RIO DE JANEIRO — 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.

Scientists at the Oswaldo Cruz Foundation, Brazil’s leading medical research institution, said in a statement that they had observed for the first time “the destruction or modification of cells provoked by Zika, which proved viral activity.”

The discovery, they said, amounts to “new paradigms for the understanding of transmission routes of the Zika virus.”

“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 comes 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 issued 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 to determine Zika’s ability to spread by contact such as kissing.

Peter Hotez, dean for the National School of Tropical Medicine at the Baylor College of Medicine in Texas, said that the finding is interesting but that scientists do not know yet whether the virus actually can be transmitted through saliva or urine. Getting that answer could alter our understanding of the ways in which the disease spreads, he said.

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

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