Disease Description
Congenital cytomegalovirus (cCMV) is the most common congenital viral infection in human beings. It refers to children born to CMV-infected mothers with CMV infection confirmed within 2 weeks of birth and is caused by intrauterine infection. The incidence of congenital CMV infection is 1.2% (0.9-1.3%) in underdeveloped countries and 0.39% (0.3-0.5%) in moderately developed countries. Cytomegalovirus is a DNA virus that belongs to the genus Herpesvirus. Only 10% of congenital CMV infections are symptomatic, such as microcephaly, cerebral edema, intracranial or intra-abdominal calcifications, etc., with a mortality rate of 30-40%. The remaining 90% are born without clinical symptoms, but 10%-15% will have sequelae, including hearing impairment and mental retardation.
Pathogenesis
Human cytomegalovirus belongs to the herpes virus, which is a DNA virus with two layers of capsid and 150-200 nm in diameter, and is the largest of the herpes viruses. The virus can be stored at -40C for several days, and is sensitive to ether, chloroform and other lipid solvents. 20% ether treatment for 2 hours, 560C for half an hour, and UV light for 5 minutes can kill the virus.
Classification
CMV infections are classified according to the time of occurrence as follows.
Congenital infection: refers to children born to CMV-infected mothers with CMV infection confirmed within 14 days of birth (including 14 days), which is the result of intrauterine infection.
Perinatal infection: refers to children born to CMV-infected mothers who do not have CMV infection within 14 days of birth, but have CMV infection confirmed within 3 to 12 weeks after birth, which is caused by the infant during birth or through suckling breast milk or close contact.
Postnatal infection or acquired infection: CMV infection was detected in the infant after 12 weeks of life.
Infection in pregnant mothers
CMV serological positivity in women of childbearing age is related to socioeconomic status, with a group positivity rate of 55% for CMV in women of childbearing age in developed countries and 85% in underdeveloped countries. According to some studies, the infection rate among women of childbearing age in China is over 90%, and the CMV infection rate among pregnant women is 79-97%, with an active rate of 11.23%. Pregnant women are often unaware of the infection because most of them do not have any symptoms, but these infected pregnant women can be a source of infection for a long time and CMV can be detected in their blood, tears, saliva, urine, amniotic fluid, and genital tract secretions. Pregnancy itself may increase a woman’s susceptibility to CMV or lead to activation of latent infection. Active maternal infection during pregnancy (including primary infection, exogenous reinfection, or reactivation of endogenous latent infection) can lead to congenital infection in the fetus and newborn. Maternal HIV infection, prematurity, and hospitalization in the neonatal intensive care unit (NICU) are all high-risk factors for congenital CMV infection.
Transmission routes
Infection of the mother in utero first infects the placenta, where a large number of white blood cells accumulate in the intervillous space and the virus then crosses the placental barrier to the fetus. Another way is that the infected white blood cells enter the fetal circulation through the umbilical vessels, resulting in blood-borne virus transmission. The virus is mainly located in the cytoplasm of endometrial stromal cells, vascular endothelial cells and leukocytes. Neutrophils can carry the virus to the endothelial cells of the uterine capillaries and further infect the trophoblastic layer of vascular endothelial cells that fix the villi, leading to placental infection and degenerative changes of the villi, which may be a cause of abnormal growth and development of the offspring. The CMV can be excreted from the urinary tract or cervix during the second trimester, and the baby can be infected by contact with the secretions of the birth canal or blood during delivery; since CMV is present in maternal saliva, breast milk and other secretions, the infection is transmitted to the newborn after birth mainly through close contact with the mother and through breast milk.
Factors affecting mother-to-child transmission
1. Primary infection or recurrent infection in pregnant women: primary infection refers to initial infection; recurrent infection refers to endogenous latent virus activation (reactivation), or reinfection (reinfection) with an exogenous strain of a different virus, or a larger number of the same strain of virus. Primary infections are more likely to transmit CMV to the fetus than re-infections. The rate of mother-to-child transmission of primary infection in pregnant women is 30-40%, while the rate of transmission of recurrent infection is 1.4-6%. Primary infection occurs in 1-4% of pregnancies and the risk of mother-to-child transmission is 30-40%; the rate of reinfection is 10-30% and the risk of virus transmission is 1-3%. The rate of detoxification in the urine of primary infection is 10 times greater than that of re-infection, the rate of symptoms and long-term sequelae in infants is higher than that of re-infection, and primary infection also increases the risk of miscarriage and stillbirth. Sequelae occur in 0.2% to 1.5% of newborns born to recurrently infected pregnant women, but serious sequelae are less common.
