Host-Microbe Interactions Chapter 14

Disease Etiology Pathogen –Primary vs. opportunistic Virulence

Contamination Infection vs. Infestation Pathogenesis Pathology

Symptoms Signs Syndrome Sequelae

Anatomical Barriers as Ecosystems Skin and mucous membranes are physical barriers to infection –May supply foundation for microbial ecosystem

Humans are usually sterile in utero Exposed to microbes during and immediately after birth –microbial populations begin to establish Normal flora –Resident flora –Transient flora Probiotics

Isolated colonies in specific body regions Dominant type of organism may change with age and situation

Factors that influence distribution of Flora: –Nutrient availability, salinity, oxygen availability, host defenses and mechanical factors

–Normal flora may offer protection from disease-causing organisms –microbial antagonism –Competitive exclusion –Bacteriocins

Symbiotic relationships form between microorganism and host –Relationships may change depending on state of host and attributes of microbes

–Mutualism (++) both partners benefit –Intestinal bacteria –Probiotics –Commensalisms (+ neutral) one partner benefits and other is unharmed –Flora on skin and conjunctiva –Parasitism (+-) microbe benefits at expense of host –Pathogens

–State of host resistance usually determines extent of infection primary infection secondary infection Sub-clinical or in-apparent infection Pathogenicity

Many people are carriers of pathogens –Viruses; Neisseria; Salmonella; Streptococcus Why are they not affected?

Predisposing factors: –gender –genetic background –climate and weather –inadequate nutrition –age –habits and lifestyle –chemotherapy –emotional disturbances

Characteristics of infectious disease: –communicable contagious Often reflects ID 50 –non-communicable disease

Etiology of Infectious Diseases Robert Koch demonstrated that specific microbes caused specific diseases –experimented with grazing animals infected with anthrax –Later work with TB got more interest

Koch developed a series of steps (Koch’s postulates): –Same pathogen must be present in each case of disease –Pathogen is isolated from diseased host and grown in pure culture –Pure culture must cause disease when inoculated into healthy animal –Pathogen must be re-isolated from inoculated animal

Exceptions to Koch’s postulates –some bacteria have unique culture requirements –some diseases are caused by multiple pathogens Polymicrobial diseases (mixed infections) –Ethical considerations

Stages of an Infectious Disease

Duration of a Disease –acute diseases –chronic diseases –latent disease

Distribution of pathogens –Local infections –Systemic infections Bacteremia Toxemia Viremia –Septicemia