the human host
-resident biota (human as habitat)
-acquiring resident biota
-initial colonization
-biota of specific regions
resident biota
-refers to a large array of microorganisms that favorably inhabit the human body in abundance
-cell for cell, microbes on the human body outnumber human cells at least ten to one
-> total cells in human body= 10(to 13th)
-> total bacteria in the mouth= 10
acquiring resident biota
-microbe accumulate over time immediately following birth by simple interaction with the environment
-microbes are found almost everywhere on and in the body but are more prominent in locations exposed to the environment (skin & digestive tract)
-levels o
initial colonization
-the uterus is normally sterile during development
-as soon as the fetal membrane breaks, microbes in the vagina can enter the womb & begin to colonize the skin
-during the birth the baby is exposed to an even larger number of microbes
-colonization of th
biota of specific regions
-skin
-gastrointestinal tract
-respiratory tract
-urogenital tract
SKIN
-biota resides on or in the skin layer
-dryness of the skin, humidity, occupational exposure, & clothing influence the make-up of the biota
-a very rich biota community is located at regions where the skin joins with the mucus membranes
-2 distinct popula
Transiet biota
-clings to the surface but doesn't usually grow there
-acquired during routine exposure to the environment or other people
-is drastically influenced by hygiene
Resident biota
-inhabits deeper portions of the epidermis & in glands & follicles
-population is more stable & predictable & less influenced by hygiene
-primarily composed of bacteria (Staphylococcus, Pseudomonas, & Janthinobacterium sp.) & fungi (Candida albicans)
GASTROINTESTINAL TRACT
-mouth & esophagus
-stomach
-large intestine & rectum
mouth & esophagus
-streptococcus, Neisseria, Lactobacillus, & Haemophilus sp. are common
Stomach
-Helicobacter pylori is the only known bacteria that can live in the stomach
Large intestines & rectum
-collectively referred to as enterics or enteric bacteria
-almost entirely composed of anaerobes
-> Bacteroides, Fusobacterium, Lactobacillus & Clostridium are prevalent
-> Coliforms, including E.coli, Enterobacter, & Citrobacter are found in smaller numb
Coliforms
-Gram-negative, lactose-fermenting, facultative anaerobic bacteria found in the colon
-contibute to intestinal odor & the discomfort caused by lactose intolerance
(ex. E. coli)
Respiratory tract
-primarily seen in upper respiratory tract & varies in different regions of the respiratory pathway
-> nasal entrance: Staphylococcus
->Nasopharynx: Neisseria
->Oropharynx: Streptococcus
->Laryngopharynx & tonsils: Haemophilus
-conditions in the lower res
Urogenital tract
-Urethra
-Vagina
Urethra
-usually sterile but can sometimes find nonpathogenic Streptococci, Staphylococci, Lactobacillus & occasionally coliforms
-the shorter female urethra contributes to their increased susceptibility to urinary tract infections (UTIs)
Vagina
-Before puberty
->Staphylococci, Streptococci & Candida are common
-> pH is about 7
-AFTER puberty
-> Lactobacilli becomes prevalent bacteria; Candida is still present
-> Estrogen causes the vaginal mucosa to secrete glycogen, which is fermented by bacter
the progress of an infection
-pathogen
-type & severity of infection depend on pathogenicity of the organism & the condition of its host
-becoming established (3 step)
-causing disease
-the process of infection & disease
-the portal of exit (vacating the host)
-reservoirs (where path
Pathogen
-a microbe whose relationships with its host is parasitic and results in infection & disease
Pathogenicity
-an organism's potential to cause infection or disease
True pathogens
-microbes with the ability to cause disease in individuals with normal immune systems
Opportunistic pathogens
-cause disease when the defenses are compromised
virulence factors
-properties that enable a microbe to invade & infect a host
-virulence
virulence
-the ability of a microbe to cause infection that takes the presence or absence of virulence factors into account; the more virulence factors an organism has, the more "virulent" it is
progress of infection: becoming established
-step one: portals of entry
-step two: attaching to the host (adhesion)
-step three: surviving host defenses
portals of entry
-the characteristic route that a microbe takes to enter body tissues is known as its portal of entry
-infectious agents that enter the skin
-the GI tract as portal
-the respiratory portal of entry
-urogenital portals of entry
-pathogens that infect during
characteristic route
-> exogenous agents enter the body from the outside environment (ex. common cold)
-> endogenous agents already exist in the body (ex. candidiasis- yeast infection)
-> many pathogens only cause disease when they enter through a specific portal
