Birth defects and nervous system disorders rose abruptly in Brazil after the arrival of Zika

We’re now more than a year into the Zika outbreak in the Americas, and the effects are starting to show in Brazil.

Over the past year, rates of birth defects in Brazil have doubled, while instances of Guillain-Barre Syndrome (GBS), a condition in which the immune system attacks the body’s nervous system, have tripled, according to a study published online in the CDC’s journal of Emerging Infectious Diseases.

On Wednesday, the World Health Organisation confirmed that Zika was a cause of GBS in adults and brain abnormalities in newborns.

The Zika virus is mainly spread by mosquitoes, although sexually transmitted cases have also been reported. Once infected, only about 20% of people ever show symptoms, which most commonly include fever, rash, joint pain, and red eyes. But for those who are pregnant, or those in which the infection leads to GBS, Zika can be a lot more serious.

The authors of the latest study noted that there were “abrupt changes” in the rates of hospitalisation for these neurological conditions that began in mid-2014, when Zika was likely introduced to Brazil. Those rates went up even more starting in November 2015, when the first public health warnings about microcephaly — a condition present at birth in which a baby’s head is abnormally small — came out. (Some of the rise may have been due to public warnings and increased vigilance about these conditions, but that’s unlikely to account for most of of the spike, the researchers write.)

At its peak, the birth defect hospitalisation rate per 100,000 live births quadrupled to 170, but has since dropped closer to 100 per 100,000 live births, the researchers reported.

Here’s a series of charts examining the different rates. Chart A represents the rates of birth defects present per 100,000 live births, with the dark line representing the Northeast region of Brazil where Zika hit the country the hardest. Chart B represents rates of hospitalizations for GBS in the same region, while chart C represent rates of cases of encephalitis, myelitis and encephalomyelitis (inflammation of the brain, spinal cord or both).

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