Cytomegalovirus infection

Victorian statutory requirement

Notification and school exclusion are not required.

Infectious agent

Cytomegalovirus (CMV) also designated as Human herpesvirus 5, is a member of the subfamily betaherpesvirus of the family herpesviridae. Other members of the herpesvirus group include herpes simplex virus types 1 and 2, varicella zoster virus (which causes chickenpox), and Epstein-Barr virus (which causes infectious mononucleosis/glandular fever). These viruses share a characteristic ability to remain dormant within the body over a long period.

Identification

Clinical features
Primary CMV infection of children and adults may cause a mononucleosis syndrome clinically indistinguishable from that caused by the Epstein-Barr virus (glandular fever). Features include fever, lymphadenopathy and mild hepatitis. More rare features include anaemia, thrombocytopaenia, pneumonitis, meningoencephalitis and Guillain-Barr? syndrome. Many infections are asymptomatic, particularly those in young children.

Pregnancy
Healthy pregnant women are not at special risk for disease from CMV infection but between 1% and 5% are infected for the first time during their pregnancy. Many women will already have been exposed to CMV and so are not at risk of a new infection during their pregnancy.

When infected with CMV, most pregnant women have no symptoms while a very few have a disease resembling mononucleosis. However, for those women who are infected for the first time during their pregnancy, one in three will pass the CMV infection on to their developing unborn child.

CMV remains the most important cause of congenital viral infections in Australia. For infants who are infected by their mothers before birth, two potential problems exist:

Generalised infection may occur with symptoms ranging from moderate enlargement of the liver and spleen with jaundice, to a fatal illness. With supportive treatment most infants with CMV disease survive. However 80% to 90% will have complications within the first few years of life that may include hearing loss, vision impairment and varying degrees of mental retardation.

Another 5% to 10% of infants who are infected but without symptoms at birth will subsequently have varying degrees of hearing and mental or coordination problems.

Immunosuppression
Other people at increased risk of severe infection include patients with impaired immunity due to HIV/AIDS infection, corticosteroid therapy, lymphoma or sarcoidosis. In these people, disease is usually due to reactivation of previous infection. Manifestations include sight-threatening retinitis, pneumonitis, gastrointestinal ulceration and inflammation, and neurological disease particularly affecting the brain and spinal cord.

Method of diagnosis
CMV may be detected by virus isolation or PCR, usually from urine. Virus may also be detected in saliva, breast milk, semen and cervical secretions during primary and reactivated infection.

CMV causes typical ‘cytomegalic’ cells in tissue culture and characteristic histologic features in affected tissues. CMV antigens may be detected using rapid antigen tests. Serology is also available where recent infection is suggested by the identification of CMV IgM or a fourfold or greater rise in serum IgG titres to CMV from paired sera.

Isolation of CMV from culture does not necessarily imply recent infection as CMV may be excreted for months to years following infection. Positive results for CMV from laboratory investigations should always be considered with clinical findings.

Incubation period

The incubation period of sporadic cases of CMV usually cannot be determined. Perinatal infection develops three to twelve weeks after delivery. In adults, illness usually occurs three to eight weeks after blood transfusion and between four weeks and four months after organ transplantation.

Public health significance & occurrence

Although infection with CMV is very common around the world, symptomatic disease is rare. The risk of severe or complicated CMV infection is increased in some groups including:

the developing infant during pregnancy
people with immunosuppression such as organ transplant recipients, people infected with human immunodeficiency virus (HIV) and those being treated for cancer.

Serosurveys of adult populations worldwide have shown wide-spread evidence of previous CMV infection with seropositivity rates ranging from 40% in highly developed countries to 100% in developing countries.

The incidence peaks during the perinatal period with a secondary peak among young adults in areas where perinatal infection is less common.

Reservoir

Humans.

Mode of transmission

CMV is excreted in urine, saliva, breast milk, cervical secretions and semen during primary and reactivated infections. CMV may be transmitted by:

transplacental infection of the foetus of a mother with primary or reactivated infection
perinatal infection of neonates via infective maternal cervical secretions or breast milk
blood transfusion or organ transplantation
intimate exposure by mucosal contact with infective tissues, secretions or excretions.

CMV is not readily spread by casual contact but requires prolonged, intimate exposure for transmission. This can occur in settings such as child care centres where toddlers shed the virus in saliva and urine and thereby spread the infection among them.

Period of communicability

CMV may be shed in the bodily fluids of any previously infected person, and thus may be found in urine, saliva, blood, tears, semen and breast milk. The shedding of virus may take place intermittently for months to years after primary infection without any detectable signs, and without causing symptoms.

Neonatal infection in particular is associated with prolonged excretion. The period of excretion seems to be shorter in adults.

Susceptibility & resistance

Once a person becomes infected, the virus may remain dormant in their body for life (latent infection). Recurrent disease rarely occurs unless the person’s immune system is suppressed due to therapeutic drugs or disease.

Control measures

Preventive measures
There is no vaccine available to protect against CMV infection.

Public health measures focus on reducing the risk of CMV transmission to pregnant women, women of childbearing age and other people at risk of more serious infections.

Women of childbearing age working in hospitals (especially obstetric and paediatric wards), child care centres and preschools should practice strict infection control precautions and regard all body fluids as potentially infectious.

The CMV status of blood and organ donors should be matched to that of recipients wherever possible. If CMV seropositive donors must be used for CMV seronegative recipients, prophylactic use of hyperimmune immunoglobulin or antiviral drugs may be considered.

Control of case
There is no specific treatment recommended for primary CMV infection of normal hosts.

Immunosuppressed persons with CMV retinitis or pneumonitis are usually treated in specialist centres with ganciclovir, foscarnet, or cidofovir/probenecid. These drugs may also be of benefit for other complications of CMV infection.

Control of contacts
None required because of the high prevalence of asymptomatic virus shedders in the community.

Control of environment
Not applicable.

Outbreak measures

Not applicable.

Additional sources of information

Centers for Disease Control and Prevention, Atlanta USA, Cytomegalovirus infection
www.cdc.gov/ncidod

top of page