INFECTOLOGY. CONCEPT OF INFECTIOUS DISEASE FEATURES OF INFECTIOUS

DIAGNOSIS, TREATMENT, PREVENTION

spreading of them began with formation of the human society

and development of a social lifestyle.

Infection does not lose the actuality because:
infectious diseases in our time remain one of the main reasons of death rate, especially in developing countries (more than a quarter of all deaths today are linked to infectious diseases);
infectious diseases have various consequences for individuals, their families, as well as their communities;
- infectious diseases lead to:
shortening of lifetime,
numerous deaths in population (at mass outbreaks),
significant economic loss

humans were moving, they were taking germs with them. And

looking at history, we find that diseases were spread throughout various continents.
1) For example, there was a Plague of Justinian around 541 after the common era, which killed many throughout Europe.
There was also the bubonic plague, which
took the lives of 25 million people
(1/3rd of the population in Europe at the
time)
2) Epidemic of cholera caused the deaths
of 20 million people.
3) The incidence of Typhus always increases
in periods of national disasters (wars, earthquakes, floods, etc.)
4) A lot of people (500 million) suffered in the first pandemic of influenza A and 20 million of them died.

year

Global mortality from infectious diseases fluctuates:

acute respiratory infections

- 3,500,000 persons
HIV- infection - 2,250,000 persons
GIT – infection - 2,250,000 persons
tuberculosis - 1,500,000 persons
malaria - 1,100,000 persons
measles - 888, 000 persons
tetanus - 410, 000 persons
- whooping cough - 350, 000 persons
- meningitis - 143, 000 persons
leishmaniasis - 42, 000 persons

Two billion people are infected with tuberculosis,

250 – 300 million people get malaria every year,

200 million are infected with schistosomiasis etc.

(ID) was unknown, it led to the formation of many

theories and assumptions.

Primary infection was associated with the concept of "miasma"– toxic transpirations of air.

In the16th centure has been proven that transmission of ID possible among the people (“man to man”),

that promoted to the appearance of version about existence “contagio”- pathogenic material of the onset of diseases

( D.Fracastoro 1546 ) and D. Samoylovich ( 1784 )

in the 19-th centure (It was period of fast development

of bacteriology and immunology) due to discoveries of R. Koch, L. Pasteur, P. Erlich, G. Minch and I. Mechnikov and etc.

R. Koch

L. Pasteur

P. Erlich

G. Minch

I. Mechnikov

their diagnostics, treatment and prophylaxis had elaborated.

Therefore majority of

epidemics are in the past, and can be registered as sporadic cases or morbidity.

Despite the appearance of new infectious diseases (HIV-infection, Marburg, Lassa and Ebola hemorrhagic fevers, Lyme disease etc.) many territories of earth were released from more infections capable to epidemic distribution, but there remains the constant threat of their penetration into the country from adverse regions.
There is described about 2500 infectious pathogens, but the doctor more common with 40 to 50 infectious diseases.

agent) in sensitive organism followed by their interaction.

Infection – is

a complex interaction between microorganism and macroorganism in special conditions of environment (can be physiological and pathological reactions).

Infectious process – is combination of pathological, protective, adaptive and compensatory reactions of micro - and macroorganism proceeding on submolecular, molecular, subcellular, cellular, tissue and organ levels.

of the macroorganism
immune status.
Variants of outcome:
destruction of organs,

cells and tissue,
complete death of macroorganism,
complete elimination of the pathogen with
subsequent formation of stable
specific immunity (more often),
- incomplete eradication of the agent and
formation of carrier state or chronization

organs and systems during the disease);
Localized
(when pathogen is

located within one organ or system during the entire infectious process):
- Epysomatic - lesions of the skin and external
mucous membranes);
- Endosomatic – damage of internal organs
(dysfunction, destruction)
(RS, GIT, UGS, NS, system blood and lymph circulation, musculoskeletal system)

simultaneously by several species of the pathogen (viral hepatitis B

and D);

Autoinfection - caused by conditionally-pathogenic flora of the body. It is based on a dysbiosis. Often develops in the tonsills, colon, RT and skin;

Associated infection – combined effect of multiple pathogenic agents in the body (simultaneous or sequential);

Reinfection - repeated disease that develops due to infection with the same pathogen;

Superinfection – infection caused by other agent until recovery from the primary disease.

influence the duration, complications and outcomes.
The agent causing a

disease must have the following
properties:
1) Pathogenicity - is ability to cause disease at
optimal conditions for the agent (sufficient infectious
dose, time of exposure, place of invasion).
This is usually a constant property, but is not absolute
and invariable value.
To this sign mark out:
pathogenic infectious agents;

conditionally – pathogenic infectious agents;

- nonpathogenic infectious agents (saprophytes).

individual property of a particular strain of the pathogenic agent.

