The Zika virus, researchers say, closely resembles some infectious agents that have been linked to the development of autism, bipolar disorder, and schizophrenia.
Reproductive health experts are warning that microcephaly may be only the most obvious consequence of the spread of the Zika virus. Even infants who appear normal at birth may be at higher risk for mental illnesses later in life if their mothers were infected during pregnancy, many researchers fear.
Schizophrenia and other debilitating mental illnesses have no single cause, experts emphasized in interviews. The conditions are thought to arise from a combination of factors, including genetic predisposition and traumas later in life, such as sexual or physical abuse, abandonment or heavy drug use.
But illnesses in utero, including viral infections, are thought to be a trigger.
Researchers in Brazil are investigating thousands of reports of microcephalic births. While there is no solid proof that Zika virus is the cause, virologists studying the outbreak strongly suspect it.
Although the virus was discovered in 1947, there has been no research into its long-term consequences. Scientists are left to draw inferences from what is known of similar infections.
In interviews, psychiatric researchers specializing in fetal development agreed with such pessimistic prognosis. A viral attack early in pregnancy can kill a fetus or stunt the growing brain, producing microcephaly, they said. An infection later in the fetus’s development, when the brain is nearly fully formed, can do damage that is less obvious but still significant.
Evidence has increased for years that mental illnesses may be linked to exposure during pregnancy to viruses like rubella, herpes and influenza, and to parasites like Toxoplasma gondii.
The possibility that in utero infection could contribute to mental illness first emerged with an observation in 1988 by Finnish researchers that children born during the 1957 Asian flu epidemic had high rates of schizophrenia later in life.
Researchers have long noted that schizophrenia is highest in adults who were born in winter and early spring — just after the peak of flu season.
But estimates of the size of the risk vary. One 2011 analysis of other studies estimated that maternal infections of any kind account for 6 percent of all cases of schizophrenia.