Cytomegalovirus (CMV) is a virus found around the world. It is
related to the viruses that cause chickenpox and infectious mononucleosis
(mono). Between 50 percent and 80 percent of adults in the United States have
had a CMV infection by age 40. Once CMV is in a person's body, it stays there
for life. CMV is spread through close contact with body fluids. Most people
with CMV don't get sick and don't know that they've been infected. But
infection with the virus can be serious in babies and people with weak immune
systems. If a woman gets CMV when she is pregnant, she can pass it on to her
baby. Usually the babies do not have health problems. But some babies can
develop lifelong disabilities.A blood test can tell whether a person has ever
been infected with CMV. Most people with CMV don't need treatment. If you have
a weakened immune system, your doctor may prescribe antiviral medicine. Good
hygiene, including proper hand washing, may help prevent infections.
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 includefever, lymphadenopathy
and mild hepatitis. More rare features include anaemia, thrombocytopaenia,pneumonitis,
meningoencephalitis and Guillain-Barrè syndrome. Many infections are
asymptomatic, particularly those in young children.
Pregnancy:
Healthy pregnant women are not at special risk for disease from
CM 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 sightthreatening 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. CMVcauses 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 CMVIgM
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 and 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 and 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.
sources of information
• Centers for Disease Control and Prevention, Atlanta USA, Cytomegalovirus infection,
·
The blue book: Guidelines
for the control of infectious diseases
·
http://www.nlm.nih.gov
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