Infection and Disease
Download
Report
Transcript Infection and Disease
Infection and Disease
The Host-Microbe Relationship
Human body maintains a symbiosis with microbes
Infection refers to:
relationship between the host and microbe
competition for supremacy between them
If the host loses the competition, disease occurs
Contact, Colonization, Infection, Disease
Infection
condition where pathogenic microbes penetrate
host defenses
enter tissues and multiply
Disease
any deviation from health, disruption of a tissue or
organ
infectious disease
Caused by microbes or their products
**Not all contacts lead to infections…….
**Not all infections lead to disease!!!!!
Resident Flora
Microbiota, transient,
resident, indigenous
Microbes that engage in
mutual or commensal
associations
most areas of the body in
contact with the outside
environment
internal organs & tissues &
fluids are microbe-free
bacterial flora benefit host by
preventing overgrowth of
harmful microbes
Initial Colonization of the Newborn
Uterus and contents normally
sterile
remain so until just before birth
Breaking of fetal membrane
exposes the infant
all subsequent handling and
feeding continue to introduce
normal flora
Pathogens….
True pathogens
capable of causing disease in
healthy persons
normal immune defenses
influenza virus, plague bacillus,
malarial protozoan
Opportunistic pathogens
cause disease when hosts
defenses are compromised
Pseudomonas sp & Candida
albicans
Pathogenicity
Ability of a microorganism to
cause disease
Severity of disease depends on
the virulence of the pathogen
Degree of pathogenicity
characteristic or structure that
contributes to the ability of a
microbe to cause disease
virulence factor
Adhesion factors
Biofilms
Extracellular enzymes
Toxins
Antiphagocytic factors
Pathogens…..
In order to become
established:
Portal of entry
Attaching
Surviving host defenses
1. Portals of entry
characteristic route a
microbe follows to enter the
tissues of the body
skin
nicks, abrasions, punctures,
incisions
gastrointestinal tract
food, drink, and other ingested
materials
Mucous membranes
urogenital tract
Sexual
transplacental
Infectious Dose (ID)
minimum number of
microbes required for
infection to proceed
microbes with small IDs have
greater virulence
1 rickettsial cell in Q fever
10 bacteria in TB, giardiasis
109 bacteria in cholera
2. Mechanisms of Adhesion
fimbrae
flagella
adhesive slimes or capsules
cilia
scolex
hooks
barbs
3. Surviving Host Defenses
Initial response of host
defenses comes from
phagocytes
Ability to survive
intracellular phagocytosis
Antiphagocytic factors
Antiphagocytic factors
Factors prevent phagocytosis by the host’s phagocytic
cells
Bacterial capsule
Composed of chemicals not recognized as foreign
Slippery; difficult for phagocytes to engulf bacteria
Antiphagocytic chemicals
Prevent fusion of lysosome and phagocytic vesicles
Leukocidins directly destroy phagocytic white blood cells
Enzymatic Destruction
Extracellular enzymes (exoenzymes)
Secreted by the pathogen
Dissolve structural chemicals in the body
Help pathogen maintain infection, invade, and avoid body defenses
Invasiveness
Coagulase
form a blood clot that protects them from phagocytosis
Streptokinase
dissolves fibrin clots and allows dissemination of the bacteria
Hyaluronidase
enhances pathogen penetration through tissues
Leukocidins
disintegrate neutrophils and macrophages
Hemolysiins
dissolve red blood cells
Virulence can be enhanced in biofilms
immune cells cannot reach bacterial cells
Toxins
toxigenicity
capacity to produce toxins at the site of multiplication
endotoxins
lipid A of LPS of gram-negative bacteria
exotoxins
proteins secreted by gram-positive and gram-negative bacteria
Toxins
Toxinoses
Disease caused by toxin
Toxemias
Spread by blood
Intoxication
Ingested
Enterotoxins
act on the gastrointestinal tract
Antitoxins
produced by the host body and
neutralize toxins
Toxoids
toxins whose toxicity has been
destroyed but still elicit an immune
response
Toxin production and viruses?
