Cytomegalovirus (CMV) Infection

1. Clinical Overview

Summary

Cytomegalovirus (CMV), also known as Human Herpesvirus 5 (HHV-5), is a ubiquitous β-herpesvirus that establishes lifelong latent infection after primary exposure. CMV infection represents a critical spectrum of disease ranging from asymptomatic seroconversion in immunocompetent hosts to life-threatening end-organ disease in immunocompromised patients. [1,2]

The virus is remarkable for its dual nature: in healthy individuals, primary infection is typically asymptomatic or presents as a self-limiting mononucleosis-like syndrome, while in immunocompromised populations—including patients with HIV/AIDS (CD4 count less than 50 cells/μL), solid organ transplant (SOT) recipients, haematopoietic stem cell transplant (HSCT) recipients, and neonates—CMV causes severe, potentially fatal disease. [3,4]

Congenital CMV infection is the leading infectious cause of permanent neurological disability and non-genetic sensorineural hearing loss in developed countries, affecting approximately 0.6-0.7% of all live births globally. [5,6] Symptomatic congenital CMV carries a 40-58% risk of long-term sequelae including hearing loss, intellectual disability, cerebral palsy, and vision impairment. [7]

In the post-transplant population, CMV is a major cause of morbidity and mortality, with donor-positive/recipient-negative (D+/R-) matching conferring the highest risk. [8] CMV disease not only causes direct tissue damage but also exerts profound indirect immunomodulatory effects, increasing risks of graft rejection, opportunistic superinfections, and malignancy. [9]

Clinical Pearls

"Monospot-Negative Mononucleosis": Primary CMV infection in immunocompetent adults presents with fever, fatigue, and atypical lymphocytosis but with a negative heterophile antibody (Monospot) test, distinguishing it from Epstein-Barr virus (EBV) infectious mononucleosis. [10]

CMV Retinitis = CD4 less than 50: In patients with advanced AIDS, CMV retinitis is the most common ocular opportunistic infection, occurring almost exclusively at CD4 counts below 50 cells/μL. Classic fundoscopic appearance includes "pizza pie" or "cottage cheese and ketchup" retinopathy. [11,12]

Congenital CMV = Leading Infectious Cause of Sensorineural Deafness: CMV surpasses rubella, toxoplasmosis, and all other congenital infections as the primary infectious aetiology of permanent hearing loss, accounting for 15-21% of all childhood hearing impairment. [13]

Transplant CMV D+/R- = Highest Risk: Seronegative transplant recipients receiving organs from seropositive donors face primary CMV infection in a profoundly immunosuppressed state, with attack rates approaching 50-75% without prophylaxis. [14,15]

Owl's Eye Inclusions = Pathognomonic: Histopathological identification of large cells with prominent basophilic intranuclear inclusions surrounded by a clear halo, plus smaller cytoplasmic inclusions, is diagnostic of CMV tissue-invasive disease. [16]

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2. Epidemiology

Prevalence and Seroprevalence

CMV is one of the most prevalent chronic viral infections worldwide. Seroprevalence varies by geographic region, socioeconomic status, ethnicity, and age:

• Global adult seroprevalence: 45-100%, with higher rates in developing countries and lower-income populations. [1,17]
• United States: 50-60% of adults by age 40; up to 80-90% in Hispanic and African American populations. [18]
• Europe: 40-70% in adults, with northern European countries showing lower rates than southern/eastern Europe. [19]
• Sub-Saharan Africa and Asia: Seroprevalence often exceeds 90% by adolescence. [20]

Transmission Routes

At-Risk Populations

Incidence of Congenital CMV

• Primary maternal infection: 1-4% of seronegative pregnant women acquire CMV during pregnancy. [31]
• Fetal transmission rate: 30-40% following primary maternal infection; 1-2% following recurrent infection/reactivation. [32]
• Symptomatic at birth: 10-15% of infected neonates show signs/symptoms. [7]
• Long-term sequelae: 40-58% of symptomatic and 10-15% of asymptomatic congenitally infected infants develop permanent disabilities. [33]

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3. Aetiology and Pathophysiology

Virology

• Classification: CMV is a member of the Betaherpesvirinae subfamily within the Herpesviridae family, designated as Human Herpesvirus 5 (HHV-5). [1]
• Genome: Double-stranded linear DNA genome of ~235 kilobase pairs, the largest genome of all human herpesviruses, encoding > 200 open reading frames. [34]
• Structure: Enveloped virus with icosahedral nucleocapsid and tegument proteins that modulate host immune responses.
• Tropism: CMV infects a broad range of cell types including epithelial cells, endothelial cells, smooth muscle cells, fibroblasts, monocytes/macrophages, dendritic cells, and polymorphonuclear cells. [35]

