Cytomegalovirus (CMV) and Associated Diseases

Introduction

Cytomegalovirus (CMV) is a member of the Herpesviridae family, specifically classified under the Betaherpesvirinae subfamily. It is a ubiquitous virus, meaning it is found widely across human populations and other primates. CMV is known for its ability to cause a range of diseases, particularly in individuals with weakened immune systems, newborns, and organ transplant recipients. The most studied and clinically significant species within this genus is the Human cytomegalovirus (HCMV), also referred to as Human betaherpesvirus 5 (HHV-5).

Diseases Caused by CMV

Congenital CMV Infection

Congenital CMV infection occurs when the virus is transmitted from a pregnant mother to her fetus. It is one of the most common congenital infections, affecting about 0.5% to 2% of all live births. While many infants may be asymptomatic at birth, some exhibit symptoms such as jaundice, hepatosplenomegaly (enlarged liver and spleen), petechiae (small red spots due to bleeding), and microcephaly (small head size). Long-term complications can include sensorineural hearing loss, vision impairment, intellectual disabilities, and motor dysfunction.

CMV Mononucleosis

In immunocompetent individuals, CMV can be transmitted through bodily fluids such as saliva, urine, blood, semen, and breast milk. CMV mononucleosis presents with symptoms similar to those of Epstein-Barr virus (EBV) mononucleosis, including prolonged fever, fatigue, sore throat, and swollen lymph nodes. However, it is typically less severe than EBV-induced mononucleosis.

CMV in Immunocompromised Patients

Individuals at high risk include those with HIV/AIDS, cancer patients undergoing chemotherapy, and organ or bone marrow transplant recipients. In these populations, CMV can cause severe and life-threatening conditions such as retinitis (leading to blindness), gastrointestinal disease (colitis, esophagitis), pneumonitis (inflammation of the lung tissue), and encephalitis (inflammation of the brain).

CMV Pneumonia

CMV pneumonia is particularly severe in transplant recipients. Symptoms include cough, dyspnea (shortness of breath), and hypoxia. Diagnosis is typically confirmed via detection of CMV in bronchoalveolar lavage fluid or lung tissue biopsies. Antiviral treatments like ganciclovir, valganciclovir, and foscarnet are used, but these can have significant side effects and the risk of developing drug resistance.

Pathophysiology and Life Cycle

CMV infects a variety of cell types but has a strong tropism for epithelial cells of the salivary glands. Once it enters the host cell, the virus undergoes a complex life cycle involving nuclear replication and assembly. CMV has a large double-stranded DNA genome that encodes over 200 proteins, contributing to its ability to evade the host immune system and establish latent infections. The virus can remain dormant within the host's body for life, with periodic reactivation occurring especially under conditions of immunosuppression.

Diagnosis and Prevention

CMV infection is diagnosed through serological tests detecting CMV-specific antibodies, PCR to detect viral DNA, and histopathological examination showing characteristic "owl's eye" intranuclear inclusions in infected cells. Preventive measures include good hygiene practices to avoid transmission, prophylactic antiviral therapy in high-risk groups, and screening of blood and organ donations.

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Self-assessment MCQs (single best answer)

What is the most common congenital infection caused by Cytomegalovirus (CMV)?

Which subfamily does Cytomegalovirus belong to?

What is a common long-term complication of congenital CMV infection?

CMV mononucleosis is most similar in presentation to which other viral infection?

Which group is at the highest risk for severe CMV disease?

What is a typical diagnostic feature of CMV infection seen in histopathology?

Which antiviral drug is commonly used to treat severe CMV infections?

How is CMV primarily transmitted?

What is a common site of CMV latency in the human body?

What is the genome type of Cytomegalovirus?