Thirty to 50% of congenital CMV infections are caused by re-infection in pregnant women. Mothers with re-infection have some immunity to CMV, and the virulence of the fetus is reduced when infected, but the infection cannot be completely avoided.
2, the viral load of pregnant women: the CMV DNA content in the blood of pregnant women indicates the strength of their viral infectivity. In a domestic study, there was no intrauterine infection in pregnant women with HCMV DNA copy number <105copies/mL, and the intrauterine infection rates were 18.75%, 28.57%, 33.33% and 60% when the DNA copy number was 105, 106, 107 and 108copies/mL, respectively. When the amount of CMV DNA in blood reaches 2.62×105copies/mL or more, the possibility of intrauterine infection should be considered.
If the mother is infected in the early stage of pregnancy, it can cause congenital malformation, miscarriage and stillbirth due to impaired development of fetal tissues and organs. If the mother is infected in late pregnancy, the infection mainly causes fetal liver, lung and kidney damage because the fetal tissues and organs are already developed and formed. Infected cells are affected by the massive replication of CMV, forming giant cell-like changes and intracellular inclusion bodies.
4. Socioeconomic status and breastfeeding: Family economic conditions also have an impact on CMV infection in pregnant women. Foreign studies found that 64.5% of pregnant women in the high-income group had negative serum CMV antibodies (a susceptible group), of which 1.6% had primary infection during pregnancy; 23.4% of pregnant women in the low-income group had negative serum CMV antibodies, and 3.7% had primary infection. Intrauterine transmission rates were similar in both groups (39% and 31%, respectively). Among congenital CMV infections, 25% were caused by primary infections in the low-income group and 63% were caused by primary infections in the high-income group. The high-income group had a higher proportion of susceptible individuals, a higher incidence of primary infection, and a greater impact on the fetus. It is a high-risk group for primary CMV infection.
Cytomegalovirus can be excreted in breast milk and can be transmitted to the infant through breastfeeding. Most term infants with breast milk transmission of CMV are asymptomatic and have a low risk of neurological sequelae and deafness. Therefore, term infants born to mothers with CMV infection may not stop breastfeeding because breastfeeding does not necessarily lead to neonatal infection at this time, and the benefits of breastfeeding outweigh the risks associated with infection. However, in preterm, low birth weight and very low birth weight infants, feeding the breast milk of a CMV seropositive mother can lead to CMV infection due to their underdeveloped immune function. Pasteurization (65 degrees, 30 minutes) is effective in eradicating the infectiousness of cytomegalovirus in breast milk; freezing (-200C) thawing reduces the infectiousness of CMV in breast milk samples in vitro, but does not completely eradicate the risk.
Diagnosis of CMV infection
(a) Diagnosis of CMV infection in pregnant women
Most pregnant women with CMV infection have no obvious clinical symptoms, less than 5% have symptoms, and very few present with mononucleosis syndrome. The common symptoms are persistent fever, myalgia, swollen lymph nodes, etc. It is difficult for pregnant women to realize that they are infected and have transmitted to the fetus. Pregnant women should be tested for CMV serology before pregnancy to determine if they have ever been infected with CMV, and those who are negative for specific antibodies are considered susceptible. A change from negative to positive characteristic antibodies after pregnancy can be diagnosed as a primary infection. CMV-IgM antibodies are an indicator of acute or recent infection and can be present in primary infection, exogenous reinfection or reactivation of endogenous latent infection and can remain positive for up to 18 months, 6-9 months after the acute phase of primary infection. It can be detected 6-9 months after the acute phase of the primary infection and can be false positive in other infections such as microvirus B19 and EBV infection.