Toxigenicity

- is ability to synthesize
of exotoxins:
diphtheria toxin - has inhibition of protein synthesis,
C. tetani and C. botulinum – have neurotoxicity,
E.coly and Vibrio cholerae – have enterotoxicity

Invasiveness – is ability to penetration and dispelling in tissues with the help of enzymes : neuraminidase, mucinase, hyaluronidase, fibrinolysinum, DNA- ase, collagenase etc.

react with antigens of the host, causing decrease an immune

answer with subsequent unfavorable current of the disease (it is detected at plague, influenza, acute intestinal diseases )

Primary factors of pathogenicity:

Adhesiveness - is ability of fixing to cells using hydrophoby, electric charge, specific receptors
(HIV-infection - receptor СD4)

Tropicity - is a selective interaction and destruction of the host tissues (VH – damage of hepatocyte, at ARVI – damage of RT epithelium)

the body
(Example: skin – malaria, erysipelas, typhus, tetanus; respiratory system

– flu, meningococcal infection; blood - dysentery, typhoid fever).

Route of penetration of microorganism in the host:
- skin (tetanus, rabies, erysipelas )
- respiratory tract (influenza, diphtheria )
- gastro-intestinal tract (dysentery, amebiasis )

Route of spreading of microorganism inside the host :
- by contact way (tick- borreliosis, diphtheria, antrax )
- via lymphatic vessels (erysipelas, tissue helminthiases)
- via blood vessels (typhus, hematosepsis, malaria )
- perineuraly

infectious agents:
Nonspecific factors of protection:

- impenetrability of skin;
-

normal microflora of organism (GIT, RT, UGT)
- high acidity of gastric juice;
- secretion of slime by epithelium and mechanical remove of
agent;
- constant presence of active substance in mucosa secret
(lysozyme, properdin and other enzymes);
- phagocytosis and complement system, interferons,
lymphokines, hydrolyzing enzymes;
- balanced feeding, normal lifestyle and absence
of chronic intoxication

(early);

- Delayed reactions of hypersensitivity;

- Immunological memory;

- Immunological tolerance;

Idiotype -

antiidiopathic
interaction.

low temperature;
- desiccation;
- radiation and insolation;

- disinfectant drugs;
- antagonism between other
microorganisms

and high humidity –
promotes rapid development of

ARVI;

- low acidity of a stomach –
risk of development of intestinal infection;

- deterioration of an ecology;

- social factors

microorganisms (viruses, bacteria and protozoa).

Infectious disease develops as a

result of interaction between two biological systems (macro - and microorganism).

Infectious disease - the highest degree of severity of infectious process (maximum expressed manifestation), when the pathological reactions prevail over compensatory reactions therefore is broken homeostasis of organism.

1) overpopulation of the planet,

2) urbanization and migration,
3) anthropogenic impact on nature,
4) ecological changes in the
environment,
5) natural and social disasters,
6) increased incidence of
immunodeficiency states

pathogen
(V.cholera >>> Cholera,
Salm. typhi >>> Typhoid fever);

cyclic course of the disease
(incubation, prodromal or initial period,
period of acute clinical manifestation - climax,
period of reconvalescence, );

formation of immunity
(cellular- humoral, specific- nonspecific, sterile- non-sterile, short- prolong- lifelong)

damage
Outcomes
Superficial or tissue invasion
Multiplication
Exracellular
Intracellular
Circulation
(blood/lymph)
Dysfunction
Destruction

of pathogen
(named after L. Gromashevsky):

1. Intestinal infection (the causative

agent is localized in the GIT),
- mechanism of transmission is fecal-oral
- routs of transmission: - watery;
- alimentary;
- contact;
(cholera, salmonellosis, typhoid, dysentery etc.)

2. Respiratory infection (the causative agent is localized in
the epithelium of the respiratory tract),
- mechanism of transmission is airborne
- routs of transmission: - air-drop;
- air-dust;
(diphtheria, meningococcal infection, ARVI).

blood),

- mechanism of transmission of vector-borne
(malaria, typhus and relapsing fever, hemorrhagic fever etc).

4. Skin infection of (the causative agent is localized on the skin
or mucous membranes),
- mechanism of transmission is contact
(via injured skin).
(rabies, erysipelas, tetanus, scabies, etc).