Pathophysiological Mechanisms

Primary Infection and Latency Establishment

1. Entry and Replication: CMV enters host cells via receptor-mediated endocytosis (receptors include platelet-derived growth factor receptor-α and epidermal growth factor receptor). Following primary infection at mucosal surfaces (respiratory, genital, oral), the virus undergoes lytic replication in epithelial and endothelial cells. [36]

2. Dissemination: Infected monocytes and dendritic cells facilitate haematogenous viral spread to multiple organs.

3. Latency: CMV establishes latency primarily in CD34+ haematopoietic progenitor cells and their myeloid progeny (monocytes/macrophages). Viral genome is maintained episomally with minimal gene expression. [37,38]

4. Persistence: Unlike other herpesviruses, CMV exhibits continuous low-level replication even in immunocompetent hosts, requiring constant immune surveillance.

Immune Evasion Strategies

CMV has evolved numerous mechanisms to evade host immunity:

• MHC Class I downregulation: Multiple viral proteins (US2, US3, US6, US11) interfere with antigen presentation, preventing recognition by CD8+ T cells. [39]
• Chemokine receptor homologues: Viral proteins sequester host chemokines, disrupting immune cell trafficking. [40]
• Anti-apoptotic proteins: CMV encodes viral inhibitors of caspase-8-induced apoptosis (vICA) and mitochondrial inhibitor of apoptosis (vMIA). [41]
• NK cell evasion: UL18 is a MHC class I homologue that inhibits natural killer (NK) cell activation. [42]

Immunopathology in Immunocompromised Hosts

In the absence of effective T-cell immunity:

1. Uncontrolled viral replication: Loss of CD4+ and CD8+ T-cell surveillance permits viral reactivation from latency or progressive primary infection.

2. Direct cytopathic effects: CMV lytic infection causes cell enlargement ("cytomegaly"), cytolysis, and organ dysfunction. Characteristic histopathology includes "owl's eye" intranuclear inclusions. [16]

3. End-organ disease: Tissue-invasive disease develops in the retina (retinitis), gastrointestinal tract (colitis, oesophagitis), lungs (pneumonitis), liver (hepatitis), and central nervous system (encephalitis, ventriculoencephalitis, polyradiculopathy). [43]

4. Indirect immunomodulatory effects: CMV infection increases expression of MHC antigens on infected cells, promotes allograft inflammation, and may increase susceptibility to bacterial and fungal superinfections. [9,44]

Congenital Infection Pathophysiology

• Primary maternal infection: Viremia during pregnancy leads to transplacental transmission. The fetus lacks mature cellular immunity, permitting widespread viral replication. [45]
• Target organs: CMV preferentially affects the developing brain (periventricular leukomalacia, microglial nodules), cochlea (hair cell destruction), retina, and liver.
• Immune-mediated injury: Fetal inflammatory responses contribute to neuronal damage and gliosis. [46]

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4. Clinical Presentation

Immunocompetent Host

Asymptomatic Infection

• Frequency: 85-90% of primary CMV infections in immunocompetent children and adults are asymptomatic. [25]
• Diagnosis: Incidental seroconversion detected during routine screening.

CMV Mononucleosis Syndrome

• Frequency: 10-15% of primary CMV infections cause symptomatic disease. [10]
• Symptoms:
  • Prolonged fever (often > 2 weeks)
  • Malaise, fatigue
  • Pharyngitis (milder than EBV; exudates less common)
  • Myalgias and arthralgias
• Signs:
  • Lymphadenopathy (less prominent than EBV)
  • Hepatosplenomegaly
  • Maculopapular rash (rare, but may occur with antibiotic administration)
• Laboratory findings:
  • Atypical lymphocytosis (> 10% atypical lymphocytes)
  • Elevated transaminases (mild, 2-3× upper limit of normal)
  • Negative heterophile antibody test (Monospot-negative)
• Course: Self-limiting; resolution over 2-6 weeks. [47]

Rare Manifestations in Immunocompetent Hosts

• Guillain-Barré syndrome: CMV accounts for ~10% of antecedent infections. [48]
• Myocarditis and pericarditis: Case reports exist but very rare. [49]
• Pneumonitis: Extremely uncommon in immunocompetent adults.

