Epidemiology and global significance
Infectious diseases remain one of the major challenges of modern healthcare. According to World Health Organization data collected at the beginning of the 21st century, this group of pathologies firmly holds third place in global prevalence. They are preceded only by cardiovascular diseases and malignant neoplasms.
Global mortality statistics look alarming: approximately a quarter of all deaths worldwide are directly linked to infections. In developing countries, this figure doubles, reaching 50%. Humanity loses more than 13 million lives annually due to the activity of pathogenic microorganisms. Recalculating these data for shorter time intervals reveals that over one and a half thousand people die from infectious diseases every hour. Especially tragic is the fact that about half of this number consists of children under the age of five.
Why is the macroorganism vulnerable?
The human body is an almost ideal environment for the colonization and active reproduction of various microbes. This is due to two fundamental factors:
- Homeostatic stability. Constant body temperature, optimal acidity level (pH), and well-balanced electrolyte composition create greenhouse conditions for the survival of pathogens.
- Resource availability. Tissues and biological fluids provide pathogens with easy and uninterrupted access to essential nutrients.
That is why, once inside, microorganisms get all the opportunities to trigger pathological reactions, including morphological damage, biochemical shifts, and immunobiological responses.
Coinfections and their consequences
In clinical practice, physicians often deal not with the isolated impact of a single pathogen, but with a combination of multiple pathogens. The specifics of metabolic processes in the body frequently create a favorable background for the development of combined lesions (e.g., virus-virus or virus-bacterium). Such associations can attack the patient simultaneously or join sequentially.
The clinical consequences of such combinations are always negative. First of all, pathomorphosis occurs—a significant alteration of classical symptoms, which critically hinders timely and accurate diagnosis. In addition, a combined course repeatedly increases the risk of multiple complications, aggravates the patient's general condition, delays recovery, and overall significantly worsens the disease outcome.
Key terminology in clinical practice
To properly assess a patient's condition, it is necessary to clearly distinguish between the variants of the pathological course:
- Bacteremia and viremia—the presence of bacteria or viruses in the systemic bloodstream without signs of their replication. This represents one of the developmental stages of a number of diseases.
- Sepsis—a severe generalized form of the infectious process caused by the active reproduction of microorganisms in the blood and frequently in other biological fluids.
- Septicopyemia—a variant of the course of sepsis characterized by the secondary development of purulent foci in various healthy tissues and organs.
- Mixed infection—a process caused simultaneously by two or more different pathogens.
- Superinfection—re-infection of the body with the same pathogen before recovery (against the background of the ongoing disease).
- Reinfection—re-emergence of a process caused by the same microorganism, but after the patient's complete recovery.
- Secondary infection—a process developing against the background of an already existing (primary) disease, but caused by a completely different microorganism.
Briefly: answers to topical questions
What are the stages (periods) of the infectious process?
Four developmental periods are distinguished in the course of the infectious process:
- Incubation period — the latent development from the moment of exposure to the pathogenic agent until the appearance of the first signs;
- Prodromal period — the period of early prodromal signs;
- Period of main manifestations (peak) — the stage of pronounced disease manifestations;
- Period of resolution — the outcome of the disease.
What microbial pathogenicity factors trigger the infectious process?
The main pathogenicity factors of microorganisms are virulence factors that ensure dissemination, adhesion, colonization, intoxication, and evasion of the immune response.
The following factors are distinguished:
- Adhesion and colonization factors — adhesins and exotoxins;
- Dissemination factors — enzymes, flagella, undulating membrane;
- Defense factors — capsules and hydrolytic enzymes;
- Toxins — exotoxins and endotoxins.
What defense barriers of the macroorganism prevent infection?
The body's defense barriers include:
- Integrity of the skin and mucous membranes;
- Glandular secretions — sebaceous and sweat glands containing antimicrobial peptides;
- Mucus layer on the respiratory epithelium;
- Mucociliary clearance — the removal of viral particles from the respiratory tract;
- Normal microflora, which competes with fungi for nutrients and niches;
- Transparent sclerosed dentin, which prevents the penetration of pathogenic microorganisms, their toxins, and decay products into the dental pulp.
What types of organism reactivity are distinguished in the infectious process?
Several types of organism reactivity are distinguished in the infectious process, dynamically succeeding one another:
- Normergic reaction — occurs upon primary contact with the pathogen;
- Hyperergy — an increased reaction in the form of immediate- or delayed-type hypersensitivity;
- Hypoergy — a decrease in reactivity to the acting pathogen;
- Anergy — a complete lack of response to the pathogen (can be positive protective or negative pathological);
- Allergy — a special altered reaction manifested at all stages of the disease.
What mechanisms, besides coinfections, can lead to the pathomorphosis of infectious diseases?
Internal and external factors can lead to the pathomorphosis of infectious diseases:
- Changes in human constitution as an internal cause of natural private pathomorphosis;
- Changes in external causes, not always known;
- Medical and social factors associated with a set of long-term socio-medical measures;
- Socio-economic and ecological factors affecting the clinical picture of infectious diseases.
To avoid confusing the terms for reinfections, remember the time and pathogen rule: «SUPER» — layers on top (same microbe, still sick), «RE» — repeat from scratch (same microbe, already recovered), «SECONDARY» — second player (different microbe, still sick with the first).
Class and exam questions
What is the difference between superinfection and reinfection?
The main difference lies in the timing of re-infection with the same pathogen. In superinfection, it occurs against the background of the ongoing disease (before recovery), whereas in reinfection, it occurs only after the patient's complete clinical recovery.
Does the presence of bacteria in the blood always mean sepsis?
No. If bacteria are simply present in the bloodstream but do not multiply there, this condition is called bacteremia (a stage of many diseases). Sepsis, on the other hand, is specifically characterized by the active multiplication of pathogens in the blood.
Why are mixed infections harder to treat?
They cause pathomorphosis (alteration of typical symptoms), which greatly complicates diagnosis. In addition, they provoke more complications, worsen the condition, and prolong the course of the disease.
What is septicopyemia in simple terms?
This is a severe complication of sepsis in which the infection is spread via the bloodstream and forms new (secondary) purulent foci in various tissues and internal organs.
What else to study on this topic
- Functional and biochemical changes in the infectious process
- Immunobiological reactions of the body to pathogen invasion
- Morphological tissue damage in various types of infections
- Mechanisms of development of viral-bacterial associations
- Pathogenesis of secondary purulent foci formation in septicopyemia
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