Epidemiology of plague

Plague is a typical zoonoses. Human infection occurs when the attack on him fleas, parasitizing on the sick animals. Further, in case of complications plague pneumonia, a disease can be transmitted from person to person by airborne droplets. The inclusion of human rights in the epidemiological chain is incidental, arising among people outbreaks always have their source plague epidemic.
To P. pestis susceptible to a wide range of mammals, but not all of them play an essential role in maintaining and spreading plague infection. Epizootologic significance of one kind or another is determined by susceptibility of the causative agent, livelihood systems, density and population numbers, and other
Despite the fact that in natural conditions there is infecting some domestic and wild ungulates, as the cases of infection from them (in particular, from the camels), any role in maintaining the epidemic, they do not play. More sensitive to plague some carnivores, insectivores and (shrews, hedgehogs, foxes, cats and other). However, they do not have independent significance in maintaining the epidemic.
The existence of natural foci of plague associated with rodents, high sensitivity which, combined with the large number and high population density, provides continuous circulation of the pathogen in the herd of animals.
The role of synanthropic rats and mice and parasitic fleas in the emergence of a plague among the people was established in the late 19th century.
For a long time believed that a reservoir of infection are synanthropic rats. D. K. Zabolotny expressed the idea that the plague may be endemic in areas where rats are missing. Proved natural focality (see) plague, D. K. Zabolotny initiated the development of epidemiology of this infection. It is now generally recognized that the disease synanthropic rodents and related human infections are the result of incursions from natural foci.
Rodents like the plague carriers are divided into primary and secondary (B. K. Fanuc). Participation in the epizootic process the first ensures the existence of natural foci. The second involved in the already ongoing on primary storage epizooty, but they can have an important, albeit temporary, epidemiological significance.
The main carriers are characterized by high and stable population, the wide and ongoing resettlement of large areas; their burrows deep that provides a constant temperature and humidity of air - factors conducive to the development of vector - fleas.
For minor temporary media typical of a changing population, focality of settlement, small depth of holes (Yu M Roll).
The main carriers of the plague on the territory of the USSR are: little souslik, gray, Ural and Siberian marmots, midday and great gerbil. Secondary media are ordinary "home" mouse, common vole and other
Natural foci can be mnogochlenami, if the epidemic is supported on a single species, or oligohaline, when the process involves several species. Natural foci of plague are available on all continents, except Australia.
From sick to healthy animals pathogen is transmitted via fleas, in which the body he falls in blood sucking. In the stomach fleas P. pestis multiplies and produces lumps, which adhere, close the entrance to the gastrointestinal tract (the so-called plague block). Subsequent blood sucking the blood can not break the block and returns to the wound from the bite with washed from lump microbes.
The ability to act as a vector of plague pathogen is set for a large number of species and subspecies of fleas. However, the value of certain types may vary greatly depending on the geographical location of the fire, and in the very hearth - the time of year. This is because the ability of the species to breed, activity of the attack and sucking blood and other manifestations of life, which is determined by their so-called infectious potential, are controlled by significant temperature and humidity.
The most active carrier of plague fleas come from the sort of Xenopsilla parasitizing on rats, gerbils and other rodents. The dominating role in tropical foci rat plague (India, China) plays a rat flea Xenopsilla cheopis. Human infection can occur not only in the attack infected fleas, but also by direct contact with rodents as a result of hit of infectious material in skin wounds and mucous membrane removing the skins with the corpses of tarbasanu, prirezka sick camel and butchering carcasses and so on).
Plague of people always have a starting point acute current epidemic among rodents. The bite of infected fleas and hit infectious material on the skin or mucous membranes determine the development of bubonic (less septic form of plague. Patient with uncomplicated bubonic form practically is not dangerous, as it does not emit pathogen into the environment. Even in the discharge of revelations of Bubnov P. pestis or nonexistent, or is contained in a very small amount. During the transformation of the bubonic form of bubonic-septic, which is characterized by bacteremia, in the presence in the premises of fleas, the patient may become a source of further infection. Of particular danger are sick pneumonic form of plague that when coughing emit into the air, a huge number of droplets of sputum containing R. pestis. The penetration of these droplets in the Airways of people around the patient, gives them the development of primary pneumonic plague.
The appearance in the course of the epidemic of pneumonic form of plague is genetically related to cases of bubonic or bubonic-septic form of plague, complicated secondary plague pneumonia. The main route of transmission of plague from person to person is airborne. Infected objects if and can play a role in the spread of the pathogen, the extremely limited and irregular, as R.
pestis very sensitive to drying and quickly perishes in the external environment. For the same reason, apparently, impossible and dust infection, and therefore a real danger of infection is limited to the immediate vicinity to the patient (the radius of 1.5-2 m), i.e. area, where there is a drop phase of aerosol. Because Pedernales and atonal condition in patients with pulmonary plague, usually with bacteremia, patients in the presence in the premises of fleas can cause bubonic form.
Highly contagious pneumonic plague causes rapid spread of the disease as within the locality, where it originated, and in settlements, related to Railways, which it put people in the incubation period.
In the course of the epidemic and its scope is significantly influenced by social factors. Diseases of pulmonary plague occur among people living in crowded, unsanitary conditions. Untimely detection and isolation of patients with a poorly developed network of medical institutions contributes to the spread of diseases.
As a rule, flash pulmonary plague occur in the area at that time of year, weather conditions, which have made people spend most of their time within the walls of dwellings (cold or very hot weather).
In the USSR the plague is not registered for many years.