Last week the World Health Organization (WHO) declared Zika virus a public health emergency of international concern.
Despite high rates of infection, the outbreak would not have been particularly alarming—since the infection is usually asymptomatic (80 percent of cases) or mild and self-limiting—had it not been for the sudden and (apparently associated) increase in numbers of infants born with microcephaly.
What Is Microcephaly?
Microcephaly is a condition in which the infant’s head is smaller than “normal” for the infant’s age and gender, because of delayed or arrested brain growth. There is no universally agreed definition. Most authorities suggest it should be defined by a head circumference of two—but some say three—standard deviations or more below the average.
