From Big Medical Encyclopedia

MECHANISM OF TRANSMISSION OF INFECTION (synonym mechanism of transfer of causative agents of infectious diseases) — process of transfer of the activator from the infected organism to healthy.

One researchers counted up to the middle of 19 century that spread of infectious diseases happens by transfer of the infectious beginning («contagion») from the patient with a healthy way of contact (this view in 16 century received the name of the kontagionistsky doctrine). Others recognized existence of a special external factor of transmission of infection — «miasma».

After opening of causative agents of infectious diseases at the end of 19 century the kontagionistsky doctrine became dominating. However supporters of this doctrine were not able to use mikrobiol, opening for comprehensive study of the mechanism of transfer of causative agents of infectious diseases. Even the assumption of the Russian doctors of G. N. Minkh (1874) and Island O. Mochutkovsky (1876) relying on experience of autoinfection that causative agents of sypny and returnable typhus under natural conditions can be transferred only by blood-sicking insects was rejected more than 30 years as contradicting kontagionistsky dogma about a way of transfer of activators.

I. I. Mechnikov, proceeding from obshchebiol, understanding of the nature of relationship between activators and the higher organism in the course of an infection, defined an infectious disease as a special case parasitism (see). On the one hand, recognition of the parasitic nature infectious, allows to consider diseases that the only natural source of its activators is the infected organism, on the other hand, a view of an organism biol, as on the habitat of a parasite assumes the owner that the parasite can exist in the nature only being adapted (adapted) for dwelling in an organism of the owner.

However only one fitness of a parasite to stay in an organism of the feral host is not enough that this parasitic look remained in the nature. With death of the owner also the parasites who are in his body perish. Ectoparasites (i.e. the forms which are freely living in the environment using the biol, owners only for food on their body) owing to mobility can easily pass in most cases from one individual to another, but slow-moving forms (e.g., louses of the person and many other types of zooparasites and plants) with death of the owner perish if they do not manage to move to the representative of the same look. Thus, parasitism is inconceivable without systematic change by a parasite of the individual owner.

In different cases transition of activators to another comes from one organism in essentially various ways since each parasitic look is adapted to certain, only to it to the inherent mechanism of transfer.

Change by a parasite of the owner shall be carried out in time, not exceeding the natural duration of process of the parasitizing which is limited to natural life expectancy of the owner, and also the parasite. If the infection is followed by bystry development immunity (see), the further existence of the activator excluding an opportunity in an organism of the owner, duration of a continuous parasitic phase is very short (sometimes not exceeding several days). Such forms of parasitism exist in the form of quickly following one behind another of infections that is possible only at especially actively operating mechanism of transfer.

So, e.g., at measles the infectious stage proceeds 6 — 8 days therefore infection of surrounding persons occurs owing to especially active (easily implementable) drop mechanism of transfer. The mosquito only in warm season can provide spread of malaria, but it is enough for preservation of the activator owing to a long current inf. process. At sypny and returnable typhus the organism is quickly exempted from activators, however these diseases in areas with a temperate climate can remain all the year round as their carriers are the louses parasitizing on the person.

Adaptedness of activators inf. diseases to parasitizing in an organism of owners it is expressed in limited, and it is frequent also in specific fitness to dwelling only in certain bodies or fabrics. The itch mite parasitizes in the thickness of skin, many helminths — in a gleam of intestines, the causative agent of trachoma — on a conjunctiva of an eye, causative agents of malaria, sypny and returnable typhus — in blood etc. In an organism of the owner the mechanism of transfer is defined by localization of the activator, by means of to-rogo the activator passes into other organism. Thus, localization of the activator in an organism and the mechanism of transfer are interdependent and specific to each inf. diseases.

There are four mechanisms of transmission of infection, each of to-rykh corresponds to one of four localizations. At localization of activators in intestines (intestinal infections) their transition to other organism is possible only after removal from intestines and the subsequent swallowing by other individual — the fecal and oral mechanism of transfer. Drop (airborne, air and dust) the mechanism of transfer is specific to respiratory infections. Blood infections, i.e. diseases with localization of activators in a blood flow, are transmitted by blood-sicking arthropods (the transmissible mechanism of transfer), specificity to-rykh is so expressed that almost each disease has special carrier (see). Causative agents of infections of outside covers according to localization (skin, hair, outside mucous membranes, a wound surface, etc.) are transferred by various environmental factors (e.g., objects of use, hurting tools, sometimes insects, etc.). Diseases which causative agents are transferred at direct contact, napr, venereal diseases, rage, a sodoka also enter into this group. The principle of interdependence of mechanisms of transfer and localization of the activator is the basis for the most reasonable classification inf. diseases.

