Diagnosis and management of ToRC

The control and diagnosis of maternal and congenital infections require that women considering pregnancy, pregnant women, clinicians and other healthcare providers be aware of:

• Preventive measures to avoid infection during pregnancy
• Diagnostic tests and algorithms for maternal and congenital infections
• Prognosis or risk of sequelae or impairments
• Appropriate patient follow up.

Toxoplasmosis is ubiquitous and is a common infection worldwide. There may be considerable differences in prevalence between populations, most often linked to cultural habits with regards to cooking of food. The prevalence ranges from <30% in the US, northern European countries and China, to 40–50% in Europe, Australia, South America and North Africa, and > 60% in Central America and in some African countries. As a consequence of the considerable differences in prevalence of the infection among general populations, there are large differences in the incidence of congenital infection. It can vary from 1/1000 live births in countries with a high prevalence, to 1/10,000 in countries with a lower prevalence.

Concerning rubella, live, attenuated rubella vaccines were licensed in the US in 1969 and introduced throughout most industrialised countries soon afterwards. Vaccination programmes have eliminated (in America) or greatly reduced (in Europe) the incidence of rubella and congenital rubella syndrome (CRS) in countries that practice universal childhood vaccination, and therefore report high maternal seroprevalence (>90%). Rubella vaccine, however, is not recommended in developing countries (for example, African countries) if high coverage cannot be guaranteed. Indeed, in this case, introduction of the vaccine could increase the susceptibility of adult women by slowing, but not interrupting, rubella transmission.(1) Although the burden of CRS is not well characterised in all countries, the World Health Organization estimates that globally more than 100,000 cases occur each year.(2)

Human cytomegalovirus (CMV) is the leading cause of viral congenital infection in developed countries, affecting 0.5–2% of all live births. For CMV, a large variation of geographic prevalence rates is reported and depends on socio-economic conditions, age, profession and parity. Seroprevalence is estimated as approximately 50% in women of childbearing age in Western Europe, but can reach almost 100% in developing countries. Seronegative women are exposed to the risk of primary CMV infection but cases of congenital CMV infection resulting from maternal secondary infection (reinfection or reactivation) are also reported in particular in populations with high seroprevalence.(3)

Toxoplasmosis is usually contracted by consumption of raw or undercooked meat or contaminated water/vegetables/fruit. Contact with cat faeces contaminated with oocysts is also a risk factor for infection.

Congenital rubella is preventable through vaccination of women of childbearing age. However, eradication of rubella infection requires universal childhood vaccination, which has proved to be highly efficient in stopping circulating rubella virus.

CMV is spread from person to person by close contact with body fluids that contain the virus. Young children play an important role in the spreading of CMV because, when infected, they shed virus in their urine and saliva for many months, and their routine care can lead to contact with their body fluids. CMV is also present in genital secretions and can be transmitted by sexual activity.

For both CMV and toxoplasmosis, education is the principal means of prevention.(4,5) In all cases, women at risk can be identified by serological testing, and appropriate prenatal counselling can then be performed (Table 1).

For toxoplasmosis, rubella and CMV infections, acute infection is often asymptomatic or associated with non-specific symptoms including: slight fever, aches/pains, swollen lymph nodes, fatigue, rash (mainly for rubella), myalgia, sore throat. Therefore, most maternal infections are clinically silent and go undiagnosed. Because clinical diagnosis is not reliable, biological confirmation is usually required.

Detection of the virus or the parasite in maternal blood is unreliable because its persistence is variable and usually quite short. Therefore, maternal diagnosis mainly relies on serology.

Specific immunoglobulin (Ig)G antibody is produced throughout life after infection. Its detection in a single sample at any titre, with any test, proves only that infection has been acquired at some time in the past.

Specific IgM antibody is almost always detected in individuals with recently acquired infection. However, this IgM may persist for months, and even years, after onset of infection (toxoplasmosis or CMV), and can also be detected for months/years after rubella vaccination.(6)  Moreover, IgM can also be observed as a result of cross-reactions (for example, between CMV and EBV), secondary infections (CMV or toxoplasmosis), or non-specific stimulation of the immune system.

Specific IgG avidity testing is particularly helpful when both IgG and IgM antibodies are detected on a first sample drawn during pregnancy. IgG avidity assay measures the functional binding affinity of IgG antibody produced in response to infection. In the first weeks after infection onset, IgG antibody of low avidity is produced, but its avidity increases over time. This maturation (depending on the virus/parasite) can be used for diagnosis to discriminate between primary and non-primary infection. For toxoplasmosis, a high avidity test result usually rules out infection acquired in the preceding three-to-five months (depending on the assay used), but low IgG avidity may persist for more than a year. Therefore, low avidity test results cannot be used to diagnose acute toxoplasmosis.

Avidity maturation of rubella-specific IgG occurs within two-to-three months of infection and therefore is used to confirm or exclude recent rubella infection. It must be pointed out that, after rubella vaccination, IgG avidity maturation is much slower than after natural infection. Under this condition, low or moderate avidity results may be observed months and even years after immunisation.

This situation must be taken into account when interpreting rubella avidity results. CMV IgG antibody of high avidity is detected in subjects with remote or non-primary infection, whereas, a low IgG avidity result usually confirms recent primary infection (<three-to-four months depending on the assay used). Whatever the virus/parasite involved, avidity testing should be performed early in pregnancy (if IgM antibody is positive), because a high avidity result seen in late stages of gestation cannot rule out primary infection having occurred in early pregnancy.

