The present study was performed to investigate the seroprevalence of CMV and rubella infection in pregnant women in the northern Angola city of Luanda. We found an overall seroprevalence rate for CMV infection of 98.5% and for Rubella infection about 88.6%. This is the first study conducted in Angola to evaluate the rates of CMV and Rubella infection in pregnant women. In a general way, there is a lack of knowledge about the epidemiology of CMV and Rubella infection in Angola. In this context, we cannot compare our seroprevalence results with others in pregnant women in Angola.
CMV infection is endemic in almost all the world, occurring throughout the year without seasonal variations. The rates of seropositivity in the population vary greatly according to geographical, ethnic and socioeconomic factors. The prevalence of CMV-specific antibodies increases with age and in the less favored socioeconomic groups of developed and developing countries [12, 13]. Other known contributing factors for CMV infection including education, sexual promiscuity, and blood transfusion [14, 15]. Also the contact with children is considered a risk factor, once the young children stands out as sources of CMV infection in pregnant women 
Our results of the seroprevalence of CMV antibodies in pregnant women were similar to previous studies in other African countries: 92% in Nigeria , 97.5% in Sudan , 96.3% in Tunisia , 87% in Gambia , 88.5% in Ethiopia , and 86% in Kenya . Moreover, our data were also similar with results report in other world countries with values between 92.6% and 100%: Iran , Palestine , China , Brazil , Turkey , Nigeria  and Cuba . In contrast, our prevalence was higher than that reported in developed countries: 42.3% in Germany , 46.8% in France, 49% in the United Kingdom , 54% in Norway , 56.3% in Finland , 58.7% in France , 65.9% in Italy , 66% in Japan , 62.4% in Poland  and 70.0% in the United States .
In the present study, all women who were CMV-IgM positive were also seropositive for IgG. In most of these cases there is a need to perform IgG avidity test as an alternative to provide the status of acute infection [37, 38]. However, in our study it was not possible define what proportion of these cases represented primary infection or reactivation because we we didn't have acess to IgG avidity test.
In USA a recent analysis of CMV IgM seroprevalence in women at reproductive age also found that 97.5 % of IgM seropositive women were CMV IgG seropositive . Other study performed in Pakistan, showed that 95.3 % of individuals who were IgM seropositive were equally seropositive for IgG . In countries with a high prevalence of CMV infection, such as Korea and Turkey, IgG avidity testing have shown that none of the women with a proflile of IgM and IgG positive had evidence of a primary infection [26, 37]. As such, we could suggest that the great majority of seropositive cases in our study represent viral recurrent reinfection or reactivation rather than primary infection. The high IgG seropositivity is alarming which calls for the need to screen these women for potential active infections. Further studies on the impact of CMV on poor pregnancy outcomes are highly recommended in the developing countries .
The profile of CMV-IgM negative/CMV-IgG positive in pregnant women (96.5%) indicates that the great majority of infections probably occurred during childhood or adolescence. Our results showed that all age groups are equally likely to be infected with CMV, being the prevalence high at all ages (15–47 years old).
Several studies showed that low socioeconomic status was found to predict CMV IgG seropositivity . The majority Angolan population is of low socioeconomic level. Although we did not have data about the socioeconomic level (through the material deprivation index; MDI) of the studied population, it should be pointed out that this study was carried out in a public maternity hospital where the majority of the attendants are women of low family income. Moreover, the majority of population in the city of Luanda reside in highly populated squatters with close contacts which favors transmission of airborne diseases.The womens participating in the present study resides in the urban area and there were no differences in CMV prevalence in relation to a specific area of residence. The high prevalence also could be explained by poor hygienic conditions that can to perpetuate the cycle of CMV transmission in the developing countries . However, in the present study we not found stastically association between basic sanitation and CMV seropositivity.
In the present study, HIV infected women were more likely to be CMV IgG seropositive than HIV negative women. WHO recommends that all the pregnant women should be advise and tested for HIV at the first prenatal visit. There is a need to improve prenatal services in our setting to ensure that all women are counseled and tested for HIV.