Mechanisms of transfer of causative agents of diseases of animals are essentially similar to mechanisms of transfer of causative agents of diseases of the person. However the drop mechanism of transfer is not enough svoystven an animal. The diseases transmitted by arthropods (blood infections) and partly intestinal infections have very wide spread occurance, especially among nek-ry animal species, owing to ecological features of their way of life.

The mechanism of transfer of causative agents of infectious diseases causes also degree of their stability out of an organism. The activators of respiratory infections which are transferred, as a rule, in a short space of time, and also causative agents of blood infections are less steady, to-rye in a phase of transfer in an organism of live carriers appear on position of parasites. Causative agents of intestinal infections, transfer to-rykh it cannot be carried out to short terms (on it hours, and sometimes and are required several days), are much steadier in the conditions of the environment. Inhabitants of intestines of vegetarians — the most firm representatives of pathogenic microbes — spore-forming bacilli of a malignant anthrax, botulism, tetanus and a mephitic gangrene treat this group. Process of historical formation of a parasitic look, so, and the disease caused by it is made with the participation of the corresponding mechanism of transfer. Therefore the new form of a disease arises, as a rule, with the participation of other mechanism of transfer. So, plague, the first cases a cut develop at the person as a result of infection from rodents through arthropod, proceeds always in a bubonic form. In the form of epidemics of pulmonary plague it extends after the introduction in operation of the new, drop mechanism of transfer. Smallpox of the person probably arose from a vaccinia several millennia ago, edges took root to the person at contact of the injured skin with a pustule of a sick animal. With the introduction in operation of the new drop mechanism of transfer the disease of the person new for those times — natural smallpox developed.

Current nek-ry inf. diseases is followed by very intensive movement of the activator in an organism of the owner. So, at rage the virus gets to an organism through a wound from a sting, then on nerve pathways gets into sialadens from where together with saliva — in an oral cavity; thus the possibility of transfer of the activator is provided. At bubonic plague and a tularemia activators get into an organism through injuries of skin (a sting of a carrier), further extend on limf, to system, causing formation of a regional bubo; after that bacteremia develops, without cut further transfer of activators arthropods is impossible.

The mechanism of transfer begins with removal (allocation) of a parasite from an organism biol, the owner. Even at the most superficial arrangement of the activator, napr, at itch or fungal diseases of skin and a hair, it is in more thickly fabric (skin, etc.) and therefore for transfer to other organism it has to be brought to a surface of the infected organism or to the environment. Removal of the activator from an organism happens at various physiological (defecation, exhaled) or pathological (exhaustion of blood an ectoparasite, release of pus, etc.) acts. Further transfer of the activator to other organism is made by means of various objects of the environment called by factors of transfer. The factor of transfer, with the help to-rogo carries out introduction (implementation, penetration) of the activator to a new organism, the mechanism of transfer usually comes to the end.

The simplest on the structure are the drop mechanism of transfer and transfer of the activator blood-sicking carriers. In the first case a factor of transfer is air, in the second — blood-sicking arthropods. Each disease (sometimes group of diseases) is transmitted by a special type of a carrier, only sometimes one disease extends several types of carriers. Much more difficult mechanism of transfer of intestinal infections. It is carried out with participation of various factors. In one cases one factor (e.g., water, milk, foodstuff, etc.), and in others — a number of the factors capable to carry out all way of fecal and oral transfer of the activator can provide transfer. Therefore at the specified diseases consecutive transfer of the activator from one factor to another is observed more often (e.g., excrements — a fly or hands — food — a mouth). Causative agents of various intestinal infections are transferred by different factors unequally. The fecal and oral mechanism of transfer in some cases is disguised (e.g., at the infectious diseases which are transmitted through intermediate owners by transfer of the activator by the contaminated hands, flies, etc.). Also various factors of transfer participate in transfer of causative agents of infections of outside covers.

The doctrine allows to resolve of mechanisms of transfer of causative agents of infectious diseases fruitfully many issues epidemiol, theories and practicians.

See also Invasion , Infectious diseases , Infection .

Bibliography: The mechanism of transmission of infection, under the editorship of L. V. Gromashevsky, Kiev, 1962.

L. V. Gromashevsky.