Human Microbe Interaction Flashcards
A condition in which pathogenic microorganisms penetrate host
defenses, enter the tissues, and multiply
Infection
A condition in which pathogenic microorganisms penetrate host
defenses, enter the tissues, and multiply
Infection
Any deviation from health
Disease
Factors that cause disease
- Infections
– Genetics
– Aging
– Malfunctions of systems or organs
Disruption of tissues or organs caused by microbes or their products
Infectious disease
- Large and diverse collection of microbes living on and in the body
- Also known as resident or indigenous biota or normal flora
- Include an array of bacteria, fungi, protozoa, and viruses
Resident biota
- Human cells contain 21,000 protein encoding genes; microbes that inhabit humans contain 8 million
- We have a lot of microbes in places we used to think were sterile
- All healthy people harbor potentially dangerous pathogens, but in low numbers
The human microbiome project
The makeup of your _____ can influence many facets of your overall health
Intestinal/gut Biota
Sites Definitively Known to Harbor Normal Microbiota:
• Skin and adjacent mucous membranes
• Upper respiratory tract
• Gastrointestinal tract, including mouth
• Outer portion of urethra
• External genitalia
• Vagina
• External ear canal
• External eye (lids, conjunctiva)
•Additional Sites Now Thought to Harbor At Least Some Normal Microbiota (or Their DNA)
• Lungs (lower respiratory tract)
• Bladder (and urine)
• Breast milk
• Amniotic fluid and fetus
• Sites in Which DNA from Microbiota Has Been Detected
• Brain
• Bloodstream
Factors That Weaken Host Defenses and Increase Susceptibility to Infection
• Age: the very young and the very old
• Genetic defects in immunity and acquired defects in immunity (AIDS)
• Pregnancy
• Surgery and organ transplants
• Underlying disease: cancer, liver malfunction, diabetes
• Chemotherapy/immunosuppressive drugs
• Physical and mental stress
• Other infections
- Caused by biota already in the body
- Can occur when normal biota is introduced to a site that was previously sterile
– Example: Escherichia coli entering the bladder, resulting in a UTI
Endogenous Infections
- A microbe whose relationship with its host is parasitic
- Results in infection and disease
Pathogen
Capable of causing disease in healthy persons with normal immune systems
True Pathogens
Cause disease when:
– The host’s defenses are compromised
Opportunistic pathogen
A system of biosafety categories adopted by the Centers for Disease Control and Prevention (CDC)
Based on the general degree of pathogenicity and the relative danger in handling these pathogens
Biosafety levels
Applies to all microorganisms
Virulence
Any characteristic or structure of the microbe that contributes to toxin production or induction of an injurious host response
Virulence factor
a minimum number of microbes required for an infection to proceed
Determined experimentally for many microbes
Microbes with a smaller infectious dose have greater virulence
Infectious dose
• A characteristic route taken by a microbe to initiate infection
• Usually through skin or mucous membranes
• Source of the infectious agent:
Portal of entry
originating from outside the body – The environment,another person,or animal
Exogenous
already existing on or in the body – Normal biota or a previously silent infection
Endogenous
Sites of entry of infectious agents
- Nicks
• Abrasions
• Punctures, some tiny and inapparent
• Intact skin is a very tough barrier that few microbes can penetrate
• Some infectious agents create their own passageways into the skin using digestive enzymes
Common infections of the fetus and neonate: TORCH
• Toxoplasmosis
• Other diseases: syphilis, coxsackievirus, varicella-zoster virus, AIDS, chlamydia
• Rubella
• Cytomegalovirus
• Herpes simplex virus
• The most serious complications are spontaneous abortion, congenital abnormalities, brain damage, prematurity, and stillbirths
• A process by which microbes gain a more stable foothold on host tissues
• Dependent on binding between specific molecules on both the host and pathogen
• A particular pathogen is limited to only those cells and organisms to which it can bind
