The concept of epidemic process

The following three obligatory factors of an epidemic process

The epidemic process in period of science-technical progress

Improvement of material and cultural conditions

Urbanisation

Technical discharge into environment

Severe ecological effects

Increasing the evolution the infection diseases

Microorganisms parasitize on host

Microorganisms causing infection disease parasitize on host and due to continuous reproduction of new generations which chance their properties in accordance with evolution of the environment conditions.

Living inside its host, the pathogenic microorganism persist for a definite period of time.

Then the pathogenic microorganism can survive by changing its residence

It is moving to another host via a corresponding transmission mechanism

This continues chain of successive transmission of infection (patient carrier)

Manifested by symptomatic or asymptomatic forms of the disease is called an epidemic process.

Microorganisms parasitize on host

The source of infection microorganism is an object which is the site of natural habitation multiplication of the pathogenic microorganisms and in which the microorganisms are accumulated.

Since pathogenic microorganisms are parasitized only a living microorganism can be such an object

An epidemic focus is the residence of infection including the surrounding territory within the boundaries of which the source can, under given condition, transmit a given disease through the agency of the pathogenic microorganisms

The focus of infection remains active until the pathogenic microorganisms are completely eradicated plus the maximal incubation period in persons that were in contact with the source of infection

Some features of epidemic process

The intensity of an epidemic process can also different. Three stages of quantities changes are usually distinguished in the epidemic course:

Sporadic incidence, epidemic and pandemic.

Sporadic incidence is a normal (minimal morbidity characteristic of a given infection (Country or region). Many Infection diseases occur as a single cases.

Some features of epidemic process

Group incidence of Infection diseases is a community is assessed (опр.разм) in every day medical practice as an epidemic outburst.

An epidemic is characterized by morbidity that 30-10 times exceeds given disease in a given locality – development of multiple epidemic foci.

Pandemic - widespread epidemic throughout large territories.

Endemic – an epidemic qualitatively. An epidemic disease constantly occurs among population of a given area. Long existence of any infection diseases in a given country can be due to presence of some natural factors.

Exotic disease – can only be brought from a foreign country.

The following three obligatory factors of an epidemic process

1. the source of pathogenic microorganisms

2. The mechanism of their transmission

3. macroorganism susceptible to infection

Infection diseases are classed according to their source as antroponoses (The source is man), and zoonoses (the source is

animal) and antropozoonoses (both man and animal) can be the source of infection.

1. the source of pathogenic microorganisms 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 release a great quantity of the pathogenic microorganisms.

Spreading of infection

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.

The pathogenic microorganisms are released into environment during the late incubation period only in measles, cholera, dysentery and some others.

The greatest quantity of microbes are released during the advanced stage of the disease which is assoсiated with some clinical manifestation such as frequent stools, vomiting, sneezing and cough

In Typhoid fever, paratyphoid A and B the patient is a danger to the surround people from the moment when the clinical symptoms become apparent.

If the disease is severe, the patient remains in bed and can only infect his relatives.

If the disease has mild course and the patient does not attend for medical aid and continues performing his routing duties (at the office, school) thus actively promoting the spread of infection.

Carriers of infection

Carriers of infection – is of another source of morbidity

Carrier state is an infection process that run an asymptomatic course. There are can healthy persons.

Carriers of infection release pathogenic microorganisms into environment the in a smaller quantity before than patient with clinically manifest diseases. But they are danger to community too since they actively associated with healthy people and spread the infection

Carrier state can persistent in person who sustained microbes in patient after their clinical recovery.

Acute carrier state can last from several days to several weeks

Chronic carriers in 3-5% of cases carrier state can persist for years or even for the rest of the life, which can be explained by defective immune system

Various concurrent diseases can promote persistence of carrier state: the bile duct diseases, the urinary diseases, the nasopharynx and others/

Healthy Carrier

Persons with asymptomatic infection

Transitory carrier state is characterized by rapid withdrowal of the pathogenic microorganisms from a subject, foci where these microorganism might multiply are absent.

From 30 to 100 carriers can be detected among people surrounding one patient with meningococcal infection or poliomyelitis.

Healthy Carrier are less dangerous for surrounding people because the pathogenic microorganisms are not usually detected in them during subsequent tests.

If a carrier of typhoid fever etc. is employed at a food cafering establishment or a children institution he is specially dangerous for the surrounding people.

Infected animal are the source of infection diseases that are common for man and animal.

Domestic animals and rodents are dangerous in the epidemiologic aspect.