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Immunocompromised Host

HIV/AIDS-Associated CMV Disease

CMV end-organ disease in HIV occurs predominantly when CD4 count falls below 50 cells/μL. [11,26]

CMV Retinitis

• Frequency: Most common CMV end-organ disease in AIDS (85% of cases). [11]
• Presentation:
  • Floaters, photopsia, scotomata (visual field defects)
  • Progressive, painless visual loss
  • Vision-threatening emergency
• Fundoscopic findings:
  • ""Pizza pie" or "cottage cheese and ketchup" appearance: Areas of fluffy white retinal necrosis with haemorrhage along retinal vessels"
  • Starts peripherally, progresses centrally
  • May be unilateral or bilateral
• Complications: Retinal detachment (15-30%), progression to blindness if untreated. [12,50]

CMV Colitis

• Frequency: 5-10% of CMV disease in AIDS. [51]
• Presentation:
  • Chronic diarrhoea (may be bloody)
  • Abdominal pain, cramping
  • Weight loss, anorexia
  • Fever
• Endoscopic findings: Diffuse colitis with mucosal ulceration; can involve any segment but commonly affects the colon.
• Complications: Bowel perforation, toxic megacolon. [52]

CMV Oesophagitis

• Presentation: Odynophagia, dysphagia, retrosternal chest pain.
• Endoscopy: Large, deep, well-circumscribed ulcers (differentiate from small HSV ulcers and white Candida plaques).
• Diagnosis: Biopsy showing owl's eye inclusions. [53]

CMV Pneumonitis

• Rare in AIDS (more common in HSCT).
• Presentation: Dyspnoea, non-productive cough, hypoxaemia.
• Imaging: Diffuse interstitial or reticulonodular infiltrates.

CMV Encephalitis and Polyradiculopathy

• CMV Ventriculoencephalitis:
  • "Presentation: Confusion, lethargy, cranial nerve palsies, nystagmus."
  • "MRI: Periventricular enhancement."
  • "CSF: Positive CMV PCR; may show polymorphonuclear pleocytosis. [54]"
• CMV Polyradiculopathy:
  • "Presentation: Ascending flaccid paraparesis, urinary retention, saddle anaesthesia."
  • "CSF: Polymorphonuclear pleocytosis with low glucose (mimics bacterial meningitis). [55]"

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Solid Organ Transplant (SOT) Recipients

CMV disease peaks 1-4 months post-transplant in the absence of prophylaxis. [27]

CMV Syndrome

• Definition: Fever, malaise, leucopenia, thrombocytopenia, with elevated CMV viral load but no evidence of end-organ disease. [56]
• Diagnosis: Clinical syndrome + positive CMV DNAemia (PCR).

Tissue-Invasive CMV Disease

• CMV Pneumonitis: Dyspnoea, cough, hypoxia; bronchoalveolar lavage (BAL) positive for CMV by PCR/culture + histopathology showing viral inclusions. [57]
• CMV Hepatitis: Transaminitis; liver biopsy showing CMV inclusions and hepatocyte necrosis.
• CMV Colitis: Diarrhoea, abdominal pain; colonoscopy with biopsy confirmation.
• CMV Nephritis (renal transplant): Graft dysfunction; biopsy showing CMV inclusions.

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Haematopoietic Stem Cell Transplant (HSCT) Recipients

• CMV Pneumonitis: Most feared complication; historically 50-80% mortality pre-ganciclovir. [28,29]
• Presentation: Fever, dyspnoea, non-productive cough, hypoxaemia 30-100 days post-transplant.
• Diagnosis: BAL with CMV detection + clinical/radiological pneumonitis.
• Risk factors: Allogeneic HSCT, graft-versus-host disease, CMV seropositivity (R+). [58]

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Congenital CMV Infection

Asymptomatic at Birth (85-90%)

• Presentation: Normal physical examination at birth.
• Risk of late-onset sequelae: 10-15% develop sensorineural hearing loss (may be progressive or delayed onset). [33,59]

Symptomatic at Birth (10-15%)

Neuroimaging Findings

• Periventricular calcifications: Pathognomonic; seen on cranial ultrasound or CT.
• Polymicrogyria, lissencephaly: Cortical malformations.
• Ventriculomegaly: Due to white matter injury.
• Cerebellar hypoplasia: Associated with poor neurodevelopmental outcomes. [61]

Long-Term Sequelae

• Sensorineural hearing loss (SNHL): Occurs in 40-60% of symptomatic and 10-15% of asymptomatic infants; may be progressive or late-onset. [59]
• Neurodevelopmental delay: Intellectual disability, cerebral palsy, seizures.
• Vision impairment: Due to chorioretinitis or optic atrophy.
• Dental enamel defects: Reported in some cases.

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5. Differential Diagnosis

CMV Mononucleosis (Immunocompetent)

CMV Retinitis (AIDS)

CMV Colitis (Immunocompromised)

Congenital Infections (TORCH)

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6. Investigations

Diagnosis of Active CMV Infection

Virological Tests

Tissue-Based Diagnosis (Biopsy)

• Histopathology: Gold standard for CMV end-organ disease.
  • Owl's eye inclusions: Large basophilic intranuclear inclusions with perinuclear halo + smaller cytoplasmic inclusions in enlarged cells ("cytomegaly"). [16]
  • "Immunohistochemistry (IHC): Antibodies against CMV antigens increase diagnostic sensitivity."
• CMV PCR on tissue: Can detect CMV DNA in biopsy specimens (lung, colon, liver).