• Once attached, a pathogen can invade body compartments
Adhesion
Chemical communication between nearby bacteria critical to establishment of infection
Quorum sensing
White blood cells that engulf and destroy pathogens by means of enzymes and antimicrobial chemicals
Phagocytes
• Virulence factor used by pathogens to avoid phagocytes
• Circumvent some part of the phagocytic process
Antiphagocytic factors
Steps Involved When a Microbe Causes Disease in a Host
- Finding a portal of entry
- Attaching firmly and negotiating the microbiome
- Surviving host defenses
- Causing damage
- Exiting host
- Secreted by pathogenic bacteria, fungi, protozoa, and worms
- Break down and inflict damage on tissues
- Dissolve host’s defense barriers and promote the spread of microbes into deeper tissues
Exoenzymes
Examples of exoenzyme
- Mucinase
- Keratinase
- Hyaluronidase
A specific chemical product of microbes, plants, and some animals that is poisonous to other organisms
Toxins
Secreted by a living bacterial cell to the infected tissues
Many types
Exotoxin
• Not actively secreted
• Shed from the outer membrane
• Only found in gram-negative bacteria
Endotoxin
is a trait not solely determined by microorganisms
Pathogenicity
• Microbe enters the body and remains confined to a specific tissue:
• Boils
• Fungal skin infections
• Warts
Localized infection
• When an infection spreads to several sites and tissue fluids, usually in the bloodstream
• Viral: measles, rubella, chickenpox, AIDS
• Bacterial: brucellosis, anthrax, typhoid
fever, syphilis
• Fungal: histoplasmosis, cryptococcosis
• Infectious agents can also travel by means of nerves (rabies) or cerebrospinal fluid (meningitis)
Systemic infection
• Exists when the infectious agent breaks loose from a local infection and is carried to other tissues
• Examples:
• Tuberculosis
• Streptococcal pharyngitis: scarlet fever
• Toxemia: infection remains localized, toxins are carried through the blood to the target tissue
Focal infection
- Several agents establish themselves simultaneously at the infection site
- Polymicrobial diseases: gas gangrene, wound infections, dental caries, human bite infections
Mixed Infection
Initial infection
Primary Infection
Occurs when a primary infection is complicated by another infection caused by a different microbe
Secondary infection
Come on rapidly
Have short lived effects
Acute infections
Progress and persist over a long period of time
Chronic infections
• Any objective evidence of disease as noted by an observer
• More precise than symptoms
Sign
Subjective evidence of disease as sensed by the patient
Symptom
A disease identified or defined by a certain complex of signs and symptoms
Syndrome
Common signs of infectious diseases
• Fever
• Septicemia
• Microbes in tissue fluids
• Chest sounds
• Skin eruptions
• Leukocytosis
• Leukopenia
• Swollen lymph nodes
• Abscesses
• Tachycardia (increased heart rate)
• Antibodies in serum
Common symptoms of infectious diseases
• Chills
• Pain, ache, soreness, irritation
• Malaise
• Fatigue
• Chest tightness
• Itching
• Headache
• Nausea
• Abdominal cramps
• Anorexia (lack of appetite)
• Sore throat
Earliest symptom of disease
Inflammation
Accumulation of fluid in afflicted tissue
Edema
Walled-off collections of inflammatory cells and microbes in the tissues
Granulomas and Abscesses
Swollen lymph nodes
Lymphadenitis
Signs of infection in blood
Leukocytosis:
• Increase in the level of white
blood cells
Leukopenia:
• Decrease in the level of white blood cells
Septicemia:
• General state in which microbes are multiplying in the blood and are present in large numbers
Bacteremia
• Small numbers of bacteria are present in the blood but not necessarily multiplying
Viremia:
• Presence of viruses in the blood, whether or not they are actively multiplying
• Host is infected but does not manifest the disease
• Patient experiences no symptoms or disease and does not seek medical attention
• Most infections are attended by some sort of sign
Asymptomatic, subclinical, or inapparent infections
• Avenue for pathogens to exit the host
• Secretion
• Excretion
• Discharge
• Sloughed tissue
Portals of exit
• The outer layer of skin and scalp is constantly being shed into the environment
