Etiology and transmission routes of cytomegalovirus
The causative agent of the disease is a DNA-containing virus — Cytomegalovirus hominis. The infection is a typical anthroponosis. Despite the ubiquitous distribution of the pathogen in the human population, clinically pronounced forms develop extremely rarely, predominantly against the background of decreased immune reactivity.
Transmission of the virus occurs through multiple routes:
- Parenteral: includes transplacental transmission from mother to fetus, as well as infection via blood transfusions and organ transplantation.
- Contact: infection is possible through saliva and blood.
- Sexual: transmission via sexual contact.
- Alimentary: a typical example is the infection of a newborn child through the mother's breast milk.
Pathogenesis and morphological features
The virus exhibits tropism for several cell types: epithelial, endothelial, neural, and immunocompetent cells. Upon entering the body, it begins latent replication in target cells. The most important link in pathogenesis is the integration of viral DNA into the host cell genome, which causes lifelong persistence of the virus.
Disease progression is triggered by viral replication in immunocompetent cells. This causes a progressive decrease in immunity, followed by a stage of viremia and hematogenous generalization. As a result, many organs are affected and systemic vasculitis develops.
Specific morphological marker: The main pathognomonic sign is the formation of giant cytomegalic epithelial cells. Visually, they are distinguished by the presence of dense rounded inclusions inside the nucleus, which are surrounded by a pale halo. This phenomenon has been figuratively named the "owl's eye".
Congenital cytomegalovirus infection
The congenital form occurs with intrauterine infection and can proceed in an acute or chronic form.
Acute congenital form Manifests during the neonatal period (usually on days 3–14 after birth). Characterized by total generalized damage to internal organs and the central nervous system (CNS). Clinical presentation: hemorrhagic syndrome, pronounced anemia, thrombocytopenia, jaundice. Organ involvement: hepatitis, liver cirrhosis, encephalitis, as well as lesions of the gastrointestinal tract, kidneys, lungs, salivary glands, and pancreas develop. Encephalitis proceeds relatively mildly, but leaves persistent residual changes. The subacute course is often accompanied by the development of atypical interstitial pneumonia. Morphologically, cytomegalic cells, foci of calcification, and perivascular lymphohistiocytic infiltration are detected in the organs.
Chronic congenital form Represents a complex of persistent residual changes in organs affected during the intrauterine period or immediately after birth. Typical manifestations include: microcephaly, hydrocephalus, biliary atresia, liver cirrhosis, and chronic pneumonia.
Acquired form and complications
Acquired infection develops via any route of transmission except transplacental. In clinical practice, it often resembles a mononucleosis-like syndrome accompanied by prolonged fever, lymphadenopathy, tonsillitis, and non-suppurative sialadenitis (parotitis).
In the salivary glands, the virus is able to persist for years in a latent form, causing tissue infiltration followed by their sclerosis.
Generalized acquired form Occurs predominantly against the background of profound immunodeficiencies (AIDS, cytostatic therapy for oncology, or post-transplantation). Key difference from the congenital form: acquired generalization lacks brain involvement. Total lymphadenopathy, severe lesions of the respiratory system, eyes, and GI tract (in particular, the development of ulcerative colitis) are characteristic.
Complications and prognosis: Frequent complications include secondary bacterial infection, cachexia, and hydrocephalus. The prognosis directly depends on the immune status, patient age, and the specific form of the disease. Congenital generalized forms most often result in death. In acquired forms, death typically ensues from the underlying background disease (HIV, neoplastic process).
Associated Infections: Cryptosporidiosis and Diphtheria
In addition to cytomegalovirus, two other pathologies are discussed in the material:
Cryptosporidiosis An infectious anthropozoonotic disease of the gastrointestinal tract caused by coccidia (Cryptosporidium parvum). The reservoir consists of animals. Transmission occurs via alimentary, contact, and aerogenic routes. Risk groups include young children. Manifestations: nausea, vomiting, fever, diarrhea (sometimes with blood), seizures. Pathomorphology reveals catarrhal or serous-hemorrhagic gastroenteritis. Upon chronic progression (especially in immunodeficient individuals), intestinal villi atrophy, leading to malabsorption syndrome.
Diphtheria Caused by the environmentally resilient diphtheria bacillus (Corynebacterium diphtheriae). The primary transmission route is airborne, less commonly contact-transmission. The pathogen invades the mucous membranes of the oropharynx, larynx, and nose (less frequently the eyes, genitals, or wounds), where it actively multiplies and releases a dangerous exotoxin.
Briefly: answers to topical questions
Which microorganism is the causative agent of meningococcal infection?
The causative agent of meningococcal infection is the bacterium meningococcus (Neisseria meningitidis). This microorganism causes an acute anthroponotic infectious disease. An important pathogenicity factor of the meningococcus is the presence of a carbohydrate capsule, which protects bacterial antigens, impedes phagocytosis, and increases the virulence of the pathogen. In most cases, the infection is limited to a local lesion of the nasopharyngeal mucosa, but it is capable of leading to severe generalized forms.