5. Mixed infection (with multiple organ localization and
multiple mechanisms of transmission)
(HIV-infection, HBV, HCV, plague)
In cutaneous form of the plague pathogen is localized in the skin, and transmission mechanism is contact; in pulmonary form of plague pathogen is localized in RT, and mechanism of transmission is airborne; in intestinal form of plague pathogen is localized in the intestine and the mechanism of transmission is fecal-oral; also, in generalized forms of plague pathogen is transferred via bite of fleas

Clinical classification of infectious diseases

and growth, where the pathogen enters the host)

1. Anthroponosis –

pathogen parasites only in human
- source of infection - sick person or carrier
(dysentery, typhus, typhoid, scarlet fever, diphtheria, measles);

2. Zoonosis – agent is localized in animal
- source of infection - wild and domestic animals
(brucellosis, leptospirosis, anthrax, rabies);

3. Sapronosis - causative agent is localized in the soil, water
- source of infection - inanimate objects of the environment
(pseudotuberculosis and intestinal yersiniosis, tetanus);

4. Mixed infections - there are a few possible sources
of the pathogen (cholera, salmonellosis, plaque)

Clinical classification of infectious diseases

- presence of typical symptoms and syndromes;

subclinical - minimal

manifestation with presence of nonspecific symptoms that often have mild severity;

latent - prolonged asymptomatic interaction of pathogen and host (agent stay inside the cell and not released in the environment), infection becomes acute when microbe is activated by some factors;

development of pathological changes in one organ or system, outcome

is always unfavorable;
carrier state - asymptomatic, subclinical or chronic interaction of pathogen and organism. May be seen as:
- transitory (excretion is possible
within 2 weeks),
- acute (within 1 month),
- subacute (up to 3 months),
- chronic (3-6 months or more).

relapses, remissions, exacerbations.
Can result in the recovery
Typical
- praesent all

pathognomonic symptoms of the disease

Atypical
- some pathognomonic symptoms may be absent

Short-term presence of the pathogen in the organism, its intense release into the environment, high contagiousness of the patient. Can result in recovery or death of the patient

Fulminant
rapid and maximal development of symptoms

Mild

Moderate

Severe

Complicated

Uncomplicated

Specific complication

Nonspecific complication

Manifested form

pathogen into the body till appearance of first clinical symptoms.

Duration various and depends on:
- virulence of a microbe;
- infectious dose;
- immune status of the person;
- location of entrance gate.
The average duration is 1 – 3 weeks.

(at first) of non-specific clinical symptoms or syndromes

(general intoxication, hyperthermia, arthralgia);

- continues till development of specific clinical
picture.
- to assume the diagnosis – possible,
to confirm - problematically.

- duration of the period on average 2 to 4 days.

syndromes until their
extinction.
The duration

depends on the causative agent and
reactivity of the macroorganism.

4. Reconvalescent period - since disappearance of
symptoms until their complete elimination –
recovery.
The duration is determined by the form,
severity of the disease and therapy.

virologic or bacteriological- isolation pure
cultures of agent;

- microscopical- visual discover of agent in
the smears;
- immunological- find antigens and
antibodies in blood;
- biological - reproduce of the disease on the
animals;

the state)

Clinico-epidemiological - principal method of diagnostics, simplify realization of

differential diagnosis;

- Allergological - using of intracutaneous and mucous tests;

Biochemical – discover the changes of metabolism of the
organism;
Clinical lab. study - ordinary test of blood, urine, sputum
and stool
Instrumental - X-ray examinations , rectoscopy (RRS), USE,
ECG, CT

the pathogen;
2) stop its multiplication;
3) complete

elimination of agent;
4) inactivation of pathogen exotoxins.
Can be used: - antibiotics, antiviral, antifungal and antiprotozoan drugs;
- serum, immunoglobulins, vaccines, phages
- Tetanus – Human tetanus immune globulin or Horse serum
(prevention and treatment)
- Diphtheria - Horse serum ( prevention and treatment)
- Botulism – Horse serum (only treatment)
- Rabies - Human Rabies immune globulin (only prevention)

patient’s state;
2) prevention of complications:

- pathogenic- affect on the some

links of pathogenesis;

symptomatic- eliminate some symptoms of illness;

- surgical treatment and palliative care –
when is necessary.

- Live attenuated vaccines

(oral polio (Sabin), measles, parotitis, rubella)

- Inactivated conjugate vaccines
(VHA, typhoid, influenza, cholera)

- Recombinant vaccines
(VHB, influenza)

3. Anatoxins – diphtheria, tetanus

4. Prophylaxis with immune globulins
(measles, tick encephalitis, rabies, VHA, VHB)

5. Prophylaxis with bacteriophages (AID)

6. Chemoprophylaxis (plague, typhoid, cholera etc.)