micro chapter 14

Chapter 14

Microbiome: Also known as Microbiota & Normal flora

·       Organisms that colonize the body's surface without causing normally causing disease

·       Microorganisms that live in & on the body

·       2 types

o   Resident Microbiota: Normal Microbiota throughout life; mostly commensal

o   Transient Microbiota: Remain in body for short period. Found in same areas as resident.

§  cannot persist in body b/c: competition from other microorganisms, elimination by the body's defense cells, chemical or physical body changes

·       acquisition of microbiome: development in womb

o   development: during birthing process, first meals (human milk microbiota) medical Staff, parents (get their microbiota on baby)

o   Resident microbiota established first few months of life

·       opportunistic Pathogens: Normal Microbiota that cause disease under certain circumstances.

o   conditions that provide opportunities: introduction of germ that your normal microbiota into unusual body site, immune suppression, Changes in normal Microbiota, Stressful conditions

o   Most pathogen can’t survive for long outside their host

o   (1) Animal reservoir

§  Zoonoses: disease naturally spread animal human

§  acquired through direct contact with animal or its Waste, eating animal, blood sucking arthropods

§  human normally dead-end host /does not spread.

§  ex: disease -Animal-how

·       Helminthic: tapeworm-dog-larvae transmitted in dog Saliva

·       protozoan: Malaria-Monkeys -Mosquito bite (plasmodium0

·       fungal: Ringworm-domestic Animals-direct Contact.

·       Bacterial: Plaque-Rodents -Flea bites

·       viral: Rabies-bats/Skunks/foxes /dogs-bite.

o   (2) Human Carriers

§  Humans with active diseases are important reservoirs of infection for other humans

·       Incubatory (transmit agent before clinical illness begins); convalescent (recovered but can still transmit to others); chronic carriers (harbor the agent for months or years after initial infection i.e., hepatitis B)

§  Asymptomatic infected individuals can be infective to others (also called passive carriers or healthy carriers)

·       Continuous source of infection (reservoir)

·       Without getting sick themselves.

o   Ex: typhoid mary”

§  Asymptomatic chronic carrier

§  Passive carrier

·       They take no precautions to prevent transmission

o   (3) nonliving reservoirs (environment)

§  Soil (clostridium), water (feces or urine), and food (fresh produce-E.coli; pouty-salmonella; beef-E.coli) can be reservoirs of infection (disease carrying pathogens found in)

·       Presence of MO often due to contamination by feces or urine

Invasion and establishment in host: infection in humans

o   Exposure to microbes:

§  Contamination

·       The mere presence of microbes in or on the body

§  Infection

·       A pathogenic organism evades body’s external defenses, multiplies, and becomes established in the body

·       May not result in disease, only if it adversely affects the body

o   Portals of entry

§  Sites which the pathogens enter the body

·       Skin

o   Broken skin, insect bite

o   Outer layer of dead skin cells act as a barrier to pathogens

o   some pathogens enter through openings or cuts

o   others enter by burrowing into (parasitic worms) or digesting outer layers of skin (fungi)

·       Mucous membranes

o   Wet linings of mouth, nose, ear, anus, eyes, etc

o   Line the bodies cavities that are open to the environment

o   Provide a moist, warm environment hospitable to pathogens

o   Respiratory tract is the most common site of entry

§  Entry is through the nose, mouth, or eyes

o   Gastrointestinal tract may be route of entry

§  Must survive the acidic pH of the stomach

·       Placenta

o   From a pregnant person to the baby

o   Typically forms an effective barrier to pathogens

o   Pathogens may cross the placenta and infect the fetus

§  Cause spontaneous abortion, birth defects, premature birth

§  Examples: pathogen- condition in adult- effect on embryo or fetus

·       Protozoan: Toxoplasma gondii- toxoplasmosis- abortion, epilepsy, encephalitis, microcephaly, mental retardation, blindness, anemia, jaundice, rash, phenomena, diarrhea, hypothermia, deafness

·       Bacteria: Treponema pallidum- syphilis- abortion, multiorgan birth defects, syphilis

·       Bacteria: listeria monocytogenes- listeriosis- granulomatosis infantiseptica (nodular inflammatory lesions and infant blood poisoning), death

·       DNA viruses: cytomegalovirus- usually asymptomatic- deafness, microcephaly, mental retardation

·       DNA viruses: Erythovirus- erythema infectiosum- abortion

·       RNA viruses: lentivirus (HIV)- AIDS- immunosuppression (AIDS)

·       RNA viruses: Rubivirus- German measles- severe birth defects or death

·       Entry via the parenteral route circumvents the usual portals.

o   Microbe skip usual ways of entry and gets directly into the body (ex: needle or injury)

o   Not a true portal of entry

o   Eans by which portals of entry can be circumvented

o   Pathogens deposited directly into tissues beneath the skin or mucous membranes

