Bbdynamics Of Infection

INFECTION Occurs when pathogenic microorganisms

penetrate host defenses, enter the tissues and multiply

DISEASE ensues when the cumulative effects of

infection or tissue/organ disruption a pathologic state or deviation from health

PATHOLOGY Study of disease Concerned with etiology (CAUSE) Concerned with PATHOGENESIS (manner in

which a disease develops) Concerned with the structure and functional changes brought about by the disease PATHOGENECITY Refers to the ability to cause a disease

FACTORS AFFECTING PATHOGENECITY MODE OF ACTION Means / ways by which microbe produce disease

VIRULENCE Degree of pathogenecity Degree in which an organism is able to cause

disease

DOSE Microbes should be in sufficient amount to cause

disease

FACTORS AFFECTING PATHOGENECITY INVASIVENESS / INFECTIVENESS Ability of microbes to invade tissues

TOXIGENICITY Microbes potential to damage host tissues

by producing / releasing toxins

SPECIFICITY Refers to the attraction of a microbe to a

specific host / range of hosts

FACTORS AFFECTING PATHOGENECITY VIABILITY Ability of microbes to invade tissues

TOXIGENICITY Microbes potential to damage host tissues

by producing / releasing toxins

SPECIFICITY Refers to the attraction of a microbe to a

specific host / range of hosts

INFECTION

DISEASE

Invasion / colonization of

Occurs when an

the body by pathogenic microorganisms May exist in the absence of detectable disease Presence of a certain microbe not normally found in the body

infection results in any change from a state of health Abnormal state in which part or all of the body is not properly adjusted or incapable of performing its normal functions

INFECTION PATHOGEN Parasitic microbe causing infection and disease

TRUE PATHOGEN Capable

of causing disease in health individuals with normal immune response

OPPORTUNISTIC PATHOGEN Cause

disease in an immunocompromised individual

INFECTIOUS AGENTS Bacteria Fungi Virus Parasites

SUSCEPTIBLE HOST Ill Immunocompromised Elderly

***harbors infectious diseases easily

“Many organisms that cause one disease if they enter one body site are harmless if they enter another, e.g., various enteric urinary-tract pathogens.

INFECTION: PORTAL OF ENTRY Route of entry of a

microbe May be endogenous or exogenous Usually corresponds to the same regions with normal flora. Majority of microbes have a specific portal of entry.

INFECTION: PORTAL OF ENTRY

INFECTION: PORTAL OF ENTRY

Rhinovirus?

Giardiasis in daycare centers.

Methicillinresistant Staphylococcus aurius (MRSA)?

Beddings are an example of a Fomite, an inanimate object that can transmit pathogens between people.

Influenza virus?

Door knobs are another good example of a fomite.

Les s one m

Measles?

tha n eter

Giardiasis from water.

an h t e r o M r e t e m e on

Mycobacterium tuberculosis?

Contact with air from clean, empty room.

Contact with air from small room containing 12 people.

Hepatitis A

Balantidium coli

VECTOR TRANSMISSION Animals that carry pathogens from 1 host to another ARTHROPODS are most important 2 METHODS

MECHANICAL TRANSMISSSION Passive transport Pathogens are on the insect’s feet / body parts Insects make contact with a host’s food BIOLOGICAL TRANSMISSION Active and more complex Vectors are part of the life cycle of the parasite

INFECTION

INFECTION: PORTALS OF EXIT A parasite is considered unsuccessful if it is

killed by the host or it does not have a provision for leaving its host and moving to another host.

Provides pathogens with adequate

conditions for survival and multiplication and opportunity for transmission FORMS Inanimate Objects (FOMITE) 

Soil and Water

Human Beings (CARRIERS) Animals (ZOONOSES 

Diseases that occur primarily in domestic animals and can be transmitted to humans

Zoonoses are Human Diseases with Animal Reservoirs.

Toxoplasmosis

Bacteremia dose not necessarily imply disease.

Contrast with “Localized.”

EXTENT OF HOST INVOLVEMENT

Localized

Confined to specific tissue

Systemic Infection spread to several sites, usually in the

bloodstream

Focal Exists when the infectious agent breaks loose from

a local infection and is carried to other tissues.