• Household dust is composed of skin cells
• A single person can shed several billion skin cells a day
Skin Scales
• A dormant state of an infectious agent
• During this state, a microbe can periodically become active and produce a recurrent disease
• The agents of syphilis, typhoid fever, tuberculosis, and malaria also enter into latent stages
Latency
• A dormant state of an infectious agent
• During this state, a microbe can periodically become active and produce a recurrent disease
• The agents of syphilis, typhoid fever, tuberculosis, and malaria also enter into latent stages
Latency
• Long-term or permanent damage to organs and tissues
• Meningitis can result in deafness, strep throat can lead to rheumatic heart disease, Lyme disease can cause arthritis, and polio can produce paralysis
Sequelae
The time from initial contact with the infectious agent to the appearance of first symptoms
Incubation period
When the earliest notable symptoms of infection appear
Prodromal period
Infectious agent multiplies at high levels, exhibits its greatest virulence, and becomes well established in its target tissue
Acute phase
Infectious agent multiplies at high levels, exhibits its greatest virulence, and becomes well established in its target tissue
Acute phase
Patient responds to infection and symptoms decline
Convalescent stage
Where do Pathogens Persist
- Reservoir:
• Primary habitat in the natural world from which a pathogen originates
• Human or animal carrier; soil, water, or plants - Source:
• Distinct from a reservoir
• Individual or object from which an infection is acquired
Where do pathogens persist
- Reservoir:
• Primary habitat in the natural world from which a pathogen originates
• Human or animal carrier; soil, water, or plants - Source:
• Distinct from a reservoir
• Individual or object from which an infection is acquired
2 types of vectors
• Biological vector:
– Actively participates in a pathogen’s life cycle, serving as a site
in which the pathogen can multiply or complete its life cycle
– Communicates the infectious agent to the human host by
biting, aerosol formation, or touch
• Mechanical vectors:
– Not necessary to the life cycle of an infectious agent
– Merely transport the pathogen without being infected
a live animal that transmits an infectious agent from one host to another
Vectors
An infection indigenous to animals but also transmissible to humans
• Human is the dead-end host and does not contribute to the natural persistence of the microbe
• Spread of disease is promoted by close associations of humans with animals
• People in animal-oriented or outdoor professions are at greatest risk
• Examples: rabies, hantavirus, West Nile virus, anthrax, plague, ringworm, toxoplasmosis, tapeworm
Zoonosis
• Microbes have adapted to nearly every habitat in the biosphere
• Soil, water, air, the built environment
• Most are saprobic and cause little harm to humans
• Some are opportunists
• A few are regular pathogens
• Example: the TB bacterium, can be directly transmitted to humans when they come in contact with contaminated soil, water, or air
Non living reservoirs
Acquisition and Transmission of Infectious Agents
- Communicable disease:
• Occurs when an infected host can transmit the infectious agent to another host and establish infection in that host - Contagious:
• The agent is highly communicable, especially through direct contact - Noncommunicable:
• Does not arise through transmission of the infectious agent from host to host
Horizontal versus Vertical Transmission
Horizontal transmission:
• Disease is spread through a population from one infected individual to another
• Direct (contact) transmission: kissing and sex (Epstein-Barr virus, gonorrhea)
Indirect transmission: fomites, vehicles, parenteral (via injection into deeper tissues)
• Vector transmission
• Vertical transmission:
• Transmission from parent to offspring via ovum, sperm, placenta, or milk
Dried microscopic residues created when microscopic pellets of mucus and saliva are ejected from the mouth and nose
Droplet nuclei
Suspensions of fine dust or moisture particles in the air that contain live pathogens
Aerosols
