Evidence of Zika link to microcephaly

Scientists claimed that laboratory tests had yielded the first evidence of a biological link between the virus and Zika.

Studies showed the virus targeted cells that were important for the development of the brain, before disabling or destroying them. The findings provide a significant breakthrough in linking the mosquito-born pathogen with microcephaly, according to Guo-li Ming, a professor of neurology at Johns Hopkins' Institute for Cell Engineering, one of the report's co-authors.

The research team used lab-grown human stem cells to look at which type of cells were selectively infected by the Zika virus. Scientists looked at three brain cell types, and found that 90 percent of human neural progenitor cells (hNPCs) were infected within three days - with many of them already dead within that time.

Like other viruses, Zika hijacks cellular machinery to make copies of itself and eventually destroys infected host cells.

'Telling' pattern of infection

The hNPCs are crucial for the development of the cortex - or outer layer - of fetal brains, and the findings would be consistent with the theory that Zika can cause microcephaly.

"It is very telling that the cells that form the cortex are potentially susceptible to the virus," said Ming.

Co-author Hongjun Song said that the results - published in the journal Stem Cell - would help identify new treatments. "Now that we know cortical neural progenitor cells are the vulnerable cells, they can likely also be used to quickly screen potential new therapies," said Song.

Outside of pregnancy, Zika is normally no more threatening than a bad cold or a mild case of the flu.

Evidence piling up

An apparent link with microcephaly emerged as the cases of infection with the virus spread, coinciding with an increase in brain defects. In Brazil, the country apparently worst-hit, the number of confirmed and suspected cases of microcephaly associated with Zika this week rose from to 4,863 from 4,690 a week earlier.

The World Health Organization (WHO) said on Friday that there was mounting evidence of a link between the virus and microcephaly, as well as the rare paralysis-causing Guillain-Barre syndrome.

The WHO Emergency Committee is due to meet on Tuesday to review "evolving information" and to re-examine recommendations on travel, trade and mosquito control.