Features of infectious diseases. Characteristics of an infectious disease
The generally accepted term "infectious diseases" was introduced by the German physician Christoph Wilhelm Hufeland. The main signs of infectious diseases:
* the presence of a specific pathogen as the direct cause of the disease;
* contagiousness (infectiousness) or the occurrence of several (many) cases of diseases caused by a common source of infection (zoonoses, sapronoses);
* often prone to wide epidemic distribution;
* cyclicity of the course (successive change of periods of the disease);
* the possibility of developing exacerbations and relapses, protracted and chronic forms;
* development immune reactions to Ag (antigen) of the pathogen;
* the possibility of developing carriage of the pathogen.
Specificity. Every infectious disease causes a specific pathogen. Bacteria, rickettsia, chlamydia, mycoplasmas, fungi, viruses, prions can be specific pathogens of infectious diseases. However, infections (for example, purulent-inflammatory processes) caused by various microbes are known.
The cyclical course is characteristic of most infectious diseases. It is expressed in the successive change of certain periods of the disease - incubation (hidden), prodromal (initial), the period of the main manifestations (the height of the disease), the extinction of symptoms (early convalescence) and recovery (convalescence).
Incubation period- the period from the moment of infection to the appearance of the first signs of the disease. During this period, the body actively reproduces and accumulates the pathogen and its toxins up to a certain threshold amount, after which the body begins to respond with certain clinical manifestations, i.e., the next, prodromal period begins. The duration of the incubation period varies on average from several days to several weeks, but it can be equal to several hours and last several months, and in leprosy - several years. It depends on a number of reasons - the magnitude of the infecting dose and the degree of pathogenicity of the pathogen, as well as on the state of resistance of the organism.
Prodromal period, or period of precursors. It is usually characterized by non-specific, general manifestations - weakness, weakness, headache, general malaise, fever, etc. Its duration varies within 24 - 48 hours.
The period of development (flourishing) of the disease. It is also often characterized by a known cyclicity. There is a stage of increasing symptoms (stage incrementum), the heyday of the disease (stage aste) and a period of extinction of symptoms (stage Decrementum). With a typical form of the disease, this period is characterized by the manifestation of symptoms specific to this disease, as well as some common symptoms, in particular, fever, intoxication, inflammation, sometimes the appearance of a rash.
Outcome period. During this period may come:
Relapse of the disease - return clinical manifestations diseases without re-infection, due to pathogens remaining in the body;
Superinfection - infection of a macroorganism with the same pathogen until recovery. If this happens after recovery, then this is called reinfection, because. it occurs as a result of a new infection with the same pathogen, as is often the case with influenza, dysentery, gonorrhea.
Bacteriocarrier, carrier of a pathogen of any infectious disease without clinical manifestations;
· Convalescence, or convalescence. Clinical recovery usually occurs earlier than pathoanatomical and bacteriological recovery. The person is practically healthy, but there are still some pathoanatomical changes at the site of the localization of the process (for example, after suffering dysentery on the mucous membrane of the colon). Reconvalescence can be complete: all processes end completely without any aggravating consequences. However, some diseases leave severe consequences, such as muscle paralysis after polio, encephalitis; cirrhosis after viral hepatitis B, etc. Particular attention should be paid to bacteriological recovery after an infectious disease, i.e., the complete release of the body from the pathogen. With various infectious diseases, the period of bacteriological recovery varies, and this is taken into account when such patients are discharged from the hospital. For example, in typhoid fever, up to 80% of convalescents are carriers during the first two weeks.
· Fatal outcome. At the same time, it must be remembered that the corpses of infectious patients are subject to mandatory disinfection, because. represent a certain epidemiological danger due to the high content of a microbial agent in them.
Properties of a pathogenic microorganism.
pathogenicity(morbidity) - the ability
microorganism cause disease.
This is a species trait that manifests itself in
susceptible organism.
Pathogenicity is characterized specificity, i.e.
the ability of a microorganism to cause a certain
infection
Eg. MTB causes tuberculosis.