infectious agents that enter the skin
-intact skin is very tough- few microbes can penetrate
-most pathogens enter through damage to the skin: nicks, abrasions, & punctures
-some create their own passageways using digestive enzymes or bites
-the conjunctiva is very susceptible to infection
the gastrointestinal tract as portal
-pathogens contained in food, drink, & other ingested substances
-adapted to survive digestive enzymes & pH changes
-most enter directly through the mucus membranes, but ulcers & other damage creates another pathway into the body
-the rectum isn't conside
the respiratory portal of entry
-the portal of entry for the greatest number of pathogens
-most enter through the mucus membranes of the URT but some can enter/infect the LRT
-most microbes entering this portal are small in size to avoid its defense
the urogenital portals of entry
-the agents sexually transmitted diseases (STDs) & urinary tract infections (UTIs) can enter here
-enter through the skin (broken or unbroken) or mucosa of penis, external genitalia, vagina, cervix, & urethra
pathogens that infect during pregnancy & birth
-some microbes can cross the placenta
-other infections occur perinatally when the child is contaminated by the birth canal
-> these agents would generally use the same portal of entry as they would with an adult
Attaching to the host - adhesion
-process by which microbes gain a more stable position in the body
-> bacteria often attach via fimbrae, flagella. pili, slime layers, or capsules
-> virus often attach to a specific receptor on the cell surface; may involve specific viral proteins (spike
surviving the host
-pathogens must then survive our host defenses to cause infection
-many have adapted ways to avoid immune destruction/detection (virulence factors)
virulence factors (specific)
-antiphagocytic factors
-leukocidins
-coagulase
-extracellular surface layer
-some can survive inside the phagocytes after ingestion
antiphagocytic factors
used by some pathogens to avoid phagocytes
leukocidins
toxic to white blood cells
coagulase
causes the formation of clots to inhibit WBC movement
extracellular surface layer
makes it difficult for the phagocyte to engulf them
causing disease: how virulence factors contribute to tissue damage
-extracellular enzymes
-bacterial toxins
extracellular enzymes
break down & inflict damage on tissues or dissolve the host's defense barriers
-mucinase
-keratinase
-collagenase
-hyaluronidase
bacterial toxins
-specific chemical product that is poisonous to other organisms (exotoxins or endotoxin)
-examples: neurotoxins, enterotoxins, or cytotoxins
-terminology...
exotoxin
-released by living bacterial cells into infected tissues
endotoxin
-released when the bacteria is damaged or destroyed
neurotoxins
damage nervous tissue
(ex. tetanospasmin & antrax toxin)
enterotoxins
cause symptoms associated with intestinal disturbances
(ex. cholera & shiga toxina)
cytotoxins
damage a variety of cells by damaging cell membranes or interfering with metabolism
(ex. streptolysin & other hemolysins)
toxigenicity
the power to produce toxins
toxinoses
a variety of diseases caused by toxigenicity
-toxemia
-intoxication
toxemia
-toxinoses in which the toxin is spread by the blood from the site of infection (tetanus & diphtheria)
intoxication
-toxinoses caused by ingestion of toxins (botulism)
the process of infection & disease
-microbes eventually settle in a particular target organ & continue to cause damage at the site (frequently weakens host tissues; necrosis)
-patterns of infection
-signs & symptoms (warning signals of disease)
necrosis
-accumulated damage leads to cell & tissue death
patterns of infection
-localized infection
-systemic infection
-focal infection
-mixed infection
-infections can be described according to their sequence (primary vs. secondary)
-infections can be described by their timeframe (acute vs. chronic)
localized infection
-a single microbe enters the body & remains confined to a specific tissue
-examples: boils & fungal skin infections
systemic infection
-an infection spreads to several sites & tissue fluids usually in the bloodstream
-examples: viral diseases such as measles, chickenpox, & AIDS; bacterial diseases such as anthrax, typhoid fever, & syphilis
-also includes diseases that travel via nerves (
focal infection
-when an infectious agent breaks free of its local infection & is carried to other tissues
mixed infection
-several microbes establish themselves simultaneously at the infection site
-examples: gas gangrene, dental caries, & wound infections
primary infection
ex. chickenpox
secondary infection
ex. skin infection following scratching of chickenpox lesion
(opportunistic once weakened by primary)
acute infection
-rapid onset with severe but short-lived symptoms
chronic infection
-progress & persist over a long period of time
warning signals of disease
-sign
-symptom
