Infectious and epidemic processes are continuous interactions at the population and species levels. The pathogen-parasite pathogen and the human body, which are heterogeneous in evolutionary-conjugate signs of relations to each other, take part in it. The infectious and epidemic process is manifested by asymptomatic and manifest forms. They are distributed among the population at risk of infection or disease, time and territory.
Historical information
Such a concept as the "epidemic process" began to be used from the beginning of the 19th century. One of the earliest ideas about this phenomenon was formulated by Ozanam in 1835. Further, a number of scientists began to develop the idea. The term "epidemic process" itself was introduced by Gromashevsky in 1941. Next Belyakov clarified the content of the definition. Later, he also put forward a provision on self-regulation in the epidemic process.
Sections
Of all three. The following sections of the epidemic process are distinguished:
- Conditions and reason.
- The mechanism of development of the epidemic process.
- Manifestations.
The first section reveals the essence of the process. It reflects the internal causes of the formation and the conditions under which it occurs. Systematization of the information in this section makes it possible in general terms to answer the question of what are the fundamentals of epidemiology. In clinical medicine - in the field where pathological conditions are studied at the organism level - a similar section is called "etiology". The second link reflects the course of the formation of the phenomenon. This section answers the question of how it begins. In clinical medicine, a similar area is called "pathogenesis".
The third section reveals the manifestations that accompany the epidemic process; systematized information reflecting the signs of the phenomenon. In clinical medicine, a similar section is called semiotics. Next, consider the categories in more detail.
Conditions and reasons
The interaction of the pathogen and the human body proceeds in space and time continuously. There are various factors in the epidemic process. These include, for example, biological. These factors of the epidemic process form the reasons why pathological interaction begins. There is also a second category. Natural and social factors provide regulation of the conditions under which the process takes place. Interaction is possible only if there is a reason and conditions.
Biological Drivers
This factor is a parasitic system in which a certain interaction takes place. Its sides are characterized by some distinctive features. So, parasites show pathogenicity, the host - susceptibility.
Social forces
These factors include a set of social conditions that contribute to or impede the course of the epidemic process. Among them are:
- Sanitary settlements.
- The activity of residents.
- Social development.
Population activity
It indirectly and directly affects the intensity of the course of the epidemic process. The stronger the social activity, the more pronounced the interaction of parasites and the body. Historically, the peak occurred in the revolutionary and military periods. The activity of the population can manifest itself at the level of a whole society or a specific family.
Sanitary improvement
Its level directly affects the intensity with which the epidemic process proceeds. The concept of sanitary improvement includes the frequency of collection and disposal of food and solid waste. It also includes the status of water disposal systems and water supply.
Social progress
The level of production and social development has an indirect effect on the conditions in which the epidemic process proceeds. Moreover, it can have both positive and negative effects. Examples of the former include improving nutrition and the quality of life of the population and, as a result, increasing the immunity of residents, as well as changes in the culture of behavior, hygienic education, and technological progress. A negative effect is manifested in an increase in the number of drug addicts and alcoholics, changes in sexual culture (the spread of viral hepatitis, HIV infection), environmental degradation, and weakening of the body's defenses.
Natural conditions
These factors include abiotic and biotic components. The latter are elements of wildlife. As an example of the regulatory effect of biotic components, we can cite a change in the intensity of the course of the epidemic process against the background of a different number of rodents during infections of the natural focal type. In transmissible zoonoses, migration and the number of arthropods have a regulatory effect on the severity of the phenomenon. Abiotic components include landscape geographical conditions and climate. For example, when approaching the equator, the diversity of nosological forms of pathologies increases.
Epidemiology of Infectious Diseases
The first law of Gromashevsky determines the course of interaction of the parasite and the human body according to the triad. So, there are the following links in the epidemic process:
- The source of the pathogen.
- Transmission mechanism.
- Susceptible organism.
The last links of the epidemic process have their own classification.
Pathogen source
It is an infected human, animal or plant organism. From it, infection of susceptible people can occur. A complex of sources forms a reservoir. For anthroponoses, the pathogen is a person who has an asymptomatic or manifest form of pathology, for zoonoses - animals (wild, synanthropic or domestic). And for sapronoses, these will be abiotic elements of the environment.
Pathogen transmission
The epidemiology of the disease involves a certain way to move parasites into a healthy body from the affected. According to the second law of Gromashevsky, the transmission of the pathogen occurs depending on its main localization. It can be blood, skin flakes, mucus, feces. The sequence and set of transmission factors by which the mechanism itself is implemented acts as a path of movement.
Methods of penetration of parasites
1. Aerosol route. It includes the following methods:
- airborne droplets (as ARVI is transmitted, meningococcal infection);
- airborne dust (pathogens of tuberculosis, scarlet fever pass along this path).
2. Fecal-oral method. It includes such paths as:
- contact household;
- water;
- food.
3. Contact way. It includes direct and indirect transmission methods.
4. The transmission path. This category includes such methods as:
- artificial (associated with medical manipulations: associated with surgery, injection, transplant, transfusion, due to diagnostic procedures);
- natural (in case of contamination, the pathogen is excreted with excrement of the carrier, in inoculation, it is introduced with saliva).