Pathogenicity is a trait that characterizes the species as a whole.
Eg. dysentery sticks are pathogenic, but within the species
there may be more or less pathogenic strains.
Virulence is the degree or measure of pathogenicity,
the individual property of this pathogen to cause
infectious disease.
This property, the species characteristic of each strain of pathogenic
organism.
All strains are divided into:
Moderately
Weak and avirulent.
Virulence is determined in laboratory animals by
the lethal dose least amount
pathogen or toxin that causes the death of all
animals infected with this dose.
And infectious dose- the minimum number of microbes,
capable of causing an infectious disease. Under
exposure to chemical, physical, biological
factors, a change in virulence is possible: weakening,
amplification, complete loss.
Factors of pathogenicity m / o.
1. Adhesion(adhesion) - the ability to attach to certain cells.
2. Colonization- reproduction on the surface of sensitive
3. Invasiveness- the ability to penetrate and spread in the tissues of the body.
4. Aggressiveness- the ability to resist the protective factors of the body.
a) antiphagocytic activity - the ability to resist phagocytosis associated with the capsule.
b) enzymes of aggression and invasion (hyaluronidase, collaginase), they allow m/o to penetrate through mucous membranes, connective tissue barriers, etc. Some m/o produce enzymes that destroy antibiotics, which determines their antibacterial resistance.
5. toxin formation- the ability of microbes to produce toxins.
Exotoxins- these substances of protein nature are secreted into
the environment with live m / o in the process
vital activity. Selectively act on certain
organs and tissues. Eg. tetanus toxin affects N.S.
Bacteria that produce exotoxin are called toxigenic.
Endotoxins- toxic substances that are part of the structure of bacteria are released when the microbial cell is destroyed. They do not have selectivity of action, cause the same type clinical picture(t, intoxication, diarrhea, cardiac disorders). Bacteria that contain endotoxins are called toxic.
The role of the macroorganism and environment.
Properties M., affecting the infectious process:
resistance
Susceptibility
a) species
b) individual.
Susceptibility depends on age, sex, physical condition, hormonal status, nature of nutrition.
Physical, chemical and biological factors are indirectly involved in the development of the infectious process. They affect a person through the social conditions of life, the level of economic and cultural development, sanitary and hygienic conditions of work and life, national and religious customs, dietary habits, and preventive vaccinations.
Features of infectious diseases.
I. Specificity- pathogenic m / o causes its own disease and is localized in accordance with the pathogenesis of the disease.
II. contagiousness(contagiousness) - the ease (probability) of transmission of the pathogen from an infected organism to an uninfected one.
III. cyclicality- the presence of successively alternating periods of the disease, the duration of which depends on the properties of the m. and the resistance of M.
Periods of infectious diseases:
1) Incubation- from the moment of introduction of m. in M. until the onset of clinical manifestations of the disease.
2) Premonitory- the appearance of the first clinical manifestations of the disease (malaise, weakness, headache, increased t), there are no specific symptoms.
3) The period of pronounced clinical manifestations- there are specific symptoms.
4) Fading of clinical manifestations or period convalescence- cessation of reproduction of the pathogen in the patient's body, the death of the pathogen and the restoration of homeostasis.
IV. immune response- after the disease: immunity or increased sensitivity to the pathogen.
How infectious patients differ from the rest, what is the peculiarity of infectious diseases .
- home distinguishing feature is that an infectious patient releases pathogens into the environment. Therefore, it is necessary to know how the infection is transmitted to healthy people, what are the ways and means of transmitting an infectious agent.
- The next feature is that an infectious disease always causes general reactions in the human body - fever, fever, toxic changes. nervous system etc.
- The third feature is that the symptoms of an acute infectious disease can quickly replace each other. For example, loose stools may persist for several hours, a skin rash may come and go quickly, and signs of dehydration may quickly escalate. Therefore, sometimes there are difficulties in diagnosing and providing medical care infectious patient.
- The fourth feature is the signs of recovery (the absence of complaints about the state of health), as a rule, ahead of the full restoration of impaired functions. Often during the recovery period, significant changes in the organs remain - the heart, liver, kidneys, liver.
