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Infectious Disease and Microbiology – Cytomegalovirus Infection
Cytomegalovirus (CMV) infection refers to a spectrum of diseases caused by Cytomegalovirus, a DNA virus belonging to the herpesvirus family (Human Herpesvirus 5). Like other herpesviruses, CMV establishes lifelong latency after primary infection and may reactivate during periods of immunosuppression. Infection may be asymptomatic, present as a mononucleosis-like syndrome, or cause severe tissue-invasive disease, particularly in immunocompromised individuals.
CMV is a common pathogen worldwide. In the United States, the incidence among individuals aged 10–49 years is approximately 1.6 infections per 100 susceptible persons per year. About 27,000 new infections occur annually among seronegative pregnant women. Seroprevalence increases with age and is higher among individuals of lower socioeconomic status. Approximately 60% of people older than 6 years in the US are seropositive, and rates exceed 90% in individuals over 80 years of age.
Immunosuppression is the primary risk factor for severe CMV disease. In solid organ transplantation (SOT), the highest risk occurs when a CMV-seronegative recipient receives an organ from a CMV-seropositive donor (CMV D+/R– mismatch). In allogeneic hematopoietic stem cell transplantation, higher risk occurs when a CMV-seropositive recipient receives a graft from a seronegative donor (CMV D–/R+). Lung, small intestine, and pancreas transplant recipients are at particularly high risk, followed by liver and heart transplant recipients, while kidney recipients have lower risk. Additional risk factors include use of lymphocyte-depleting agents (e.g., anti-thymocyte globulin), acute allograft rejection, graft-versus-host disease, and HIV infection with CD4 counts below 50 cells/mm³. CMV is also associated with bone marrow transplantation, AIDS, and hematologic malignancies such as lymphoma and leukemia.
Pathophysiologically, primary infection in transplant recipients occurs through donor transmission (CMV D+/R–), while reactivation occurs when latent virus in a seropositive recipient becomes active during immunosuppression. CMV infection may be asymptomatic (subclinical infection) or symptomatic. Symptomatic infection is classified as CMV syndrome (fever and systemic symptoms without organ involvement) or tissue-invasive disease affecting specific organs. The transplanted organ is particularly vulnerable to tissue-invasive disease.
In immunocompetent individuals, CMV infection is often asymptomatic or presents as a mononucleosis-like illness with fever, malaise, myalgias, lymphadenopathy, splenomegaly, and sometimes rash. In immunosuppressed patients, CMV syndrome presents with fever, malaise, myalgias, and arthralgias. Tissue-invasive disease may involve multiple organs. CMV colitis is common and presents with abdominal pain and diarrhea. CMV gastritis may cause odynophagia, nausea, and vomiting. Pneumonitis presents with fever, cough, and dyspnea and is particularly severe in bone marrow transplant recipients. Hepatitis and myocarditis may occur. CMV retinitis, especially in advanced HIV infection, causes progressive visual loss and characteristic peripheral retinal lesions with yellow-white exudates and hemorrhage. Meningoencephalitis presents with headache, photophobia, and lethargy. Spinal cord involvement (myelitis or polyradiculitis) may cause back pain and ascending weakness, particularly in HIV-infected patients.
Laboratory findings may include anemia, thrombocytopenia, and atypical lymphocytosis. CMV IgG indicates prior exposure and latent infection; IgM may indicate acute infection or reactivation but is often unreliable in immunosuppressed individuals. Because of rapid turnaround time and high sensitivity, nucleic acid amplification testing (real-time PCR) and pp65 antigenemia assays are now preferred diagnostic tools. Antigenemia testing detects CMV pp65 protein in leukocytes but is less useful in neutropenic patients. Viral culture may demonstrate cytopathic effects after several weeks; shell vial assays provide results within 24–48 hours. Drug resistance should be suspected if viral load fails to decline after two weeks of full-dose therapy. Mutations in UL97 are associated with ganciclovir resistance, while UL54 mutations may confer cross-resistance to ganciclovir, foscarnet, and cidofovir.
Imaging findings depend on organ involvement. CMV pneumonitis shows interstitial infiltrates on chest imaging. CMV colitis may show bowel wall thickening on CT. Brain MRI in CMV encephalitis may demonstrate periventricular inflammation or meningeal enhancement. Tissue biopsy reveals characteristic cytopathic changes with large intranuclear inclusions surrounded by a clear halo (“owl’s eye” appearance), sometimes accompanied by cytoplasmic inclusions.
The differential diagnosis varies by presentation and includes infectious mononucleosis, toxoplasmosis, acute HIV infection, human herpesvirus 6 infection, viral hepatitis, viral gastroenteritis, cryptosporidiosis, and Clostridioides difficile infection.
In immunocompetent individuals, CMV syndrome is usually self-limited and does not require treatment. In immunocompromised patients, antiviral therapy is essential. First-line therapy is intravenous ganciclovir (5 mg/kg twice daily, dose-adjusted for renal function). Oral valganciclovir (900 mg twice daily) may be used for mild-to-moderate disease and as step-down therapy. For CMV retinitis in AIDS patients, systemic therapy combined with intraocular ganciclovir implant improves outcomes. Second-line agents for ganciclovir-resistant CMV include foscarnet and cidofovir. High-dose ganciclovir may be considered in low-level resistance. Reduction of immunosuppressive therapy is recommended when possible, and CMV immunoglobulin may be used in severe disease, particularly pneumonitis.
Patients receiving treatment should undergo weekly monitoring of viral load. Therapy typically continues for at least 2–4 weeks and preferably until viremia clears, with additional maintenance therapy in high-risk individuals. Prognosis varies with immune status; severe disease such as pneumonitis or encephalitis carries high mortality. CMV colitis may lead to perforation and peritonitis, myocarditis may cause heart failure, and in HIV-infected patients CMV may cause cauda equina syndrome. In transplant recipients, indirect CMV effects include acute rejection, chronic graft failure, bronchiolitis obliterans, accelerated vasculopathy, vanishing bile duct syndrome, and chronic kidney injury.
Congenital CMV infection is a major cause of congenital anomalies in industrialized countries and may result in fetal loss, neonatal jaundice, anemia, and central nervous system damage. There is currently no available CMV vaccine.
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