Human cytomegalovirus (CMV) otherwise known as human herpes virus 5 is a highly host specific virus of the Herpesviridae family1. CMV was isolated in three laboratories simultaneously in 1956. Margaret G. Smith recovered the virus from the submaxillary gland of a dead infant1 while Weller named it as cytomegalovirus owing to its characteristic cytopathic effects2. CMV can be a potential killer or a silent companion lifelong thus it is considered as the virus of paradoxes3. CMV is highly prevalent in both developed and developing countries and poses an important public health problem4,5. CMV infection can be transmitted to the fetus following both primary as well as recurrent infections and has been associated with congenital abnormalities, Intrauterine growth retardation and intrauterine death along with developmental delays, blindness and deafness as a sequel after birth6,7.The prevalence of CMV specific antibodies in adult population is estimated to be about 80-90% in India7,8. But not much data is available on the prevalence of the occurrence of primary CMV infection in antenatal women. Hence the present study was designed to estimate the seroprevalence of CMV specific IgG and IgM antibodies in the local antenatal population in our area.
MATERIALS AND METHODS
Assuming 95% Confidence Interval, α of 5%, precision of 5% and seroprevalence of CMV in pregnant women to be 60% the required sample size was calculated to be 369. Over a period of two years, 370 pregnant women reporting for antenatal care were selected for the study. The subjects were selected at random including primigravida and women with adverse as well as normal previous pregnancy outcomes. Following informed consent, blood samples were collected taking all aseptic precautions and sera were separated and stored at -20⁰C until analyzed. Serum samples were tested for IgG and IgM antibodies at a dilution of 1:100 using ELISATest (Omega diagnostics, Scotland, U.K.) following the manufacturer’s instructions.Absorbance reading was taken using 450 nm filter (referencing at 650 nm).
Semi-quantitative estimation of antibody concentration:
The optical densities of the standards against their concentration were plotted and a line was drawn through the points. Concentrations below 3 IU/ml were considered negative whereas values above 3 IU/ml were regarded as positive. Values above 30 IU/ml were re-assayed at a higher dilution.
Results and discussion
Of the 370 samples tested, 83.24% were seropositive for CMV IgG and 9.46% were seropositive for CMV IgM. All IgM positive cases were positive for CMV IgG as well.16.76% were both IgG and IgM negative. Seroprevalence of CMV IgG and IgM among all pregnant women are given in table -1.The difference was statistically significant with a p value of 0.0107. Age of the patients ranged from 18 to 40 years with a mean age of 24.62 ± 4.04. Table-2 illustrates serological status of different age groups. Patients in the age group of 18 – 30 years showed high prevalence of anti-CMV-IgG antibodies ( 83.82 %) which is statistically significant with a p value of 0.0161 whereas age group of 31- 40 years showed 76.67 % prevalence which is not significant (p valve =0.4193).
9.7% of Patients in the age group of 18 -30 years showed prevalence of anti-CMV-IgM antibodies while the age group of 31 – 40 years had 6.67% prevalence. There is no statistically significant difference between the two groups.
The maximum seroprevalence of IgG (83.66%) was in first trimester followed by (77.78%) in third trimester and (75%) in second trimester. Maximum seroprevalence of IgM was (16.67%) in second trimester followed (11.1%) in third trimester and (9.17%) in first trimester. The p-value of 0.0177 for first trimester showed that the difference between IgG&IgM was statistically significant and p-value of 0.3711 in second trimester and p- value 0.5708 in third trimester showed that the differences were not statistically significant.
As for the number of pregnancy were concerned the maximum seroprevalence of IgG was (89.16%) for second pregnancy followed (82.31%) by first pregnancy and (60%) for third pregnancy, maximum seroprevalence of IgM (10.47%) was seen in first pregnancy followed (7.23%) by second pregnancy and (0%) for third pregnancy. p value of 0.0173 for first pregnancy showed that the difference was statistically significant. p value of 0.8373 for second pregnancy showed no statistical significance and for third pregnancy no statistical correlation existed.
The seroprevalence of IgG was (83.99%) for group without abortions which was not significant (p. value = 0.7372) while the seroprevalence of IgM was (14.29%) in cases with history of abortion which was statistically significant with a p value of 0.0171.
CMV is the most common congenital infection worldwide with estimated incidence of 0.2-2.2% and seroprevalence ranging between 45-100%13,14. While the seroprevalence in adult population in India is about 80-90%7,8. The present study showed a seroprevalence of 83.24% for CMV IgG which is similar to the studies which showed a prevalence of 80-90%1 and 87.4%15. However positivity of 9.46% for CMV IgM is less as compared to the study which showed seroprevalence of 22.03% for CMV IgM in Punjab16, while another study showed seroprevalence of 15.98% CMV IgM in Kashmir17 and 12.9% in Delhi18.
