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Disease-
abnormal state in which part or all of the body is not properly adjusted or is incapable of performing its normal functions
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Infectious Disease-
disease resulting from a microbial infection
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•Pathogenicity:
the ability to cause disease
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Types of pathogens
- 1. Primary Pathogen
- 2. Opportunistic Pathogen
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Primary pathogen-
causes disease in host is normal mode of operation
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Opportubistic pathogen
Normally non-pathogenic, but can causes disease under certain conditions
Example: perforated large intestine and gram negative bacteria
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Virulence-
degree of pathogenicity
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Virulence factors-
Characteristics of microbe that make it pathogenic
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Infection
microbe growing in/on its host.
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Infectivity-
ability to establish a discrete point of infection
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Invasiveness-
ability to spread from initial site of infection
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Epidemiology-
study of disease in populations
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1848-1840 outbreak of cholarea in London was researched by... where he....
John Snow....indentified contaminated water from the Board Street pump as the source of the outbreak
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Who used statistical data to argue for improved conditions in British military hospitals?
Florence Nightingale
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Prevalence=
number of individuals with the disease at a given time
“snap shot” of population at one time point
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Mortility
• number of individuals in the population who die from a particular cause in a given time interval
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Case Fataity Rate-
proportion of infected individuals who will be killed by the disease
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Morbidity and CFR data can help you make decisions on how to allocate resources
which diseases are more significant threats at any given time in a particular populationexample: a disease with low CFR and high morbidity may be more of a threat than a very high (100%) CFR with very low morbidity
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•Frequency
endemic-
- disease is always present in the population
- •prevalence usually varies
- •cyclic seasonal variations are common in many
- •humans can act as reservoirs
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Frequency
Sporadic-
- infected individuals are not always present in the population
- •non-human reservoirs exist
- •isolated from populations in which it is endemic
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Outbreak-
significant increase in prevalence of a disease
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Epidemic-
outbreak of more or less limited geographic extent
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Pandemic-
outbreak that involves several continents, or world-wide
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Epidemiological Surveillance
- •Many governments have agencies
- that collect and analyze epidemiological data.
- –United States: Centers for Disease Control and Prevention (CDC)
- •Headquarters in
- Atlanta, GA
- •Collects data and does research on pathogens world-wide
- •publication: Morbidity and Mortality Weekly Report (MMWR) - available free online
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Notifiable Diseases
–cases of certain diseases must be reported to the CDC
–establish long-term patterns
–early recognition of potential outbreaks
•possibility of quick containment
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Gather information about a disease (4)
–reservoirs and modes of transmission
–who is most at risk (predisposing factors)
–best methods for control
–how best to use limited resources to combat disease
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Reservoirs
- sources of disease organisms in the environment
- –Humans
•individuals showing S & S
•carriers - infected but without serious S & S
–chronic, latent, subacute, subclinical, asymptomatic, incubation
–examples: HIV, diphtheria, hepatitis, gonorrhea, streptococcal infections, typhoid fever
- •eradication may be possible for diseases with humans as the only reservoir, and if an effective vaccine is available
- –smallpox (variola) - late 1970s
- –poliovirus - close
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Resevoirs cont..
•Animals
–zoonoses: can cause disease in animals and can be transmitted to humans
•over 150 known: Table 33.1
•control is difficult if in wild animal populations
–some have no visible effect on infected animals
•Trypanosomes and game animals in Africa
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•Non-living Reservoirs
–to be a reservoir, microbes must be capable of long term survival and reproduction in these environments
- –Examples
- •soil and water
- •food
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Transfer mechanisms can be classified into two major categories.
–Direct Contact
–Indirect Contact
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Direct Contact
person to person
staphylococcal infections, measles, cold viruses, influenza, STDs
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Indirect Contact-Fomites
–contact contaminates an inanimate object that is contacted by an uninfected host
•towels,utensils, drinking cups, money, syringes, etc
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Droplet Transmission-
–droplet: larger mucus and saliva particles that remain airborne for only short distances
•usually less than one meter after coughing
–example: influenza
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Airborne Transmission
–agents on tiny particles that can remain airborne for long periods of time
•dust, mucus, saliva, aerosols
- •longer exposure
- to drying, UV, lack of nutrients
–measles, tuberculosis, Legionella, Streptococcus, fungal spores (systemic infections)
–entry by ingestion, inhalation, through cuts in skin
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Vehicle Transmission-Contaminated Food and/or Water
–Fecal/Oral transmission: exit host in feces, enter new host by ingestion of contaminated food or water
•many examples: mostly gastrointestinal diseases
–Shigella, Salmonella, enteropathogenic E. coli, cholera, Norovirus, Polio, amoebic dysentary
•associated with poor sewage and drinking water treatment, and unsanitary food preparation techniques
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Vector Transmission (2 types)
- Mechanical Transmission
- Biological Transmission
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Mechanical Transmission-
passive transport on surface of animal.
Ex. Houseflies and fecal microbes
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Biology Transmission-
specific association btwn a particular animal and a microbe.
Most vectors are blood sucking anthropods. Ex. fleas, mosquitos, tickes, flies, lice
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Vector Transmission-
–Vector control is often a viable strategy for control of these diseases
–Range of vector often determines where a disease can occur
–examples: Table 14.3
- •Plasmodium and
- Anopheles mosquitoes
•Rickettsias and ticks
•Typhus and lice or fleas
•Lyme disease and deer ticks
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Spread of Disease-
•Common Source Diseases:
–infection from contaminated, non-living source
•examples: most food poisoning, food infections
–less likely to become epidemic/pandemic
–rapid, localized increase and rapid decline after identification and treatment of source
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Spread of Disease- Propagated Diseases
–spread by contact with infected individual (direct, droplet, airborne) or by vectors
–slower increase that may be less localized
–greater potential to become epidemic/pandemic
–more difficult to identify early and to control once it begins to spread
•made worse by modern transportation systems
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Emerging Infectious Diseases...Diseases are increasing in prevalence..why?
–return of previously better controlled microbes
•drug resistance (malaria, staph and strep)
•new pool of susceptible individuals (TB in HIV patients in US and western europe)
•breakdown in public health measures
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Emerging Infectious Diseases
–Evolution of microbes: new species that infect humans
•HIV
–Humans interact with the surrounding environment in new ways - changes frequency and pattern of contact with microbes.
•Lyme Disease: predator depletion and suburban lifestyle
•changes in patterns of human habitation and hemorrhagic diseases such as ebola and hantavirus
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Emerging Infectious Diseases- Lifestyle Changes:
Legionnaire's Diesease and air-conditioning systems
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Emerging Infectious Diseases- Climate Change-
Global warming and changes in vector ranges.
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