Introduction and Historical Perspective of Infectious Disease Flashcards
Early treatment options for infectious disease
-Isolation -Destruction of “soiled” materials -Natural remedies -Bloodletting
Variolation
Preventive measure for smallpox where dried pox crusts were inhaled or inserted into open wounds to confer protection. Inconsistent and dangerous
Anton van Leeuwenhoek
First direct observation of microbes “animalcules”
Edward Jenner
Vaccine development Previous ix with cowpox confers protection against smallpox.
Ignaz Semmelweiss
Importance of hand washing
John Snow
Disease transmission via polluted water
Louis Pasteur
-Mild heating of food delays spoilage -Development of Germ Theory -Development of attenuated vaccines (cholera) -Development of rabies vaccine
Joseph Lister
Use of aseptic surgical technique to reduce postoperative ix’s
Robert Koch
-Proof of Germ Theory -Developed Koch’s postulates - isolation of MO and re-ix
Alexander Fleming
Discovery of penicillin as chemotherapeutic agent
Further Development in ID
-VACCINES -Vaccines against viral ix’s -Vaccines against childhood disease -Eradication of smallpox
% Deaths caused by infectious agents worldwide
20
4 major death causing infectious agents worldwide
-Lower RT ix’s -Diarrheal ix’s -Tuberculosis -HIV/AIDS
Current state of infectious disease
-Still major problem worldwide, much more prevalent in developing world -New ix’s continue to emerge -Some ix’s are re-emerging
Examples of emerging/re-emerging infectious diseases
-HIV -Hantavirus -HTLV 1 2 3 4 -Herpes viruses -E coli strains -Borrelia burgdorferi
Aspects of modern life that encourage disease transmission
-Climate change -Slowed development of vaccines, antimicrobials -Altered sexual behavior -Altered patterns of trade -Altered agricultural practice -Overuse/misuse of antibiotics -Population growth -Emergence of new strains/ix’s -Bioterrorism
Prokaryotes
-No membrane bound nucleus or organelles -70S ribosome -No histones -One circular chromosome +/- plasmids -Cell wall usually present
Eukaryotes
-Membrane bound nucleus and organelles -80S ribosome -Multiple linear chromosomes -Histones present -Cell wall only in fungi
Bacteria
-Prokaryotic -Cell wall of peptidoglycan (target for abx) -Replication either IC or EC -Small (1-20 micrometers) -Variety of shapes
Fungi
-Eukaryotic -Exist in two forms: -Yeast form - unicellular, reproduce asexually -Filamentous mold form - multicellular, reproduce asexually or sexually -Thick cell wall
Parasites
-Eukaryotic -Range in size -Protozoa - small -Arthropods - insects -Helminths - worms
Viruses
-Not cellular -Nucleic acid surrounded by protein coat and sometimes enveloped -Obligate IC parasite
Prions
-Not cellular -Spongiform encephalopathies -Abnormally folded proteins that induce abnormal folding in other proteins -Resistant to disinfection -eg. Creutzfeld-Jakob
Medical Nomenclature
Genus name + species name
Subspecies
Members of same species with subtle physical, metabolic or biochemical differences -eg. E. coli strains
Host
Animal capable of supporting growth of MO
Pathogen
Agent that causes disease
Pathogenicity
Ability to cause disease
Virulence
Degree/intensity of pathogenicity
Colonization
Microbial reproduction on host without disease
Infection
Presence of MO on/in a host
Infectious Disease
When presence of ix results in a diseased state, due to MO factors or host immune response
Outcome of interaction between MO and host depends on (3)
-Site of ix -Host’s immune response -Virulence of MO
Strict pathogens
Always cause disease
Opportunistic pathogens
MO that does not usually cause disease but can cause disease if introduced into sterile site or in immunocompromised patients eg. S. aureus, E. coli
Normal flora
-Normal microbial population found associated with healthy hosts in nose, GI tracts, urinary tract, -Mostly bacteria -10(14) cells
Development of normal flora
-Fetus is sterile -Initial normal flora from mother’s genital tract, hospital setting, colonizes nasopharyngeal area, GI tract -Influenced by diet (eg. breast milk results in lactobacillus in flora) -Can have permanent and transient components
Alterations of normal flora done by (4)
Physiological conditions -pH, nutrient status, oxygen concentration -antimicrobial substances (eg. lysozyme) -types of other flora present Host factors: -age, diet, health status, hygiene
Common flora of large bowel
-Strep faecalis -Bacteroides -Fusobacterium -Escherichia coli
Common flora of fecal material
-Bacteroides -Bifidobacterium -Eubacteria
Beneficial effects of normal flora (4)
-Involved in metabolism (eg. oxalates) -Involved in nutrient production (eg. vitamin K, B) -Immune system development -Protects against infections
Normal flora protects against other ix’s (3)
-Exclusion of other MO’s -Production of toxic metabolites (eg. Bifidobacterium reduces pH in gut) -Production of antibacterial factors
Negative effects of flora (2)
-Source of pathogens -Metabolic activity of flora can be detrimental -eg. biotransformation into carcinogens
Manipulating & Altering Normal Flora
Unintentional