§  Hypodermic needle, nail, surgery, stab wound

·       Examples:

o   Otic: outer ear infection by P. aeruginosa (swimmers ear)

o   Respiratory mucosa: pertussis, measles, influenza

o   GI mucosa: cholera, salmonella, c. difficile

o   Urogenital/reproductive system:

§  Genitalia: gonorrhea, chlamydia, certain papillomaviruses

§  Urinary: bladder, kidney, and urethra infections (E.coli)

o   Ocular: conjunctivitis (various bacteria and viruses)

o   Skin: s.aureus wound infection

o   Parenteral: hepatitis B and C

o   Transplacental: HIV, rubella, toxoplasmosis

o   The role of adhesion in infection

§  Process by which microorganisms attach themselves to cells

§  Required to establish colonies successfully within the host

§  Uses adhesion factors:

·       Specialized structures (hooks, suckers)

·       Attachment molecules

o   Ligands

o   Adhesins in bacteria

o   Attachment proteins on viruses

§  The interaction of adhesion proteins and receptors can determine host cell specificity

§  Changing/blocking a ligand or its receptor can prevent infection

§  Inability to make attachment proteins or adhesions renders microorganisms avirulent

§  Some bacterial pathogens attach to each other to a form a biofilm

The nature of infectious diseases

o   Infection is the invasion of the host by a pathogen

§  Infection does not always lead to disease

o   Disease results if the invading pathogen alters normal body functions

§  The time frame between infection and development of disease could be years

o   Disease is also referred to as morbidity

§  Any change from a state of health

o   Symptoms:

§  Subjective characteristics felt only by the patient

·       Ex: headache, nausea, headache, chills, sore throat, fatigue/lethargy, malaise, itching, abnormal cramps

o   Signs

§  Objective manifestations of disease observed or measured by others

·       Ex: swelling, rash, vomiting, diarrhea, fever, pus formation, anemia, bubo, bradycardia

o   Syndrome

§  Symptoms and signs that characterize a disease or an abnormal condition

o   Asymptomatic, or subclinical, infections lack symptoms but still may have signs of infection

o   causation of disease: etiology

§  study of the cause of disease

·       such as: Hereditary, congenital, degenerative, nutritional, endocrine, mental, immunological, neoplastic, infectious, iatrogenic (medical treatment or procedure), idiopathic (unknown),nosocomial (HAIs).

§  Using Koch’s postulates

·       Germ theory of disease

o   Infections by pathogenic microorganisms cause disease

·       Robert Koch developed a set of postulates one must satisfy to prove that a particular pathogen causes a particular disease

·       Exceptions to Koch’s postulates

o   Some pathogens can't be cultured in the laboratory

o   Diseases caused by a combination of pathogens and other cofactors

o   Ethical considerations prevent applying Koch’s postulates to pathogens that require a human host

·       Difficulties in satisfying Koch’s postulates

o   Diseases can be caused by more than one pathogen

o   Pathogens that are ignored as potential causes of disease

§  Ex: H.pyloru and stomach ulcers

o   Virulence factors of infectious agents

§  Pathogenicity

·       Ability of a microorganism to cause disease

§  Virulence

·       Degree of pathogenicity

o   Ability of pathogen to infect host and cause disease

·       Virulence factors include:

o   Adhesion factors

o   Biofilms

o   Extracellular enzymes

o   Toxins

o   Antiphagocytic factors

§  Relative virulence of some microbial pathogens

·       Francisella tularensis (rabbit fever): most virulent (potential bioweapon)

·       Lactobacilli, diphtheroids: least virulent

§  Extracellular enzymes

·       Secreted by the pathogen

·       Dissolve structural chemicals in the body

·       Help pathogen maintain infection, invade, and avoid body defenses

·       Important to virulence of the pathogen

o   Mutant species that do not secrete the enzymes are often avirulent

§  Toxins

·       Chemicals that harm tissues or trigger host immune responses that cause damage

·       Toxemia refers to the presence of toxins in the bloodstream

·       The toxins are carried beyond the site of infection

·       Two types:

o   Exotoxins: releases

o   Endotoxins: within

o   Enterotoxin: digestive tract, type of exotoxins

§  Antiphagocytic factors

·       Factors prevent phagocytosis of MO by the host’s phagocytic cells

·       Allow pathogens to remain in a host for a longer time

o   Bacterial capsule

§  Composed of chemicals not recognized as foreign

§  Slippery and difficult for phagocytes to engulf

o    Antiphagocytic chemicals

§  Prevent fusion of lysosome and phagocytic vesicles

§  Leukocidins directly destroy phagocytic white blood cells

§  Some virulence factors

·       (a) extracellular enzymes

o   Hyaluronidase and collagenase

§  These enzymes degrade structural proteins between cells in our tissues so microbes can gain access