-syndrome
-asymptomatic, subclinical, or inapparent infections
sign
-any objective evidence of disease as noted by an observer
(related terms: leukocytosis, leukopenia, bacteremia, septicemia, viremia, & toxemia)
leukocytosis
-an increase in WBC count
leukopenia
-a decrease in WBC count
bacteremia
-circulation of bacteria in the bloodstream
septicemia
-acute illness caused by bacteria or toxin in the blood (aka blood poisoning)
viremia
-circulation of a virus in the blood
toxemia
-the agent remains localized but its toxins are spread throughout the body
symptom
-the subjective evidence of disease as sensed by the patient
syndrome
-when a disease can be identified or defined by a certain complex of signs or symptoms
asymptomatic, subclinical, or inapparent infections
-infections with no obvious signs/symptoms
Portal of Exit: vacating the host
-specific route taken by pathogens to leave the host
-often the exit is the same as the portal of entry
-respiratory & salivary portals
-skin scales
-fecal exit
-urogenital tract
-blood
respiratory & salivary portals
-mucus, sputum, saliva, nasal drainage, or other moist secretions act as media for exit
-breathing, coughing, sneezing, laughing, & talking push these pathogens into the environment
skin scales
-most individuals shed billions of dead skin cells each day and it is the largest component of household dust
-potential exit for the agents of fungal skin infections, syphilis, herpes simplex, & smallpox
fecal exit
-common exit for intestinal pathogens & helminth worms (specifically eggs or larva)
-fecal contamination of drinking water & its use as a fertilizer often raise public health issues
urogenital tract
-vaginal discharge/semen
-> STD's
-> vagina is also location of neonatal infectious agents
-urine
-> high acidity make less common mode of exit but agents of typhoid fever & tuberculosis may exit in urine
blood
-there is no natural exit for blood except menses
-blood-feeeding insects often carry pathogens from human blood
-shared needles and small abrasions caused by intercourse can also result in the transmission of pathogens especially HIV and hepatitis
reservoirs: where pathogens persist
-reservoir
-source
-human reservoirs
-animals as reservoirs & sources
-nonliving reservoirs
reservoir
-the primary habitat in the natural world form which a pathogen originates
source
-the individual or object from which an infection is actually acquired
human reservoirs
-most significant source of the majority of communicable human diseases
-people who have symptomatic infection & are obvious sources (ex. chickenpox)
-carrier
-diseases confined to human reservoirs are the easiest to control
carrier
-any person who inconspicuously shelters a pathogen that can be spread to others
-asymptomatic
-passive
asymptomatic carriers
-incubation carriers
-convalescent carriers
-chronic carriers
animals as reservoirs & sources
-vector
-zoonosis
vector
-a live animal that transmits an infectious agent from one host to another
-types of vectors
-examples of common arthropod vectors
types of vectors
-mechanical
-biological
mechanical vector
-organism carries the microbe on their body from one place to another
biological vector
-often required for part of the parasite's life cycle; carries the microbe in its body
common arthropod vectors
-mosquitoes: malaria
-ticks: lyme disease
-flies (biting): African Sleeping Sickness &River blindness
-fleas: plague
Zoonosis
-an infection indigenous to animals but naturally transmissible to humans
-> at least 150 known zoonoses worldwide (ex. bird flu, hantavirus, rabies)
-> diseases that can be spread via animals are probably impossible to eliminate
Nonliving reservoirs
-pathogens with environmental reservoirs are the hardest to eliminate
-> soil (agents for anthrax & tetanus)
-> water (agents for Legionnaires disease & Pseudomonas)
acquisition & transmission of infectious agents
-communicable disease
-noncommunicable disease
-patterns of transmission in communicable diseases
communicable disease
-when an infected host can transmit the infectious agent to another host & establish infection in that host
-contagious agent: highly communicable
noncommunicable disease
-does not arise through transmission of the infectious agent form host to host
(ex. from biota or soil) (cancer)
patterns of transmission
-horizontal transmission
-vertical transmission
-transmission can be accomplished by: contact transmission, food & water, air
horizontal transmission
-transfer from one person to another through contact, ingestion of food or water, or via a living agent such as an insect
vertical transmission
-transfer from a pregnant woman to the fetus, or from a mother to her infant during childbirth
contact transmission
-direct contact
-indirect contact
-droplet transmission
direct contact
-"person to person" transmission by touching, kissing, sexual intercourse, etc.