Mixed Primary Secondary

 Symptom = indications of disease that cannot be objectively measured, e.g., “It hurts!”  Sign = indications of disease that can be objectively measured, e.g., body temperature.  Syndrome = a collection of signs and symptoms that typically are associated with a given cause.  Subclinical or Inapparent Infection = symptoms are sufficiently mild that they go unnoticed.

Warning Signals of Disease Signs

Symptoms

Fever

Chills

Septicemia

Pain, irritation

Microbes in the fluids

Nausea

Chest sounds (wheezes, crackles)

Malaise, fatigue

Skin lesions

Chest tightness

Leukocytosis

Itching

Leukopenia

Headache

Lymphadenopathy

Abdominal discomfort

Tachycardia

Anorexia

Presence of antibodies in serum

Sore throat

 An infectious disease is caused by a microorganism, but is not necessarily communicable.  A Communicable Disease can be passed from person to person.  A Contagious Disease (contrary to what your text says) can be described as a communicable disease that is easily passed from person to person (i.e., highly communicable).  We can measure the potential for infection associated with a pathogen in terms of its Infectious Dose.  An individual who is asymptomatic but still contagious is described as a carrier.

INFECTION: SIZE OF INOCULUM Quantity of microbes in the inoculating dose INFECTIOUS DOSE Minimum number of microbes required to initiate

an infection LOW INFECTIOUS DOSE, HIGH VIRULENCE

INFECTIOUS DOSE: Gonorrhea: 1,000 cells Typhoid Fever: 10,000 cells Cholera:1,000,000,000

SEVERITY / DURATION OF DSE ACUTE One that develops rapidly only a short time

CHRONIC Develops more slowly and the body’s reactions

may be less severe, but this disease is likely to be continual or recurrent

SUBACUTE Intermediate between acute and chronic

LATENT Causative agent remains inactive for a time but

becomes active to produce symptoms of disease

Convalescence is a time of recuperation and recovery from illness.

Incubation period is the interval between exposure and illness onset.

Depending on various factors an individual may still be infectious during either incubation or convalescence.

OCCURENCE OF DISEASE SPORADIC Particular disease occurs only OCCASIONALLY

ENDEMIC Disease constantly present in a population

EPIDEMIC Disease acquired by many people in a given area

in a relatively short period

PANDEMIC Epidemic disease that occurs WORLDWIDE

Production and delivery of various factors

Attachment to host tissues

Replication and evasion of immunity

Damage to host tissues

 To cause disease, microbes do most of the following: • Gain access to the host (contamination) • Adhere to the host (adherence) • Replicate on the host (colonization) • Invade tissues (invasion) • And produce toxins or other agents that cause host harm (damage)

VIRULENCE and VIRULENCE FACTORS VIRULENCE Degree of pathogenicity of a microbe Takes into account a microbe’s invasiveness and

toxigenicity. VIRULENCE FACTORS Adaptations of a microbe to invade and establish itself in the host  Determine the degree of tissue damage that occurs  Are usually proteins coded by genes in chromosomal DNA, bacteriophage DNA or plasmids 

HOW VIRULENCE FACTORS CAUSE DISEASE? Adhesion and

Colonization Factors Bacteria attach by

fimbriae, adhesive slimes and capsules and at times by flagella Viruses use specialized receptors

HOW VIRULENCE FACTORS CAUSE DISEASE? Invasion Factors Act extracellularly, breaking down host defenses at the local level and easing the passage of the infection. Most are enzymes, affecting physical barriers like tissue matrices and cell membranes. There are several classes of invasive enzymes: Mucinase Keratinase Collagenase Hyaluronidase

HOW VIRULENCE FACTORS CAUSE DISEASE? Anti-Phagocytic

Factors Some bacteria and

parasites have the ability to survive and multiply inside phagocytic cells.

HOW VIRULENCE FACTORS CAUSE DISEASE?

Toxins EXOTOXIN  Secreted by a living bacterial cell into infected tissues  Damage the cell membrane or disrupt intracellular function

ENDOTOXIN  Released

when the cell(bacterium) is damaged or lysed  Cause septic shock:  hypotension  disseminated intravascular coagulation  fever  lack of effective oxygenation  overall system failure