What is the main transmission mechanism of meningococcal infection?
The main transmission mechanism of meningococcal infection is airborne. The source of infection is a sick person or a bacillus carrier. The infection can be of an epidemic nature. The penetration of the pathogen into the meninges during generalization occurs via a hematogenous route.
Which forms of meningococcal infection are classified as localized?
Primary localized forms of meningococcal infection include the following conditions:
- Meningococcal carriage — asymptomatic course of the infection.
- Acute nasopharyngitis — local lesion of the nasopharyngeal mucosa.
- Pneumonia — inflammatory lesion of the lungs.
These forms are clinically indistinguishable from other acute respiratory infections and ultimately lead to the development of immunity.
Which forms of meningococcal infection are classified as generalized?
Hematogenously generalized forms of meningococcal infection include:
- Meningococcemia — acute meningococcal sepsis (typical, fulminant, and chronic forms).
- Meningitis — purulent inflammation of the meninges.
- Meningoencephalitis — spread of inflammation to the brain parenchyma.
- Mixed form — a combination of meningococcemia and meningitis.
- Rare forms — endocarditis, arthritis, iridocyclitis.
They develop when the host organism's susceptibility is increased.
What type of exudative inflammation is characteristic of meningococcal meningitis?
Meningococcal meningitis is characterized by the development of acute purulent inflammation of the meninges. In the dynamics of the inflammatory process, the initially turbid serous exudate rapidly thickens and by the end of the second day acquires a pronounced purulent character (whitish, yellowish, or greenish color). By days 5–6, a fibrinous exudate joins it, giving the exudate a more viscous consistency.
What do the pia and arachnoid maters look like macroscopically in meningococcal meningitis?
Macroscopically, in meningococcal meningitis, the pia mater is hyperemic and covered with a continuous layer of yellowish purulent masses. The purulent exudate accumulates on both the basal and convex surfaces of the brain (predominantly in the frontal and parietal lobes), forming a characteristic "cap" or "beanie" appearance. Meanwhile, the brain tissue appears moist and flabby, and the gyri are flattened due to edema.
What clinical and morphological syndrome develops in fulminant meningococcemia?
Waterhouse-Friderichsen syndrome develops in fulminant meningococcemia. This severe complication is acute adrenal insufficiency resulting from bilateral massive adrenal hemorrhage against the background of acute sepsis and pronounced disseminated intravascular coagulation (DIC).
What pathomorphological changes occur in the adrenal glands in Waterhouse-Friderichsen syndrome?
In Waterhouse-Friderichsen syndrome, mild or massive corticomedullary hemorrhagic necrosis develops in the adrenal glands. Pathomorphologically, this manifests as bilateral massive hemorrhage into the adrenal tissue, with the lesion typically being more pronounced on the right side. These changes lead to acute adrenal insufficiency.
What is the character of the skin rash in generalized meningococcemia?
In meningococcemia, the skin rash is hemorrhagic in nature: ranging from hemorrhagic petechiae to large stellate hemorrhages. It appears on days 1–2 of the illness against the background of a pronounced intoxication syndrome. A rash appearing at the very beginning of the first day of the disease has been described for meningococcemia: large, abundant, rapidly spreading across the entire body, often with a necrotic component. In the fulminant course, rash elements appear very early, tend to coalesce, and present as ecchymoses.
What intracranial complications develop with the progression of purulent meningitis?
With the progression of purulent meningitis, the following intracranial complications develop:
- Brain edema and swelling — leads to brain displacement, herniation of the cerebellar tonsils, and entrapment of the medulla oblongata.
- Vascular lesions — cerebral arteritis, phlebitis, arterial and venous thrombosis.
- Cerebral infarctions — including hemorrhagic ones, occurring as a consequence of thrombosis.
- Inflammatory complications — spread of the infection to meningoencephalitis or the development of purulent ependymitis.
To memorize the main morphological feature of CMV: "CytoMegaloVirus — Aims Past, Sees like an Owl" (giant cells with "owl-eye" inclusions).
Class and exam questions
What is the main morphological difference of cells affected by cytomegalovirus?
In the formation of giant cytomegalic epithelial cells with dense nuclear inclusions surrounded by a clear halo (the "owl's eye" phenomenon).
How does the generalized acquired form of CMV differ from the congenital form?
In the acquired generalized form, unlike the congenital one, there is no brain involvement.
Which cells are target cells for cytomegalovirus?
The virus exhibits tropism for epithelial, endothelial, neural, and immunocompetent cells of the body.
What else to study on this topic
- Morphological differences of atypical interstitial pneumonia in CMV
- Pathogenesis of ulcerative colitis development in acquired CMV infection
- Mechanism of malabsorption syndrome formation in chronic cryptosporidiosis
- Effect of Corynebacterium diphtheriae exotoxin on host tissues
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