CMV is a virus that has a great potential to proliferate in humans for several reasons. The infection is usually subclinical allowing that infected individuals remain active and thus maintain the possibility of transmission to other susceptible individuals. Moreover, the CMV is not eradicated from the host after the primary infection, remaining in the body for the rest of its life , and occasionally may be reactivated (endogenous infection). In addition, the host although infected do not acquire immunity and can undergo further infection by different strains of the virus (exogenous reinfection) . Another explanation for the easy spread of CMV is that its excretion may persist for an extended period of time. For example, it is known that in the case of congenital infections, viral excretion by children may occur for years, increasing the likelihood of transmission to other individuals [42, 43]. On the other hand, some studies have observed that closed environments with many children are sites that facilitate the spread of the virus. In all these cases the transmission occurs mainly through contact with urine or saliva of infected children . We analyzed the influence of the contact of pregnat women with children through the number of births and children at home. The women with children at home had a greater seroprevalence of CMV infection than those without children at home.
An additional finding of our study was that the majority of pregnant women with IgG and IgM positive were in the first trimester of gestation, the period of highest risk to the fetus in case of virus transmission . It is reasonable to hypothesize that some infections would have been avoided had these women been informed at an earlier stage of pregnancy. Ideally, all women should be tested for CMV antibody and informed before pregnancy. Indeed, in a population of women receiving fertility treatment, preconception screening and counseling, seems to have a risk reduced to CMV infection in pregnancy . Moreover, preconception testing would also reduce problems arising from the detection and interpretation of CMV-specific IgM antibody in pregnant woman [47, 48].
CMV stands out as the major cause of congenital infection, reaching rates between 0.2 and 2.6% of the total number of births worldwide, being responsible for cases of neonatal mortality and morbidity . Fetal CMV infection occurs in approximately 40% of cases of maternal primary infection . Therefore, it would be beneficial to inform pregnant women about the need for follow-up to detect prenatal infection and to plan appropriate intervention such as the use of drugs to control infection and / or prevent fetus infection .
The epidemiological importance of Rubella virus is related to the Congenital Rubella Syndrome (CRS) that affects the fetus or the newborn due to the infection contracted by the mother during pregnancy. The overall seroprevalence of rubella among pregnant women in the present study was 88.6%. Similar results has been reported from other African countries such as Ethiopia (89%) , Senegal (90.1%) , Namibia (85.0%)  Burkina Faso (95%)  and Zimbabwe (92%) . Also in other countries of the world the prevalence is high: 88.1% and 93.5% in Turkey [56, 57]; 87% in United States of America (USA); 98% in Spain; and 96.3% Iran [58, 59]. In contrast, the seroprevalence in this study is higher than reports from Democratic Republic of Congo (58.97%) , Sudan (65%)  and Nigeria (68%) . These variations might be due to the difference in the endemicity of the virus, the sample size of the studies, and the laboratory methods used.
The profile of IgM and IgG immunoglobulins is important to characterizing infection in a given area . The presence of only IgM or both IgM and IgG antibodies at the same time indicates an acute/recent rubella virus infection. However, the presence of IgG antibody in the absence of IgM is a seromarker of immunity against rubella virus . The absence of both IgM and IgG antibodies indicates susceptibility to acquiring rubella infection.
In the present study, both rubella-specific IgM and IgG antibodies were analyzed among pregnant women to determine acute/recent infections and the levels of immunity against rubella virus infection in Luanda, Angola. Despite the general very high seroprevalence of rubella infection, 11.4 % of the pregnant woman were seronegative. The susceptibility rate in among adult women could result in outbreaks of CRS [51, 65]. Therefore, attention must be paid to the susceptible group of women in this study in order to reduce the risk of CRS in their future pregnancies.
Based on the previous recommendations of the US National Committee for Clinical Laboratory Standards (NCCLS)  and international agreements and guidelines , in the absence of IgM, the pregnant women who had rubella IgG levels ≥ 10 IU/ml were classified as immune and those with IgG levels < 10 IU/ml were classified as susceptible. In the present study, 87.6% of the pregnant women had IgG levels of > 10 IU/ml (Tabela 1). None of these pregnant women had a previous history of rubella vaccination and they were immune from rubella infections. This might be due to the endemicity of the virus in the study area that sustained previous infections of the participants before conception or during their childhood, as rubella infection is common among children and teenagers in some countries [51, 68].
