The Emergence of Epidemic Process

The Emergence of Epidemic Process

For the infectious process, three main conditions are needed to develop the epidemic process:

1) the source of infection,

2) the mechanisms (routes) of the disease transmission,

3) susceptible population affected by the causative agent.

The origin of infection is the place of actual habitation of the causative agent, its propagation and removal into the environment.
Alive microorganisms are the major sources of infection (sick humans or animals and microbial carriers).
The deposition of infection protect the pathogen in the environment but usually, the infectious agent cannot propagate in the reservoir.
There is a huge complex of several mechanisms (or routes) of transmission of infectious diseases. These are:
1. faecal-oral route that involves alimentary (food-borne),
2. water-borne, contact (via fomites) and other possible routes;
3. air-borne route (e.g., air-droplet or dust disease transmission);
4. vector-borne route associated with different vectors – insects, arthropods, etc.
5. Connection route with the disease transmission by sexual intercourse or by direct contact;
6. Un-natural route based predominantly on disease transmission by medical manipulations (iatrogenic route);
7. vertical transmission (from mother to fetus).

The Emergence of Epidemic Process — TRANSMISSION OF INFECTIOUS DISEASES

Multiple auxiliary vehicles provide support to certain routes of transmission of infection. For instance, the faecal-oral route can be realized via, the dirty hands, absorbing pathogenic bacteria, or by flies, carrying infectious agents.
Various objects, surfaces or substances contaminated with microorganisms could carry the pathogens from one susceptible person to another.
The air-borne route is associated with air and dust flows, air conditioning state, etc.
According to the main localization of the causative agent, all infections are divided into
- intestinal (affecting the gastrointestinal tract with faecal-oral transmission).
- respiratory (of the respiratory tract); blood infections (with primary localization of pathogen in the blood due mainly to vector-borne disease transmission or by artificial route).
- infections of integument tissues (causative agents are localized on the skin or mucosal tissues), “vertical” infections with disease transmission from mother to fetus.
According to specific habitation of the causative agents, infectious diseases are classified as anthroponoses, zoonoses and prognoses.
If a pathogen infects only humans, the disease type is anthroponosis. The disease, caused to animals, is regarded as a zoonosis.
The causative agents of zoonoses can also affect humans resulting in zooanthroponoses.
And the last group comprises the number of diseases with the substantial role of the external environment in their spread (so-called prognoses).
For example, anthrax spores stay viable in the soil for several years before infecting.
This is true for most of the sporogenic bacteria. Water is the environment of vibrio cholera habitation, as well as for leptospirosis agent.
In general, disease distribution within some population varies strongly, depending on infectious agent nature and population susceptibility.
Infectious diseases may be sporadic (separate cases of the disease, registered in some area during a certain period of time).
Usually sporadic reflects an ordinary level of morbidity.
The great rise of incidence of a certain disease that affects the large territories is known as an epidemic (or epizootic in animals).
Disease outbreak is “a small epidemic” – restricted by time and area sharp raise of the disease, where individual disease cases are closely related.
And when the epidemic covers unusually large territories or spreads over many countries or even continents, it is called a pandemic.
A special form of infectious diseases spread is known as endemic.
Endemic is referred to as the disease retaining in some locality for a long period of time.
Sometimes it can be restricted by vector habitat, or by the geographical barriers. Nevertheless, the endemic is an effective threat of massive disease outbreak due to developed people communications – travelling, air flights, etc.

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