Etiology and epidemiological features
The causative agent of the disease is the Varicella-Zoster Virus (Varicella-Zoster Virus, HHV-3). The sole source of infection is an infected human (presenting with either chickenpox or shingles).
Transmission occurs predominantly via airborne droplets (aerosol inhalation). Contact-transmissive and vertical (transplacental fetal infection) routes are significantly less common.
The incidence shows a pronounced autumn-winter seasonality, with the peak frequency of cases recorded among preschool children. Infants in the first months of life are virtually unsusceptible to the virus due to transplacentally acquired maternal antibodies. A prior infection confers lifelong, lasting immunity; reinfection cases are exceptionally rare.
Pathogenesis timeline
The infectious process has a distinct staging that reflects the migration of the virus within the patient's body:
- Day Zero (D 0): the pathogen settles on the mucous membranes of the upper respiratory tract or conjunctiva, actively invading the epithelium.
- Lymphogenic phase: the virus travels to regional lymph nodes for further replication.
- D 4–6 (Primary viremia): breaching of the lymphatic barrier. The pathogen is carried via the bloodstream to parenchymal organs (spleen, liver), where large-scale assembly of new virions takes place.
- Secondary viremia: massive release of the virus from internal organs back into the systemic circulation.
- D 11–21 (Clinical manifestation): the virus disseminates to the skin and mucous membranes, causing the characteristic rash.
Characteristics and evolution of the rash
The virus exhibits high epitheliotropism. Settling in the stratum spinosum of the epidermis, it causes ballooning degeneration of epithelial cells. Cell necrosis leads to the formation of cavities filled with serous fluid, which are typical vesicles.
The resolution of an individual element takes several hours and goes through the stages: macula (spot) → papule → unilocular vesicle with a hyperemic halo → crust (dries up in 1–2 days). Since the damage does not affect the deep skin layer (dermis), no scars remain after the crusts fall off.
The most important clinical markers of chickenpox are:
- Polymorphism of the rash: elements at different stages (from spot to crust) are present simultaneously in the same skin area. This is due to the phenomenon of daily (successive) eruptions.
- Localization: the scalp is invariably affected, with elements present on the oral mucosa, larynx, or conjunctiva (enanthema).
- Association with fever: each new wave of eruptions is accompanied by a temperature spike (usually 37.5–38.5 °C) and malaise.
Specific and secondary complications
In modern practice, chickenpox runs a predominantly mild or moderate course, with normalization of temperature by days 3–5. Complications are rare, but possible, and fall into two categories:
- Specific (viral): caused by the direct action of HHV-3. Due to its neurotropism, the virus can affect the central nervous system (meningoencephalitis, myelitis). Against the background of profound immunodeficiency, the infection becomes generalized into a visceral form (involvement of parenchymal organs, specific pneumonia, and hepatitis).
- Bacterial: associated with secondary pyogenic flora joining the rash elements. This can lead to abscesses, phlegmons, purulent conjunctivitis, and secondary pneumonia.
Distinguishing chickenpox from other infections is aided by the "hair and clean palms" rule: the rash invariably hides on the scalp (a pathognomonic sign), but practically never affects the palms and soles.
Class and exam questions
What is the "rash syndrome" in chickenpox?
This is a transient prodromal rash that may precede typical vesicles. It resembles the rash of measles or scarlet fever, but disappears without a trace in just a few hours.
Why is rash polymorphism called "false"?
Polymorphism is called false because the skin features not fundamentally different types of rash, but rather successive evolutionary phases of the same element (from spot to papule, then vesicle and crust), arising due to the wave-like nature of the eruptions.
How to distinguish a chickenpox vesicle from a herpetic one?
Chickenpox is characterized by a unilocular vesicle with clear contents and a thin wall that easily collapses when punctured. Herpes simplex elements are typically multilocular.
What else to study on this topic
- Morphological differences between chickenpox vesicles and bacterial infection pustules
- Differential diagnosis with measles, scarlet fever, and enteroviral exanthema
- Features of the visceral form in immunodeficient states
- Pathogenesis of nervous tissue involvement (neurotropism of Varicella-Zoster Virus)
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