The prevalence of rubella IgG (87.6%) in this study was greater than reported in Burkina Faso (77%) , in Niger (53%)  and southern India (65%) . However, the IgG positivity rate was lower than that found in studies conducted in other countries like Nigeria (97.9%) , Cameroon (88.6%) , Turkey (96.1%) , Italy (85.8%)  and Mexico (97.1%) . These variations in rubella IgG positivity in different countries might be due to the difference in the endemicity of the rubella virus and the presence or absence of rubella vaccination in their immunization programs.
In the present study, 1.0 % of the total pregnant women had both rubella IgM and IgG antibodies. The rubella virus re-infection following natural immunity is very rare . Therefore, the pregnant women might be in stages of primary rubella infection. Since these pregnant women were in the first and second trimester of pregnancy, they might have acquired the infection during the pregnancy and subsequently developed IgG antibodies within 30 days of infection . This indicates that these pregnant women might not be immune before pregnancies and the fetuses can not be excluded from rubella-associated risks.
Although there are no data of CRS in Angola, the newborns from women infected with rubella during early pregnancy might acquire a congenital rubella infection and be born with rubella-associated congenital anomalies or CRS. Therefore, the screening of women of child-bearing age before conception or during pregnancy might be crucial to reduce the consequences of acute rubella infection during pregnancy .
In the multivariate logistic regression analysis, a statistically significant association was found between rubella IgG positivity with spontaneous abortions during the study; all pregnant women who had a spontaneus abortions were seropositive for anti-rubella-IgG. The rubella was considered as an etiologic agent for miscarriages in many countries [57, 77]. Therefore, more attention should placed on those pregnant women who had recent or acute infections due to the teratogenic nature of the virus . Moreover, pregnant women who have a previous bad obstetric history may be more vulnerable to acquiring acute rubella infections . Although the mechanism is not clear and further studies are needed, a similar finding has also been reported in other studies [77, 80].
No statistically significant difference was found between anti-Rubella antibodies positivity and socio-demographic characteristics of the pregnant women. A similar finding was also reported in Namibia , Southern Ethiopia , and Nigeria .
All the pregnant participants in the present study live in urban settings. The high population density in urban areas might increase the contact rate and pregnant women without protective levels of rubella immunity might acquire the infections . A finding was reported in the pre-vaccine era in other countries [83, 84, 85].
To reduce the circulation of the Rubella virus, vaccination is essential and is the only way to prevent the disease [57, 86]. Rubella is commonly mistaken for other diseases because symptoms such as sore throats and headaches are common to other infections, making it difficult to diagnose . Although not serious, rubella is particularly dangerous in the congenital form. In this case, it may leave irreversible sequels in the fetus as glaucoma, cataract, cardiac malformation, delayed growth, deafness and others. Therefore, prevention should be focused .
The WHO  suggests the following strategies for the prevention of Rubella: (i) Provide right to protection to school-age women and / or girls (ii) Vaccinate to provide indirect protection by reducing the transmission of rubella virus infection (iii) a combination of these approaches. The rubella vaccine was included in the Angolan national vaccination plan in April 2018 an initial stage only covered children up to 14 years of age .
The prevalence of CMV and Rubella infection can be attributed to low socioeconomic status and poor hygienic. Currently, about 36% of the population lives below the poverty line and with limited access to basic public services (water, sanitation, energy, health, education and housing). In the education sector, Angola is considered by UNESCO as a low educational development index country, ranking 111th out of 120 countries in the UNESCO Education for All 2012, with a value of 0.685 and a gender parity index of 0.734 .
There is no way to know how many cases of CMV and Rubella are identified each year in Angola. Thus, there aren´t effective intervention to control CMV and Rubella infection in the country. In the case of CMV, preventive measures including changes in hygiene behavior of seronegative pregnant women should be implemmented as well as routine maternal screening for primary infection. Moreover, treatment with hyperimmune human immunoglobulin and the administration of aciclovir or its derivative valaciclovir should be considered once do not have teratogenic side effects when administered in the early stages of pregnancy [89, 90].