• Cytomegaloviruses are herpesviruses
• The name for the classic cytomegalic inclusion
disease derives from the property for massive
enlargement of cytomegalovirus-infected cells.
• Cytomegalic inclusion disease is a generalized
infection of infants caused by intrauterine or early
postnatal infection with the cytomegaloviruses.
• Cytomegalovirus poses an important public health
problem because of its high frequency of congenital
infections, which may lead to severe congenital
• Inapparent infection is common during childhood
• Severe cytomegalovirus infections are frequently
found in adults who are immunosuppressed.
Properties of the Virus
• Cytomegalovirus has the largest genetic content of the human
herpesviruses. Its DNA genome 240kbp
• Cytomegaloviruses are very species-specific and cell type-specific
• Human cytomegalovirus replicates in vitro only in human fibroblasts.
• Cytomegalovirus replicates very slowly in cultured cells
• infection is spread primarily cell-to-cell.
• It may take several weeks for an entire monolayer of cultured cells to
• Cytomegalovirus produces a characteristic cytopathic effect . Perinuclear
cytoplasmic inclusions ,intranuclear inclusions. Multinucleated cells are
seen. Many affected cells become greatly enlarged.
• Inclusion-bearing cytomegalic cells can be found in samples from infected
Pathogenesis & Pathology
I- Normal host
• transmitted person-to-person in several different ways, all requiring
close contact with virus-bearing material
• There is a 4- to 8-week incubation period in normal older children
and adults after viral exposure.
• The virus causes a systemic infection; it has been isolated from
lung, liver, esophagus, colon, kidneys, monocytes, and T and B
• The disease is an infectious mononucleosis-like syndrome,
although most cytomegalovirus infections are subclinical.
• cytomegalovirus establishes lifelong latent infections.
• Virus can be shed intermittently from the pharynx and in the urine
for months to years after primary infection .
• Salivary gland involvement is common and is probably chronic.
Primary cytomegalovirus infections in immunosuppressed hosts are much more
severe than in normal hosts. Individuals at greatest risk for cytomegalovirus
disease are those receiving organ transplants, those with malignant tumors who
are receiving chemotherapy, and those with AIDS.
Viral excretion is increased and prolonged, and the infection is more liable to
Pneumonia is the most common complication.
The host immune response presumably maintains cytomegalovirus in a latent state
in seropositive individuals.
Reactivated infections are associated with disease much more often in
immunocompromised patients than in normal hosts.
Although usually less severe, reactivated infections may be as virulent as primary
III-Congenital and Perinatal Infections
• Fetal and newborn infections with
cytomegalovirus may be severe.
• About 1% of live births annually in the United
States have congenital cytomegalovirus infections
and about 5–10% of those will suffer cytomegalic
• Babies with this disease will exhibit
developmental defects and mental retardation.
• The virus can be transmitted in utero with both primary and reactivated
• About one-third of pregnant women with primary infection transmit the virus.
• Generalized cytomegalic inclusion disease results most often from primary
• There is no evidence that gestational age at the time of maternal infection
affects expression of disease in the fetus.
• Intrauterine transmission occurs in about 1% of seropositive women. Fetal
damage seldom results from these reactivated maternal infections; the infection
of the infant remains subclinical though chronic .
• Cytomegalovirus can also be acquired by the infant from exposure to virus in the
mother's genital tract during delivery and from maternal breast milk. In these
cases, the infants usually have received some maternal antibody, and the
perinatally acquired cytomegalovirus infections tend to be subclinical.
• Transfusion-acquired cytomegalovirus infections in newborns will vary,
depending on the amount of virus received and the serologic status of the blood
• Whether cytomegalovirus is acquired in utero or perinatally, a more chronic
infection results—with respect to viral excretion—than when the virus is
acquired later in life
Primary cytomegalovirus infection of older children and adults is usually
asymptomatic but occasionally causes a spontaneous infectious mononucleosis
syndrome. The disease is characterized by malaise, myalgia, protracted fever, liver
function abnormalities, and lymphocytosis. Cytomegalovirus is estimated to cause
20–50% of heterophil-negative (non-Epstein-Barr virus) mononucleosis cases.