Cerebrospinal Fluid (CSF) Analysis

• Indication: Suspected CMV encephalitis, ventriculoencephalitis, or polyradiculopathy.
• Findings:
  • "CMV DNA PCR: Positive in 80-90% of CMV CNS disease. [82]"
  • "Cell count: Polymorphonuclear pleocytosis (unusual for viral infection; mimics bacterial meningitis)."
  • "Protein: Elevated."
  • "Glucose: May be low in polyradiculopathy. [55]"

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Diagnosis of Congenital CMV Infection

Important: CMV detected > 3 weeks after birth cannot reliably distinguish congenital from perinatal infection. Universal newborn screening for CMV is not currently standard but is under investigation. [86]

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Transplant-Specific Monitoring

Pre-Transplant Risk Stratification

• Donor and Recipient CMV Serology (IgG):
  • "D+/R- (Donor seropositive, Recipient seronegative): Highest risk (50-75% incidence without prophylaxis). [14,15]"
  • "D+/R+ or D-/R+: Moderate risk (20-40%)."
  • "D-/R-: Lowest risk (less than 5%), but remains at risk from blood transfusions."

Post-Transplant Surveillance

• Universal prophylaxis: CMV PCR monitored intermittently during and after prophylaxis.
• Pre-emptive therapy: Weekly CMV PCR (whole blood or plasma) for 3-6 months post-transplant. Treat when viral load exceeds threshold (e.g., > 1000 IU/mL; varies by centre). [87,88]

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Investigations for CMV End-Organ Disease

CMV Retinitis

• Dilated fundoscopy by ophthalmologist: Diagnostic; characteristic "pizza pie" appearance. [11,12]
• CMV PCR (blood/vitreous): Supportive but not required for diagnosis if classic findings present.

CMV Colitis

• Colonoscopy with biopsy:
  • "Macroscopic: Mucosal oedema, erythema, ulceration."
  • "Histopathology: Owl's eye inclusions + IHC for CMV antigens. [51,52]"

CMV Pneumonitis

• High-resolution CT chest: Diffuse ground-glass opacities, interstitial infiltrates, or nodular lesions. [57]
• Bronchoalveolar lavage (BAL):
  • CMV PCR positive.
  • Cytology/culture may reveal CMV.
  • "Histopathology (transbronchial biopsy): Inclusions + IHC. [89]"

CMV Hepatitis

• Liver function tests: Elevated transaminases, bilirubin.
• Liver biopsy: Owl's eye inclusions, hepatocyte necrosis, CMV IHC. [90]

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7. Classification and Definitions

CMV Infection vs. CMV Disease (Transplant Context)

Congenital CMV Classification

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8. Management

Management Algorithm

┌─────────────────────────────────────────────────────┐
│         CMV INFECTION IDENTIFIED                    │
│  (Serology / PCR / Tissue Diagnosis)                │
└──────────────────────┬──────────────────────────────┘
                       │
       ┌───────────────┴────────────────┐
       │                                │
  IMMUNOCOMPETENT                 IMMUNOCOMPROMISED
       │                          (HIV, Transplant, etc.)
       │                                │
       ▼                                ▼
 ASSESS SEVERITY               ASSESS FOR END-ORGAN DISEASE
       │                                │
  ┌────┴────┐                  ┌────────┴────────┐
  │         │                  │                 │
Mild     Severe        CMV Viraemia       CMV Disease
Mononucleosis  (Rare)  (Asymptomatic      (Retinitis, Colitis,
  │         │           or CMV Syndrome)   Pneumonitis, etc.)
  │         │                  │                 │
  ▼         ▼                  ▼                 ▼
Supportive  Consider     Pre-emptive/      TREAT with
Care Only   Antivirals   Prophylactic      Ganciclovir/
                         Therapy           Valganciclovir
                                           (Induction + Maintenance)
                                                 │
                                                 ▼
                                           Monitor Viral Load
                                           + Clinical Response
                                                 │
                                   ┌─────────────┴───────────┐
                                   │                         │
                                Response                 Failure
                              (Viral Load ↓)        (Viral Load ↑)
                                   │                         │
                                   ▼                         ▼
                            Continue Therapy      Consider Resistance
                            Complete Course       + Second-Line Agents
                                                  (Foscarnet, Cidofovir)

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Treatment of CMV Disease

First-Line Antiviral Therapy

Duration of Therapy:

• CMV retinitis in AIDS: Induction 14-21 days; maintenance therapy until immune reconstitution (CD4 > 100 cells/μL for ≥3-6 months on ART). [96,97]
• CMV colitis/pneumonitis/encephalitis: Induction 14-21 days; may continue until CMV PCR negative or clinical resolution (often 3-6 weeks total). [93,98]
• Transplant CMV disease: Minimum 2-3 weeks; continue until CMV PCR negative on 2 consecutive tests 1 week apart. [99,100]

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Second-Line Antiviral Therapy

Used for ganciclovir resistance or ganciclovir intolerance.