- Long term abx use (make pt susceptible to C. diff infections)
- Hospitalization (replacement of normal flora with Gram (-) rods
Intentional
- Bone marrow transplant pt’s (remove flora so that they can’t cause opportunistic infections
- Probiotics - consumptions of live bacteria to alter flora (often Lactobacillus and Bifidobacterium, enteric coating used to get to GI tract)
- Prebiotics - consumption of non-digestible foods to stimulate growth and activity in GI tract (eg. soluble fibre)
Probiotics useful for (4)
- Bloating and diarrhea due to lactose intolerance
- Diarrhea to rotavirus enteritis in infants
- Diarrhea due to abx use
- Ix’s in digestive tract
Stages of Infectious Disease
- Attachment
- Spread
- Multiplication
- Evasion of host defenses
- Exit (shedding)
- Transmission
- Damage to host
Entry, Exit, Transmission
MO must be able to attach/penetrate host defense, multiply, and exit from host to find another in order to be infective
Modes of Transmission (6)
- Ingestion
- Inhalation
- Trauma
- Needlestick injuries
- Arthropod bites
- Sexual transmission
Receptor molecules
- Present on cells, provides specificity of ix
- Have normal function
- After binding, MO’s can either enter cell or replicate on surface
- Presence/absence of receptor molecules determines whether ix will occur or not
Intracellular Pathogens
- Use cellular nutrients for own growth
- Protected against host defenses somewhat
- More difficult to target with therapeutics
- Some are obligate - only replicate inside cells
Extracellular pathogens
- Take nutrients from tissue fluids or directly from cells
- Able to grow and reproduce freely
- Can spread throughout body
- Size and protective coating can protect against phagocytosis
- Vulnerable to host immune host defenses
Exit and Transmission
- To be infective, MO must exit host and spread to new host
- If unable to spread host to host, not going to affect population as a whole
Factors Affecting Transmission (3)
- Number of MO’s shed (not all shed are infective, MO’s that induce large shedding most likely to be more infective
- Number of MO’s required to infect (ID) - varies greatly
- Stability in environment (resistant to drying, thermal inactivation or able to sporulate makes MO more infective)
Other Factors Affecting Transmission
- Microbial genetic factors (Different strains have different transmission rates)
- Activity of host (eg. coughing, sneezing, diarrhea makes transmission easier)
- Coughing, sneezing, diarrhea benefits host by clearing MO’s and benefits MO’s by making transmission easier
Three Types of Transmission
- Human to human (respiratory, fecal oral, sexually transmitted)
- Verterbrate to human (through animal consumption or pets) (called zoonoses)
- Biting arthropod (eg. malaria through mosquitos)
Two Types of Human to Human Transmission
- Vertical transmission (from parent to child through sperm, ova, blood, breast milk)
- Horizontal transmission (transmisison to both related and unrelated individuals)
- Respiratory, fecal-oral, sexually transmitted
Types of Biting Arthropod Transmission (3)
- Passive transmission (uncommon)
- insect carries MO on body, in intestine, transmits from human to human, eg. C. trachomatis to eyes - Biologic transmission (more common)
- arthropod is essential step in MO’s life cycle, can’t be transmitted to new human without going through arthropod first
- either through direct injection or contamination of blood at time of feeding
- eg. malaria, typhoid, plague - Passive transmission via invertebrates used for food
- invertebrate accumulates MO in body, humans consume invertebrate and become infected
- eg. V. cholerae in shellfish
Zoonoses
- Animal diseases that are transmitted to humans via animal vectors
- Transmisison by inhalation, scratches, ingestion of animal, contact, bites, contamination of food and water
Epidemiology of zoonoses depends on (3)
- Geography (local food preferences, habitat overlap)
- Occupation (eg. butchers, farm workers)
- Contact with domestic animals (eg. pets)
Reservoir
Site or location in environment where MO is found living and can be transmitted to humans
Carrier
Infected individual who is potential source of infection
Acute Carrier
Carrier who is in acute phase of disease
Convalescent Carrier
Carrier who has recovered from disease but is still harboring MO and can infect others
Healthy Carrier
Harbors pathogen but is not showing symptoms
Incubatory Carri
Carries pathogen but is not yet ill
Fomites
Inanimate objects that can carry pathogenic organisms (eg. bedding, utensils)
Vectors
Organisms that can transmit pathogen (eg. arthropods, animals)
Sporadic Disease
Occuring occasionally at irregular intervals (eg. typhoid)
Endemic Disease
Low level frequency at somewhat regular intervals (eg. common cold)
Hyperendemic Disease
Increase in frequency above endemic rates but not yet epidemic rates
eg. common cold in winter months
Epidemic Disease
Sudden increase beyond expected levels (eg. influenza in some years)
Pandemic Disease
Increase in frequency in large population over wide ranges of area
(eg. influenza in 1960’s, AIDS)
