HHV-5

Cytomegalovirus (CMV/HHV-5) is a large, enveloped, double-stranded DNA virus that establishes lifelong latency in monocytes, macrophages, and CD34+ progenitor cells after primary infection. Transmission occurs via saliva, urine, sexual contact, blood transfusion, organ transplantation, and vertically (transplacental, perinatal, or breast milk). In immunocompetent individuals, primary infection is often asymptomatic or presents as a heterophile-negative mononucleosis syndrome (fever, malaise, atypical lymphocytosis) - clinically similar to EBV mononucleosis but Monospot negative. Congenital CMV is the most common congenital infection in the US and a leading cause of nonhereditary sensorineural hearing loss; classic findings include periventricular calcifications, microcephaly, hepatosplenomegaly, jaundice, petechiae ('blueberry muffin' rash), and chorioretinitis - contrast with toxoplasmosis's diffuse calcifications. In immunocompromised hosts (transplant recipients, AIDS with CD4 <50), CMV reactivation causes retinitis (floaters, vision loss, 'pizza pie' fundus with hemorrhages and exudates), esophagitis/colitis (linear ulcers), pneumonitis, and hepatitis. Owl's eye intranuclear inclusion bodies are the classic histopathologic finding. Diagnosis relies on PCR viral load, pp65 antigenemia, or serology (IgM for acute infection); tissue biopsy showing inclusion bodies confirms end-organ disease. Treatment includes ganciclovir/valganciclovir (first-line; requires monitoring for myelosuppression), foscarnet (nephrotoxic, used in ganciclovir resistance or renal impairment allows avoiding myelosuppression), and cidofovir (nephrotoxic). Prophylaxis with valganciclovir is standard post-transplant in CMV-mismatched recipients (donor+/recipient-).