Bruno Gomes Antunes shows a picture of his daughter, who was born with microcephaly, at a hospital in Rio de Janeiro on Thursday. (Lianne Milton/Panos Pictures/For the Washington Post)

Brazilian researchers said Friday that they had found the “active” presence of the Zika virus in saliva and urine samples, raising the possibility that the infection could be spread through kissing and other contact involving bodily fluids.

Until now, Zika was believed to be mostly transmitted by mosquitoes, although in some cases it is suspected of having moved from one person to another through sexual intercourse or a blood transfusion. Researchers said the latest discovery meant extra care was needed, especially in contacts with pregnant women, given the possible link of the virus to a sharp increase here in reports of the birth defect microcephaly.

Specifically, authorities said pregnant women should stay away from crowds and avoid sharing cups or cutlery with anyone suspected of being infected with the virus. If such women are in touch with someone showing the symptoms of Zika, “do not kiss them, obviously,” said Paulo Gadelha, president of the Oswaldo Cruz Foundation, Brazil’s leading ­medical research institution.

Scientists at the foundation said in a statement that they had ­observed for the first time in saliva and urine “the destruction or modification of cells provoked by Zika, which proved viral activity.”

“It was already known that the virus could be present in urine and saliva. This is the first time that we showed that the virus is active — in other words, with the potential to provoke infection,” Myrna Bonaldo, a researcher and one of the team leaders, said in the statement.

Infectious-disease specialists said the discovery should not take the focus away from the battle to control the mosquito that carries the virus.

Brazil is in the midst of a Zika epidemic that the government blames for potentially thousands of cases of microcephaly, a rare congenital disorder that causes babies to be born with small heads and possible brain damage. Friday’s news came at the beginning of the annual Carnival festivities here and across the Americas, when revelers often kiss strangers in the streets and casually engage in other forms of intimate contact.

The World Heath Organization has declared a global public health emergency over Zika and its suspected link to complications in newborns but has not scientifically confirmed a definite connection between Zika and­ ­microcephaly.

Doctors cautioned that the results released Friday are preliminary and said more testing was needed.

Peter Hotez, dean for the National School of Tropical Medicine at the Baylor College of Medicine in Texas, said that scientists do not know yet whether the virus actually can be transmitted through saliva or urine.

“That’s the big question,” Hotez said.

Jesse Alves, a specialist at the Emílio Ribas Institute of Infectious Diseases, a government hospital in Sao Paulo, Brazil, said the relevance of the findings is unclear. “It is more information, but it does not necessarily mean that this is a source of contamination,” he said.

Alves added that many other viruses are also present in saliva.

“An example is the HIV virus,” he said. “You can identify it in saliva, but this does not make it a relevant transmission source.”

Still, the new discovery could make saliva testing a more effective way to identify the disease, Alves said. Research performed in French Polynesia during an outbreak of Zika in 2013 and 2014 found more traces of Zika in saliva than it did in blood.

The Oswaldo Cruz Foundation team examined samples from two patients with Zika symptoms, it said. Researchers first identified genetic material from the Zika virus. A molecular biology test was then used to confirm the results.

The foundation developed the test, which could offer a weapon in Brazil’s battle to control the health crisis.

The test can distinguish Zika from dengue and chikungunya, two similar viruses carried by the same Aedes aegypti mosquito, said Marco Krieger, a molecular biologist and technical director of the Oswaldo Cruz Foundation’s production facility in Curitiba, in southern Brazil. And it can do it in just four hours.

Brazil’s Health Ministry plans to distribute 500,000 test kits by the end of the year. “It could be done with blood, it can be done with urine, and it can be done with saliva as well,” Krieger said.

Brady Dennis and Lena H. Sun in Washington contributed to this report.

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Today's coverage from Post correspondents around the world