Topic 1: Bacterial Diseases and Vocabulary - Disease-causing microorganisms constitute only a very small fraction of microbes - Infectious diseases account for 30% of deaths Infection and disease Infection: colonization of human body(host) by pathogenic bacteria Disease: damage to the body that impairs function Pathogenicity: ability of a bacterium to cause diseases (qualitative) · Pathogen: bacterium capable of harming a normal host (defenses not compromised) · Opportunistic pathogen: only capable of harming a compromised host (immunodeficiency, prior infection, disease, wound etc.) Virulence: measure of the pathogenicity of a bacterium (quantitative) · Virulent - most · Avirulent - rarely Bacterial infections Primary infection: initial acute infection Secondary infection: a later infection caused by an opportunistic organism after a primary infection Clinical infection: host exhibits signs and/or symptoms of disease Subclinical infection: host has no signs/symptoms Nosocomial infection: acquired because of hospitalization · Endogenous: caused by microbiota · Exogenous: transmitted from individual · latrogenic: a result from surgery, diagnostic procedures or medical implants (doctor induced) Non-nosocomial infection: acquired in the community
Invasiveness: the ability of the organism to invade into the host's body · Local infection: small area of the body (non-invasive organisms) · Focal infection: begins in a restricted area, then spreads throughout the body · Systemic (generalized) infection: spread throughout the body - often disseminated throughout the body via the blood Bacteremia: presence of bacteria in the blood Septicemia: bacteria multiplying in blood Epidemiology: study of when and where diseases occur and how they are spread Incidence of disease: fraction of a population that contracts the disease during a time period Prevalence of disease: fraction of a population having the symptoms of the disease during a time period Sporadic disease: occasional occurrence in geographically separated areas Endemic disease: continuous occurrence at a low level (not very virulent pathogen, or majority of individuals are immune) Epidemic disease: sporadic occurrence at an elevated level and continuous at a low level between outbreaks Pandemic disease: widely distributed epidemic Disease outbreak: when number of cases increases in an area which had only sporadic cases previously Mode of transmission · Contract transmission: direct human contact (e.g. skin pathogens) · Common vehicle transmission: inanimate objects (fomites), food, water, blood, drugs, etc. · Airborne transmission: droplets or dust (e.g. respiratory pathogens) · Vector transmission: living agents such as insects, ticks, mites, fleas, rodents, animals (e.g. skin and blood-borne pathogen)
Reservoirs of disease: sites which viable infectious agents remain · Human reservoirs - Symptomatic: currently have the disease - Convalescent: recovering but still harbour the agent - Carriers: have no disease symptoms but carry the pathogen · Animal reservoirs - Zoonoses: diseases occur primarily in wild or domestic animals but can be transmitted to humans · Insect reservoirs - fleas, lice and flies - insects that fly: broader home ranges and harder to control (significant epidemiological implications) · Inanimate or nonliving reservoirs - present and transmitted from water or soil - he surface of the vaginal wall to prevent infections