Although mother-to-foetus transmission may occur at any time during pregnancy, severe complications in the foetus are only observed when maternal primary infection occurs during the first half of gestation (Table 2).

For rubella, transmission rate is very high in the first trimester (70–90%), decreases to 25% at 25 weeks gestation and increases again to >70% at the end of gestation. By contrast, for toxoplasmosis and CMV infection, transmission is very low in the first trimester (10% for toxoplasmosis and 25% for CMV) and increases throughout pregnancy to reach approximately 70% in the third trimester.

Placental transmission of rubella virus to the foetus during the first trimester of pregnancy frequently results in CRS (>70%). CRS is characterised by persistent infection of the foetus with significant adverse effects: purpura, exanthematosis, pneumonia, hepatitis, meningoencephalitis and congenital malformations of the heart, eye and ear.

For toxoplasmosis, the rate of severe sequelae/stillbirths among infected infants decreases from around 40% (if infected during the first trimester) to almost 0% (if infected during the third trimester). Consequences of CMV congenital infection are usually more severe and occur in 20–30% of infected children when maternal primary infection occurs before 20 weeks gestation. However, considering all CMV congenitally infected children, >80% of them will remain asymptomatic throughout childhood.(7)

For ToRC infections, it is essential to define a diagnostic/prognostic approach at a time when a plausible decision can be made to either terminate the pregnancy, or treat (toxoplasmosis), or carry the foetus to full term.

In prenatal follow-up, the challenge is to identify affected foetuses at risk of severe sequelae (Table 2). To detect foetal impairment, ultrasound examination is the method of choice. It can be performed either on a routine basis during pregnancy or after diagnosis of maternal primary infection. For the latter, tight follow-up is recommended.

The reference method for diagnosis of foetal infection is virus/parasite detection by polymerase chain reaction (PCR) testing of amniotic fluid. Improved sensitivity of PCR compared with viral culture is clearly demonstrated in the literature.(8) Selection of a sensitive PCR test is crucial for reliable prenatal diagnosis (such tests should amplify all strains and include an internal control in order to detect possible PCR inhibitors). Furthermore, it is very important to closely schedule the time of amniocentesis: never before 18 weeks’ gestation, and, preferably after 21 weeks, and at least six weeks after maternal primary infection. In these optimal conditions, sensitivity of prenatal diagnosis is >90%(9,10) Positive molecular test results in amniotic fluid definitively proves that the foetus is congenitally infected but give no indication on the severity of the disease.

For toxoplasmosis, parasitic load can contribute to prognosis evaluation as it has been shown that maternal infection acquired before 20 weeks’ gestation associated with a parasitic load >100/ml is highly predictive of poor outcome, even if ultrasound scan is normal at time of amniocentesis.(11)

Unfortunately, for CMV, viral load in amniotic fluid is not predictive of infection severity, particularly because viral DNA accumulates in the amniotic fluid over time.(12) Foetal blood can also be collected for PCR testing as well as for the measurement of platelet levels. While the prognosis value of foetal thrombocytopenia now appears to be established, the prognostic value of viral load in foetal blood has not yet been demonstrated.(13)

Specific attention must be paid regarding the conditions of transportation and storage of rubella samples. Because rubella virus is very fragile, all samples collected for diagnosis should be frozen until analysed. Congenital infection can also be diagnosed in the prenatal period by testing specific-IgM in foetal blood. This procedure is specific, but sensitive enough only for rubella. To achieve the highest sensitivity, foetal blood samples must be collected after 21 weeks’ gestation and at least six weeks after maternal primary infection.

If recently acquired maternal infection is confirmed, and depending on the weeks of gestation, treatment with either spiramycin or a combination of pyrimethamine/sulfadiazine can be given in an attempt to prevent toxoplasma congenital infection and/or congenital defects. The efficacy of these treatments is controversial; however, it has been stated that treatment during pregnancy can result in a 60–70% prevention rate of congenital infection.(4)

The only intervention available for congenital rubella infection is termination of pregnancy. Careful use of prenatal maternal and foetal diagnostic tests along with prognostic markers (mainly time of gestation at infection) should help parents make their decision.

Preliminary studies show that CMV hyper-immunoglobulins may reduce the risk of transmission to the foetus but studies are still ongoing. Only ganciclovir has been evaluated in the treatment of infants with disease symptoms.

Depending on the country, ToRC infections can still represent a public health problem. Emphasis should be placed on prevention. In developed countries, thanks to vaccination programmes, rubella should be eradicated. Maternal and congenital infection diagnosis remains challenging and reference to specialists is highly recommended to help confirm or exclude ToRC infections. Efforts must also be focused on the development of effective treatment to decrease the rate of materno-foetal ToRC transmission and the severity of congenital defects.

• Toxoplasmosis is ubiquitous and is a common infection worldwide.
• As a consequence of the considerable differences in prevalence of the infection among general populations, there are large differences in the incidence of congenital infection. It can vary from 1/1000 live births in countries with a high prevalence, to 1/10,000 in countries with a lower prevalence.
• For both cytomegalovirus and toxoplasmosis, education is the principal means of prevention.
• If recently acquired maternal infection is confirmed, and depending on the weeks of gestation, treatment with either spiramycin or a combination of pyrimethamine/sulfadiazine can be given in an attempt to prevent toxoplasma congenital infection and/or congenital defects.
• The only intervention available for congenital rubella infection is termination of pregnancy. Careful use of prenatal maternal and foetal diagnostic tests along with prognostic markers (mainly time of gestation at infection) should help parents make their decision.

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