A new case control study published in Lancet Infectious Diseases fills gaps in science and gives the strongest evidence yet that Zika virus causes the birth defect microcephaly.
"Although there is a strong scientific consensus that Zika virus is a cause of microcephaly, the early findings from this case control study are the missing pieces in the jigsaw in terms of proving the link," said Laura Rodrigues, PhD, professor of infectious disease epidemiology at the London School of Hygiene & Tropical Medicine and one of the study's authors.
The study, conducted by an international team of researchers, was requested by the Brazilian Ministry of Health. Researchers studied all infants born with microcephaly in eight public hospitals in Brazil between Jan. 15 and May 2. For each baby with microcephaly, two control babies were also studied — the control infants were the first two infants born the following morning without microcephaly at one of the eight hospitals.
Researchers collected blood samples from case and control infants and mothers, and cerebrospinal fluid samples were taken from the babies with microcephaly. The samples were tested for Zika and dengue viruses.
Results showed 24 of 30 mothers (80 percent) of infants with microcephaly were infected with Zika, compared to 39 of 61 (64 percent) of mothers of infants without the birth defect. Thirteen of 32 babies with microcephaly (41 percent) tested positive for Zika virus in blood or cerebrospinal fluid samples, while none of the control babies tested positive.
"The evidence [that Zika caused microcephaly] was very strong before this, enough to get a conviction out of most juries. Now they have essentially found the gun in the defendant's glove compartment. There is overwhelming evidence and there is really no room for doubt," Andrew Pavia, MD, a pediatric infectious disease specialist with Salt Lake City-based University of Utah, told The Washington Post of the study's findings.