PRINCIPLES OF DISEASE

Symbiosis Relationship between 2 or more species Mutualism- both benefit,

Symbiosis Commensalism-one benefits and other unaffected

Parasitism One benefits at expense of other Pathogen-causes disease Metabolically unstable relationship Host dies or eliminates pathogen Most successful parasites

Parasitism Host under continuous pressure from infection Battle between host & parasite Emergence of new & return of old infectious diseases

Pathogenicity Capacity to produce disease –Adherence –Multiply on host –Ability to invade host or cause damage –Avoid being damaged by host’ defenses –Depends upon # of organisms

Virulence Intensity of disease produced

Terms Contamination Infection- multiples and invades tissue Disease- disrupts state of health

Normal Flora 1 x10 13 body cells with 1 X10 14 bacterial cell Resident flora always present

Normal Flora Resident flora Transient flora

Opportunists Usually cause no disease Conditions allow them to cause disease

Opportunists Intro of bug into unusual body sites Disturbance of normal flora

Advantage of Normal Flora Ensures normal development of immune system Prevent over growth of harmful organism- microbial antagonism

Microbial Antagonism Normal flora in colon prevents overgrowth of C. difficile E. coli produces bacteriocins

Disadvantage of Normal Flora Potential for spread into sterile parts of body Intestine may perforate Skin broken Extraction of tooth Perianal skin flora enters urinary tract

Etiology Cause of disease Koch’s postulates-organism causes disease

Frequency of Disease Endemic –Always present in population Epidemic –Occurs in unusually high number of people Pandemic- –Epidemics world wide

Types of Infectious Diseases Acute -develops rapidly but lasts for short time- influenza Chronic disease -develops more slowly and continues or recurs for long periods -TB, hepatitis B Latent- agent remains inactive for a time and later becomes active-shingles

Herd Immunity Proportion of people in community who are immune Important in cyclic diseases If high, disease can only spread among susceptible people Loss of herd can lead to reemergence of disease

Extent of Disease Local infection-limited to small area of body- boils Focal - starts as local infection (sinus or teeth) then enter blood or lymph and spreads Systemic -organisms or products spread through out body-measles Bacteremia- presence of bacteria in blood

Extent of Disease Septicemia-bacteria multiplies in blood Toxemia-toxins in blood Viremia-virus in blood Subclinical (inapparent )- no noticeable illness-hepatitis A Primary disease- initial acute infection Secondary infection -opportunistic infection

Stages of Disease Incubation period-time between initial infection and first appearance of S&S

Prodromal Period Short period–only in some diseases

Invasive Period Period of illness-most acute Overt signs and symptoms Cough, sore throat

Decline/Convalescence S&S subside Regain strength and recovery

Epidemiology Study of mechanism and factors involved in the frequency and spread of disease Incidence of diseases Prevalence of diseases

People Food Equipment Entry Transmission Reservoir Portalof Exit Infecting Agents Susceptible Host Bacteria Parasites Viruses Respiratory System GI & GU System Direct Contact Indirect Contact Airborne Droplet Broken Skin Respiratory System GI & GU System Elderly & Young Pts w/ Chronic Illness Diabetic Use of Invasive Equip Chain of Infection

Spread of Disease Chain of infection Agent- pathogen Reservoir-source/site of organism Human reservoirs Animal reservoirs -zoonoses

Humans Sick people Carriers –Incubatory or asymptomatic carriers HIV but not AIDS Hepatitis C –Chronic carriers Typhoid Mary excreted salmonella for years in feces S. pyogenes in throat

Animals Domestic and wild Mammals carry rabies-exposure to saliva Consume contaminated animals or products Arthropod borne-West Nile Zoonoses –Lyme disease: wild deer and mice –Hantavirus pulmonary disease: rodents

Environmental Reservoirs Able to survive in nonliving reservoirs Soil: C. tetani –Humans produces toxin –Survives in soil by forming endospores Contaminated water

Portal of Exit Via body fluid or feces –Respiratory tract –GI –GU –Nonintact skin-lesions, wounds

Modes of Transmission Airborne –Tiny droplet nuclei vs large droplets –Dust particles –Suspended in air don’t fall –More likely to reach lower resp tract –Resistant to drying TB, measles and chicken pox –Spread rapidly in crowded conditions

Droplet Large droplets, short distances Mucous droplets -coughing, sneezing Pertussis, influenza, SARS Talking less transmission

Contact Direct- person to person, touching,sex, colds –Horizontal transmission –Fecal-oral transmission especially if public health & hygiene lacking

Contact Vertical –Parent to offspring-birth canal, breast milk, placenta Indirect-via fomites-tissues, diapers, door knobs- hands –Normal person sheds skin atrr rate of 5 x10 8 per day Hep B, C, D, lice, STDs

Vehicle Via medium-water, food, blood - Shigella in water or food, S. aureus Vector-arthropod –Mechanical-passive –Biological- active

Portals of Entry Respiratory GI - in food and water GU-sexually transmitted microbes Non intact skin- parenteral

Susceptible Host Imunocompromised Old age or young Not vaccinated Large inoculum

Healthcare Infections Healthcare acquired –Exogenous –Endogenous

Consequences Serious illness or death Prolonged hospital stay Need for antimicrobial therapy Foci for spreading infection

Controlling Disease Transmission Standard precautions-everyone Isolation for communicable diseases or bugs

Prevention SSIs –prophylactic antibiotics Devices- central lines & ventilators

Prevention Quarantine Immunization- influenza & pneumococcal Vector control