Most pregnant women with primary CMV-IgM positive and IgG negative, or with IgM positive and/or IgG switching from negative to positive or with a significant increase in potency 3 weeks apart, also indicate primary infection. Most women have been infected with CMV before pregnancy and have positive serum CMV-IgG. If CMV latent in the body during pregnancy is activated or reinfected with exogenous CMV, the fetus can still be infected through the placenta and is IgM positive at this time, therefore pregnant women should be tested for both CMV-IgM and IgG antibodies to determine primary infection and reinfection.
CMV-IgG avidity (IgG avidity) is currently the most reliable test to determine primary infection, and antibody avidity represents the ability of multivalent antibodies to bind to multivalent antigens. Antibodies produced during primary infection have a much lower affinity for antigens than those produced during re-infection, and as the immune response matures, the affinity slowly increases, so low affinity represents acute or recent CMV infection. Antibody affinity measured at 16-18 weeks of gestation identifies all pregnant women with possible fetal and neonatal infections with 100% sensitivity. However, the sensitivity decreases significantly after 20 weeks of gestation, to 62.5%.
Neonatal diagnosis
1. Clinical symptoms: Most CMV infections are asymptomatic at birth, and only 10% are symptomatic infections, which can manifest as systemic infections with microcephaly and cranial ultrasound or CT can reveal periventricular calcifications. In some cases, infant pneumonia can be caused by CMV infection. However, pneumonia often occurs in the first few months of life and is therefore not easily distinguished from other causes of pneumonia. Ocular lesions can also occur in the neonatal period, with chorioretinitis, cataracts and blindness accounting for 10-20% of cases. Other organs can also be damaged and may include deafness, hepatomegaly, splenomegaly, jaundice, and thrombocytopenic purpura. It can also manifest as a single organ damage, such as simple thrombocytopenia, CMV hepatitis (intra- and extrahepatic biliary obstruction, jaundice); 90% are occult infections, asymptomatic at birth, with late onset of symptoms later, such as hepatitis, with progressive increase in transaminases, loss of appetite, nausea, vomiting and other hepatitis symptoms. Neurological symptoms, such as mental retardation, hearing impairment, etc., may also appear.
2.Serological test In the diagnosis of congenital CMV infection, serological test is less sensitive and specific than viral test. CMV-IgG in newborns can come from the mother through the placenta, while IgM antibodies cannot pass through the placenta. Therefore, a positive CMV-IgM antibody within 2-3 weeks after birth indicates congenital CMV infection, but there are also false positives and false negatives. About 27% of infected infants cannot produce IgM, and negative IgM antibodies cannot exclude the possibility of HCMV infection.
3. Rapid culture technique: This method can detect CMV in 24 to 48 h. After adding diagnostic samples to the monolayer cells, antibodies labeled with immunofluorescence or immunoperoxidase are added to detect early antigens produced by CMV-infected cells.
4. Virus isolation and PCR techniques: Taking specimens of blood, urine, saliva, etc. and inoculating them into fibroblasts, culturing them and isolating the virus is the gold standard for diagnosis. However, the operation is cumbersome and not widely used. Polymerase chain reaction (PCR) is widely used for CMV genome detection, and its sensitivity and specificity depend on the CMV gene range of the probes used and the method used. Although nested PCR is more sensitive, it also increases the risk of false positives. Although this method is highly sensitive, it cannot distinguish primary from secondary infection. It is believed that positive plasma CMV-DNA represents active infection.
5, CMV antigenemia detection: immunostaining of CMVpp65 antigen in leukocytes and its detection. the diagnosis of CMV antigenemia can help in the early diagnosis of CMV infection or can be used for morbidity prediction. It is now widely used in organ transplant patients and HIV-infected patients with severe CMV infections such as CMV retinitis and interstitial pneumonia, for morbidity prediction and outcome determination. The diagnosis of intrauterine CMV infection can be confirmed with positive antigenemia, but its sensitivity is only 45.5%.
