GGRB28 Notes from assigned readings

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Published on 30 Jun 2012
Changing patterns of infectious disease
-most of the twentieth century, the predominant feeling infectious diseases was optimism
-the development and successes of antibiotics and immunizations
-victory declared, increasing emphasis was directed at the non-infectious diseases such as cancer
and heart disease
-In much of the developed world, the public had forgotten the impact of infectious diseases
-This optimism shaken by a series of outbreaks and epidemics
Infectious diseases in the twentieth century
-At the beginning of the twentieth century, infectious diseases were the leading cause of death
-tb, pneumonia and diarrheal disease
-high child mortality rates and low life expectancy
-by 1900, morbidity and mortality from infectious diseases had already considerably improved in
much of the developed world.
-attributed to a series of factors that were decreasing host susceptibility and curtailing
disease transmission: better nutrition and housing, safer food etc
-the introduction of antimicrobial agents in the mid-twentieth century accelerated this
-By the end of the twentieth century, in most of the developed world, mortality from infectious
diseases had been replaced by mortality from chronic illnesses
-infectious disease remained a major cause of morbidity in the developing world
-by the end of the 20th century, new infectious agents had the potential for rapid international
-also re emergence of old infectious diseases such as ebola
- Resistance to antimicrobial agents was becoming a serious global problem.
- in 1992, the Institute of Medicine (IOM) issued report defined an emerging infection as a “new,
reemerging, or drug-resistant infection whose incidence has increased in the last two decades, or
whose incidence threatens to increase”
Factors influencing emergence:
- Emergence is often the consequence of societal and technological change and is frequently
unexpected and unpredictable.
- Ironically, some factors that have resulted in a decline in one disease can contribute to an increase
in another. The development of refrigeration provided an advantage to organisms such as Listeria
- The recurring theme throughout all of these factors that influence the emergence of infectious
diseases is change.
6 factors contributing to re emergence follow:
- Changes in demographics and behaviour:
- Demographic changes fall into several broad areas: changes in population, such as the
increasing prevalence of persons with susceptibility to infection; societal changes and moments of
infected ppl
- Changes in behaviour include increases in recognized risky behaviours
- increase in susceptible populations
- Ageing of the population, increases in underlying diseases, and technological
advances in health care have all contributed.
- Medical technology is also increasing the survival of persons with other
-Sexual activity is an important behavioural risk factor that has contributed to emergence
-also smoking and iv drug use, geographical moves
- One of the strongest influences on the emergence of resistance has been the unnecessary
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use of antimicrobial agents
- Changes in technology and industry
- changes in food production and distribution allows for the emergence of food borne illness
- Environmental change and land use:
- Changes in environment and in land use are global activities that include both natural and
man-made changes.
- preserving deer populations, have led to the spread of Lyme disease.
- Climate change, whether natural or man-made, is also contributing to the emergence of
infectious diseases
- International travel and commerce:
- travel facilitates the global transmission of diseases spread by infections, too, can spread
more rapidly
- Diseases that would normally have a limited geographic distribution have become part of
the differential diagnosis of the unwell traveller.
- International food-borne disease outbreaks
- Microbial adaptation and change:
- As society and technology change, so do microorganism
-change can be the result of selective pressure
- Breakdown of public health measures:
- Some infectious diseases have emerged or re-emerged because the public health systems
established to prevent or control them have broken down
-due to complacency from past successes against infectious diseases, limited
resources and competing priorities in public health, social unrest, wars, and population movements
-TB = good example of these factors
Emerging infections in the twenty-first century:
- During one century, most of the developed world experienced vast improvements in health
However, much of the improvement was limited in the developing world
- Societal and technological change accounted for both the control and the emergence of infectious
- One lesson learned from history is that change leads to the continued emergence of infectious
- Food-borne disease:
-early in our history there were diseased animals, unsafe food handling, unsafe drinking
water and malnutrion
- incidence of food-borne diseases was soon reduced by a series of regulatory and
technological changes including food inspection
- Nutrition was improved by the fortification of food with vitamins and minerals, and social
programmes to feed the poor
- It is ironic that for present generations, malnutrition from excessive amounts or types of
food is increasing susceptibility to infectious diseases by contributing to heart disease & diabetes
- Resistance to antimicrobial agents
- Microbes that once were easily controlled by antimicrobial drugs are, more and more
often, causing infections that no longer respond to treatment with these drugs
- A combination of increased selective pressure from the use of antimicrobials, increased
disease transmission and a decline in the development of new antibiotics has raised the spectre of
once treatable infections becoming untreatable
-LOOK UP VRE (related to drug resistance)
Communities have also experienced problems
- Drug resistance in the developed world has been increasing in food-borne pathogens
- One of the most worrying problems for the community has been the emergence of drug-
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resistant Strep. pneumoniae (DRSP) -> causes deadly pneumonia in children and adults
Addressing emerging infections in the twenty-first century:
- One plan developed by the Centers for Disease Control and Prevention identifies four major
strategies: (1) enhancing surveillance and response, (2) encouraging applied research, (3)
strengthening the infrastructure for public health and providing training opportunities, and (4)
developing, implementing and evaluating strategies for prevention and control
- surveillance is necessary
- The relative importance of each strategy varies from problem to problem. The nature of the
problem might be different in the developed and developing worlds
- For some infections, applied research might best be directed towards (1) new antimicrobial
agents, (2) mechanisms to decrease host susceptibility through vaccines or immunomodulators,(3)
new surveillance techniques, (4) genetic studies to improve our understanding of the host and
pathogen, or (5) techniques to improve the use of antimicrobial agents
- Effectively addressing these problems will require awareness, flexibility, resources and longterm
Environmental and social influences on emerging infectious diseases: past, present and
- The three great historical transitions since the initial advent of agriculture and livestock herding,
from ca. 10 000 years ago, occurred when: (i) early agrarian-based settlements enabled sylvatic
enzootic microbes to make contact with Homo sapiens; (ii) early Eurasian civilizations came into
military and commercial contact swapping their dominant infections; and (iii) European
expansionism, over the past five centuries, caused the transoceanic spread of often lethal infectious
-we are living in the 4th transitional period where The contemporary spread and increased
lability of various infectious diseases, new and old, reflect the combined and increasingly
widespread impacts of demographic, environmental, behavioural, technological and other rapid
changes in human ecology
- Cholera
- ancestral home of cholera was apparently the Ganges delta, in India
- The initial spread occurred as a result from a great numbers of pilgrims from all over India
coming to bathe in the sacred waters and their subsequent dispersal in association with british
-steamboats allowed it to cross the Atlantic
-the newest (7th) pandemic reflects increased move of humans b/w continents, the rapidity
of shipping based trade and the proliferation of urban slums
- US Institute of Medicine defined ‘emerging’ as subsuming three things:
(i) established infectious diseases undergoing increased incidence,
(ii) newly discovered infections, and
(iii) newly evolving (newly occurring) infections.
- War, Conquest, Famine and Pestilence. Two millennia ago in the eastern Mediterranean region,
these were the four main recurring scourges of human happiness, health and survival
- the resurgence of previously well-established infectious diseases has been primarily attributable
to changes in social conditions and behaviours
- poverty, crowding and the weakening of public health infrastructure
- Epidemics have often accompanied periods of great social and demographic transition
- Various environmental influences also influence the resurgence of some of these infectious
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