CMV Resistance:

• Suspect if viral load plateau or rebound despite therapy after initial response.
• UL97 gene mutations (most common): Confer resistance to ganciclovir/valganciclovir. [104]
• UL54 (DNA polymerase) mutations: Confer resistance to ganciclovir, foscarnet, and cidofovir. [105]
• Resistance testing: Genotypic assays on plasma or tissue; available at reference laboratories.

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Adjunctive Therapy for CMV Pneumonitis (HSCT)

• CMV immunoglobulin (CMV-IG): Historically combined with ganciclovir for CMV pneumonitis post-HSCT. [106]
• Dose: 400 mg/kg IV every other day × 3 doses, then weekly.
• Evidence: Older studies suggested benefit; current data inconclusive. Practice varies by centre. [107]

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Key Side Effects and Monitoring

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CMV Management in HIV/AIDS

CMV Retinitis

1. Urgent ophthalmology referral: Vision-threatening emergency.
2. Antiviral therapy:
   • Immediately sight-threatening (lesions near macula/optic disc): Induction with IV ganciclovir 5 mg/kg BD or intravitreal ganciclovir/foscarnet (if systemic therapy contraindicated).
   • Non-immediately sight-threatening: Valganciclovir 900 mg PO BD induction. [111]
3. Maintenance therapy: Continue until immune reconstitution on ART (CD4 > 100 cells/μL for ≥3-6 months). [96,97]
4. Antiretroviral therapy (ART): Initiate or optimise ART to restore CD4 count. Immune reconstitution is definitive treatment. [112]
5. Immune Reconstitution Inflammatory Syndrome (IRIS): May occur 2-12 weeks after starting ART; presents with vitritis, worsening vision. Treat with topical/systemic corticosteroids + continue anti-CMV therapy. [113]

CMV Colitis/Oesophagitis/Pneumonitis

• Induction: Ganciclovir 5 mg/kg IV BD or valganciclovir 900 mg PO BD for 3-6 weeks (until symptom resolution + negative CMV PCR). [98,114]
• Maintenance: Not routinely recommended if ART initiated and CD4 recovering.
• ART: Start or optimise.

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CMV Prevention and Management in Transplant Recipients

Pre-Transplant Risk Stratification

• Serological testing: Determine donor (D) and recipient (R) CMV IgG status. [14,15]

Prophylaxis Strategy

Universal prophylaxis: Administer antiviral to all at-risk patients for defined duration post-transplant. [115,116]

Dose adjustment: Reduce dose for renal impairment (e.g., 450 mg OD if CrCl 40-59 mL/min). [119]

Limitations: Risk of late-onset CMV disease after prophylaxis cessation (15-20% in D+/R-). [120]

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Pre-Emptive Therapy Strategy

Weekly CMV PCR monitoring for 12-16 weeks post-transplant. Initiate treatment when viral load exceeds pre-defined threshold (varies by centre; e.g., 1000-10,000 IU/mL). [87,88,121]

Pre-emptive treatment:

• Valganciclovir 900 mg PO BD until CMV PCR negative on 2 consecutive weekly tests.

Advantages: Avoids unnecessary antiviral exposure; reduces drug toxicity and cost.

Disadvantages: Requires intensive monitoring; risk of breakthrough disease if non-compliance with monitoring.

Choice of strategy (prophylaxis vs. pre-emptive) varies by transplant type, local protocols, and patient factors. [122]

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Congenital CMV Treatment

Symptomatic Congenital CMV

Valganciclovir 6-month therapy:

• Indication: Symptomatic congenital CMV with CNS involvement (microcephaly, intracranial calcifications, abnormal neuroimaging, hearing loss). [123,124]
• Dose: 16 mg/kg PO BD for 6 months.
• Evidence: Randomised controlled trial showed improved hearing and neurodevelopmental outcomes at 2 years compared to no treatment or 6 weeks of IV ganciclovir. [125,126]
• Monitoring: FBC weekly for first month, then every 2 weeks (risk of neutropenia).
• Timing: Initiate within first month of life for maximal benefit. [127]

Asymptomatic Congenital CMV

• No treatment recommended currently for asymptomatic infants.
• Audiological surveillance: Serial hearing assessments (ABR) at 1, 3, 6, 12, 18, 24, 30, and 36 months (hearing loss may be delayed or progressive). [85]

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Special Populations

Pregnancy

• Ganciclovir/valganciclovir: Contraindicated in pregnancy (teratogenic in animal studies). [128]
• Maternal primary CMV: No proven antiviral therapy for maternal infection during pregnancy to prevent fetal transmission. CMV hyperimmune globulin under investigation. [129,130]
• Prenatal diagnosis: Amniocentesis (CMV PCR on amniotic fluid) can diagnose fetal infection but does not predict severity. [131]

Neonates (Perinatal CMV)

• Breast milk transmission: Common in seropositive mothers; usually asymptomatic in term infants.
• Premature infants: May develop symptomatic CMV from breast milk; some advocate pasteurisation or freezing of breast milk. [132]

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9. Complications

Complications by Host and Organ System

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10. Prognosis and Outcomes

Immunocompetent Hosts

• CMV mononucleosis: Excellent prognosis; self-limiting illness. Full recovery within 2-6 weeks. Rare long-term sequelae. [47]
• Post-infectious fatigue: Some patients report prolonged fatigue lasting weeks to months.

