CMV Infections

• Introduction.
• Primary infection.
• Latency.
• Reactivation.

Introduction

• CMV (HHV5) is a beta-herpesvirus that only naturally occurs in humans. There are no animal reservoirs.
• The naming of CMV reflects that it tends to enlarge the cells that it infects (cyto = cell, mega = big).
• CMV was first isolated from salivary gland tissue.
• CMV is an important human pathogen, particularly amongst immunocompromised patients including those who have AIDS or are immunosuppressed, for example following organ transplantation:
  • CMV infection in immunocompromised patients is associated with high morbidity and can cause death.
• CMV is of direct relevance to the practice of dentistry as:
  • Appropriate Cross Infection practices will prevent unnecessary spread of CMV infections in the dental surgery.
  • It can cause an illness similar to infectious mononucleosis (see Glandular Fever-Like Syndromes).
  • It can cause CMV sialadenitis.
  • It can cause severe oral mucosal ulceration in immunocompromised patients (particularly those with AIDS).
  • It is the most common congenital viral infection in the United Kingdom.
    • CMV viraemia associated with primary infection or reactivation can cross the placenta and infect the developing foetus.
    • This can result in severe developmental abnormalities with long-term morbidity including hearing loss, mental retardation and cerebral palsy.
    • Similar congenital abnormalities may also follow infection with either Toxoplasmosis, Rubella or HSV (ToRCH syndrome, where C is CMV infection).
• There are obvious advantages to vaccination against CMV infection, but to date, it has not been possible to produce an effective vaccine.
• CMV, in common with other HHVs, causes primary infection, latency for life, and reactivation that may be symptomatic.

1. Primary Infection

• Secretions from an infected person shedding virus are transferred directly (not by aerosol) to mucosal surfaces of an uninfected individual. CMV can also be spread via blood transfusions and organ transplantation.
  • In developed countries, infection prevalence is low in children (up to 15%), but increases to approximately 50% in young adults.
    • Prevalence rates are greater in lower, compared to higher socioeconomic groups.
  • In common with other HHVs, infection prevalence in developing countries is higher at an earlier age (90% by 2 years old).
• CMV is able to infect a wide range of different human cells including those found in salivary glands.
• Symptomatic primary infection is much more likely in immunocompromised patients than individuals who are immunocompetent.
• Symptomatic primary infection manifests as
  • A Glandular Fever-Like Syndrome.
    • Compared to Infectious Mononucleosis (EBV):
      • Lymphadenopathy is usually less prominent.
      • Pharyngitis is typically less severe.
  • CMV Sialadentitis, which may occur with glandular fever-like symptoms, and is characterised by acute onset of:
    • Painful, swollen major salivary glands.
    • Diminished saliva production and xerostomia, with an increased risk of developing an ascending bacterial infection.

2. Latency

• Latency is established at the time of primary infection.
• During this time the host defences are unable to detect and eliminate CMV from the body.
  • Accordingly, CMV infections are lifelong.

3. Reactivation

• In some individuals, CMV can be reactivated from the latent state.
• Control of reactivation remains poorly understood, although immune status is important.
• In immunecompetent individuals reactivation is mostly asymptomatic.
  • Some patients experience Glandular Fever-Like Syndrome symptoms that relapse and remit over time.
• By contrast, severe clinical illness occurs during reactivation in immunocompromised patients:
  • Many different organs and tissues can be affected:
    • For example, in AIDS, CMV can cause:
      • Severe oral ulceration.
      • Sialadenitis with xerostomia.
      • Retinitis, encephalitis, colitis and oesophagitis.
  • Management is specialised, complex and not always successful in controlling CMV reactivation in immunocompromised patients.

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