MADRID/Brasilia - Spain said Thursday that a pregnant woman who had returned from Colombia had been diagnosed with the Zika virus, in the first such known European case.

“One of the patients diagnosed in (the northeastern region of) Catalonia is a pregnant woman, who showed symptoms after having travelled to Colombia,” the health ministry announced, adding she is one of seven cases in Spain and all are in good condition.

The mosquito-borne virus — thought to cause birth defects — has seen an outbreak in the Americas and health authorities have warned it could infect up to four million people on the continent and spread worldwide. The disease starts with a mosquito bite and normally causes little more than a fever and rash.

But since October, Brazil has reported 404 confirmed cases of microcephaly where the baby’s head is abnormally small — up from 147 in 2014 — plus 3,670 suspected cases. The timing has fuelled strong suspicions that Zika is causing the birth defect. The virus has also been linked to a potentially paralysing nerve disorder called Guillain-Barre syndrome in some patients.

Spain’s health ministry nevertheless sought to ease concerns, pointing out that all seven patients had caught the disease abroad. “Up to now, the diagnosed cases of Zika virus in Spain... don’t risk spreading the virus in our country as they are imported cases,” it said. So far in Europe, all those diagnosed with the disease caught it while travelling abroad, and none of them were pregnant — until now.

The news comes a day after South American health ministers held an emergency meeting in Uruguay on the disease. The meeting focused on ways to control the mosquito population spreading the virus, though reports of a US patient catching the disease by having sex fuelled fears that it will not be easy to contain. Brazil said it was sending more than 500,000 personnel out to clean up mosquito breeding grounds and advise people about the disease.

The World Health Organization has declared the spike in serious birth defects an international emergency and launched a global Zika response unit. Colombia, Ecuador, El Salvador, Jamaica and the US territory of Puerto Rico have all warned women not to get pregnant. There is no specific treatment for Zika, and several pharmaceutical companies are developing vaccines against it. Indian drugs company Bharat Biotech, for instance, said it was developing the world’s first Zika vaccine and was ready to test it on animals. French pharmaceutical giant Sanofi has also begun researching a vaccine. Moreover, Brazilian health authorities confirmed on Thursday a case of transmission of Zika through a transfusion of blood from a donor who had been infected with the mosquito-borne virus that is spreading rapidly through the Americas.

The health department of Campinas, an industrial city near Sao Paulo, said a man with gunshot wounds became infected with Zika after multiple blood transfusions in April 2015. Officials said they determined that one of the people whose donated blood was used in the transfusion had been infected with Zika.

Zika is usually contracted via mosquito bites, so transmission of the illness through blood transfusions adds another concern to efforts to contain the outbreak. Some countries have tightened procedures for blood donations, to protect blood supplies.

Zika has been reported in 30 countries since it first appeared in the Americas last year in Brazil, where it has been linked to thousands of babies being born with microcephaly.

This is a condition where infants have abnormally small heads and often have underdeveloped brains.

Campinas health officials said the donor of the contaminated blood developed symptoms afterwards that were mistaken for dengue, a virus borne by the same mosquito that transmits Zika.

A blood test that showed he had Zika was not completed until Jan. 28 this year.

The blood center at the University of Campinas said a second person who donated blood in May developed symptoms and tested positive for Zika, though the recipient of the contaminated blood has not developed symptoms of the virus. Brazil’s Health Ministry said the first recipient died of his wounds and not from the Zika infection. It said it was reinforcing instructions to blood banks that people infected with Zika or dengue not be permitted to donate blood for 30 days after full recovery from the active stage of Zika infection.

On Tuesday, the American Red Cross urged prospective donors who have visited Zika outbreak zones to wait at least 28 days before giving blood, but said the risk of transmitting the virus through blood donations was “extremely” low in the continental United States. The agency asked donors who give blood and subsequently develop symptoms consistent with Zika within 14 days to notify the Red Cross so the product can be quarantined. Also causing concern is the possiblity of transmission through sexual contact. Health officials in Texas reported on Tuesday that a person in Dallas became infected after having sex with another person who had traveled in Venezuela, where the virus is circulating.