The main characteristic of natural focal diseases is that their pathogens are transmitted to humans from birds or animals. As a rule, transmission occurs through the bites of blood-sucking insects, such as mosquitoes. Several pathogens can coexist in one natural outbreak - bacteria, viruses, helminths, protozoa, etc. In order to protect against natural focal diseases, many of which pose a serious threat to people's lives, it is important to have information on transmission routes and methods of prevention diseases.
What is a "natural center"?
The phrase "natural focus" directly indicates that the source of infection exists in nature. Transmissible and natural focal diseases are associated with certain biogeocenoses. The causative agents of natural focal diseases have the property of being transmitted from humans to animals, which means that a person who finds himself in a similar biogeocenosis may become infected. In this case, pathogens are transmitted in various ways: through insect bites, by inhalation of dried excrement of infected animals, etc.
Teaching of Academician E.N. Pavlovsky
The doctrine of focal diseases Academician Pavlovsky is one of the most outstanding achievements of biological science.
Pavlovsky’s teachings say that in some landscapes there are foci of diseases that can be transmitted to humans. These foci are formed during the long evolutionary development of biogeocenosis.
A natural focal disease occurs when three links occur simultaneously:
- pathogen population;
- a population of animals that are hosts (reservoirs) of pathogens;
- vector of disease pathogens.
For example, natural focal diseases include pendin ulcer, common in some parts of Central Asia. The causative agent of the disease are Leishmania. The reservoir of Leishmania are gerbils - small rodents that live in deserts. And Leishmania is transmitted through mosquito bites.
In one territory, foci of several diseases can be simultaneously present, which is important to consider when developing preventive measures.
Varieties of natural foci
Natural focal disease can be of two types:
- monovector - in the transmission of pathogens from one organism to another, only one carrier can take part;
- multivector - transmission can be carried out by several types of carriers.
E.N. Pavlovsky distinguished another kind of natural foci - anthropurgical. The appearance of these foci is due to human activity and the ability of some vectors to switch to a synanthropic existence. Such vectors, such as mosquitoes or ticks, are found mainly in urban or rural conditions, that is, near a person’s home.
Carriers of natural focal diseases
Natural focal infectious diseases can spread by two types of carriers: specific and non-specific. In specific carrier organisms, the causative agent of the disease goes through some of the stages of its life cycle: it multiplies, accumulates, or even turns from an egg into a larva. The causative agent can maintain its vital activity only in the body of a particular carrier, adapting to it in the process of evolutionary development.
Nonspecific carriers move pathogens mechanically. In this case, the pathogen stays for some time either on the proboscis or in the intestines of the distributor.
How can infection happen?
Infection with natural focal diseases can occur in various ways:
- industrial infection is associated with work carried out in or near the forests, infection can occur during construction or forestry operations, during the harvesting of flax, vegetables, etc .;
- infection when working in a summer cottage: often rodents, which are carriers of infections, live in cottages or sheds, infection can occur when inhaled dried feces of mice and rats;
- domestic infection, which often occurs in houses located near forests, is caused by the fact that rodents penetrate into sheds, cellars or into residential premises;
- infection with a short stay in the forest, for example, on a walk or on a camping trip.
The most common diseases
Tick-borne encephalitis is a natural focal disease characterized by severe intoxication and damage to the brain and spinal cord. Patients develop persistent irreversible neurological disorders, a fatal outcome is possible.
Japanese encephalitis is an acute disease that occurs with damage to the brain and its membranes. The carriers of Japanese encephalitis are mosquitoes. The main symptoms are lethargy, fatigue, speech and vision disorders, fever, chills and vomiting. Fatal outcome is observed in 40-70% of cases.
Rabies is one of the most dangerous natural focal diseases. Signs are anxiety, hypersensitivity to bright light, insomnia, convulsions, and fear of water. The patient sees hallucinations, becomes aggressive.
Foot and mouth disease is a natural focal disease that affects the mucous membranes, periungual bed and folds between the fingers. The causative agent enters the body through food. The onset of foot and mouth disease is quite sharp, flowing with a sharp increase in temperature. The prognosis is often favorable, although serious complications may occur in children.
Anthrax is a disease that has two forms: skin and septic. The skin form is characterized by the appearance of numerous ulcers. This form develops rather slowly and responds well to treatment. The septic form is more dangerous, death can occur in just a few days.
Prevention of natural focal diseases
Pavlovsky’s doctrine on natural focal diseases had a huge impact on the approach to prevention. If initially the main measure for preventing epidemics was the treatment of infected people and the destruction of vectors, such as mosquitoes or ticks, nowadays the main goal is to eliminate animal reservoirs.
In order to protect yourself from natural focal diseases, it is important to follow a number of preventive measures: do vaccinations in a timely manner, do not visit the habitats of animals that are carriers of the causative agents of the disease, and also protect yourself from the bites of insect vectors using closed clothing or using special repellents .