Conditions for distribution.
For the spread of an infectious disease, 3 conditions are necessary:
- the presence of a source of infection
- the presence of a way of its transmission
- the presence of people susceptible to this infection
Ways of transmission of infection:
- contact - as a result of contact with a sick person or animal, as well as with their secretions. This includes infection through the skin and mucous membranes. Sometimes the sexual route of transmission is also called contact, but more often it is distinguished as a separate column.
- food (doctors call it alimentary) is the most common route of transmission, since microorganisms are not only well preserved in food products, but also multiply. These include intestinal infections with fecal-oral transmission (that is, infection through the mouth) and waterborne transmission
- airborne transmission (or aerosol) is characteristic of diseases whose pathogens are excreted by patients (or carriers of infections) with droplets of saliva and mucus when sneezing, coughing, talking
- airborne dust infections - a number of pathogens retain the ability to survive even when dried; they become a source of disease for healthy people who inhale them with dust
- the transmission path is the transmission of the pathogen from a sick person to a healthy person through a carrier - a blood-sucking insect (lice, fleas, mosquitoes, mosquitoes, ticks, etc.); insects carry the pathogen from a sick animal
- sometimes there are blood non-transmissible (that is, not associated with blood-sucking insects) - with various medical procedures (injections, surgical interventions, dental and other manipulations). AT last years due to the widespread use of disposable medical instruments, this route of transmission is minimized. This includes the transmission of infection through intravenous administration drugs when using reusable syringes
- the transfusion route of transmission during the transfusion of infected donor blood, as well as the transplant route during organ transplantation. Cases of transfusion transmission of the pathogen are rare due to the introduction of stringent requirements for the study of donated blood.
- sexual way - with vaginal, anal, oral contacts, with artificial insemination of a woman through infected sperm.
The epidemic focus is the location of the source of infection (a sick person or a carrier of an infection, an infected animal), as well as the entire territory within which its pathogen can spread from this source of infection.
There is a concept of the intensity of the spread of an infectious disease:
- sporadic incidence - when there are single cases of the disease
- epidemics - mass spread of diseases
- Pandemics are epidemics that affect the population of several countries.
The constant presence of an infectious disease in a particular region is called endemic.
Social factors are of primary importance in the spread of the epidemic - population density, social disasters (war, forced migration, famine), material well-being, health and nutrition, living conditions and public amenities (compactness, availability of water supply and sewerage, ventilation, as well as the presence of insects, rodents, domestic animals, collection and disposal of waste), the level of sanitary and general culture, the availability of medical care.
Read also " How do infectious diseases progress?» « The concept of the infectious process» «
The role of the macroorganism in the infectious process.
Susceptibility- a genetically determined trait, this is the ability to respond to the introduction of a microorganism by the development of an infectious process; associated with cell reactivity.
resistance― stability of an organism which is caused by nonspecific factors of anti-infectious protection. Factors that weaken the protective functions of the body contribute to the spread of infection, while those that increase resistance prevent it.
Entrance "gates" of infection- these are tissues that are deprived of physiological protection against specific microorganisms (i.e., the place through which the microorganism penetrates into the macroorganism).
Infection- one of the phases of the development of an infectious process (terminal phase), its extreme degree of manifestation.
1. Etiological (each infectious disease is caused by a specific pathogen).
2. Contagiousness (contagiousness, contagiousness).
3. Epidemic (tendency to spread). Can be:
sporadic diseases - isolated cases of a disease in a given region;
Epidemics - outbreaks of a disease of various sizes;
Pandemic - A disease that spreads over a wide area.
4. Specificity of localization in certain organs and tissues.
5. Specificity of transmission mechanisms .
Transfer mechanism― the way a pathogen moves from an infected organism to a susceptible one.
Transmission factors― elements of the environment that ensure the transfer of the pathogen from one organism to another (water, food, air, live arthropods, environmental objects).
Transmission routes― specific elements of the external environment or their combinations that ensure the penetration of the pathogen from one organism to another under certain external conditions.