Cytomegalovirus mononucleosis is a mild disease, and complications are rare.
Subclinical hepatitis is common. In younger children (under 7 years old),
hepatosplenomegaly is frequently observed.
An association has been observed between the presence of cytomegalovirus and
restenosis following coronary angioplasty. It is speculated that the virus may be
contributing to the proliferation of smooth muscle cells, leading to restenosis.
• Both morbidity and mortality rates are increased with primary and recurrent
cytomegalovirus infections in immunocompromised individuals.
Pneumonia is a frequent complication. Interstitial pneumonitis caused by
cytomegalovirus occurs in 10–20% of bone marrow transplant recipients.
• Virus-associated leukopenia is common in solid organ transplant recipients; also
seen are obliterative bronchiolitis in lung transplants, graft atherosclerosis after
heart transplantation, and cytomegalovirus-related rejection of renal allografts.
• Cytomegalovirus often causes disseminated disease in untreated AIDS patients;
gastroenteritis and chorioretinitis are common problems, the latter often leading
to progressive blindness
III-Congenital and Perinatal Infections
• Congenital infection may result in death of the fetus in utero .
• Cytomegalic inclusion disease of newborns is characterized
by involvement of the central nervous system and the
reticuloendothelial system. Clinical features include
intrauterine growth retardation, jaundice,
hepatosplenomegaly, thrombocytopenia, microcephaly, and
• Mortality rates are about 20%. The majority of survivors will
develop significant central nervous system defects within 2
years; severe hearing loss, ocular abnormalities, and mental
retardation are common.
• About 10% of infants with subclinical congenital
cytomegalovirus infection will develop deafness.
• Many women infected previously with cytomegalovirus show reactivation and begin to
excrete the virus from the cervix during pregnancy.
• At the time of delivery through the infected birth canal, infants may become infected,
though they possess high titers of maternal antibody acquired transplacentally.
• These infants begin to shed virus at about 8–12 weeks of age.
They continue to excrete the virus for several years but remain healthy.
• Acquired infection with cytomegalovirus is common and usually inapparent. The virus is
shed in the saliva and urine of infected individuals for weeks or months. Cytomegalovirus
may be a cause of isolated pneumonia in infants less than 6 months of age
• Antibodies to cytomegalovirus occur in most
• Cytomegalovirus-specific antibodies of the IgM,
IgA, and IgG classes have all been detected.
• Reactivation of latent infection occurs in the
presence of humoral immunity.
• The presence of antibody in breast milk does not
prevent transmission of infection to breastfeeding infants.
• Maternal antibody protects more against
development of serious disease in the infant than
• 1. Humoral Response : CMV specific IgM antibodies are produced
during the primary infection and persists for 3 or 4 months, but are not produced
in recurrent infections in immunocompetent individuals. However,
immunocompromised individuals may fail to produce IgM with primary infection
and 1/3rd of them have IgM detectable with recurrent infection. CMV IgG
antibodies are produced at the time of primary infection and persists lifelong. With
intrauterine infections, both IgM and IgG are produced by the fetus but the fetal
IgG response can only be detected as the passively acquired IgG from the mother
is catabolized. Although there is evidence to suggest that the humoral response
may be beneficial, eg. immunocompromised patients who fail to develop IgM run
a high risk of developing disseminated infection, the exact role of the humoral
response remain uncertain.
• 2. CMI: CMI is thought to play a key role in the suppression of CMV infection.
The test most widely used to measure CMI is the lymphocyte transformation
response (LTR) which measures the recognition, not the effector function of T
lymphocytes. Most seropositive adults have a positive LTR, whereas few
congenitally or perinatally infected infants can respond. This failure of LTR recovers
with time and there is a direct correlation between cessation of viruria and
acquisition of LTR responsiveness at 3 -5 years of age.