6, ultrasound: ultrasound examination can make a judgment on the prognosis of CMV infection. Ultrasound abnormalities mainly include periventricular and ventricular calcification, ventricular enlargement, sac formation, and cerebellar damage. Children with laboratory and clinical signs of CMV are more likely to have brain ultrasound abnormalities. Cranial CT is not superior to ultrasound, whereas cranial MRI may miss calcifications but can detect more abnormalities than ultrasound, such as impaired neural migration, cerebral white matter dystrophy, delayed myelination, and cysts that are missed by ultrasound. Therefore, for symptomatic congenital CMV infection, ultrasonography can be used as a screening tool to estimate the prognosis, which is more economical and convenient than other imaging methods and can be done at the bedside.
7. Hearing examination: Since hearing impairment can occur after CMV infection, regular hearing examinations, including auditory evoked potentials, should be performed for infants with CMV infection for early detection of hearing impairment and timely treatment.
Congenital CMV infection and long-term sequelae
1. Neurogenic deafness (SNHL): SNHL is the most common and important of all sequelae caused by congenital CMV and can be the only manifestation of congenital CMV infection, and hearing loss can progress and worsen throughout childhood. SNHL occurs in 35-65% of symptomatic neonates with congenital CMV infection and in 7-15% of asymptomatic cases, and in 12% of congenital bilateral deafness caused by congenital CMV.
Deafness caused by CMV infection is not evident in the neonatal period, but progresses gradually during childhood. In a study of newborns with asymptomatic congenital CMV infection, SNHL was found to occur in 7.2%, half of whom had worsening hearing impairment. Their median age was 18 months. Late onset SNHL occurred in 18.2%, with a median age of 27 months. Newborns with congenital CMV infection should be monitored throughout childhood for early detection of SNHL, and newborn hearing screening can detect SNHL due to congenital CMV infection in less than half of cases. Because SNHL is progressive, hearing screening should be combined with CMV screening. When newborns have evidence of CMV infection and a normal hearing screen, these children should be monitored for evidence of SNHL throughout childhood. Viral inclusion bodies can invade the endolymphatic and ectolymphatic fluid of the vagus during viremia, causing degeneration and loss of internal and external hair cells but the mechanism is unknown. It is possible that CMV infects hair cells directly and causes their loss, and can also cause hair cell damage and inner ear damage at the time and later through the inflammatory response of the inner ear. In addition, the occurrence of SHNL is associated with host genetic susceptibility to CMV. Most newborns with congenital CMV infection are asymptomatic at birth, but 15% have sensory hearing loss by 72 months postnatally. In addition viral load is associated with SNHL, and those who develop SNHL have a higher viral load. When the viral load is < 1000 copies per 105 polymorphonuclear leukocytes, SNHL is less likely to occur.
2. CMV and epilepsy: In infants with neonatal CMV infection, neurological sequelae occur in 90% of those with symptoms and 10-15% of those without symptoms. The main ones are mental retardation, cerebral palsy, visual impairment, and convulsions, but the relationship between CMV infection and epilepsy has been little studied because it is generally described as convulsions. A Japanese study on congenital CMV infection and epilepsy found that among 19 children with congenital CMV infection, a total of 7 cases developed epilepsy, of which 6/16 (38%) were symptomatic CMV infections and 1/3 (33%) were asymptomatic children. There was no difference in epileptogenesis between the two groups. 3 cases developed within 1 year of age and 4 cases developed between 1 and 4 years of age, with a mean age of onset of 20 months. Seizure types: infantile spasms in 3 cases, partial seizures in 3 cases, and partial seizures with generalized tonic clonic seizures in 2 cases.
Parental misconceptions
Once an infant is diagnosed with CMV infection or CMV hepatitis parents find it unbelievable. Many mothers think that how can they be infected with CMV when everything was normal during pregnancy? Other mothers think that they have been tested for CMV antibodies during pregnancy and have confirmed that they do not have any viral infection, so how can their child have CMV? This is because most adults with CMV infection have no symptoms, and if they do, they are mild and cannot be easily distinguished from the flu. In addition, the virological tests given to pregnant women in obstetrics are usually done in the early stages of pregnancy, mostly in the first 3 months of pregnancy. However, just because a pregnant woman is confirmed to be free of infection in the first trimester does not mean that she is free of infection throughout her pregnancy. Infection in the early stages of pregnancy may lead to miscarriage and malformations, while infection in the later stages of pregnancy may not only be asymptomatic, but may also result in newborns with no abnormalities or unexplained hyperbilirubinemia.
