Epidemiological
determinants
of infectious diseases
MUDr. Marie Kolářová, CSc.
Ústav ochrany a podpory zdraví LF MU
Spring 2018
Face lesions on boy with smallpox.
Source: CDC/Cheryl Tyron
Polio_Iores134
Fysiological
colonisation of
humans
by micro-
organisms.
Many parts of the body are colonized by normal flora, which
can be the source of endogenous infection. Large numbers
of micro-organisms are found in moist areas of the skin (e.g.
the groin, between the toes), the upper respiratory tract, the
digestive tract (e.g. the mouth, the nasopharynx), the ileum
and large intestine, the anterior parts of the urethra and the
vagina.
Other routes are interhuman transmission of infections and
exposure to exogenous contamination.
Fysiological
colonisation of
humans
by micro-
organisms.
Healthy newborn = germ-free organism
Gradual colonization:
* Skin - when passing through the mother's birth
paths
* breathing paths - at first breath
* GIT - at first swallowing
... ended until the 8th day
Fysiological
colonisation of
humans
by micro-
organisms.
Permanent colonization, eumicrobia,
Types of bacteria event. fungi (never virus!)
are for a given system:
* characteristic,
* non-pathogenic,
* constant composition
Fysiological
colonisation of
humans
by micro-
organisms.
Constantly restored balance between the host and the
micro-organism.
Balance distorts:
a) external changes (chemical, physical)
b) host properties (hormonal, immune status,
drugs - ATB, corticosteroids, cytostatics)
Fysiological
colonisation of
humans
by micro-
organisms.
The importance of physiological microflora
+ affects digestion, absorption, peristalsis
+ produces vitamins
+ protection of skin and mucous membranes from
microbes with higher pathogenicity
Negative influence:
- the risk of endogenous infections in
immunosuppressed persons
- complications of interpretation of serological
examinations)
Pathogenesis
of infectious
diseases
Parasitism - survival and multiplication of host
microbes with host abuse
Comensalism - the microbe uses the host but
does not damage it
Symbiosis - hosts and microorganisms benefit
from coexistence
Carriage - the state of immunobiological balance
Development of immunoglobulin levels
21.3.2018
Šedivá A. Čes.-slov. Pediat., 2005, roč.60, č.11, s. 617-624
Maturation
of the immune
systém;
defense.
Etiological
structure of
infections
Bacteria
 Gram positive
 Gram negative
Acid-resistant rod .--. Mycobacteria
Viruses
 Enveloped - HIV, HBV, measles, mumps, influenza, rabies
 Unenveloped - adenoviruses, HPV, Polio
Prions
Parasites (Eukaryotic Pathogen)
Fungi - Candida, Aspergillus
Protozoa - Plasmodium, Schistosoma
Worms - Ascaris, Taenia
Etiological
structure of
infections
The agent of infection – important characteristic:
infectivity – capacity to multiply in host
pathogenicity – capacity to cause disease in host
virulence - pathogenicity in a specific host
immunogenicity – capacity to induce specific and
lasting immunity in host
antigenic stability – can induce long-life immunity
resistance - in environment
Resistance of
microorganism
s in inanimate
environment
The viability of micro-organisms and their survival in the external
environment depends on:
 on their properties and
 on the environment in which they are located.
(by combining - low temperatures,
- lower humidity,
- absence of toxic substances, and
- the presence of colloidal substances that
have a protective effect).
Resistance of
microorganism
s in inanimate
environment
Organisms vary in their capacity to survive and to
withstand adverse environmental conditions, for
example:
* heat, cold, dryness.
Sporo-forming organisms, such as tetanus bacilli
which can survive for years in a dormant state,
have a major advantage over an organisms like
the gonococcus which survive for only a very short
time outside the human host.
Pathogenesis
of infectious
diseases
1. entry of the etiological agent to a susceptible
individual;
2. adherence of the agent to the target tissue;
3. reproduction and invasion;
4. host damage by toxins or other mechanisms;
5. exclusion of the agent through some of the
biological materials
6. possible survival of agents for a long time in an
inanimate external environment
Pathogenesis
of infectious
diseases
Infection is the entry and development or multiplication of
an infectious agent in the body of man or animals. An
infection does not always cause illness.
There are several levels of infection (Gradients of
infection):
Colonization (S. aureus in skin and normal
nasopharynx)
Subclinical or inapparent infection (polio)
Latent infection (virus of herpes simplex)
Manifest or clinical infection
Virulence
factors
For all pathogens are important Infective and lethal
doses.
Virulence factors affecting their pathogenicity:
1. Pilli that ease attachment
2. Covers that interfere with phagocytosis
3. Exotoxins
4. Endotoxins
5. Proteases that degrade antibodies
6. Ability to change the antigens that escape the
fragments
Chain of infections
(epidemic proces)
THE CAUSATIVE AGENT OF INFECTION (bacteria, viruses, fungi, prions, protozoa)
1. the presence of rezervoir (source) of infection
man, animal at the ende of incubation period
acute stage
cariers
2. the way of transmission A/ direct contact
touching, kissing or sexual intercourse (Staphylococcus spp., Gonococcus spp.,HIV …),
- vertical transmission – from mother to fetus (VHB, VHC, HIV, listeria, rubella,
cytomegalovirus…)
B/ indirect contact
- inhalation of droplets containing the infectious agents (TBC, measles, influenza…)
- ingestion of food or water that is contaminated (salmonella, giardia, Norwalk virus, VHA….)