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HIV/AIDS

• Pre-ART era: CMV retinitis led to blindness in > 90% without treatment; median survival 6-12 months. [136]
• ART era: With effective ART + anti-CMV therapy, immune reconstitution prevents progression. Mortality significantly reduced. [112]
• Immune reconstitution: CD4 > 100-150 cells/μL for ≥3-6 months allows discontinuation of CMV maintenance therapy (secondary prophylaxis). [96,97]
• IRIS: Occurs in 15-30% starting ART with CMV retinitis; usually manageable. [113]

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Solid Organ Transplant

• CMV syndrome: Generally good prognosis with antiviral therapy; resolution in 2-4 weeks. [56]
• CMV tissue-invasive disease: Higher morbidity; graft dysfunction in 20-30%; mortality 5-10% (higher in lung transplant). [137,138]
• Late-onset CMV disease: Occurs in 10-20% after prophylaxis cessation; associated with higher graft loss. [120]
• Graft survival: CMV disease independently associated with reduced long-term graft survival. [135,139]

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Haematopoietic Stem Cell Transplant

• CMV reactivation: Common (30-70% in seropositive recipients); most managed with pre-emptive therapy. [58]
• CMV pneumonitis: Historically 50-80% mortality; improved to 20-50% with ganciclovir ± CMV-IG. [28,29,106]
• Impact on overall survival: CMV reactivation associated with increased non-relapse mortality and reduced overall survival. [140]

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Congenital CMV

Prognostic factors for poor outcome:

• Symptomatic disease at birth (especially microcephaly, intracranial calcifications, chorioretinitis). [7,33]
• Severe thrombocytopenia, petechiae.
• Neuroimaging abnormalities (periventricular calcifications, polymicrogyria, cerebellar hypoplasia). [61]

Impact of antiviral therapy: 6 months of valganciclovir improves hearing and neurodevelopmental outcomes at 2 years. [125,126]

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11. Prevention and Screening

Primary Prevention

General Population

• Hand hygiene: Frequent handwashing, especially after contact with children's saliva or urine (major transmission route in daycare settings). [141]
• Avoiding saliva contact: Pregnant women (especially seronegative) should avoid sharing utensils, cups, toothbrushes with young children; avoid kissing children on lips. [142]
• Safe sex practices: Condom use reduces sexual transmission.

Healthcare Settings

• Standard precautions: Contact precautions for patients with active CMV excretion (urine, saliva) in neonatal/paediatric units.

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Blood Product Screening

• Leucoreduction: Reduces CMV transmission from blood transfusions (CMV resides in leucocytes). [143]
• CMV-seronegative blood products: For high-risk seronegative recipients (e.g., D-/R- transplant, premature neonates). [24]

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Vaccination

• No licensed CMV vaccine currently available. Multiple vaccine candidates in development (glycoprotein B, pp65, DNA vaccines). [144,145]

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Screening Programs

Transplantation

• Universal screening: All transplant donors and recipients undergo CMV serology pre-transplant to guide prophylaxis/monitoring strategies. [14,15]

Pregnancy

• Routine prenatal CMV screening: Not recommended in most countries (UK, USA) due to lack of proven intervention to prevent fetal transmission. [146,147]
• Targeted screening: Some advocate screening women with high-risk exposures (daycare workers, healthcare workers) or with ultrasound abnormalities suggestive of congenital infection. [148]

Newborn Screening

• Universal newborn CMV screening: Not currently standard in most countries, but under active investigation. [86]
• Targeted screening: Infants who fail newborn hearing screen should undergo CMV testing (urine/saliva PCR within 3 weeks). [149,150]

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12. Key Guidelines

International Consensus Guidelines

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13. Examination Focus

High-Yield Exam Topics

MRCP / FRACP / General Medicine

1. CMV mononucleosis vs. EBV: Monospot-negative, atypical lymphocytosis, elevated transaminases.
2. CMV retinitis in AIDS: CD4 less than 50, "pizza pie" fundus, urgent ophthalmology referral, ganciclovir/valganciclovir + ART.
3. Transplant CMV prophylaxis: D+/R- highest risk; valganciclovir 3-6 months post-transplant.
4. CMV colitis: Chronic diarrhoea in immunocompromised; colonoscopy with biopsy (owl's eye inclusions).
5. Ganciclovir side effects: Myelosuppression (neutropenia, thrombocytopenia); monitor FBC.

