Transcript unit 7 host parasite notes

Unit 7 HOST PARASITE RELATIONSHIP
• A Delicate relationship exist between pathogenic
microorganismand the body defenses.
• When the defenses resist the pathogens, the body
remains healthy.
• But when the pathogens overcome the defenses, the
result is disease.
• So inspite of our defenses, we are still susceptible to
pathogenic
microorganisms.
• Pathology; the scientific study of diseases.
PATHOLOGY:
1. First concerned with cause (etiology) of disease.
2. Deals with pathogenesis ( manner in which diseases
develops)
3. Concerned with pathology (structure) and functional
changes brought about by disease and with its final
effect on body.
INFECTION AND DISEASE
• Infection: Invasion or colonization of body by
pathogenic microorganism.
• Also defined as the presence's of a particular type of
microorganism in a part of the body where it is not
normally found.
• Ex E. coli normally found in intestines but considered an
infection if found in the urinary tract.
• Disease; Occurs when infection results in any change
from a state of health.
• Normal flora; the population of
microorganisms found where the body tissues
interface with the environment.
• Much of the normal flora is permanent, but some
portions are transient.
• Transient flora: present for a time and then
disappears.
Types of relationships between normal flora
and body:
1. symbiosis; means living together
a. commensalism: when one organism benefits and the
other remains
unaffected.
b. mutualism; when both organisms benefit one another.
c. parasitism; when one organism damages the other.
d. phoresy; to carry something Ex flies carry parasites on
legs
2. Opportunistic organisms; are potentially pathogenic
organisms that normally do not cause disease.
•
However in a compromised host, the organism may see
"opportunity" to invade the tissues.
•
Ex AIDS individuals often are susceptible to
•
Pneumocystic carinii which invade the lung tissues and
causes a lethal pneumonia
ETIOLOGY OR DEVELOPMENT OF
INFECTIOUS DISEASE;
• In order to relate a particular organisms to a particular
disease, KOCH'S POSTULATE must be fulfilled.
• Remember; Koch's postulates are a series of procedures
for identifying the cause of a particular disease.
EXCEPTIONS to Koch's postulates;
• There are a few exceptions to Koch's postulate.
• Ex Treponema pallidum is the causative agent of
syphilis, but has never been cultured in artificial media.
• Some pathogens cause several pathologies ex.
Mycobacterium tuberculosis disease of lungs , skin,
bones and intestinal organs
SYMPTOMS AND SIGNS;
• Infections diseases are usually characterized by
changes in body function known as symptoms.
•
Symptoms are subjective changes not always apparent
to the observer.
• The patient may also exhibit signs, which are objective
changes that can be measured. Ex fever, skin rash.
• When a specific group of symptoms or signs
accompanies a disease, the group is called a
syndrome.
• Predilection site: where you expect to find the parasite
or disease in the host.
TRANSMISSION AND INCIDENCE
• Diseases are often classified in terms of how they
behave within the host or within a given population.
• Infections diseases may be classified according to their
transmissibility.
a. Communicable disease: a disease that spreads from
one host to another. Ex chicken pox, measles, herpes
b. Contagious; Those communicable diseases transmitted
with ease.
c. Noncommunicable; diseases that are not spread
between host. Ex Clostridium tetani
• Incidence; refers to the percent of the
population that contracts a disease over a
particular period of time.
• Prevalence of a disease; the percentage of a
population having the disease at a particular
time.
Classification of Disease Occurrence;
1. Sporadic disease: when a disease occurs only
occasionally. Ex Typhoid fever
2. Endemic; When a disease is present in a
population at all times. Ex common cold
3. Epidemic; A disease that breaks out in a
population in a short period of time. Ex
influenza, AIDS
4. Pandemic: an epidemic disease occurring
throughout the world. Ex AIDS
Categories of human population during an
epidemic;
1. suffering class: show all symptoms
2. suffering asymptomatic class: source of infection, don't
know they have it.
3. immune or vaccinated class
4. susceptible but not yet infected: not exposed.
•
The more there are of classes 1,2,4 the greater the
epidemic spread.
•
The more there are of class 3, the less probability of a
major epidemic.
To limit or end an epidemic;
1.
2.
3.
4.
isolate victims
isolate potential victims
treatment
quarantine: typical time period about 40 days.
TYPES OF DISEASES; (based on severity
and duration)
1. acute disease: occurs rapidly and last a short time. Ex
influenza
2. chronic disease: develops slowly and lasts a long time.
Ex tuberculosis
3. subacute disease: disease with vague symptoms and
lasts relatively long time. Ex sclerosing panencephalitis
(rare brain disease decreases intelligence and nervous
function)
4. latent disease: remains inactive in host for a time then
becomes active. Ex shingles
Scope of diseases;
1. local infection: those restricted to a small area of the
body.
2. systemic infection: spread throughout body system.
Also called
generalized infection.
3. septicemia: presence's of multiplying microorganisms
in the blood.
(Toxemia— toxins in blood, Viremia=\\rus in blood,
Bacteremia=bacteria in blood)
4. focal infection', agent of local infection enters
blood/lymph and spread to other body parts.
CAUSE OF DISEASES:
1.
2.
3.
4.
5.
bacterial
fungal
viral
rickettseal
protozoan
MODES OF DISEASE TRANSMISSION
1. Reservoir of infection: when a disease remains in a
population, this is the source of the pathogen ( soil,
animal, human, plant, inanimate objects...ect)
2. Carrier: human/animal reservoir who has had the
disease and recovered but continues to shed the
infectious organisms (zoonose: animal disease spread
to humans)
3. Contact: may be direct or indirect
a. direct transmission: form person to person ex
touching, kissing ect.
b. indirect transmission: when a nonliving object is
intermediary between 2 humans.