6. Repeatability or non-repeatability (as a result of the emergence of immunity.)
7. Cyclicity of the course (i.e., the presence of certain periods of the disease).
Periods of infectious disease
1) Incubation period- the time from the moment the pathogen enters the body until the first clinical symptoms of the disease appear in the patient; the duration of incubation can vary greatly - from several hours, days, weeks, months - up to several years.
2) Prodromal (the period of precursors of the disease) - characterized by the appearance of the first non-specific symptoms (general weakness, headache, fever, chills, muscle pain, etc.)
3) The period of clinical manifestations (the height of the disease) - the most pronounced non-specific, as well as specific symptoms, characteristic only for this disease.
4) Exodus period:
Reconvalescence (complete recovery with microbiological sanitation);
convalescent microcarrier;
transition to chronic form;
· fatal outcome.
Forms of infections (invasions)
1. By the nature of the pathogen:- bacterial
Viral
fungal
Protozoan
2. By the number of pathogens:- monoinfection
Mixed infection
3. According to the localization of the pathogen in the host organism:
Local (focal)
General (generalized):
bacteremia (viremia)
septicemia
septicopyemia
toxic-septic shock
toxemia
· toxinemia
4. According to the mechanism of occurrence (origin):
exogenous
Endogenous
Autoinfection
5. Repeated diseases:
reinfection
Superinfection
secondary infection
relapse
6. According to the main source of infection:
Anthroponoses (source of infection - human)
Zoonoses (source of infection - animal)
Sapronoses (source of infection - external/abiotic environment)
7. According to the mechanism of transmission and localization of the pathogen in the body:
Intestinal with fecal-oral transmission mechanism
infections respiratory tract with aerosol transfer mechanism
Blood with a transmissible transmission mechanism
Infections of the external integument with a contact mechanism of transmission
8. By place of occurrence:- out-of-hospital
Nosocomial (HBI)
Natural focal
9. By distribution:
sporadic cases
Epidemics
pandemics
Endemic (attachment of an infectious disease to a particular region)
10. According to the duration of the flow:
Persistent (latent, chronic, slow)
10. By the nature of the flow:
Asymptomatic (microcarriage)
Erased (subclinical)
Manifesto
Fulminant
Forms of infections - basic concepts.
Monoinfection- an infectious disease caused by one type of pathogen.
Mixed infection(mixed) - two or more types of pathogens cause an infectious disease.
secondary infection- another infection caused by an opportunistic pathogen joins the initial (main) infection.
reinfection- re-infection with the same pathogen after recovery against the background of unformed immunity.
Superinfection- re-infection with the same pathogen against the background of the current disease.
relapse- recurrent disease due to endogenous infection.
At exogenous infection the pathogen enters the body from the environment (from the outside), when endogenous― is in the body itself.
Autoinfection- an endogenous infection caused by the body's own opportunistic microflora.
persistence- prolonged presence of microorganisms in the body in an inactive state.
microbearing(bacteriocarrier, virus carrier) is the presence (carriage) of a microorganism in a macroorganism without clinical manifestations of infection. Maybe: healthy microcarriage - develops in healthy individuals who have been in contact with patients or carriers of the corresponding pathogenic species; convalescent microcarriage - a condition in which the release of the pathogen continues after the clinical recovery of the patient; most often formed with a weak tension of post-infectious immunity.
Focal infection- an infection in which the process is localized in a specific organ or tissue and does not spread throughout the body. However focal infection at the slightest imbalance between macro- and micro-organisms, it can go into a generalized form.
Generalized infection- an infection in which pathogens spread mainly through the lympho-hematogenous route throughout the macroorganism.