Some ability of bacteria to produce
toxins due to presence of a
lysogenic prophage in the bacterial
chromosome
phage contains the structural gene
for the toxin molecule
Phage encoded virulence factors
Portals of Exit
Respiratory, saliva
Skin
Fecal exit
Urogenital tract
Removal of blood
Establishment of Infection and Disease
incubation period
time between entry of the
microbe and symptom
appearance
prodromal phase I
time of mild signs or symptoms
acme period (climax)
signs and symptoms are most
intense
period of decline
As sign and symptoms subside
period of convalescence
body systems return to normal
Patterns of Infection
localized infection
remains confined to a specific tissue
focal infection
when infectious agent breaks loose from a local infection
carried to other tissues
systemic infection
infection spreads to several sites and tissue fluids
usually in the bloodstream
Patterns of Infection
Mixed infection
several microbes grow
simultaneously at the infection
site
Primary infection
initial infection
Secondary infection
another infection by a different
microbe
Warning Signals of Disease
Sign
objective evidence of disease as
noted by an observer
Symptom
subjective evidence of disease
as sensed by the patient
Syndrome
Disease is defined by complex
of signs and symptoms
Signs and Symptoms of
Inflammation
Earliest symptoms of disease as a result of the
activation of the body defenses
fever, pain, soreness, swelling
Signs of inflammation:
edema
accumulation of fluid
granulomas and abscesses
walled-off collections of inflammatory cells
and microbes
Lesion
General term for site of infections or
disease
Signs of Infection in the Blood
Changes in the number
of circulating white blood
cells
leukocytosis
increase in white blood
cells
leukopenia
decrease in white blood
cells
Signs of Infection in the Blood
septicemia
microorganisms multiplying in the blood and present
in large numbers
bacteremia
small numbers of bacteria present in blood
not necessarily multiplying
viremia
small number of viruses present
not necessarily multiplying
Infections That Go Unnoticed
Asymptomatic
subclinical infections
although infected, the host doesn’t show any signs of
disease
Inapparent infection
person doesn’t seek medical attention
Persistence of Microbes and
Pathologic Conditions
Latency
microbe can periodically become active
produce a recurrent disease
person may or may not shed it during the latent stage
Sequelae
long-term or permanent damage to tissues or organs
Acute diseases
develop rapidly
cause severe symptoms
fade quickly
Chronic diseases
linger for long periods of time
slower to develop and recede
Reservoirs: Where Pathogens
Persist
Reservoir
primary habitat of pathogen in the
natural world
human or animal carrier, soil, water,
plants
Source
individual or object from which an
infection is actually acquired
Animals as Reservoirs and Sources
vector
live animal that transmits an
infectious agent from one host to
another
Arthropods
fleas, mosquitoes, flies, and ticks
larger animals
mammals, birds, lower vertebrates
Animals as Reservoirs and Sources
zoonosis
infection indigenous to animals
but naturally transmissible to
humans
humans do not transmit the
disease to others
Acquisition and Transmission of
Infectious Agents
Communicable disease
an infected host can transmit the infectious agent to another
host
Highly communicable disease is contagious
Non-communicable infectious disease
does not arise through transmission from host to host
occurs primarily when a compromised person is invaded by
his or her own normal microflora
contact with organism in natural, non-living reservoir
Patterns of
Transmission
Direct contact
physical contact, droplet nuclei,
aerosols
Indirect contact
passes from infected host to
intermediate conveyor and then to
another host
vehicle
food, water, biological products,
fomites
Nosocomial Infections
Health care-associated
infections (HAIs)
occur as a result of
receiving treatment for
another condition
Nosocomial infections are
HAIs associated with
hospitals
They occur as a result of
chains of transmission
Nosocomial Infections
From surgical procedures,
equipment, personnel, and
exposure to drug-resistant
microorganisms
More than 1/3rd of nosocomial
infections could be prevented
2 to 4 million cases/year in U.S.
approximately 90,000 deaths
Most common organisms involved
Gram-negative intestinal flora
E. coli, Pseudomonas,
Staphylococcus
Epidemiology
study of the frequency and distribution of
disease & health-related factors in human
populations
Surveillance
collecting, analyzing, & reporting data on rates of
occurrence, mortality, morbidity and transmission of
infections
Reportable, notifiable diseases must be
reported to authorities
Epidemiology
Centers for Disease Control and Prevention (CDC) in
Atlanta, GA
principal government agency responsible for keeping track
of infectious diseases nationwide
http://www.cdc.gov
Epidemiology
Prevalence
total number of existing cases with respect to the entire
population usually represented by a percentage of the
population
Prevalence=
Total # of cases in pop
Total # of persons in pop
X 100
Epidemiology
Incidence
measures the number of new cases over a certain time
period, as compared with the general healthy population
Incidence =
# of new cases
= ratio
# of healthy persons
The incidence and estimated
prevalence of AIDS
Epidemiology
Mortality rate
total number of deaths in a population due to a certain
disease
Morbidity rate
number of people afflicted with a certain disease
Epidemiology
Endemic
disease that exhibits a relatively
steady frequency over a long period of
time in a particular geographic locale
Sporadic
when occasional cases are reported at
irregular intervals
Epidemic
when prevalence of a disease is
increasing beyond what is expected
Pandemic
epidemic across continents