•
Fomite: an inanimate object that serves as a means to
transmit a disease. Ex nail fomite for Clostridium tetani
• droplet nuclei: bits of mucus, and saliva that spread
between individuals
4. Vectors: an arthropod that transmits an infectious agent
from an infected host to a susceptible host. May be
mechanical (carried on body part such as legs) or
biological (in saliva, or feces)
5. Vehicles; lifeless objects such as food, water, and air.
Which may be contaminated by human feces,
pathogens from soil or droplet nuclei.
Ways Arthropods transmit diseases
1.
2.
3.
4.
5.
•
•
bite
regurgitation
abrasion
contamination
combination of above
HOST: an organism, simple or complex including
human, capable of being infected by a specific agent.
PORTALS OF EXIT: In order for infection to be
transmitted, microorganism must leave the body. Ex
intestinal, mouth, skin surface, are generally the same
as the infected body part.
DEVELOPMENT OF AN INFECTIOUS
DISEASE:
• Infectious diseases result from a competition for
supremacy between the parasite and the host.
• If the parasite overcomes the host, there is a change in
the general state of good health and disease develops
• Several contributing factors are involved in the
establishment of infectious diseases.
CONTRIBUTING FACTORS:
1. PORTAL OF ENTRY
•
The way an infectious agent enters a host.
• The most common portals of entry are: respiratory tract,
and gastrointestinal tract, but may also include skin
wounds and urogenital tract.
• Many pathogens have a preferred portal of entry and
using it is a prerequisite to their causing a disease. Ex
Salmonella typhi: must be swallowed to cause typhoid
fever, hookworms(Necator americanus) through the skin
• Nosocomial infections: Infections acquired during a
hospital stay. 5 to15% of all hospital patients acquire
noscomial infections.
• In the past it was gram positive Staphylococcus aureus.
2.
DOSE:
• The dose of an organism refers to the number of
microorganism required to establish an infection.
• LD50 The does of microorganisms that will kill 50% of
the hosts it enters.
• ID50: (infectious dose) dose required to produce a
demonstratable infection in 50% test animals
3. INVASIVENESS:
• The ability of the pathogens to penetrate into the
tissue. Ex Entamoeba histolytica (causes intestinal
ulcers) penetrates tissue effectively.
• Tissue invasion often begins with adherence, the ability
of the pathogens to attach to the tissue by using
structures such aspili.
• Capsules: structures possessed by some pneumonia
• Ex Streptococcus pneumonia
•
•
COMPROMISED HOST:
• One whose resistance to infection is impaired by
disease, therapy or burns.
• —3 conditions that can compromise a host
a. broken skin/mucous membranes
b. suppressed immune system
c. impaired cell activity
DISEASE PATTERNS:
1.
Period of incubation: time between the entry of the parasite into toehost
and the appearance of symptoms. Varies.
2.
Prodrome period: mild symptoms such as aches, fever and early signsof
the disease.
3.
Period of illness: disease is most acute. Signs and symptoms are most
apparent and each disease has its own characteristic appearance.
4.
Period of decline: signs and symptoms subside
5.
Period of convalescence: person returns to normal.
•
EPIDEMIOLOGY: The study of the distribution and determinant of a
diseases in the human population. (1854 John Snow—questioned victims
of cholera and traced the path of the disease)—giving rise to modern
epidemiology.
ENZYMES AND TOXINS:
• Many pathogens produce a series of enzymes to help overcome
body defenses and establish themselves in host.
•
1.
2.
3.
Enzyme Examples:
leukoicidens (enzymes that destroy WBC)
hemolysins (bacterial enzyme destroys RBC)
coasulases: enzyme that clots blood...helps staphylococci avoid
body's
phagocytes and contributes to its pathgenicity.
4. streptokinase: streptococcal enzyme that dissolved blood colts,
helps
organism escape body's attempt to wall off infection
5. hyaluronidase: destroys hyaluronic acid, a polysaccharide that
"cements" cells together in tissue.
6. collasenase: breaks down collagen in the connective tissue of
muscles
thus spreading the disease.
• Toxins: poisonous substances produced by bacteria,
they act on the body's cells, tissues, and organs and
interfere with important body processes, thereby
interrupting normal body functions.
Types of toxins(2):
• 1. Exotoxins: proteins produced by bacteria during their
growth and released into their surroundings.
•
Produced mainly by gram positive bacteria. Ex
neurotoxins: interfere with the nervous system,
enterotoxins: interfere with gastrointestinal tract
• The body produces special antibodies called antitoxins:
which neutralize toxins and provide defense against the
disease.
• 2.Endotoxins: portions of the cell wall of Gram negative
bacteria.
• They consist primarily of lipopolysaccharides and are
released when bacteria break apart during the process
of lysis.
• Since lysis occurs during antibiotic therapy, the effects
ofendotoxins can bring about worsening of symptoms
during the recovery period, (endotoxin shock: fever,
chills, aches and cardiovascular collapse)
PATHOGENIC VIRUSES:
• Because viruses lack metabolic capabilities, they rely on
other means for overcoming body defenses and causing
disease.
• Viruses avoid body defenses by multiplying within host
cells, where antibodies and other components of the
immune system cannot reach them.
• The effect occurring in host cells during viral invasion is
referred to as the cytopathic effect (in some cases the
virus causes the cell's lysosomes to release enzymes
which then destroy the cell)