General regularities of infectious diseases
Any infectious disease is characterized by certain general features that must be considered during pathomorphological analysis. A key concept is the cyclical nature of infectious diseases. To correctly assess pathogenesis, it is necessary to provide a clear definition of this term and a detailed description of all phases in the development of the infectious process.
Furthermore, pathogen invasion induces a series of stereotyped reactions in the macroorganism. When studying this topic, one must compile an exhaustive list and characterize the systemic changes in the body that predictably develop against the background of an infectious lesion.
Specifics of respiratory and intestinal infections
Although the principles of pathogenesis are uniform, different pathogens form a unique morphological picture:
- Influenza: The study of this nosology requires a classification of the clinical and morphological forms of influenza and their detailed pathomorphological description. The pathogenesis and morphogenesis of the disease are directly determined by the properties of the influenza virus itself, which cause specific morphological manifestations.
- Typhoid fever: The pathomorphology of this disease is inextricably linked to the stages of its course. Special attention is paid to the morphogenesis of intestinal lesions — a detailed pathogenetic justification of the causes leading to necrosis of Peyer's patches in the small intestine is required.
Pathomorphology of tuberculosis
Tuberculosis remains one of the most important problems in infectology. Within the course, the general epidemiological characteristics of this disease and the classification of its clinical and morphological forms are studied.
Three main categories are distinguished, each with its own specific features of progression and course:
- Primary tuberculosis: specific forms of its progression are examined.
- Hematogenous tuberculosis: requires knowledge of the classification and variants of development.
- Secondary tuberculosis: forms and specific features of the clinical course are studied.
An important aspect is the concept of pathomorphosis — one must understand the essence of the changes in the classical clinical and morphological picture of modern tuberculosis under current conditions.
Particularly dangerous and quarantine infections
A separate group comprises diseases that pose an exceptional epidemiological threat. It is necessary to clearly distinguish the definitions of particularly dangerous infections (PDIs) and quarantine infections, as well as to know the exact list of nosologies belonging to each of these groups.
In pathomorphological practice, working with such infections is regulated by strict protocols. Subjects of study include the specific rules for performing autopsies on human corpses dead from quarantine infections, as well as special sanitary and epidemiological requirements for their subsequent burial.
Sepsis and comorbid infections: study base
For an in-depth understanding of the pathological anatomy of sepsis and severe infections, a specialized database of scientific data is used. When studying sepsis, its pathological anatomy, classification issues, initial mechanisms of development, and clinical and morphological parallels are examined (based on the works of authors such as Yu.G. Parkhomenko, V.S. Paukov, M.G. Rybakova).
Additionally, within the framework of special infectology, the epidemiology and prevention of HIV infection, the spectrum of AIDS-associated diseases, the features of Klebsiella infections, acute non-influenza respiratory pathologies, and sexually transmitted diseases are investigated.
Briefly: answers to topical questions
What macroscopic and microscopic changes occur in the spleen during acute malaria?
In acute malaria, the spleen significantly increases in size, its mass can reach 3 kg (splenomegaly). Macroscopically, the organ becomes soft. Microscopic changes are characterized by pronounced hyperemia and hyperplasia of reticular cells. Disintegrating erythrocytes also enter the spleen, where macrophages and cells of the reticuloendothelial system capture the released hemomelanin and hemoglobin fragments, giving the organ a dark grey, almost black color.
What specific pigment is formed upon the destruction of erythrocytes by malaria plasmodia and accumulates in organs?
Upon the destruction of erythrocytes by malaria plasmodia, a specific malarial pigment is formed — hemomelanin (hemozoin). It is an amorphous brown pigment synthesized from the prosthetic part of hemoglobin as a result of its hydrolysis by parasite enzymes. After entering the bloodstream, hemomelanin is phagocytosed by macrophages and accumulates in the organs of the reticuloendothelial system (spleen, liver, bone marrow, lymph nodes), as well as in glial cells of the brain. Due to the deposition of this pigment, the organs acquire a characteristic slate-grey color.
What are Dürck's granulomas and in which organ do they localize in malaria?
Dürck's granulomas are specific nodular accumulations of cells formed by proliferating oligodendrogliocytes and macrophages. In malaria, they are localized in the brain. Their formation is associated with the development of brain tissue ischemia, which leads to neuronal death. These pathomorphological changes are characteristic of severe tropical malaria and are one of the main causes of high mortality among children.
What pathomorphological changes develop in the liver in malaria?
In malaria, hepatomegaly develops in the liver, and the nature of the changes depends on the stage of the disease.
