A rare case of the Zika virus being transmitted through sexual contact, rather than mosquito bite, has been reported by a patient in Dallas, Texas..

The US Center for Disease Control (CDC) says the person had not travelled to an infected area, but their partner had recently returned from Venezuela.

Zika is transmitted by infected mosquitoes, and has been linked to the birth of thousands of babies with underdeveloped brains in South and Central America.

The World Health Organisation has declared the outbreak of the virus a “global public health emergency”.

It is spreading through the Americas and the World Health Organization (WHO) has declared the disease linked to the virus a global public health emergency.

Elsewhere, both Australia and Ireland have each confirmed two cases of the Zika virus.

Last week the UK confirmed the first three cases of the virus, in people who had been infected by mosquito bites in Colombia, Suriname and Guyana.

Brazil, the country worst hit by the outbreak, has revealed it is investigating 3,670 suspected cases of microcephaly in babies linked to the Zika virus. The health ministry suspects 76 infant deaths, either during pregnancy or shortly after birth, were the result of microcephaly, believed to be linked to the virus.