Various questions are being asked on how Zika virus can be transmitted as the disease spreads from Caribbean and Latin America, and threatens to hit parts of the US such as Florida. The virus has been linked to birth defects in thousands of Brazilian babies, born with heads smaller than normal and undeveloped brains.
Symptoms include a rash, fever, conjunctivitis and headache and to date, 21 countries have been affected.
At the moment, there is clear scientific evidence the virus is transmitted by the same type of mosquito that spreads other tropical diseases, such as dengue fever, chikungunya and yellow fever.
But there are also fears the virus may be passed on through sex, following two reports in medical literature.
One states that Zika was found in the semen of a man from Tahiti, the other that the virus was passed from a husband to his wife after intercourse.
But is there really a risk?
In a statement issued this week, the World Health Organisation said there was still insufficient evidence to make the link, but these research papers argue otherwise.