What is an infectious disease?
Illness caused by a specific infectious agent or its toxic product that results from transmission of that agent or its product from an infected person, animal or reservoir to a susceptible host, either directly or indirectly through an intermediate plant of animal host vector or inanimate environment
Differentiate between infectious agents
Prions: only a protein, no nucleic acid, non-living
Viruses: RNA/DNA, protein coat and maybe lipid bilayer/envelope, non-living
Bacteria: prokaryotic single cell living organism. No organelles, nucleus or nuclear envelope
Fungi: eukaryotic, exists as molds or yeasts
Protozoans: eukaryotic, unicellular parasites
Helminthes: multicellular eukaryotic parasites
Ectoparasites: lice, usually arthropods that live on the skin
can cause disease in virtually any susceptible host including normal, health hosts with intact immune systems. Known as true pathogens
Potentially infectious agents that rarely cause disease in individuals with healthy immune systems
Usually cause disease in people with compromised immune systems due to age, genetic defects, medical procedures
Commensalism: shelter and food
Mutualism: reciprocal benefit
Parasitism: unilateral benefit
What are Koch's postulates?
Organism must be isolated from every patient with the disease
Organism must be isolated free from all other organisms and grown in pure culture in vitro
Pure organism must cause the disease in a healthy, susceptible animal
Organism must be recovered from the inoculated animal
What is a reservoir?
Reservoir: where the microbe in normally before infecting a susceptible persion
How do you break the chain of infection?
Prevention and control measure for human reservoirs
Diagnosis and treatment, screening, isolation and reporting
Prevention and control measures for animal reservoir
Vaccination, treatment and euthanasia
Prevention measures of susceptible hosts
Vaccination, chemoprophylaxis, maintain a healthy lifestyle and limiting exposure to reservoir of infection
Natural history of infection
Incubation period (no signs or symptoms)
Prodromal period (vague, general symptoms)
Illness (most severe signs and symptoms)
Decline (declining signs and symptoms)
Convalescence (no signs or symptoms)
Six basic processes of microbial pathogenesis
Microbial encounter with and entry into the host
Microbial adherence: a potential pathogen must anchor itself to a tissue or tissue factor using adhesins, unless directly inoculated into the bloodstream
HIV uses viral and cellular proteins
Bacteria also use adhesins
Microbial growth after entry
Viruses are obligate intracellular parasites. Must generate new progeny inside a host cell
Avoidance of innate host defenses
Tissue invasion and tropism
Tissue damage and disease
Transmission to new hosts
What issues arise with Koch postulates?
What if the pathogen is found in healthy asymptomatic patients?
What if multiple pathogens cause the same disease?
What if the pathogen cannot be cultured?
What if there is no good animal model?
What if the pathogen does not cause disease in all subjects?
What is a zoonosis?
A disease that rises from an animal vector
What is a formit?
Bacteria that can be transmited via a nonliving surface in the enviroment.
Example: doorknob, water fountain, etc
What are exits from the chain of infection?
Exits from human reservoir
Exit: can be from a human or non-human reservior
Exit from non-human reservior: Pets, insects, animals, food, inanimate object
What are the three types of transmission?
Direct, indirect, and vertical
What are direct methods of transmission?
Direct modes of transmission: direct physical contact with blood or body fluids
Person to person transmission. Touching, respiratory droplets, sexual intercourse, talking, or sneezing
What are examples of vertical transmission?
Vertical transmission: mother to infant
What are examples of indirect transmission?
Indirect methods of transmission: infectious agents are transmitted to new hosts through intermediates
Airborne, vehicle-borne, vector-borne, zoonotic
What are examples of infectious factors?
Susceptibility of the population
Infectiousness of the infected person
Environment: type of contacts between infectious and susceptible individuals and number of contacts.
What are examples of pathogen entry routes?
Susceptible host Infectious agent
What are the 6 main risk factors for infectious diseases?
Poor personal hygiene
Inadequate sewage treatment
Poor control of reservoirs
Unprotected sex with multiple partners
Injected drug use
What are example of times of low levels of immunity?
Immature Immune System
Compromised immunity (advanced age, medicines, disease)
What is a viral immunomodulartory protiens?
Large DNA-containing viruses encode a plethora of gene products that are homologous to cellular proteins and key for their success in nature. This is due to the viruses co-evolution with humans and thus they have captured human cellular genes and duplicate them thus makeing these protiens capable of mimicking or interfering with the original host funtion and since they look like host protiens the immune system ignores them.
What is tropism?
The specificity of a virus for a particular host tissuem determined in part by the interaction of viral surface structures with host cell surface receptors.
What is an example of cellular tropism?
HIV normally infects macrophages but not neurons.
What is an example if tissue tropisim?
Influenza virus normally infects lung tissue but not brain tissue
What is an example of Host Tropism?
Myxoma virus normally infects rabbits but not humans.
What are activities that increase the exposure to infectious agents?
Population movements, urbinization, long distance travel, natural disasters, global climate change, and new technologies.
What are activities that increase susceptibility to infectious agents?
Microbial adaptation, poverty/social inequality, war/famine, natural disasters, global climate change, and opting out of vaccinations.
What is prevalence in relation to disease in a population?
Includes both new cases and those who contracted the disease in the past and are still surviving.
A measure of prevalence is preferred if the focus is on the overall number of cases surviving in the population.
What is incidence in relation to disease in a population?
Tells us about a change in status from non-disease to disease, thus being limited to new cases.
Is favored if the rapidity with which new disease is occuring in the population of interest.
What is a pandemic?
Present in a widespread region or worldwide
Which has a better chance of transmission a more or less virulent virus?
Less virulent have a better ability for transmission because the host lives longer and is more likely to move about and contact other hosts.
What is an epidemic?
Present at a higher level that usually found in a community or population.
Not worldwide but a large area.
What is an outbreak?
Suddely present in a distinct population (localized)
What is endemic?
Present in a population at a fairly constat level (steady to a certain level)
What does it mean if a disease is seasonal?
Incidence peaks during a specific time of year
What does it mean if a disease is eliminated?
No longer circulating in a given geographical region, control measures still necessary
What does it mean if a disease is eradicated?
Permanently eliminated from circulation worldwide, controls measures no longer necessary.
What does it meain if by: Emerging infectious disease?
Previously unknown or undetected infectious agents.
What does it mean by: Reemerging infectious disease?
Known pathogens who incidence had decreased in the past but has reapperared.
What is a Deliberating emerging infectious disease?
Agents with potential to be used for bioterrorism
What is required for a pathogen to become established?
A susceptible population must be exposed and the agent must be able to be transmitted efficiently.
What are examples of infectious agents?
prions, viruses, bacteria, parasites (endo/exo), fungi, protozoans, and helminthes.