Naturally acquired immunity against Zika virus

During their study of Zika infection in pregnant mice, the researchers built-up immunity in previously infected mothers that continued into pregnancy and protected fetal tissues. Because the mothers had already cleared their non-symptomatic Zika infections, they developed high levels of protective immunoglobulin antibodies against the virus that researchers found in the animals. Detection of these protective antibodies points to the possibility of developing diagnostic tests to identify naturally immune women and distinguish them from women at high risk of infection.

The ability to identify high-risk women would help develop focused therapeutic strategies for prevention, combining protective antibodies with an eventual vaccine, which could synergistically provide more a robust level of protection against Zika. Built-up immunoglobulin antibodies protect against Zika infection in mothers and their developing fetal offspring.

Researchers said expectant mothers are susceptible to Zika infection compared to non-pregnant women. If the virus is active during pregnancy, it usually spreads to vital tissues of a developing fetus. Because Zika virus infection in healthy non-pregnant women is mostly asymptomatic, many women of reproductive age in high-risk regions have a cleared infection before pregnancy.

Susceptibility to Zika virus infection was markedly reduced in mice that had previously cleared a prior infection compared to those undergoing a first infection during pregnancy. Mice that didn't have prior Zika infections developed clinical symptoms and sharply increased levels of Zika virus in their blood, which spread to fetal tissues.

Zika virus could not be found in most of the baby mice from mothers with resolved infection prior to pregnancy. Protection found in Zika-resistant mice could be transferred to susceptible mice with Zika virus neutralizing antibodies found in the blood of mice with prior asymptomatic infection.
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