MRCPCH / Paediatrics

1. Congenital CMV: Leading infectious cause of congenital deafness; periventricular calcifications on imaging.
2. Symptomatic congenital CMV: Petechiae, microcephaly, hepatosplenomegaly, IUGR.
3. Treatment: Valganciclovir 6 months for symptomatic congenital CMV improves hearing/neurodevelopment.
4. Screening: Urine/saliva CMV PCR within 3 weeks of birth to diagnose congenital infection.
5. Audiological surveillance: Serial hearing assessments (hearing loss may be delayed/progressive).

Infectious Diseases / HIV Medicine

1. CMV end-organ disease in AIDS: Retinitis, colitis, oesophagitis, encephalitis, polyradiculopathy.
2. Immune reconstitution with ART: Definitive treatment; allows discontinuation of CMV maintenance therapy.
3. CMV IRIS: Vitritis, worsening vision 2-12 weeks post-ART initiation; treat with corticosteroids.
4. Resistance: UL97 mutations → ganciclovir resistance; switch to foscarnet.

Transplant Medicine

1. Prophylaxis vs. pre-emptive therapy: Both acceptable strategies; choice varies by centre and transplant type.
2. Late-onset CMV disease: Occurs after prophylaxis cessation; higher risk of graft dysfunction.
3. CMV indirect effects: Increased risk of graft rejection, opportunistic infections, PTLD, chronic allograft dysfunction.

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Common Exam Questions

SBA (Single Best Answer) Style

Q1: A 32-year-old man with newly diagnosed HIV (CD4 count 28 cells/μL) presents with 2 weeks of floaters and blurred vision in his right eye. Fundoscopy reveals areas of fluffy white retinal infiltrates with haemorrhage. What is the most appropriate initial management?

A. Intravitreal anti-VEGF injection
B. Oral aciclovir 800 mg five times daily
C. Urgent ophthalmology referral and intravenous ganciclovir
D. Topical corticosteroids
E. Observation and start antiretroviral therapy

Answer: C. This is CMV retinitis (CD4 less than 50, classic "pizza pie" fundus). Vision-threatening emergency requiring urgent ophthalmology assessment and IV ganciclovir or oral valganciclovir induction therapy. ART should be initiated but anti-CMV therapy is urgent. [11,96,152]

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Q2: A 4-month-old infant is referred after failing newborn hearing screening. Urine CMV PCR is positive. Which investigation is most important for prognostication?

A. CMV serology (IgG and IgM)
B. Cranial MRI
C. Liver ultrasound
D. Echocardiography
E. Full blood count

Answer: B. Neuroimaging (MRI or CT) showing periventricular calcifications, ventriculomegaly, or cortical malformations predicts poor neurodevelopmental outcomes in congenital CMV. [61,154]

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Q3: A 55-year-old woman undergoes renal transplantation. She is CMV IgG-negative; the donor is CMV IgG-positive. What is the most appropriate CMV management strategy?

A. No prophylaxis required
B. Oral valganciclovir 900 mg daily for 3-6 months
C. Weekly CMV PCR with no prophylaxis
D. Intravenous ganciclovir 5 mg/kg twice daily for 2 weeks
E. CMV hyperimmune globulin infusion

Answer: B. D+/R- is the highest risk group for CMV disease post-transplant. Universal prophylaxis with valganciclovir 900 mg daily (dose-adjusted for renal function) for 3-6 months is recommended. [151]

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Viva/Oral Examination Points

Opening Statement: "Cytomegalovirus is a ubiquitous herpesvirus that causes lifelong latent infection. While asymptomatic in most immunocompetent individuals, it is a major cause of morbidity in immunocompromised hosts, including HIV/AIDS patients, transplant recipients, and neonates with congenital infection. CMV retinitis in AIDS occurs at CD4 counts below 50 cells/μL and presents as painless vision loss with characteristic fundoscopic findings. Congenital CMV is the leading infectious cause of sensorineural hearing loss and neurodevelopmental disability."

