"Approved"
on a methodical conference
department of infectious diseases and epidemiology
"
" __________ 2008
Protocol №
Сhief of dept, professor
V.D. Moskaliuk
METHODOLOGICAL INSTRUCTIONS
To a fifth year student of the Faculty of Medicine
On independent preparation for practical training
Topic: Human as a source of infection. Prophylactic and
Anti epidemic measures. Epidemiologic Role of animals.
Veterinary measures in zoonotic foci.
Subject:
Major:
Educational degree and
qualification degree:
Year of study:
Hours:
Prepared by
epidemiology
Medicine
Specialist
5
4
Sydorchuk A.S., MD., PhD.
1. Topic: Human as a source of infection. Prophylactic and Anti epidemic
measures. Epidemiologic Role of animals. Veterinary measures in zoonotic foci.
2. Lesson duration: 4 hours.
3. Aims of the lesson:
3.1. Students are to know:
• The source of contagium is the infected (patient, and sometimes healthy) organism
of man or animals (at zoonosis). At the sapronosis source of infections can be an
environment (1th law of epidemiology).
• Localization of contagium can be in the organism of man or animal: on to the
mucous membrane of intestine, mucous membrane of respiratory tracts, in blood,
on a skin and external mucous membranes (4th law of epidemiology).
• Mechanism of transmission of the infectious agent: fecal-oral, air-drop, by
blood, contact.
• Specific localization of causative agent of infectious diseases in an organism and
proper by it mechanism of transmission served a base for classification of infectious
diseases: intestinal, bloody, respiratory tracts, external covers (3th law of
epidemiology).
• Constituents of epidemic process:
1. source of contagium;
2. mechanism of transmission;
3. receptivity of population (4th law of epidemiology).
3.2. Students are to be able:
• To collect epidemiology anamnesis for infectious patients.
• At intestinal infection to expose the possible source of contagium and factors
of transmission: water, food products, hands and articles of environment, flies.
• To organize the leadthrough of deratization in the foci of zoonotic infection.
• At the infections of external covers to expose the source of contagium and
isolation of him from a healthy collective.
3.3. Students are to acquire the following skills:
• By the method of collection of epidemiology anamnesis: whether the sick did not
communicate with infectious patients, or not patients in family, at home, at work,
among those, that used a that meal, whether was not in touch with by patients by
animals, presence of wound, operations, blood transfusion and other damages of skin,
about the bites of home or wild animals, insects and other
• By the method of inspection of epidemic focus: exposure of source of contagium,
mechanism of infection and factors of transmission (water, food products, especially
milk, articles of the home use, rodents), looking after pin and early exposure of the
repeated cases of disease.
4. Advices to the student:
• During the leadthrough of inspection of epidemic focus and at collection of
epidemiology anamnesis at patient, to remember that every patient is the source
of contagium, and that is why it is needed to following to the rules of the personal
hygiene.
• At questioning of patient and his family members to set questions concrete,
which would not humiliate dignity of man, following to the rules of medical ethics.
• Able critically to estimate the achievements and failings at the inspection of
epidemiology focus.
Infectious diseases are classed according to their source as anthroponoses (the source of
infection is man), zoonoses (the source of infection is animal), and anthropozoonoses
(both man and animal can be the source of infection).
An infected macroorganism (man or animal), being the sole source of infection, can
have either clinically manifest or asymptomatic form of the disease.
A diseased person is the primary source from which the infection spreads. A patient is
the most dangerous source of infection because he or she releases a great quantity of the
pathogenic microorganisms.
The danger of infection spreading from the patient depends on the period of the disease.
During the incubation period the role of the patient is not great because the pathogenic
microorganism resides inside tissues and is seldom released from the infected organism.