Additional classification
There are several transmission factors. In particular, final, intermediate and initial are distinguished. Transmission factors are conditionally also divided into additional and basic. The phases of the movement of the parasite include:
- Excretion from the carrier.
- Stay in the environment.
- Penetration into a pathological organism.
Susceptibility
It represents the ability of the host to become infected with pathologies provoked by parasites. This is manifested in the form of pathological and response protective specific (immune system) and non-specific (resistance) reactions. The following types of susceptibility are distinguished:
- Individual (pheno- and genotypic).
- Species.
Immunity acts as a specific response to the penetration of a foreign agent. Stability (resistance) is a complex of protective reactions of a non-specific type.
Description of the epidemic process
The interaction of the parasite and humans is manifested in the form of infection of the latter. Subsequently, the susceptible host may become ill or become a carrier of the pathogen. At the population-species level, manifestations are presented in the form of sporadic incidence, the presence of an epidemic (epiphytotic, epizootic) or natural outbreak, outbreak, epidemic, or pandemic.
Intensity
Sporadic distribution is peculiar to a certain team, season, territory. Epidemic morbidity is a temporary increase in the level of infection. Subsequent classification in this case is carried out in accordance with the time and territorial parameters. An epidemic outbreak is a short-term increase in the incidence of a specific team. It continues for one or two incubation periods. An epidemic is an increase in the incidence rate to an area or region. As a rule, it covers one season a year. A pandemic characterizes the level of infection that lasts for several years or decades. Pathology is spreading in this case to continents.
Uneven manifestation
It may relate to territories, time, and population groups. In the first case, the classification is based on the distribution zone of the reservoir. In particular, they distinguish:
- Global range. In this case, the interaction is between the person and the reservoir of anthroponoses.
- The regional area is natural focal zoonoses.
Time unevenness:
- Cycling.
- Seasonality
- Irregularity of infection rises.
Unevenness by population groups is classified according to epidemiologically significant and formal characteristics. The latter include groups:
- Age.
- Professional.
- Depending on the place of residence (urban or rural area).
- Unorganized and organized.
Distribution in accordance with epidemiologically significant signs is carried out on the basis of the logical conclusions of specialists. It may include various factors, such as, for example, vaccination.
Social and environmental concept
It is based on the positions of a systematic approach. Through this tool, the concept reveals the hierarchical structure of the process. It also reveals the functional interaction between the phenomena characteristic of each level. In accordance with the concept, the epidemic process is presented in the form of a complex multi-stage system. It ensures the existence, reproduction and spread of parasitic forms of microorganisms among people. In the structure, 2 levels were distinguished: eco-and socio-ecosystem.
Parasitic system
It is discrete. This means that it consists of individual individuals in the host population. In the body, the infectious process progresses, expressed in the form of carriage or expressed clinically pathologies. When one or another transmission path is realized, the interaction of the pathogen and the susceptible organism turns into an interpopulation one. In this regard, the parasitic system contains a hierarchy of many infectious processes. The concept of an epidemic process becomes abstract without understanding the meaning of the transmission mechanism.
Hierarchical structure
It is distinguished by a multi-level nature and includes several subordinate layers:
- Organized . In this case, we are talking directly about the infectious process. In it, interacting systems are presented in the form of an organismic subpopulation of the pathogen and organization of the biological balance of the macroorganism.
- Cellular At this level, there is a system consisting of a separate specimen of the parasite and the cells of the target organism.
- Fabric and organ. At this level, a local subpopulation of the parasite interacts with the specific organization of certain tissues and organs of the host.
- Subcellular (molecular). Here, the genetic apparatus interacts with the biological molecules of the parasites and the host.
The highest in the structure of the epidemic process is the socio-ecosystem level, into which the ecosystem is included as one of the internal subcategories. The second is presented in the form of a social organization of society. The reason for the appearance and further development of the epidemic process is precisely the interaction of these two subsystems. At the same time, phenomena in the eco-structure are regulated through a social unit.
Example
In February 2014, the Ebola epidemic began in Guinea (West Africa) . It continues to this day. At the same time, the Ebola epidemic went beyond the borders of the state and spread to other countries. The infection zone included, in particular, Sierra Leone, Liberia, USA, Senegal, Mali, Spain, Nigeria. This case is unique because the disease first began in West Africa. Doctors in countries where the pathology has spread have no experience in dealing with it. The situation is aggravated by the likelihood of panic among the population due to misinformation. Funds and personnel from various international and national organizations have been allocated to help the Guinean government. In particular, assistance was provided by: Center for Epidemiology of the USA, Russia, Rospotrebnadzor, European Commission. Assistance was also sent by the Economic Community of Western Europe. In Guinea, an epidemiology laboratory worked. Specialists collected and analyzed disease information. The Center for Epidemiology provided support to the population, isolated the infected from healthy residents. As WHO Director General Keiji Fukuda noted, the outbreak has become the strongest of all in practice.