Key Facts to Mention:

1. Epidemiology: 50-80% adult seroprevalence; 0.6-0.7% of live births affected by congenital CMV. [1,5]
2. Pathophysiology: Establishes latency in CD34+ myeloid progenitors; reactivates during immunosuppression. [37,38]
3. Clinical syndromes: Asymptomatic in immunocompetent; retinitis/colitis/pneumonitis in immunocompromised; hearing loss/microcephaly in congenital CMV.
4. Diagnosis: CMV DNA PCR (quantitative) for viraemia; histopathology (owl's eye inclusions) for tissue-invasive disease. [77,78]
5. Treatment: Ganciclovir or valganciclovir first-line; foscarnet for resistance. [92-95]
6. Transplant prophylaxis: D+/R- highest risk; valganciclovir prophylaxis or pre-emptive therapy with weekly PCR monitoring. [151]
7. Congenital CMV: Valganciclovir 6 months for symptomatic disease improves hearing and neurodevelopmental outcomes. [125,126]

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Common Mistakes

❌ Failing to recognise CD4 less than 50 threshold for CMV retinitis: CMV retinitis in AIDS is almost exclusively seen with CD4 less than 50 cells/μL. Always check CD4 count. [11]

❌ Treating CMV mononucleosis with antivirals in immunocompetent patients: CMV mononucleosis in immunocompetent hosts is self-limiting; antivirals not indicated. [47]

❌ Confusing Monospot-positive (EBV) with Monospot-negative (CMV) mononucleosis: CMV is the most common cause of heterophile-negative mononucleosis. [10]

❌ Missing the diagnosis of congenital CMV: Urine/saliva CMV testing must be done within 3 weeks of birth to distinguish congenital from perinatal infection. [83,149]

❌ Not dose-adjusting ganciclovir/valganciclovir for renal function: Both drugs are renally excreted; failure to adjust doses leads to toxicity or treatment failure. [119]

❌ Forgetting CMV indirect effects in transplant: CMV increases risks of graft rejection, opportunistic infections, and PTLD—not just direct tissue damage. [9,44]

❌ Using ganciclovir in pregnancy: Ganciclovir is teratogenic in animal studies and contraindicated in pregnancy. [128]

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Model Answers

Q: A 28-year-old pregnant woman asks about the risk of CMV to her unborn baby. How would you counsel her?

A: "Cytomegalovirus is a common virus that most people acquire during childhood or young adulthood. About 50-60% of women of childbearing age have been previously infected. If you are already immune (CMV IgG-positive), the risk of transmitting CMV to your baby is very low, around 1-2%, and almost all babies born with CMV in this scenario are healthy. [32]

However, if you have never had CMV before and acquire it for the first time during pregnancy (which happens in 1-4% of seronegative pregnant women), the risk of transmission to the baby is higher, around 30-40%. [31,32] About 10% of infected babies will have symptoms at birth such as hearing loss, small head size, or developmental problems. Another 10-15% of babies who appear normal at birth may develop hearing loss later in childhood. [7,59]

To reduce your risk of acquiring CMV during pregnancy, I recommend frequent handwashing, especially after changing nappies or handling children's toys and saliva, avoiding sharing utensils or cups with young children, and not kissing young children on the mouth. [141,142]

Unfortunately, we do not routinely screen all pregnant women for CMV because there is currently no proven treatment to prevent transmission to the baby. If you develop symptoms suggestive of CMV or if an ultrasound shows abnormalities, we can perform blood tests and possibly amniocentesis to check for infection. If your baby is diagnosed with CMV at birth, treatment with antiviral medication may improve outcomes, particularly for hearing." [154,155]

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Q: Describe your approach to managing CMV disease in a renal transplant recipient.

A: "My approach would be systematic. First, I would confirm the diagnosis: CMV disease requires evidence of CMV viraemia (detectable CMV DNA by PCR, ideally quantitative) plus clinical symptoms or signs of organ involvement. I would distinguish between CMV syndrome (fever, malaise, leucopenia without end-organ disease) and tissue-invasive disease (e.g., colitis, pneumonitis), as the latter may require biopsy confirmation with histopathology showing CMV inclusions. [56,91]

For treatment, I would initiate antiviral therapy with either intravenous ganciclovir 5 mg/kg twice daily or oral valganciclovir 900 mg twice daily (dose-adjusted for renal function) for induction therapy. [92,99] The choice depends on disease severity: IV ganciclovir is preferred for severe disease (e.g., pneumonitis), while valganciclovir can be used for less severe manifestations such as CMV syndrome or mild colitis. [151]

I would monitor CMV viral load weekly during treatment. Therapy should continue for a minimum of 2-3 weeks and until the CMV PCR is negative on two consecutive tests one week apart. [99,100]

I would also reduce immunosuppression in consultation with the transplant team, as this helps restore antiviral immunity, though this must be balanced against the risk of rejection. [151]

Key monitoring includes full blood count twice weekly (ganciclovir causes myelosuppression), renal function, and CMV viral load. If the patient develops neutropenia, I would consider dose reduction or adding G-CSF support. [108]

If viral load fails to decline or rebounds despite therapy, I would suspect antiviral resistance and send samples for genotypic resistance testing. Resistance would prompt switching to second-line therapy with foscarnet. [101,102,104]

Finally, I would ensure close follow-up after completing therapy, as relapse can occur, and patients may require extended secondary prophylaxis depending on their immunosuppression status." [151]

---

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