Pinning down further details about this link can help with the development of drugs and vaccines, researchers said.

Researchers working with lab-grown human stem cells "suspect they have discovered how the Zika virus probably causes microcephaly in fetuses", reported the journal Cell Stem Cell.

On February 1, the World Health Organization declared the spread of the Zika virus to be an global public health emergency.

The sickness is carried by the Aedes aegypti mosquito, which also spreads dengue fever.

For the study, two labs at Hopkins produced the specialized stem cells that could grow into brain tissue.

This is the sort of research that helped doctors understand and combat other infections that cause birth defects, she said.

This malformation, severe and irreversible, is characterized by an abnormally small skull and brains of newborns. Two microcephaly cases linked to a stay in Brazil were reported in the United States and Slovenia.

Much remains unknown about Zika, including whether the virus actually causes microcephaly.

"We have found a strong link between Zika and adverse pregnancy outcomes, which haven't been documented before", said study senior author Dr. Karin Nielsen, professor of clinical pediatrics in the division of pediatric infectious diseases at the David Geffen School of Medicine at UCLA.

In a separate report, other scientists suggested a mechanism for the damage, showing that the virus targets and destroys foetal cells that eventually form the brain's cortex.

Nielsen noted that this new research is important not only in finding further evidence of a direct link between abnormal pregnancies and the mosquito-borne Zika virus, but because it could dispel the theory that the disease could be caused by pesticides that have been used in the area for mosquito control, leading to calls to stop using the pesticides.

USA federal health officials expect the first locally transmitted cases of the Zika virus in the continental United States by June or July. They immediately prepared different cells, including so-called pluripotent stem cells that are made by reprogramming mature cells so they can become any type of cell in the body.

The paper by Ming and colleagues, he said, shows that Zika virus has a "tropism" to human cortical neural progenitor cells.

They sent the cells and a pair of experienced graduate students to Florida and then to Emory to assist in the research.

Nielsen said microcephaly may be one of many abnormalities in what she referred to as Zika Virus Congenital Syndrome.

The cells died or failed to divide normally, which in a fetus would stall brain development - the hallmark of microcephaly. Please see our terms of service for more information. However, it's very hard to study that in humans because what is missing is a model system where we can address causality, " said neurology and neuroscience Professor Hongjun Song.

Zika has been linked to numerous cases of microcephally in South America, particularly in Brazil where the current outbreak seems to have started.

The health minister has said original estimates of microcephaly cases may be too high. "Now suddenly, over the last month I've seen 15 (brain scans), all with the same pattern, all from northern Brazil".

The study said blood and urine tests found 72 of the 88 women had the Zika virus. Either the outbreaks weren't big enough or public health infrastructure in the affected countries wasn't sufficient to recognize and report it. Also in past outbreaks in Africa, he said people may have had Zika infections earlier in their lives and developed protective antibodies.

More evidence that aspirin lowers risk of cancer
Researchers looked at data from 1986 of 88,084 women (aged 30-55) and 47,881 men (aged 40-75) participating in two large studies . And for bowel cancer , which affects 41,000 people in Britain every year, the risk of diagnosis was reduced by 19 per cent.