The pathogenic agents are released into environment during the late incubation period
only in measles, cholera, dysentery, and some other diseases. The greatest quantity of
microbes are released during the advanced stage of the disease which is associated with
some clinical manifestations of the disease such as frequent stools (dysentery), frequent
stools and vomiting cholera), sneezing and cough (airway infections). The danger of
infection spreading during the early period of the disease depends on pathogenesis of a
particular infectious disease. For example, in typhoid fever or paratyphoid A and B, the
patients are not dangerous to the surrounding people during the first week of the disease,
while in respiratory infections, the patient is a danger to the surrounding people from the
moment when the clinical symptoms of the disease become apparent.
Severity of the disease is of great epidemiologic importance for determining "the source
of infection". If the disease is severe, the patient remains in bed and can only infect his
relatives. But it is difficult to diagnose the disease if it runs a mild course; besides, the
patient often does not attend for medical aid and continues performing his routine duties
(at the office, school, and the like) thus actively promoting the spread of infection.
Carrier of infection is another source of morbidity. According to modern views, carrier
state is an infectious process that runs an asymptomatic course. But those who sustained
an infectious disease, tularaemia, plague, leptospirosis, rickettsiosis, encephalitis,
leishmaniasis and some other diseases.
Main and secondary sources of infection are distinguished in zoonosis. The main source
are animals which are a harbour of pathogenic microorganisms and they create natural
nidi of tularaemia, plague, and other diseases. Secondary sources of infection become
involved periodically in epizootic.
Humans can be infected by wild animals when hunting, during stay in wild environment
contaminated with excrements, when drinking water or eating food that may be
contaminated with excrements of wild animals. Birds can also be transmitters of
infection (ornitosis, salmonellosis, etc.).
Mechanism of transmission. For the epidemic to break out it is not sufficient to have a
source of infection alone. The causative agent can survive only if it is transmitted from
one host to another, because any given macroorganism destroys the pathogenic
microorganisms by specific antibodies that are formed in it in response to the ingress of
these microorganisms. Death of an individual host terminates the life of the parasitizing
microorganisms. The only exception are spore-forming microbes (causative agents of
anthrax, tetanus, botulism).
The combination of routes by which the pathogenic microorganisms are transmitted
from an infected macroorganism to a healthy one is called the mechanism of infection
transmission.
Four mechanisms of infection transmission are distinguished according to the primary
localization of pathogenic agents in macroorganisms: (1) faecal-oral (intestinal
localization); (2) air-borne (airways localization); (3) transmissive (localization in the
blood circulating system); (4) contact (transmission of infection through direct contact
with another person or environmental objects).
Three phases are distinguished in the transmission of infection from one macroorganism
to another: (1) excretion from an infected macroorganism; (2) presence in the
environment; (3) ingress into a healthy macroorganism.
The method by which microbes are excreted from an infected macroorganism (the first
phase) depends on the locus of infection in the infected individual or a carrier. If
pathogenic microorganisms reside on respiratory mucosa (influenza, measles, pertussis)
they can be released from the patient only with expired air or with droplets of
nasopharyngeal mucus. If the infection is localized in the intestine, the pathogenic
microorganisms can be excreted with faeces (dysentery). The pathogenic organisms in
the blood infect blood-sucking arthropods.
5. Control questions:
1. Epidemiology role of sick man in different periods of illness.
2. Name infectious diseases, at which the source of infection are home and wild animals,
rodents, birds.
3. Name localization of contagium in the organism of sick man, bacillicarrier and
sick animal.
4. Mechanism of transmission of infectious agent from an organism, stay of him in an
environment and penetration of him in a new organism.
5. Describe the mechanism of infection at infectious diseases,
localization of
contagium, classification of infectious diseases.
5. What is epidemic process?
6. Name the laws of epidemiology, formulated by Gromashevsky.
7.What does value for a doctor to have collection of epidemiology anamnesis?
6. Literature:
6.1. Basic:
1. Lecture
2.Epidemiology and Fundamentals of Infectious Diseases. M.L. Volovskaya. Mir
Publisher. Moscow.