indirect contact
-transfer of the pathogen via a "vehicle"
-> vehicle: any inanimate material commonly used by humans that can transmit infectious agents (food, water, biological products, fomites)(or vector)
droplet transmission
-respiratory droplets can spread disease if persons are in close proximity (no more that 1 meter)
food & water
-food-borne pathogens can originate from the animal reservoirs or from contamination during food preparation
-> fecal-oral route
-> cross-contamination
-waterborne pathogens frequently originate form sewer contamination (chlorination & filtration can redu
fecal-oral route
-food/water contaminated with fecal matter
-> reduced by proper hand-washing
cross-contamination
-bacteria from one food product is transferred to another food product then ingested
air
-small fluid droplets dry, leaving 1 or 2 organisms attached to a thin coat of the dried material, creating an airborne particle
-dead skin cells, household dust, & soil disturbed by wind, may also carry pathogens
-airborne transmission of pathogens is di
Nosocomial infections : hospital as source of disease
-nosocomial infections
-common examples of nosocomial infections (Enterococcus sp., E.coli, & Staphylococcus sp.)
nosocomial infections
-infections acquired by patients during their hospital stay
-conditions in a hospital make an ideal situation for the contraction of disease
-> high density population with many reservoirs/carriers
-> patients tend to be immunosuppressed
-> antibiotic-res
Enterococcus sp.
-normal intestinal biota; frequently cause UTI's, wound, & blood infections
E. coli
-normal intestinal biota; commonly causes hospital-acquired pneumonia
Staphylococcus sp.
-normal skin biota in many people; commonly causes pneumonia, surgical wound infections, bed (sores ?)
Epidemiology: the study of disease in populations
-epidemiology
-epidemiological statistics
-other terminology (endemic disease, sporadic disease, epidemic, pandemic)
-factors that influence epidemiology
epidemiology
-the study of the frequency & distribution of disease & other health-related factors in defined human populations
epidemiological statistics: frequency of cases
-prevalence
-attack rate
-incidence
-mortality rate
prevalence
-percentage of the population having a particular disease at a given time
-ex. if 5 out of 50 people in a classroom get the flu, the prevalence is 10% (5 infected/ 50 total people)
attack rate
-percentage of exposed individuals who contract the disease
-ex. tainted food is served at a party of 400 people resulting in 20 cases of food poisoning, however only 200 people ate the contaminated food, the attack rate is 10% (20 infected/200 exposed)
incidence (aka morbidity rate)
-reflects the number of new cases in a specific time period in a given population at risk; it is a comparison of infected and healthy people
-ex. if 10 out of 50 people get the flu but only 5 of those cases occurred in the past week, then the incidence fo
mortality rate
-the rate of death within a defined population as a result of the disease
-ex. if 150 out of 1000 infected people in a community die from the swine flu, the mortality rate in that community is 15% (150 deaths/1000 total people)
endemic disease
-when a disease exhibits a relative steady frequency over a long period of time in a specific geographic region (lyme disease, common cold)
sporadic disease (outbreak)
-one which is reported at irregular intervals in unpredictable locations (E. coli)
Epidemic
-an unusually large number of cases within the population
(epidemics may arise from endemic diseases (influenza) or sporadic diseases that are not normally found in the population (cholera))
pandemic
-when an epidemic spreads worldwide (AIDS)
Factors that influence epidemiology
-the dose
-the incubation period
-the characteristics of the population
the dose
-a certain minimum number of pathogenic cells are required in the body to produce enough damage to cause symptoms
-the number of organisms required to produce disease varies per pathogen
-> 10-100 Shigella are required
-> 1,000,000 Salmonella are required
the incubation period
-period of time necessary for an agent to multiply enough times to cause disease
-the immune system can generally fight off infections that require long incubation periods
-symptoms may not occur during the incubation period but the agent itself can often
the characteristics of the population
-immunity to the pathogen
-general health
-age
-gender
-religious & cultural practices
-genetic background
-occupational exposure
immunity to the pathogen
-a disease is less likely to spread in a population that is immune to the pathogen
general health
-malnutrition, overcrowding, & fatigue increase susceptibility
age
-the very young & the elderly are generally more susceptible
gender
-influenced by the anatomy and physiology (ex. UTIs- length of urethra, shorter= more common in women)
religious & cultural practices
-distribution of disease may be influenced by cultural practices such as eating certain dishes or breastfeeding infants
genetic background
-natural immunity may vary with genetic background
occupational exposure
-different professions result in different exposures (ex. hospital worker vs. farmer)
(-hobbies, etc)