Microbial Mechanisms of Pathogenicity PDF

Microbial Mechanisms of Pathogenicity Joanna Hillman, PhD  Pathogen A Microorganism that can cause disease in a host  Infection When a pathogen successfully colonizes a host Infection can lead to disease The normal structure/function of the body is damaged Infectious dise...

Microbial Mechanisms of Pathogenicity Joanna Hillman, PhD  Pathogen A Microorganism that can cause disease in a host  Infection When a pathogen successfully colonizes a host Infection can lead to disease The normal structure/function of the body is damaged Infectious disease Disease caused by a pathogen Infectious Diseases can be: Communicable: can Noncommunicable: be spread from Is not spread from person to person person to person  Noncommunicable Disease Transmission +Tetanus: skin wound +Legionnaires: breathing in contaminated water This Photo by Unknown Author is licensed under CC BY-NC-ND Communicable Disease can be Contagious +Contagious: easily spread +Degree of contagiousness is influenced by transmission method +Example: sneeze/cough versus intimate contact Communicable Disease +Iatrogenic: infected during medical procedure +Wounds, catheters, surgery +Nosocomial: infected in a hospital setting +Sick patients bring in pathogens +Sick patients are immunocompromised +Medical equipment may not be properly sterilized +Improper handwashing by hospital staff +Frequent antibiotic use in hospital → antibiotic resistant bacteria Zoonotic + Rabies (viral): bite/saliva Diseases spread + Yellow fever (viral): mosquito bite + Rocky Mountain Spotted Fever (bacteria): tick from animals to bite humans + Malaria (protozoan): mosquito bite This Photo by Unknown Author is licensed under CC BY How do you know when you are sick? Signs: measurable (ex. fever, rash) Symptoms: subjective (ex. headache, nausea) How do you know + It is difficult to tell based on signs and symptoms + Signs and symptoms of different infections overlap WHAT got you + Fever, diarrhea, runny nose, cough sick? + Testing methods include microscopy, molecular testing, immunoassays, culturing This Photo by Unknown Author is licensed under CC BY-SA-NC  Period of Disease /Stages of Infection 1. Incubation 2. Prodromal 3. Period of illness 4. Period of decline 5. Period of convalescence Incubation +Patient does not know they are sick (no signs/symptoms) +Pathogen has entered and started multiplying +Time of incubation varies +Strength of pathogen +Strength of host immune system +Site of infection +Infectious dose +Type of infection Prodromal +Immune system activated → signs/symptoms Period of Illness +Severe signs and symptoms Period of Decline +Pathogen numbers decreasing +Signs/symptoms improve +More susceptible to secondary infection due to weakened immune system Period of Convalescence +Back to normal +May still be contagious (depends on the pathogen and transmission type) Different pathogens are contagious during different periods of illness +Bacterial meningitis + Contagious from incubation for up to a week before prodromal +Viral meningitis + Contagious with first signs/symptoms +Viral rashes + From incubation for up to a week before rash appears +Respiratory illnesses + Contagious at prodromal period (when symptoms start) +Diarrheal diseases + Can continue to shed long after signs/symptoms are gone and be spread person to person Disease can be: +Acute: fast onset and short time of illness +Chronic: disease process happens over a long time (months, years, lifetime) + Chronic Lyme disease + H. pylori (chronic gastritis) +Latent: pathogen goes dormant and can be reactivated with stress or immunosuppression + Herpes, chickenpox, mononucleosis + Herpes → sores on mouth or genitals + Chicken pox → shingles + Mononucleosis caused by EBV → latent in B cells → B cell lymphoma later in life Latent: pathogen goes dormant and can be reactivated with stress or immunosuppression Pathogenicity vs. Virulence Pathogenicity: Ability to cause disease Virulence: degree of pathogenicity Avirulent: not harmful Highly virulent: almost always leads to disease Example: B. anthracis (anthrax)  Indicators of Virulence ID50: number of LD50: number of cells/virions needed to cells/virions needed to cause an active cause death in 50% of infection in 50% of animals animals LD50: median lethal dose ID50 can vary significantly based on the person being infected +Route of entry +Example: Susceptibility of the organism to acidic pH of stomach (if ingested) +Age +Health +Immune status ID50 does not correlate with disease severity +S. enterica serotype Typhimurium – a single cell can lead to an active infection +Salmonellosis (nausea, vomiting, diarrhea) +1% mortality in healthy adults +S. enterica serotype Typhi – active infection requires about 1000 cells +Typhoid fever (severe symptoms) +10% mortality rate Table 15.2.215.2.2: ID50 for Selected Foodborne Diseases Pathogen ID50 Viruses Hepatitis 10–100 A virus Norovirus 1–10 Rotavirus 10–100 Bacteria Escherichia coli, enterohemorrhagic (EHEC, serotype 10–100 O157) E. coli, enteroinvasive (EIEC) 200–5,000 E. coli, enteropathogenic (EPEC) 10,000,000–10,000,000,000 E. coli, enterotoxigenic (ETEC) 10,000,000–10,000,000,000 Salmonella enterica serovar