Mechanisms of transmission and modes of transmission

The emergence of infectious diseases

The main characteristic of bacterial and viral infections (infectious diseases) are the mechanisms and routes of transmission of infection from individual to individual. This refers to the mechanism of transmission of infection from person to person or from animal to human.

The possibility of infectious disease transmission caused by spreading of the pathogen. The disease can be transmitted by various microorganisms. Usually, they are represented by bacteria and viruses as well as protozoa or fungi. Microorganism to cause disease, must be characterized by certain properties. For example, stability in the environment, which allows it to be transferred, the ability to penetrate skin or mucous membranes in the body or the ability to withstand the immune system.

The spread of infection routes of transmission becomes possible when there is the following chain:

• source of infection,
• route of transmission,
• inspector infection.

Source of infection

Often it is a sick contagious people, but the ability to transmit viral and bacterial infections may be preceded by symptoms of disease (e.g., inflammatory viral hepatitis from 5 to 14 days) or, conversely, to continue even after the disappearance of symptoms. Less often the infectiousness persists for a long time or even permanently, infections are transmitted without the man had severe health problems. In this case he is a carrier.

The infectiousness is the ability of the individual to be a source of infection to infect others.

Do not forget that infectious diseases can occur even without symptoms.

Asymptomatic carrier represents the most dangerous source of infection because he is not aware of their infectiousness, and not taking steps to prevent transmission of infectious diseases.

The source of transmission of the pathogen is not necessarily the person. There is not a single infectious disease, transmitted to humans from animals – called zoonoses.

Route of transmission*

The mechanism and ways of transmission are divided into 3 ways:

Direct transfer method – is happening in the environment in which is present the source and the recipient (e.g., airborne transmission through sneezing characteristic of the transmission of influenza, the transmission of infectious disease through dirty hands is the main for hepatitis A).

Indirect methods of transmission of the infection occurs indirectly through objects, water, food, etc. – for example, household contact transmission of infection.

Mechanisms of transmission medium we are talking about a living organism which is your body (flies), or (mosquitoes, ticks) carries the pathogen from the source to the receiver.

*Main modes of transmission of infection and mechanisms are described in more detail below.

Receptive inspector infection

The susceptibility of the individual (in our case person), is the antithesis of the concept of resistance or immunity. We are talking about a person who is not resistant to a particular pathogen, and therefore may fall ill.

Epidemic it is a condition in which both (in the same place at about the same time) hurts more people.

Conversely, if for a long time in a certain place in a certain region there is diseases that do not occur in other places, we are talking about the endemic. This is characteristic of diseases with natural foci already mentioned tick-borne encephalitis or an exotic yellow fever.

Some diseases can be spread so widely that affect the whole world (all mankind). In this case, it refers to pandemics (AIDS, pandemic influenza).

The symptoms of an infectious disease usually do not appear immediately after infection, but only after a period of incubation (1, 5, 14 and more days). This is a very important information, from which conclusions can be drawn when and where a person has been infected, also helps to determine the range of other potentially sick people, if you know the infectiousness during the incubation period of the disease.

Means (mechanism) that are transmitted infection is the way that the causative agent of the disease (etiological agent, EA) is ingested by a susceptible person. He is somehow excluded from your source, and must have resistance to external conditions andmechanisms for entrance into the susceptible organism. There is, as EA passed on a specific route, and EA with multiple possible transfer modes.

Direct transmission

Some pathogens are transmitted by direct transmission during close contact with a susceptible individual is the source of disease.

The contact mechanism of transmission through touching, kissing, sexual intercourse, bites, scratches. For example, infectious mononucleosis, AIDS, rabies.

Airborne path – EA is transmitted by droplets from the respiratory source in the respiratory tract of susceptible person (also – aerosol mechanism of transmission). So transmitted of acute respiratory viral diseases: influenza, parainfluenza, and others.

Perinatal transmission (vertical path) infection in susceptible individuals during the passage through the birth canal. For example, Streptococcus group B, E. coli, gonorrhea.

Indirect (indirect) transfer

The proliferation of indirect contact the pathogen is ingested by a susceptible person via a contaminated object (usually the object of daily use).

The spread of injection – susceptible pathogen enters the body through contaminated instruments and devices (surgery, invasive methods of examination), or contained in one or other biological products (blood products, blood, blood plasma, transplants). For example, hepatitis b and C, cytomegalovirus, HIV, nosocomial illness.

Air/dust transfer path the infected droplets from the respiratory tract, in addition to direct infection, contaminated items and create contaminated dust remaining in the air for various periods, therefore, are able to propagate relatively far from the source. For example, respiratory infections (acute respiratory diseases, whooping cough, diphtheria, tuberculosis, etc.), skin infection (Staphylococcus aureus), zoonoses (tularemia, pneumonic plague, anthrax).

Alimentary route of infection after consumption of contaminated products EA enters the body of the susceptible person via the digestive tract. Alimentary route of infection include:

1. Water transfer path from the water when drinking, washing, bathing, washing dishes or preparing cold dishes. When water pollution occur explosive epidemic depending on the number of people consuming that water during the presence of the pathogen (it depends on the characteristics of water). By water spreading, for example, typhoid, paratyphoid, cholera, polio, leptospirosis.
2. Nutrition – the consumption of contaminated food usually causes a rapid rise of the epidemic. EA often multiplies and produces toxins. The source of infection may be food of animal origin (contaminated mainly from animal or during secondary processing) as well as vegetables and fruits.
3. Milk can be contaminated, mainly zoonoses (bovine tuberculosis, fever Ku, tick encephalitis, brucellosis).
4. Eggs can be a source of Salmonella, which can be destroyed by boiling for 8-10 min.
5. Meat products may contain Salmonella, Trichinella, or Toxoplasma, Clostridium botulinum.

Vector-borne transmission – occurs through the media, in particular, different types of arthropods. Vector-borne method includes the following paths:

1. Biological media are playing an active role in the life of the pathogen (reproduction, part of the cycle), to the disease, which carry blood-sucking arthropods are, in particular, malaria, trypanosomiasis, leishmaniasis, tularemia, rickettsiosis, plague, Q-fever.
2. Mechanical carrier contaminated with their excrement, wipes on foods (Salmonella, Shigella, enteroviruses).

Placental transfer from mother to fetus, e.g. rubella, HIV, cytomegalovirus, Toxoplasma gondii, Treponema pallidum.

Transfer from the soil – for example, tetanus, fungal infections (where the source is a person or animal).

Natural factor:

• climate, geographical position, altitude, amount of precipitation, humidity – these factors affect the survival of pathogens, mostly of natural foci of the disease.
• climatic conditions are related to seasonal occurrence of infections.

  

Socio-economic factors:

• hygiene and health awareness among the population regarding health, which is closely related to the actual level of personal hygiene.
• catering, industrial food production.