In this case it develops:
1) bacteremia - a state of the body in which microorganisms circulate in the blood, but do not multiply;
2) viremia - a state of the body in which viruses circulate in its blood (generalized viral infection);
3) sepsis - the presence of microorganisms in the blood and their reproduction;
4) septicemia - a form of sepsis, in which microorganisms circulate and multiply in the blood without the formation of secondary foci of infection;
5) septicopyemia - a form of sepsis, in which microorganisms not only circulate and multiply in the blood, but also form purulent metastatic foci in various organs;
6) toxemia - a state of the body in which bacterial endotoxins circulate to the blood;
7) toxinemia - a state of the body in which a bacterial exotoxin or other toxin circulates in the blood (with botulism, tetanus and other diseases);
8) with a massive intake of bacteria and their toxins into the blood, it develops bacterial or toxic-septic shock.
Epidemiology— the science of the epidemic process. It studies the occurrence and spread of infectious diseases among the population.
Links of the epidemic chain:
1. Source and reservoir of infection.
2. Mechanisms and factors of transmission of pathogens (transmission factor can be water, food, air, etc.).
3. Susceptible organism.
By influencing these links, it is possible to prevent or even eliminate the epidemic process that has already arisen.
Unlike somatic diseases, infectious diseases caused by pathogenic microorganisms are characterized by the following features:
ü specificity: each pathogenic microbe causes its own infectious disease and is localized based on pathogenesis in a particular organ or tissue;
ü contagiousness (contagiousness) - the ease with which the pathogen is transmitted from an infected organism to an uninfected one, or the speed with which an infection spreads among a susceptible population;
ü cyclicity: successively alternating periods of the disease, the duration of which depends on the properties of microbes and the resistance of the macroorganism.
Development of the infectious process:
1. The incubation period is the period from the introduction of an infectious agent into the body until the onset of clinical manifestations.
2. The prodromal period develops with the appearance of the first clinical manifestations of the disease (fever, malaise, headache, weakness). Specific clinical symptoms are absent during this period.
3. The period of the main clinical manifestations (high) is characterized by the appearance of the most significant for the diagnosis of specific clinical and laboratory symptoms and syndromes.
4. Period of disease outcome:
ü recovery: characterized by the cessation of reproduction of the pathogen in the patient's body, the death of the pathogen in the patient's body and the complete restoration of homeostasis;
ü lethal outcome;
ü carrier.
Ticks
Their development is carried out by metamorphoses. A larva with three pairs of legs hatches from the egg, then the larva turns into a nymph with 4 pairs of legs, the reproductive system is not developed. After the second metamorphosis, the nymph turns into an adult - a sexually mature individual.
An adult tick feeds on the blood of cattle, wild ungulates, foxes, and dogs.
The dog tick is found in mixed deciduous forests across most of Eurasia, with a lifespan of 7 years.
The taiga tick is common in the taiga part of Eurasia from Far East to Central Europe, life span - 3 years.
The wide distribution of ixodid ticks has led to the spread of the taiga encephalitis virus over a vast area. The spread of the virus and its adaptation to different types vectors and a large species of natural reservoirs contributed to the emergence of various strains that differ in the degree of virulence. The Far Eastern strain is highly virulent.
To avoid contracting tick-borne encephalitis, precautions should be taken, especially when walking in the forest in summer or late spring. It is advisable to wear deaf clothes with buttoned sleeves and a collar, and it is also obligatory to wear a headdress.
Tick Removal:
It is most convenient to remove with curved tweezers or a surgical clip. The tick is captured as close to the proboscis as possible. Then it is gently sipped and at the same time rotated around its axis in a convenient direction. After 1-3 turns, the tick is removed entirely along with the proboscis. If you try to pull out the tick, then there is a high probability of a rupture.
If there are no tools, then you can remove it with a loop from a coarse thread. With a loop, the tick is captured as close to the skin as possible and gently, staggering to the sides, is pulled out.
Oiling will not cause the tick to take out its proboscis. The oil will only kill him by clogging his breathing holes. The oil will cause the tick to regurgitate its contents into the wound, which can increase the risk of infection. Therefore, oil cannot be used.
After removal, the wound is treated with iodine or another antiseptic for the skin. But you don’t need to pour a lot of iodine, as you can burn the skin.
Hands and tools after removing the tick should be thoroughly washed.
