Mild concern over Zika's advent in the West turned to dismay when Brazilian doctors began to find record numbers of microcephaly cases in the maternity wards of Pernambuco. The northeastern state of 9 million people typically saw just nine cases of microcephaly out of 129,000 births each year. In November 2015, they reported 646 such births, with neighboring states Bahía and Paraíba soon following suit [sources: McNeil et al., Wade]. Brazilian health officials were facing 4,000-plus possible cases; by mid-February 2016, they had verified around 400, compared to the country's average rate of 150 to 163 microcephaly cases per 3 million annual births [sources: Berkrot and Boadle, McNeil et al., Rampton and Hirschler, Wade].
The sheer prevalence was enough to shock physicians, but doctors were taken aback by the severity of the cases as well. Beyond the characteristic small heads and brains, they found eye malformations, intracranial calcifications (aka "brain stones"), malformed cerebral cortexes, or abundant spinal fluid suggesting that the brain had grown and then abruptly shriveled [sources: CDC, Berkrot and Boadle, Rogers]. In many cases, mothers were confirmed to have Zika or Zikalike symptoms while pregnant [sources: CDC, Wade]. Zika had also been found in placentas, amniotic fluid and fetal brain tissue, proving that the virus could cross the placental barrier [sources: Steenhuysen, Wade].
Meanwhile, another disorder began spiking in suspected Zika patients — Guillain-Barré syndrome (GBS), a slowly paralyzing attack on the body's nervous system by its own immune system [sources: CDC, NINDS, Rogers]. One Pernambuco neurologist reported 50 patients in 2015, compared to 14 the year before [source: McNeil et al.]. A similar uptick had occurred before, during the Polynesian outbreak of 2013, but the Zika link in that case, if true, remains unknown [sources: CDC, Rogers].
Indeed, tracing a clear causal link between Zika and microcephaly has proven tricky — in part, because it's baffling. As one Pan American Health Organization epidemiologist told The New York Times, no one has ever seen a "congenital malformation by mosquito before." Moreover, the microcephaly link is unconfirmed and largely circumstantial — a matter of co-occurrence in some regions but not others. Further blurring the picture: false positives, varying diagnostic standards and spikes in diagnoses thanks to heightened awareness [sources: CDC, McNeil et al., Wade].
Fire or no, there is plenty of smoke. In 17 of the 400 cases mentioned above, Zika has been confirmed in mother or baby. In a different study of 35 Brazilian babies born with microcephaly, all of the mothers involved had spent time in a known Zika area while pregnant [sources: Berkrot and Boadle, Rampton and Hirschler].
Clearly, caution is called for, as well as a good set of guidelines for avoiding spreading the disease to women who were, or might become, pregnant. If only it were that simple.