Treatment
Infants infected with CMV can detoxify for months or even years, so it is important to isolate them from pregnant women to prevent them from being infected. The disease is difficult to treat and currently the main drug used to treat CMV infection in China is ganciclovir.
Ganciclovir GCV is a broad-spectrum anti-herpes virus drug that is effective against CMV, and is the first synthetic drug approved by the FDA to treat CMV retinitis and prevent CMV infection after organ transplantation. Intravenous GCV 5mg/kg. times is sufficient to inhibit CMV in subretinal fluid, cerebrospinal fluid, and brain tissue. most of GCV is excreted through urine with a clearance half-life of 2-3 hours, and the dose needs to be reduced in patients with impaired renal function. The pharmacokinetics in neonates are similar to those in adults. Protection against hearing impairment in neonates can last for more than one year with intravenous 6 mg/kg twice daily for 6 weeks. The bioavailability of oral ganciclovir is very low, with less than 10% absorption.
The main side effects of GCV are myelosuppression and dose-related granulocytopenia, which occurs in 40% and is reversible with discontinuation of the drug. 20% of patients develop thrombocytopenia (≤50,000) and 2% have anemia. A small number of patients experienced headache, confusion, hallucinations, nightmares, anxiety, ataxia, convulsions, fever, rash, abnormal blood liver enzymes, and renal impairment. GCV has also been shown to be mutagenic, carcinogenic, and teratogenic in preclinical animal studies. However, they have not been confirmed in humans. Ganciclovir is cleared by the kidneys, so the dose should be reduced in the presence of renal insufficiency. Resistance in treatment may occur, but there are no reports of treatment of neonatal congenital CMV infection with GCV resulting in drug resistance.
Because GCV is only available in intravenous formulations and is administered twice daily, it is difficult for parents of children to adhere to long-term therapy. The oral formulation, called valganciclovir, is a single valacyclovir precursor drug for GCV, which is quickly converted to GCV after oral absorption, and was approved by the FDA in 2000 for the treatment of CMV retinitis in AIDS patients combined with CMV, and later approved for the prevention of CMV in solid organ transplant recipients. pharmacogenetic studies of oral valganciclovir syrup have been completed in neonates. However, this drug is not yet available in China, and it is hoped that it will be introduced in our country in the near future. Other anti-CMV drugs include phosphonate and cidofovir, but they are rarely used in neonates because of their side effects.
Treatment experience: Six weeks of intravenous GCV treatment for symptomatic congenital CMV infection improved auditory evoked potentials at six months, and for those with normal hearing at enrollment, normal hearing was maintained at six months. 84% of those with GCV had improved or maintained normal hearing at six months, while only 59% of the control group had improved or stabilized. Forty-three children had brainstem auditory evoked potentials before and at 12 months of treatment, and it was found that 21% of the GCV-treated group and 68% of the control group had worsened hearing impairment.
There is no uniform treatment protocol for GCV treatment at home and abroad, but many foreign studies on the treatment of neonatal CMV infection have used a regimen of 6 mg per kg body weight per day for 6 weeks for clinical efficacy and prognosis.
Most of the treatment targets are symptomatic CMV-infected patients.
Current status of treatment and treatment recommendations in China
The indications and treatment methods for the treatment of congenital CMV infection in China are still confusing, some indications are too broad, for example, some doctors start treatment as soon as CMV IgM antibody is positive or CMV DNA is detected in urine, and most use a two-week regimen, but the recurrence rate is high. Therefore, it is recommended that asymptomatic infants with confirmed CMV infection be monitored for liver function, neurodevelopment, and regular hearing examinations without immediate treatment with GCV, and that treatment be considered only when signs and symptoms of CMV infection are present. For example, treatment should only be considered when there is hepatitis, hearing impairment, or neurodevelopmental abnormalities in infants, and parents should be informed of the side effects and possible hazards of the medication and should make a careful decision. Once the decision is made to treat with antiviral therapy try to adhere to the treatment for 4-6 weeks, otherwise there may be a relapse after stopping the medication.