- Acute stage — macroscopically, the organ is enlarged, hyperemic, and has a dark-grey color on the cut surface. Microscopically, hyperplasia of stellate endotheliocytes (Kupffer cells) with the deposition of hemomelanin and hemosiderin pigments in them is observed.
- Chronic course — pronounced fibrosis develops in the liver. Prolonged absorption of hemomelanin by macrophages leads to hemomelanosis and hemosiderosis, which ultimately contributes to organ sclerosis.
What is the pathogenesis and morphological picture of malarial coma in tropical malaria?
The pathogenesis of malarial coma in tropical malaria is caused by microcirculatory disorders in the central nervous system. Clogging of brain capillaries by parasitic thrombi occurs, causing ischemia and subsequent neuronal death.
The morphological picture is characterized by:
- Dürck's granulomas — nodules formed by proliferating oligodendrogliocytes and macrophages.
- Pigmentation — deposition of malarial pigment (hemomelanin) in glial cells of the brain.
Clinically, the process goes through the stages of encephalopathy (somnolence, sopor, and coma) and often leads to a fatal outcome.
What changes in the kidneys are characteristic of blackwater fever (a complication of malaria)?
In blackwater fever, resulting from massive intravascular hemolysis, pronounced pathomorphological changes develop in the kidneys, leading to acute kidney injury (AKI). Morphologically, congestive hyperemia is observed, malarial pigment hemomelanin is deposited in the renal glomeruli, and hemoglobin casts form in the lumens of the tubules. A severe course is accompanied by profound damage to the renal tissue up to tubular necrosis. Clinically, these changes manifest as brown or black urine, oliguria, anuria, as well as pronounced proteinuria, cylindruria, and microhematuria.
In which cells of the macroorganism does tissue (exoerythrocytic) schizogony of malaria plasmodia occur?
Tissue (exoerythrocytic) schizogony of malaria plasmodia occurs in liver cells — hepatocytes. After an infected mosquito bite, sporozoites enter the bloodstream and penetrate hepatocytes within 30 minutes. Inside these cells, the plasmodia multiply to form tissue schizonts. This stage is asymptomatic and lasts from 1 to 12 weeks, resulting in the formation of more than 30,000 merozoites from a single sporozoite, which are then released into the blood.
What characterizes the pathomorphological picture of chronic malaria?
The pathomorphological picture of chronic malaria is characterized by systemic involvement of the organs of the reticuloendothelial system (RES) resulting in sclerosis. As a result of continuous erythrocyte destruction, macrophages phagocytose pigment, leading to pronounced hemomelanosis and hemosiderosis. The prolonged course of these processes causes the following changes:
- Spleen — sclerotic changes and tissue induration develop.
- Liver — pronounced liver fibrosis is formed.
- Kidneys — in Plasmodium malariae invasion, the chronic course is accompanied by the development of nephrotic syndrome.
What are the main causes of death in patients with severe malaria?
The main cause of death in patients with severe malaria is the development of the cerebral form (malarial coma) in the setting of falciparum malaria. About 80% of all fatal outcomes of the disease are associated with this complication. In addition, fatal consequences can be caused by:
- Infectious-toxic shock (ITS) — results in acute heart failure.
- Acute kidney injury (AKI) — often develops as a consequence of blackwater fever (massive intravascular hemolysis).
- Pulmonary edema — one of the most severe complications.
Which species of malaria parasite causes the most severe form of the disease with central nervous system involvement?
The most severe form of the disease with central nervous system involvement is caused by Plasmodium falciparum, the causative agent of falciparum malaria. This is the only species of malaria parasite capable of a malignant course leading to a fatal outcome. The severe course of the disease is frequently complicated by cerebral malaria (malarial coma), which is caused by microcirculatory disorders and blockage of cerebral capillaries by parasitic thrombi.
Class and exam questions
What is the cyclical nature of the infectious process?
This is a predictable sequence of the infection development phases from the moment of pathogen invasion to the outcome of the disease, determining the morphological changes at each stage.
What is the pathomorphosis of tuberculosis?
This is a persistent change in the clinical and morphological picture of modern tuberculosis compared to its classical descriptions.
What are the specifics of autopsy in quarantinable infections?
Autopsies and subsequent burial of corpses of individuals who died from quarantinable infections are carried out according to strict specific rules to prevent epidemiological threat.
What else to study on this topic
- Pathogenetic rationale for necrosis of Peyer's patches in typhoid fever
- Properties of the influenza virus and their impact on disease morphogenesis
- Forms of progression of primary and hematogenous tuberculosis
- Initial mechanisms of sepsis development
- Pathological anatomy of AIDS-associated diseases
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