Polymerase Chain Reaction and Antigen Detection Assays
PCR assays have replaced virus isolation for routine detection of cytomegalovirus infections. Cell
culture methods of viral isolation are too slow to be useful in guiding therapy, particularly in
immunosuppressed patients. The PCR assays are designed to detect replicating virus, not latent viral
genomes. Blood and urine are most commonly tested. PCR assays can provide viral load data, which
appears to be important in predicting cytomegalovirus disease. Monoclonal antibodies against viral
antigens can be used to detect virus-positive leukocytes from patients.
Isolation of Virus
Human fibroblasts are used for virus isolation attempts. The virus can be recovered most readily from
throat washings and urine. In cultures, 2–3 weeks are usually needed for the appearance of cytologic
changes, consisting of small foci of swollen, translucent cells with large intranuclear inclusions. The
virus stays cell-associated.
Many types of assays can detect cytomegalovirus IgG antibodies, indicative of past infection (and the
potential to undergo reactivation). Detection of viral IgM antibodies suggests a current infection.
Serologic assays are not informative for immunocompromised patients. Furthermore, serologic
techniques cannot distinguish strain differences among clinical isolates.
• 1. Virus Isolation ;- Urine, saliva, blood and biopsy
samples can be used for virus isolation.
• Urine should be collected a sterile container without
• Saliva samples should first be soaked on to a swab
which is then broken off into transport medium.
• Blood should be collected into a heparinized bottle
containing 500 units of heparin.
• Tissue biopsies should be placed in sterile plastic
containers. The specimens can be treated in the
following ways ;• .
• (a) Cell culture - Human embryo lung fibroblasts are most commonly used.
The specimen is inoculated into HEL cells and kept for 28 days with a blind
passage at 14 days. CMV produces a typical focal cytopathic effect.
• (b) DEAFF ( Detection of early antigen fluorescent foci ) ;- This is a method
used for the early diagnosis of CMV infection. In immunocompromised
patients, a sensitivity of 78% and a specificity of 100%. The specimen is
inoculated into cell culture which is examined 24 hours later by
immunofluorescence for expressed CMV encoded early proteins. The
monoclonal antibodies must be able to cover most, if not all strains of
CMV. Rapid culture methods other then the DEAFF tests are also available.
• (c) Histopathology - Cytomegalic inclusions can be recognized from biopsy
material by the typical "owl 's eyes appearance "
• (d) Tissue immunofluorescence - Infected lung and liver cells may be
stained by specific anti-CMV antibodies. Broncheolavage specimens can
also be examined in this manner. Results of high sensitivity and specificity.
e) Electron microscopy - Virions in the urine of congenitally infected infants may be
visualized by EM in up to 80% of cases. However this is of no real value as rapid
diagnosis is not required. In immunocompromised individuals though, the viral
titres are generally lower than neonates and other herpesviruses are often present
in the urine.
(f) ELISAs for CMV antigen in the urine - these tests carry low sensitivity as CMV is
complexed to ß2-microglobulin in the urine.
(g) Detection of CMV DNA by PCR - the use of PCR in the diagnosis of CMV
infection had been widely studied. PCR offers the advantages of being rapid and
sensitive. However, its inherent sensitivity poses a problem since latent CMV
genomes, which are present in practically all seropositive individuals, may be
detected. Therefore, it is critical to adjust the sensitivity of the PCR so that latent
genomes are not detected.
(h) CMV antigenaemia test - this test is based upon the detection of pp65, a
structural protein expressed on the surface of infected polymorphonyclear
leucocytes. The number of infected leucocytes present had been reported to
correlate with the severity of infection. The main advantage of this test is that it is
very rapid so that a result can be available within the same day. As a result, this
test is now widely used especially in the monitoring of transplant recipients
II- Serology ;
- CMV IgM antibodies are detected in primary infection and lasts 3 - 4 months. It is
not detectable in recurrent infection except in immunocompromised patients
where it is detectable in about a third of the cases.
CMV IgM may be undetectable in primary infection in immunocompromised
Solid phase sandwich or antibody capture ELISAs or RIAs are now in routine use.
