Chickenpox

Varicella-zoster virus (VZV) spreads primarily through inhalation of respiratory droplets from infected individuals or direct contact with vesicular fluid from skin lesions. The virus enters the upper respiratory tract and infects the mucosal epithelium, initiating infection. This dual transmission route makes chickenpox highly contagious, particularly in crowded environments where respiratory droplet exposure is common.

During primary viremia, immune cells capture the virus from respiratory epithelial cells and transport it to lymph nodes, then into the bloodstream. The virus then reaches organs like the liver and spleen for further replication. Secondary viremia follows, allowing the virus to disseminate to the skin, where it produces the characteristic rash that evolves from macules to vesicles and crusted lesions.

During secondary viremia, varicella-zoster virus reaches the skin and infects epithelial cells, triggering a centripetal rash that appears in successive waves. The rash progresses through distinct stages: macules, papules, vesicles, and crusted lesions. This characteristic progression results from the virus's tropism for skin tissue and the host's inflammatory response to viral replication in dermal cells.

Humoral immunity produces neutralizing antibodies that limit viral dissemination, while cellular immunity—particularly CD8+ cytotoxic T lymphocytes—clears infected cells. These coordinated immune responses activate during infection to control viral spread and eventually resolve the acute disease. However, despite effective immune control, the virus establishes latency in sensory dorsal root ganglia, evading complete elimination.

Herpes zoster (shingles) results from reactivation of latent varicella-zoster virus that persists in dorsal root ganglia after primary chickenpox infection resolves. Reactivation typically occurs due to immunosuppression or age-related decline in cell-mediated immunity. Unlike chickenpox, herpes zoster causes painful, unilateral dermatomal eruptions and is frequently associated with complications such as postherpetic neuralgia.

Following resolution of primary infection, varicella-zoster virus exhibits neurotropism and establishes latency in sensory dorsal root ganglia. During latency, the viral genome persists in a non-replicative state with minimal transcriptional activity, allowing it to evade immune detection indefinitely. This latent infection can reactivate later in life, causing herpes zoster in susceptible individuals.

Although generally self-limiting in children, chickenpox can lead to severe complications in neonates, adults, and immunocompromised individuals whose cellular immunity is insufficient to control viral dissemination. Age-related and immunosuppression-related declines in CD8+ cytotoxic T lymphocyte function increase disease severity. Widespread immunization with the live-attenuated varicella vaccine has markedly reduced incidence and severity in vaccinated populations.