- Good example: Bovine Spongiform Encephalopathy, a disease of cattle which affects the central nervous system. Measure implemented without scientific certainty BUT CORRECT
Burden of disease
Worldwide: 1 in 5 deaths are children <5 years old
of every 10 deaths: 6 are non-communicable disease, 3 communicable/nutritional, 1 from injury/trauma.
Leading cause of death:
- CV disease
- Cancer
- Infectious and parasitic disease
Causes of mortality throughout the world
- Burden of disease is different between countries (economic development)
- Diahorreal diseases have decreased deaths- interventions worldwide are working.