Interference by rheumatoid factor should be excluded.
CMV IgM can be sought for in the cord blood samples from infants who are
suspected of being congenitally infected and the titre present is generally related
to the outcome. However the best method for diagnosing congenital CMV
infection remains virus isolation.
CMV IgG is produced early in primary infection and persists lifelong. The detection
of CMV IgG is useful as an "immune status screen" (Seropositive individuals are
not protected from reactivation of reinfection). Rising titres of IgG can be used as
markers of acute infection. This is particularly useful in diagnosing recurrent
infections in normal individuals, and in immunocompromised patients who may
not develop a IgM response to primary infection. Various methods are used for
detecting CMV IgG including CFT, IFT, latex agglutination, ELISAs and RIAs.
Where possible, serological investigation should be backed by virus culture,
especially in the case of immunocompromised patients who may fail to mount an
immune response. CMV IgG may also be transferred by blood products which may
produce false positive results.
Cytomegalovirus is endemic in all parts of the world; epidemics are unknown. It is
present throughout the year, with no seasonal variation seen in infection rates.
The prevalence of infection varies with socioeconomic status, living conditions, and
Humans are the only known host for cytomegalovirus.
Transmission requires close person-to-person contact.
Virus may be shed in urine, saliva, semen, breast milk, and cervical secretions and is
carried in circulating white blood cells.
Oral and respiratory spread are probably the dominant routes of cytomegalovirus
It can also be spread transplacentally, by blood transfusion, by organ
transplantation, and by sexual contact.
New infections are almost always asymptomatic. After infection, virus is shed from
multiple sites. Viral shedding may continue for years, often intermittently, as latent
virus becomes reactivated. Thus, exposures to cytomegalovirus are widespread and
• Intrauterine infection may produce serious disease in the newborn.
• The majority have subclinical but chronic infections; 5–10% have
cytomegalic inclusion disease with attendant developmental defects
and high mortality.
• Congenital infections, whether subclinical or clinically apparent,
result in chronic infections, with viral shedding detectable for years.
• Many more infants become infected with cytomegalovirus in the first
months of life, often from infected breast milk or by nursery spread.
Most of these infections are subclinical but are usually chronic, with
persistent viral shedding.(acquired)
• Cytomegalovirus can be transmitted by blood transfusion.
• Seronegative solid organ transplantation recipients are at risk, as a
seropositive organ transmits the virus in 60–80% of cases.
• Cytomegalovirus infections are markedly increased in
immunosuppressed populations; transplant recipients often develop
infections, most of which are due to reactivations of their own latent
Treatment & Control
• Drug treatments of cytomegalovirus infections have shown some
encouraging results. Ganciclovir, a nucleoside structurally related to
acyclovir, has been used successfully to treat life-threatening
cytomegalovirus infections in immunosuppressed patients.
• The severity of cytomegalovirus retinitis, esophagitis, and colitis is
reduced by ganciclovir. In addition, early treatment with ganciclovir
reduces the incidence of cytomegalovirus pneumonia in bone
marrow allograft recipients.
• Ganciclovir also controls progressive hearing loss in neonates with
congenital infections. renal transplant patients.
• Specific control measures are not available to prevent
cytomegalovirus spread. Isolation of newborns with generalized
cytomegalic inclusion disease from other newborns is advisable.
• Screening of transplant donors and recipients for cytomegalovirus
antibody may prevent some transmissions of primary
• The cytomegalovirus-seronegative transplant recipient population
represents a high-risk group for cytomegalovirus infections.
Administration of human IgG prepared from plasma pools obtained
from healthy persons with high titers of cytomegalovirus
antibodies (cytomegalovirus immune globulin) has given
discordant results in tests to decrease the incidence of viral
infections in transplant recipients. Cytomegalovirus immune
globulin is in limited supply.
• The use of blood from seronegative donors has been
recommended when infants will require multiple transfusions. This
approach would eliminate transfusion-acquired cytomegalovirus
infections, but it is difficult to implement.
• Both live and recombinant cytomegalovirus vaccines are under