o   Coagulase and kinase

§  These enzymes enable microbes to hide from hosts immune system

§  Clots: bacteria can hide in the clot

·       (b) toxins

o   Exotoxin

§  Produced by gram positive and gram negative bacteria

§  Protein or short peptide released

o   Endotoxin

§  Produced by the gram negative bacteria

§  LPS or lipid A endotoxin is released when these bacteria die

o   Cytotoxin

§  Kill host cells affect their functioning

o   Neurotoxins: interfere with nerve cell functioning

o   Enterotoxins: affect cells that line the GIT

·       (C) Antiphagocytic factors

o   Phagocytosis blocked by capsule

§  Capsule is similar to the host and also make bacterium too slippery to engulf

o   Incomplete phagocytosis

§  Chemicals are produced by bacterium to prevent digestion to lysosome

o   Stages of infectious disease

§  The disease process occurs following infection

§  Patient may be infectious at every stage of disease

§  Many infectious diseases have five stages following infection (in order):

·       Incubation period (no signs or symptoms)

o   Depends on:

§  Virulence of infecting agent

§  # of them infecting you

§  Reproductive time

§  Health status

o   Incubation periods of selected infectious diseases

§  Staphylococcus foodborne infection: less than 1 day

§  Influenza: about 1 day

§  Cholera: 2 to 3 days

§  Genital herpes: about 5 days

§  Tetanus: 5 to 15 days

§  Syphilis: 10 to 21 days

§  Hep b: 70 to 100 days

§  AIDS: 1 to 8 years

§  Leprosy: 10 to over 30 years

§  Depends on virulence of infective agent and infective dose

·       Prodromal period (vague, general symptoms)

o   Symptoms may be non-specific and can be easily mistaken for other illnesses

·       Illness (acute)

o   Most severe signs and symptoms

o   Damage/harm to the body is happening

·       Decline (declining signs and symptoms)

o   Immune system is in high gear

o   If disease does not decline, fatal

·       Convalescence (no signs or symptoms)

o   Tissues repaired and a return to normal

o   Pathogen exit portals

§  Pathogens leave host through portals of exit

§  Many portals of exit are the same as portals of entry

§  Pathogens often leave hosts in materials the body secretes or excretes

§  Examples:

·       Otic (ear): pus or drainage may contain infectious agent

·       Respiratory mucosa: sneezes and coughs; mucus discharge from nose or mouth

·       GI mucosa: infectious agents in excrement, saliva, and mucosal secretions

·       Urogenital: urine, semen, vaginal secretions

·       Ocular: itchy eyes stimulate rubbing which transfers pathogen to the hands

·       Skin: pus or wound drainage may be rich in pathogens

·       Parenteral: food borne pathogens

o   Modes of infectious disease transmission

§  Transmission is from a reservoir or a portal of exit to another host’s portal of entry

§  Three groups of transmission:

·       1. Contact transmission

o   Direct contact transmission

§  Usually involves body contact between hosts

§  Transmission within a single individual can also occur

§  Ex: pink eye can go from 1 eye to another

o   Indirect contact transmission

§  Pathogens are spread from host to host by fomites (inanimate objects)

§  Ex: pencil, doorknob

o   Droplet transmission

o   Spread of pathogens in droplets of mucus by exhaling, coughing, and sneezing (<1m) (close)

·       2. Vehicle transmission

o   Vehicle Transmission

§  Airborne transmission (under contact)

·       When pathogens travel more than 1m via an aerosol

·       Aerosols can occur from various activities

o   Sneezing, coughing, air-conditioning systems, sweeping

o   A virus may remain suspended in the air (measles -3 hrs)

§  Take away immune memory cells that you already have

§  Waterborne transmission

·       Spread of pathogens via drinking water

·       Important in the spread of many gastrointestinal diseases

·       Fecal-oral infection

o   Major source of disease in the world

o   Inadequate handwashing carnes fecal material to everything they touch (vehicle like food, water, utensil)

o   Enter new host through mouth

·       3. Vector transmission (body fluid transmission)

o   Foodborne transmission

§  Spread of pathogens in and on foods

§  Inadequately processed (because of their intestines), cooked, or refrigerated foods

§  Foods may become contaminated with feces

§  Poorly stored foods can harbor pathogens and transmit diseases

o   Bodily fluid transmission

§  When cleaning/handling items with bodily fluids on them must be mindful that they can carry pathogens

§  Bodily fluids such as blood, urine, and saliva can carry pathogens

§  Prevent contact with conjunctiva or breaks in the skin or mucous membranes

§  Wear proper PPE

o   Biological vectors (mosquitos, ticks, fleas, lice)

§  Transmit pathogens and serve as host for some stage of the pathogen’s life cycle

