Brazilian health officials battling the vigorous spread of the Zika virus have revealed they have identified two cases in which the virus was transmitted through blood transfusion.

While Zika virus was thought to be a mosquito-borne disease, a report from the US this week showed a case in which a person communicated the disease through sexual contact.

Meanwhile, Spanish health authorities said they have diagnosed a pregnant woman with Zika virus, reporting the first known European case of the virus in a pregnant woman.

Zika virus causes microcephaly, a foetal deformation in which infants are born with smaller-than-usual brains. Brazil has confided hundreds of cases of microcephaly in children while dozens of children have died from the disease.

The World Health Organisation (WHO) has declared the rise in cases of brain damage in newborn babies caused by Zika virus a global public health emergency.

The latest Zika update from Brazil revealing another form of transmission adds to the challenges at hand for the World Health Organisation and other national agencies fighting to contain the virus.

Genetic testing confirmed that a man who received a blood transfusion using blood from a donor with Zika became infected with the virus, the director of the Blood Center at the Sao Paulo state University of Campinas told Reuters.

The case happened in March 2015 and the infected person did not develop symptoms.

The agency said another man, who was treated for gunshot wounds, was infected with Zika after multiple blood transfusions in April 2015. The patient died from his gunshot wounds and not the Zika infection.

"The two cases can be considered transmission of the virus through blood transfusion, with greater certainty in the first because we did genetic sequencing comparing the virus in the donor and to the virus in the recipient," the official told Reuters.

According to the WHO the virus has spread to 25 countries in the central and south Americas. Cases have also been reported in the Southeast Asia, Europe and New Zealand.

In Colombia, more than 2,000 pregnant women were infected with the virus, reports said, raising alarm about the disease that has the worst impact on pregnant women.

Vaccines are not available to counter the disease and there is no specific treatment for it. Meanwhile, scientists in the US, who likened Zika outbreak to the Ebola crisis, said it could be years before a vaccine is publicly available.

Several drugmakers have begun research for developing a Zika vaccine.

Zika in Europe

The disease spread to Europe last week, with a Danish resident being diagnosed with the virus. Health authorities from the Danish city of Aarhus said the unnamed patient had traveled to Central and South America.

This was followed by reports from Germany and Portugal that Zika virus had been found in people who returned from South America. As many as six cases have been reported in UK, Public Health England has said.

While Zika is not known to be particularly harmful to most people, its impact on pregnant women and newborn babies has proved to be dangerous.