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This study determined the seroprevalence in antenatal women and according to the results of serologic assay the participants could be divided into four groups as under:
Group 1: Antenatal Women with negative serology for IgG and IgM antibodies they are not infected with CMV and are susceptible to CMV (primary infection). There is a high risk for antenatal transmission of the virus to the fetus in this group19.
Group 2: Antenatal women with IgM seropositivity and negative for IgG antibody.
Group 3: Antenatal Women with positive serology for IgG and negative for IgM antibodies, these women are considered immune and their primary infection with CMV is assumed to have taken place before the current pregnancy. This revealed that most of women in delivery group were immune against primary CMV infection.
Group 4: Women with positive serology for both anti CMV IgG and IgM antibodies, these women are considered to be possibly infected with CMV during the current pregnancy or a chronic infection which could be confirmed by IgG avidity test because antibody binds to the antigen with less avidity during acute infection than chronic infection20.
The results of our study indicate that the prevalence of CMV seropositivity in this region is high but a definite relationship between CMV infection and abortion could not be established. Most of the antenatal women in this area were immune against CMV infection and maternal immunity has a protective role in the fetus21. In the present study 16.76% of the women were susceptible to CMV infection because of lack of IgG. Maternal immunity prior to conception is highly protective against congenital CMV infection whereas acquired immunity due to CMV infection reduces congenital CMV infection in future pregnancies by 69%21. Although primary infection in any stage of pregnancy presents a risk for intrauterine infection from 30-50% but congenital infection in seropostive mothers is only from 0.2 to 1.5%22.
CMV infection can occur during intrauterine, perinatal or postnatal period whereas Children typically become infected in early childhood especially in the child care centers. Such infections are asymptomatic in these children. CMV infection produces symptoms mainly in a fetus when mother acquires CMV infection primarily during pregnancy. Postnatal transmission can also occur by consumption of breast milk from a mother carrying the virus. Hence the prevention of CMV infection includes preventing congenital CMV infection during antenatal period, preventing ingestion of infected maternal genital secretion during delivery, avoiding breastfeed, preventing contact with saliva and other body fluid containing CMV. Routine hygienic precaution is essential especially in pregnant females since it causes irreversible damage to the fetus 23.
Screening of antenatal women for CMV specific IgM antibodies is necessary to alert the physician/pediatrician regarding risk of infection to the new born. Newborns with high risk can further be tested for CMV specific IgM antibodies which will help in timely medical intervention and will also prevent the spread of infection to other kids. Moreover primary infection in pregnancy has a higher risk of producing symptomatic congenital infection and fetal loss23. However, infected newborns can be asymptomatic at birth with 10-15% of them developing the late sequelae like visual and auditory defects.6,10,11,24,25. Hence in developed countries it will be better to screen all the females falling in the child bearing age group for CMV specific IgM antibodies. It will lessen tortuous/ fatal outcomes of the pregnancy and also promote appropriate follow up (developing the late sequelae like visual and auditory defects) of the newborns delivered by the infected mothers6. Cytomegalovirus (CMV) infection during pregnancy is more complex than other infections, due to virus reactivation during the child bearing age and be transmitted to the fetus in spite of maternal immunity7.
The prevalence of CMV antibodies among women varies with geographical location, socio – economic status and occupation12. Risk factors for CMV infection have been correlated with the socioeconomic status within a community. This study showed that CMV infection was more prevalent in low socio economic status group21,26,27.
CMV is a virus that can affect the fetal organs throughout the whole pregnancy. The damage seems to be more severe in infections occurring during the first half of the pregnancy, while infections in the second half would result in reduced morbidity28.Various ways of transmitting the virus to the fetus have been suggested, whereas the hematogenous spreading across the placenta with subsequent infection of placental and amniotic tissue seems to be the most common transmission way29.
To conclude, CMV is an important cause of congenital infection and can result in significant perinatal morbidity and health care expense.We can diagnose high risk pregnancy even with serological tests in areas with insufficient equipment; but we suggest that confirmation of congenital CMV infection is difficult in this area and also there is high immunity for CMV in pregnant women and congenital infection is rare in seropositive mothers30, therefore we recommend pregnant women especially with bad obstetric history should be attentive on personal hygiene during Pregnancy, especially hand washing after handling diapers or oral secretions. We also recommend that high risk pregnant women or health care workers should be mandatorily screened for CMV during pregnancy in addition to screening for other maternal infection such as Toxoplasmosis, Rubella, and Herpes simplex.
In the absence of effective therapies for congenital CMV infection, prevention is critical. Most importantly, patients, especially those exposed to young children, should be counseled about the importance of careful hand hygiene practices, an intervention that will decrease the risk of primary CMV infection and subsequent fetal transmission.