Emerging + Re-emerging Infectious Diseases Flashcards
What is an emerging infectious disease?
= infections that have recently appeared within a population
= those whose incidence or geographic range is rapidly increasing or threatens to increase in the near future
= can be caused by previously undetected or unknown infectious agents
e.g. Ebolavirus, E.coli 0157:H7, Borrelia burgdorferi
(= all have different economic impacts and mortality risks associated)
What are re-emerging infectious diseases?
= diseases that once were major health problems + then declined dramatically
BUT = are again becoming health problems for a significant proportion of the population
e.g. Malaria / Tuberculosis
What are some factors contributing to emergence - the agent?
Evolution of pathogenic infectious agents
= microbial adaptation + change
= increasing virulence of microbes
(change in antigenic structure, new strains)
Development of resistance to drugs
Resistance of vectors to pesticides
How does Zoonoses affect emerging diseases?
= 2/3 emerging infections originate from animals
(wild and domestic)
= emerging influenza infections in humans associated with Geese, Chickens + pigs
(close proximity)
= animal displacement in search of food after deforestation / climate change (Lassa fever)
= humans themselves penetrate / modify unpopulated regions + come closer to animal reservoirs / vectors
(e.g. yellow fever, malaria)
What are factors contributing to emergence - the host?
Human demographic change
= inhabiting new areas
Mass migration of people
= natural and man-made disasters
= q/ concomitant rehabilitation of displaced people in temporary human settlements under unhygienic conditions
International travel
= trade / tourism
= global dispersion of disease agents, disease reservoirs + vectors (deliver)
Human susceptibility to infection
(e.g. immunosuppression)
Poverty + social inequality
Unsafe sexual practices (HIV, Gonorrhoea, Syphilis)
Changes in agricultural + food production patterns
= food-borne infectious agents (E.coli)
Increased international travel (influenza)
Outdoor activity
What are factors contributing to emergence - the environment?
Climate and changing ecosystem
Economic development + land use
= urbanisation, deforestation
Technology + industry
= food processing + handling
International travel + commerce
Breakdown of public health measure
= war, unrest, overcrowding-refugee camps, cities
Deterioration in surveillance systems
= lack of political will
What are some examples of climate and environmental changes?
Deforestation
= forces animals into closer human contact
= increases possibility for agents to breach species barrier
Climate changes
= e.g. spread of Malaria, Dengue, Leishmaniasis
= natural disasters + related outbreaks of infectious diseases
= changes in the habitat of disease vectors
= greater rainfall
= higher temperatures
= changes in direction of bird migration
What affect does poverty, neglect and weakening of health infrastructure have?
Poor populations
= major reservoir + source of continued transmission
Poverty = leads to malnutrition = leads to severe infectious disease cycle
Lack of funding
= poor prioritisation of health funds
= failure to develop adequate health delivery systems
What is the affect of uncontrolled urbanisation and population displacement?
Growth of densely populated cities
= informal settlements, substandard housing, unsafe water, poor sanitation, overcrowding, indoor air pollution
= uninhibited + reckless industrialisation leading to migration of labor population from rural to urban areas in unhygienic squatter settlements
Problem of refugees + displaced persons
= diarrhoea + intestinal parasitic diseases
Changes in ecology, increasing deer populations
= lyme disease (Borrelia burgdorferi)
What is the impact of Antimicrobial Drug Resistance? (causes and consequences)
Causes:
= incorrect prescribing patterns
= non-adherence by patients
= counterfit drugs
= use of anti-infective drugs in animals + plants
= loss of effectiveness
= community-acquired (e.g. TB)
= hospital acquired (e.g. MRSA)
Consequences:
= prolonged hospital admissions
= higher death rates from infection
= requires more expensive, more toxic drugs
= higher healthcare costs
Why is disease causation important?
Defining causation can be complex in an emerging disease
Cause
= initiation of a condition in an individual
= NOT previously affected
Critical Issues
= is exposure A casually related to outcome B?
= sometimes imprecisely used
Complications
= effect is small + competing causal factors are present
Framework developed
= in which causation can be assessed when considering environmental factors
= robust, simple tool that is not dogmatic
= e.g. Koch’s postulates, Bradford-Hill framework, Precautionary principle
What is Koch’s postulates?
Determining the causative agents of infectious disease:
= find evidence of particular microbe in every case of a disease
= isolate that microbe from an infected subject + cultivate it artificially in the laboratory
= inoculate a susceptible healthy subject with the laboratory isolate + observe the resultant disease
= re-isolate the agent from this subject
What is the Bradford-Hill framework?
Strength
= large effect makes causal relationship more likely
= BUT strong association is o more likely to be causal than weak
= strong relationships allow co-variable to be identified
Consistency
= is there evidence for the same findings form more than one study also in 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
What is the precautionary principle (PP)?
Exposure A is cause of outcome B
= reduce A , it will reduce B at an individual or population level
Exposure A is LIKELY to cause outcome B
= PP says waiting for clear information of exposure A to outcome B is unacceptable
(must reduce A now)
= complicated by how to achieve reduction
= can cause hysteria in the media
= separating genetic and environmental factors
= e.g. covid
= e.g. BSE
What is the disease burden?
Of every 10 deaths
= 6 non-communicable diseases
= 3 communicable diseases, reproductive or nutritional conditions
= 1 injury / trauma
1 in 5 of all deaths = children <5 y.o
(often access to safe clean water - need to break the cycle)
Leading causes of death
= cardiovascular diseases, cancer, infectious + parasitic diseases
Burden is different globally
(economic development)
Factors affecting health status
= social / political environment
(economics, warfare, immigration, socioeconomic class)
= healthcare
(access , development level)
