Maternal-fetal arboviruses

The maternal-fetal transmission of arboviruses is well-known and concerns Dengue, Japonese encephalitis, West Nile and Chikungunya viruses. Pathogenic development is on the rise following the global increase of arboviruses transmitted by mosquitos. Certain arboviruses belonging to the Flavivirus and Alphavirus groups are capable of crossing the placental barrier in a small number of pregnant women.

Aedes aegypti in the Antilles and Aedes albopictus in Metropolitan France and in the Reunion Island are vectors of dengue and Chikungunya. These mosquitos bite during the day (outside) and principally at dawn and at dusk.

These viruses can impact the pregnancy at any stage during the term but generally, maternal-fetal transmissions of arboviruses in early pregnancy are rare but severe, and transmissions towards the end of term are more frequent and less severe. Delivery during a maternal viremia episode greatly increases the risk of transmission to the newborn.

Dengue

The four flaviviruses of dengue (DEN 1, DEN 2, DEN 3 and DEN 4) are capable of interrupting a pregnancy and threatening the life of the unborn child.

Clinical presentation of the pregnant women does not differ from the usual form (sudden and high fever, lasting from 2-7 days with vague algic syndrome, exanthema and petechia). During pregnancy and up until several days before the delivery, maternal dengue presents itself under the usual form of dengue (sudden, high fever with algic and haemorragic syndrome) and is exacerbated by pregnancy complications: thromopenia, hemolysis, increase in hepatic enzymes.

The main obstetric consequences are as follows:

• A higher rate of spontaneous miscarriage in the 1st trimester, and an increase rate of in-utero death (13% versus 1.8% in the general population).
• There are no teratogenic effects reported.
• A higher rate of premature delivery (21% versus 11.5% in the general population).
• An increased risk of acute uterine haemorrhage during childbirth. Congenital dengue is caused by the transplacental transmission of the virus in the days prior to delivery (direct transmission of the virus to the child).

Congenital dengue is seen and reported on in endemic zones. The first symptoms appear in newborns, between the 1st and 11th day and last from 1-5 days. Symptoms in children vary greatly going from asymptomatic forms to classic dengue forms: high fever accompanied by thrombopenias, to serious forms with respiratory distress or haemodynamic failure which can lead to the death of the newborn.

Maternal antibodies cross the placental barrier and protect the child up to 6 months of age. Individual protection against mosquitos is the only way of effective prevention to date. A vaccine is in the process of being commercialised.

Chikungunya

The alpha virus responsible for Chikungunya is also transmitted by an Aedes mosquito bite. This virus can be transmitted during pregnancy from the mother to the child. Maternal-fetal transmission before the 22th week of amenorrheoa is very rare and can be confirmed by RT-PCR on amniotic fluid. The prognosis is not favorable with a high risk of in-utero death. Beyond the 22th week of amenorrheoa, foetal risk is weak to inexistent.

The majority of maternal-fetal transmission take place peripartum, from D-2 to D+2 of delivery, via a viremic mother. The maternal-fetal transmission in this case is 50%. Certain mothers can be asymptomatic and the diagnosis is therefore retrospective but most present a febrile syndrome with vague algic syndrome, notably arthralgias and skin rashes. The newborn is asymptomatic at birth and presents an erhtrodermia 3-7 days after its mother, followed by fever and algic syndrome, then digestive symptoms (refusal to feed, diarrhoea), followed by serious swelling and shedding of skin on the extremities. There can also be neurological complications (convulsions, abnormalities in the neurological exam and EEG). There can also be haemostasis problems (DIC) and intra-cerebral haemorrhages.

Prevention relies mainly on the antivectorial struggle (against natural and artificial stagnant water) and individual protection against mosquitos.

West Nile Virus

This is a flavivirus type arbovirus, transmitted by a female Culex mosquito bite, of which the reservoir is represented by wild birds and migrators, and of which humans and horses are the accidental hosts.

This pathology is epidemic in Asia, Africa, the Middle East and Central Europe, but also in the USA as well as the Mediteranean region in France since the turn of this century. On the clinical plan, the forms are asymptomatic in 80% of cases and in other cases, the symptoms include a sudden, high fever with cephalus, algic syndrome, cervical adenopathies and meningoencephalis type neurological complications in 1% of cases. Maternal-fetal transmission is possible but very rare. During the first trimester of pregnancy, there is an increased risk of spontaneous abortion, but there are also cases reported of newborns that are born in good health to mothers having presented a meningoencephalitis to West Nile in the beginning of their pregnancy. Congenital transmission is possible but very rare, with a malformative syndrome, notably encephalitis. Maternal-fetal transmission during the last month of pregnancy with a severe, central neurological picture in the newborn has also been described.

The weak risk of transmission is probably due to a weak viremia in the mother. Prevention also relies on the antivectorial struggle and the individual protection against mosquitos.

Japonese encephalitis

This Flavivirus infection is widely spread over Asia and leads to serious neurological problems, which affect 1 infected subjected in 25-1000. It is the primary cause of encephalitis in Asia. Maternal-fetal transmission cases are rare. There is a major risk of foetal loss in the first half of pregnancy. Mothers infected during the second half of pregnancy have given birth to seemingly healthy newborns. There is a vaccine available in several Asian countries.