Transcript Doctrine about infection

Medical biology, microbiology, virology,
immunology department
by As. Prof. O.V. Pokryshko
The interaction of the susceptible
human organism and the pathogenic
microorganism in certain conditions
of
the
external
and
social
environment which gives rise to an
obvious or latent pathological process
is called an infectious process.
The term infection (L. infectio to
infect) signifies the sum of biological
processes which take place in the
macroorganism upon the penetration of
pathogenic microorganisms into it.
Infectious disease designates one
of the extreme degrees of
manifestation of the infectious
process.
Infectious diseases are considered
to
be
phenomena
including
biological and social factors.
Infectious diseases differ from other
diseases in that
they are caused by live causative agents
of a plant and animal origin
and are contagious,
the presence of a latent period,
specific reactions of the body to
the causative agent
and production of immunity
Koch’s postulates.
For the origination and development of
the infectious process three conditions are
necessary:
1. the presence of pathogenic microbe,
2. its penetration in to a susceptible
macroorganism,
3. certain environmental conditions in which
the interaction between the microorganism
and macroorganism takes place.
What is an Epidemic?
The occurrence of more cases of
disease than expected in a given area or
among a specific group of people over a
particular period of time*.
Epidemic
What is a Pandemic?
An epidemic occurring over a very wide
area (several countries or continents)
and usually affecting a large proportion
of the population.
Examples:
– Cholera
– AIDS
– Pandemic Influenza
Pandemic
Source of infection:
Sick men
Sick animal
Carrier
Transmission factor: infected food,
water, dirty hands, flies, fomites.
Vectors of pathogenic microorganims:
ticks, louses, fleas mosquitos.
Routes of diseases transmission
There are various modes which pathogens
are transmitted from a source to a susceptible
individual.
 airborne transmission
foodborne transmission
sexual transmission
direct contact transmission
parenteral route
Respiratory tract
and airborne transmission.
Airborne transmission occurs when
pathogenic microorganisms are transferred
from an infected to a susceptible individual
via the air. Droplets regularly become
airborne during normal breathing, but the
coughing and sneezing associated with
respiratory tract infections are primarily
responsible for the spread of pathogens in
aerosols and thus the airborne transmission
of disease.
High-speed photograph of an aerosol generated
by an unstifled sneeze.
Gastrointestinal tract—water
and foodborne transmission.
Microorganisms routinely enter the
gastrointestinal tract in association with
ingested food and water. Waterborne and
foodborne pathogens can infect the
digestive system and cause gastrointestinal
symptoms.
Genitourinary tract – sexual
transmission.
The genitourinary tract provides the portal
of entry for pathogens that are directly
transmitted during sexual intercourse. Such
infections are known as venereal or sexually transmitted diseases.
Superficial body tissues –
direct contact transmission.
In some cases the deposition of pathogenic
microorganisms on the skin surface can
lead to an infectious disease. Since they
require direct contact between skin and
microorganisms for transmission to occur,
these diseases are called contact diseases.
Some diseases transmitted in this manner
are superficial skin infections.
Parenteral route.
Punctures, injections, bites, cuts, wounds,
surgical incisions, and cracking skin due to
swelling or drying establish portals of entry
to a host for a potential pathogen. Such
access is called the parenteral route (from
Greek para [beside] and enterik [intestinal
tract]. Microorganisms thus gain entry to the
body by being deposited directly into the
tissues beneath the skin or into the mucous
membrane.
Portals of entry.
The routes of entry are
 the respiratory tract,
 gastrotestinal tract,
 genitourinary tract,
 skin, and wounds.
The invasive properties of specific
pathogens permit them to penetrate the body's
defense mechanisms through a specific portal
of entry. Most pathogenic microorganisms
will cause disease only if they enter the body
via this specific route.
The dynamics of the development of the
infectious process consists of
1. the incubation period
2. prodromal period,
3. the height of the disease
4. period of recovery
( convalescence).
A certain period of time elapses from the
moment of penetration of the pathogenic
microbe to the onset of the first sings of the
disease, which has been named the
incubation period of the disease.
The sites at which microorganisms leave the body are called
portals of exit. Pathogens of the
genitourinary and gastrointestinal
systems generally exit the body
with body fluids or feces.
Pathogens of the respiratory system exit through the nose or mouth
in fluids expelled during coughing,
sneezing, and speaking. Some
pathogens, such as the bacteria
that cause tuberculosis, are
resistant to desiccation and can
remain viable in the air for a long
while. These organisms can be
transmited via the air, and
inhalation of contaminated air can
lead to infection.