Brazil has had abnormally high levels of the birth defect microcephaly - reduced head size and potentially stunted brain development - for three years before the current Zika outbreak.  That's according to a doctor who had for years been collecting data on Brazilian babies in the heart of the outbreak region.

And it's leading some to question how the mosquito-born Zika virus could be the cause, or at least the sole cause, of 4,000 cases of microcephaly since October.  

This revelation comes after Brazilian pediatric cardiologist Dr Sandra Mattos reviewed four years worth of data on 100,000 babies she and her colleagues collected to track a congenital heart defect in infants.  They separated out information that indicated the symptoms of microcephaly, and discovered Paraiba State averaged about 1,000 more cases of the birth defect than they expected.  But since the summer of 2015, the documented cases are more severe. 

The Brazilian government and many international health officials believe Zika - discovered in the country only a year ago - is linked to microcephaly, but the link hasn't been proven yet.  As health care workers spread out to advise people how to abate mosquitoes by eliminating standing water, they're discovering another unifying thread to the birth defects:  poverty.

"Most mothers with children with microcephaly have come from poor communities," said Claudio Maierovitch, director of the Communicable Disease Surveillance Department at Brazil's health ministry.  Brazil's favelas are rife with problems such as malnutrition, drug and alcohol abuse, exposure to toxic chemicals, and other infections. 

"It could be that Zika is causing (microcephaly) with another factor, which is definitely possible," said University of Wisconsin mosquito-borne virus researcher Kristin Bernard, who commented separately from the new information from Paraiba state.  "There could be other environmental factors, there could be co-infections that cause the unfortunate microcephaly, and at this point there is just not enough evidence to say it is causing it."