- biological transmission by insects (malaria, borellia….)
3. the susceptibility of the population or its individual members to the
organism concerned Host factors : a g e , n u t r i t i o n, g e n e t i c s
i m m u n i t y – natural (nonspecific),
- acquired
THE INFECTION
= 1. prezence of rezervoir (source) of infection
……….
The chain of
infections
1. the presence
of source of
infection
is the site or sites in which a disease agent normally lives and
reproduces.
May be classified as:
- human - at the ende incubation period,
if is ill,
reconvalescent,
carriers – healthy,
chronic diseases
- animals - at the ende incubation period,
if is ill,
carriers – healthy,
reconvalescent, chronic
The chain of
infections
2. the metod of
transmission
A/ direct contact
touching, kissing or sexual intercourse (Staphylococcus
spp., Gonococcus spp.,HIV …),
- vertical transmission – from mother to fetus (VHB,
VHC, HIV, listeria, rubella, cytomegalovirus…)
B/ indirect contact
- inhalation of droplets containing the infectious agents
(TBC, measles, influenza…)
- ingestion of food or water that is contaminated
(salmonella, giardia, Norwalk virus, VHA….)
- biological transmission by insects (malaria,
borellia….)
The chain of
infections
3. the susceptibility
of the population or
its individual
member to the
organism
concerned, and the
characteristic of the
organism itself.
Host factors :
Non specific immunity
Barrier action (natural barrier)
External barrier:
skin , mucosa
Secretion of skin and mucosa
Accessory organ
Internal barrier: placenta, blood-brain barrier
Phagocytosis
Humoral action :
Complement, Lysozyme, Fibronection, Cytokines.
Specific immunity
Humoral immunity
Immunoglobulin: IgG, IgM, IgE, IgA, IgD
Cell mediated immunity
The chain of
infections
3. the susceptibility
of the population or
its individual
member to the
organism
concerned, and the
characteristic of the
organism itself.
Host factors :
Non specific immunity
Barrier action (natural barrier)
External barrier:
skin , mucosa
Secretion of skin and mucosa
Accessory organ
Internal barrier: placenta, blood-brain barrier
Phagocytosis
Humoral action :
Complement, Lysozyme, Fibronection, Cytokines.
Specific immunity
Humoral immunity
Immunoglobulin: IgG, IgM, IgE, IgA, IgD
Cell mediated immunity
22
Isolation of patients:
- Dpt. of infectious diseases,
- „high degree of isolation“ (ebola)
- at home,
- barriers nursing technique
SOURCE
OF INFECTION
MODE
OF TRANSMISSION
SUSCEPTIBLE
ORGANISM
Prevention of
infectious
diseases
23
SOURCE
OF INFECTION
MODE
OF TRANSMISSION
SUSCEPTIBLE
ORGANISM
HANDWASHING, DISINFECTION OF HANDS
LINEN WASHING,
CLEANING
GOOD PREPARING OF FOOD, SAFE
WATER……..,
………
DISINFECTION
STERILIZATION
Prevention of
infectious
diseases
24
SOURCE
OF INFECTION
MODE
OF TRANSMISSION
SUSCEPTIBLE
ORGANISM
i m m u n i t y
– natural (nonspecific),
- acquired (vaccination)
Prevention of
infectious
diseases
Principles of
Vaccination
Active immunisation
A live or inactivated substance (e.g., a protein, polysaccharide)
capable of producing an immune response is administered to the
organism to target specific antibodies against that antigen.
Protein molecules (immunoglobulin) produced by B lymphocytes
to help eliminate an antigen
Passive immunisation
Transfer of antibodies produced by one human or other animal to
another.
Temporary protection
Transplacental most important source in infancy
Preventive,
repressive
measures
If the epidemiology is know, we can interfere
with transmission:
„BREAKING THE CHAIN OF INFECTION“
Different infections have different
epidemiologies and thus require different
methods of control
Preventive,
repressive
measures
In the practical part it is preoccupied with
preventive measures
repressive measures
related to infectious diseases
28
The distribution of the
smallpox rash is usually
similar to that shown here.
It is most dense on the
face, arms and hands, legs
and feet.
The trunk has fewer pocks
than the extremities.
Smallpox
eradication
29
Smallpox is a disfiguring disease.
Three out of ten cases may die.
It is caused by variola virus.
The disease is spread by secretions
from the patient's mouth and nose,
and by material from pocks or scabs.
It is transmitted directly from one
person to the next.
Close contact with patients, or their
clothing or bedding, is thus required for
infection.
Apatient who has developed the
distinctive symptoms of smallpox will
have been exposed to the virus about
two weeks previously.
Smallpox
eradication
Smallpox eradication was
officially announced
at the 33rd General Assembly WHO
8. May 1980.