The degree of their danger as source of infection depends on the relations between people and animals, on the socioeconomic and living conditions.

People can get infection during management of diseased animals, cooking and eating their meat (antrax, brucelosis, Q-fever)

2. The mechanism of infection transmission

The causative agent can survive only if its transmitted from one of host to another, because any given microorganisms destroys the pathogenic microorganisms by specific antibodies than are formed in it response to the ingress of these microorganisms.

Death of an individual host terminates the life of the parasitizing microorganisms.

The only exception are sporeforming microbes (Antrax, Tetanus, Botulism)

4 mechanisms of infection transmission are distinguished according to the primary localization of pathogenic microorganisms in macroorganisms:

1. 1. Faecal-oral ( food and water-born - intestinal localization)

2. 2. Air-born (dust-born - airways localization)

3. 3. Transmission (by arthropods - localization in the blood circulation system)

4. 4. Contact (transmission infection through direct contact with another person (through the placenta, by through skin manipulations) or environment objects

Three phases are distinguished in the transmission

Three phases are distinguished in the transmission of infection from one microorganisms to another:

1. Excretion from an infected macroorganism

2. Presence in the environment

3. Ingress into a healthy macroorganism

The methods of excretion from an infected macroorganism (depends on the locus of infection):

1. Residence – respiratory mucosa – influenza, measles, pertussis –they can be released with expired air or with droples of nasopharyngeal mucus.

2. If the infection is localized in the intestine - pathogenic microorganisms can be excreted with faeces

3. The pathogenic organisms in the blood infect blood sucking arthropodos

Main factors are involved in transmission of infection:

Air, water, foods, utensils, arthropods (living agents)

Dust infection is feacable only with those microorganisms that persist in the environment and can survive in the absence of water. Tuberculosis can survive in dust for weeks, agent causing Smallpox, Q-fever , Antrax, Tularemia can be transmitted with dust

Water is another important medium by which infection can be transmitted

Spontaneous purification of water depends on ambient temperature, chemical composition, aeration degree, exposure to sun rise, the property of microorganisms and other factors.

1. By Drinking contaminated Water

2. Using Water for domestic purposes, bathing

3. If potable water gets contaminated with feaces can became epidemic with rapid spreading. Sewage water-born infection may develop.

The pathogenic organisms excreted from intestine get on soil, linen, household objects and water, while those liberated from the always are born in air.

Transmission factors – the environment objects that transmit the pathogenic agents

Transplacental transmission of infection

Transmission of infection with food

The pathogenic organisms can multiply in food staffs

Food can be infected by contact with infected person or a carrier, by insects of rodents.

Food can be infected during transportation, storage and cooking.

Epidemically important: uncooked natural food, thermally processed food, hot or cold foods.

Intestinal diseases are often transmitted through vegetables, fruits

Soil is contaminated by excrements of human or animals. Various wastes, dead human and animals.

Contaminated of soil is an important epidemical factor because soil is the habitate and site of multiplication of flies, rodents, etc..

Eggs of some helmints are incubated in soil (ascarides)

The pathogenic organisms of soil can pass into water, vegetable are grown. Tetanus, gangrene and anthrax are transmitted through soil.

It is especially dangerous to use faecal sewage to fertilize soil where cucumbers, tomatoes and other vegetables are grown.

Transmissin of infection

Living objects transmitted infection can be divided in two groups

Specific and non-specific (mechanical)

Specific Carriers are lice, body louse (вши), flears (блохи), mosquitoes, ticks transmit infection by sucking blood (inoculation) of contaminating human skin with their excrements.

Inside specific transmitters of infection the pathogenic organisms multiply, accumulate to the surrounding environment

A louse sucks blood of a typhoid fever patient and excretes the pathogenic organisms with faeces only in 4-5 days.

Non-specific carrier transmit the pathogenic organisms by purely mechanical method.

The form of realization of the transmission mechanism, Including the combination of factors involved in spreading of a corresponding diseases are known as the transmission routes of the infective agent. Flies carry microbes of dysentery, typhoid fever, Viral hepatitis. Gadflies transmit microbes of anthrax and tularemia by their stinging apparatus.

3. macroorganism susceptible to infection

Susceptibility an immunity

Susceptibility of an individual b of a community are distinguished

1. Susceptibility to a disease is a biological property of tissues of a human or an animal, characterized by optimum condition for multiplication of pathogenic microorganisms

Susceptibility is a specific property, that is transmitted by hereditary trait.

Many infections can affect only a certain species of animals.

Animals are protected by hereditary (species) immunity to

human infections