§  Biting arthropods transmit many diseases to humans (malaria)

o   Mechanical vectors

§  Passively transmit pathogens present on their body to new hosts

§  Houseful lands on garbage, then lands on food that is eaten

§  E.coli, salmonella

o   Examples:

§  Mosquitos

·       Anopheles aedes

o   Malaria: plasmodium spp. (protozoan)

o   yellow fever: flavirus sp. (virus)

o   elephantiasis: wuchereria bancrofti (helminth)

o   dengue: flavivirus spp. (virus)

o   viral encephalitis: alphavirus spp. (virus)

§  ticks

·       Ixodes

o   lyme disease: borrelia burgdorferi

·       Dermacentor

o   rocky mountain spotted fever: rickettsia rickettsii

§  fleas

·       xenopsylla

o   bubonic plague: Yersinia pestis

o   endemic typhus: rickettsia typhi

§  houseflies

·       musca

o   foodborne infections: shigella spp., salmonella spp., E. coli

§  cockroaches

·       blatella, periplaneta

o   foodborne infection: foodborne infections: shigella spp., salmonella spp., E. coli

o   classification of infectious diseases

§  Diseases can be classified in a number of ways:

·       Taxonomic categories: type of pathogen (bacterial, viral)

·       The body system they affect: site infected (UTIs)

·       Their longevity and severity: acute (a cold). “long cold”

·       How they are spread to their host: transmission routes

·       The effects they have on populations: impact (pandemic)

§  Acute disease: disease in which symptoms develop rapidly and that runs its course quickly

§  Chronic disease: disease with usually mild symptoms that develop slowly and last a long time

§  Communicable disease: disease transmitted from one host to another

§  Local infection: infection confined to a small region of the body

§  Systemic infection: widespread infection in many systems of the body; often travels in the blood or lymph

§  Focal infection: infection site that serves as a source of pathogens for infections at other sites in the body (gums (endocarditis))

Epidemiology

§  The study of where and when diseases occur and how they are transmitted in populations

§  Endemic: normally occurs in a given area

§  Sporadic: few scattered cases occur in a given area

§  Epidemic: disease occurs at a greater than normal frequency

·       New strain, human behavior change, environmental condition, reduced immunity

·       Epidemics may have fewer cases than non epidemics

§  Pandemic: if an epidemic occurs on more than one continent

§  Epidemiologists report data in a variety of ways: annual incidence by state, by week of onset, by age, etc

§  Frequency of Disease

·       Disease occurrence tracked using two measures

o   Incidence

§  Number of new cases of a disease in a given area during a given period of time

o   Prevalence

§  Number of total cases of a disease in a given area during a given period of time

o   Occurrence also evaluated in terms of frequency and geographic distribution

§  Epidemiological studies

·       Descriptive epidemiology

o   Careful tabulation of data concerning a disease

§  Record location and time of the cases of disease

§  Collect patient information

o   try to identify the index case of the disease

o   ex: the broad street pump; try to find source. Identify that it is waterborne

·       Analytical epidemiology

o   Seeks to determine the probable cause, mode of transmission, and methods of prevention

o   Useful in situations when Koch’s postulates can’t be applied

o   Often retrospective

§  Investigation occurs after an outbreak has occurred

·       Experimental epidemiology

o   Tests a hypothesis concerning the cause of a disease

o   Application of Koch’s postulates

o   Determine the efficacy of drug treatment or preventative measure

§  Hospital Epidemiology: Healthcare-Associated (nosocomial) Infections

·       Types of healthcare-associated infections

o   Exogenous

§  Pathogen acquired from the health care environment

§  Frome a surface, healthcare worker

§  Ex: hospital acquired COVID

o   Endogenous

§  Pathogen arises from normal microbiota within patient

§  immunocompremized

o   Iatrogenic

§  Results from modern medical procedures

§  Surgery, catheter, medical devices

o   Superinfections

§  Use of antimicrobial drugs inhibits some resident microbiota, allowing other microbes to thrive

·       Control of healthcare-associated infections

o   Requires aggressive control measures

o   Handwashing is the most effective way to reduce healthcare- associated infections

§  Epidemiology and Public Health – Canada

·       Sharing of data among public health organizations

o   Agencies at the municipal, provincial/territorial, national, and global level

·       Government of Canada’s Health Portfolio (Minister of Health)

o   Health Canada

o   Public Health Association of Canada (collaborates with CDC)

§  Chief Public Health Officer

·       Only came out after SARS (2004)

·       World Health Organization (WHO)

o   Coordinates public health efforts worldwide

·       Role of public health agencies in interrupting disease transmission

o   Public health agencies work to limit disease transmission

§  Enforce cleanliness of water and food supplies

§  Work to reduce disease vectors and reservoirs

§  Establish and enforce immunization schedules

§  Locate and treat individuals exposed to contagious pathogens

§  Establish isolation and quarantine measures