If a head with a proboscis remains in the wound, then there is nothing terrible in this. A proboscis in a wound is no worse than a splinter. If the proboscis of the tick sticks out above the surface of the skin, then it can be removed by holding it with tweezers and unscrewing it. You can also remove it from the surgeon in the clinic. If the proboscis is left, then a small abscess appears, and after a while the proboscis comes out.
When removing a tick, do not:
Oil the tick
Apply caustic liquids to the bite site - ammonia, gasoline, and others. Burning a tick with a cigarette
Pull the tick sharply - it will break off
Poking around in the wound with a dirty needle
Apply various compresses to the bite site
Squeeze a tick with your fingers
The removed tick can be destroyed or left for analysis by placing it in a jar. If everything is normal, then the wound heals in a week.
3. Chromosomal diseases - Down's syndrome, Edward's syndrome, Patau's syndrome.
The chromosome complex of normal somatic cells of modern humans consists of 46 chromosomes (2n = 46). In the cells of a female individual, in addition to 44 autosomes, there is a pair of sex chromosomes XX, and in males - XY. Accepted formulas for the image: 46, XX; 46, XY.
Chromosomal diseases are a large group of congenital pathological conditions with multiple congenital malformations, the cause of which is a change in the number or structure of chromosomes. Chromosomal diseases result from mutations in the germ cells of one of the parents. No more than 3-5% of them are passed from generation to generation. Chromosomal abnormalities are responsible for approximately 50% of spontaneous abortions and 7% of all stillbirths.
All chromosomal diseases are usually divided into two groups:
1) anomalies in the number of chromosomes. This group includes three subgroups:
Diseases caused by a violation of the number of chromosomes,
Diseases associated with an increase or decrease in the number of sex X and Y chromosomes
Diseases caused by polyploidy - a multiple increase in the haploid set of chromosomes
2) violations of the structure (aberrations) of chromosomes. Their reasons are:
Translocations - exchange rearrangements between non-homologous chromosomes
Deletions - loss of a section of a chromosome
Inversions - rotations of a chromosome segment by 180 °
Duplications - duplication of a section of a chromosome
Isochromosomy - chromosomes with repeated genetic material in both arms
Occurrence of ring chromosomes - connection of two terminal deletions in both arms of a chromosome
Diseases caused by a violation of the number of autosomes
Down syndrome - trisomy on chromosome 21, the signs include: dementia, growth retardation, characteristic appearance, changes in dermatoglyphics (patterns on the skin of the palmar side of the hands and feet of a person). The syndrome was named after the English physician John Down who first described it in 1866. The connection between the origin of the congenital syndrome and the change in the number of chromosomes was revealed only in 1959 by the French geneticist Jérôme Lejeune. The frequency of births of children with Down syndrome is 1 in 800 or 1000. Down syndrome occurs in all ethnic groups and among all economic classes. The age of the mother affects the chances of conceiving a child with Down syndrome. If the mother is between 20 and 24, the chance is 1 in 1562, between 35 and 39 is 1 in 214, and over the age of 45, the chance is 1 in 19. Trisomy occurs because the chromosomes do not separate during meiosis. When fused with a gamete of the opposite sex, the embryo produces 47 chromosomes, and not 46, as without trisomy.
Patau syndrome - trisomy on chromosome 13, characterized by multiple malformations, idiocy, often - polydactyly, violations of the structure of the genital organs, deafness; Almost all patients do not live up to one year. Occurs with a frequency of 1:7000-1:14000. The survivors suffer from deep idiocy.
Edwards syndrome - trisomy 18, lower jaw and the mouth opening is small, palpebral fissures narrow and short auricles deformed; 60% of children die before the age of 3 months, only 10% live up to a year, the main cause is respiratory arrest and disruption of the heart. The population frequency is approximately 1:7000. Children with trisomy 18 are more often born to older mothers, the relationship with the age of the mother is less pronounced than in cases of trisomy chromosomes 21 and 13. For women over 45 years of age, the risk of giving birth to a sick child is 0.7%. Girls with Edwards syndrome are born three times more often than boys.
