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Active Zika virus has been detected in saliva and urine, Brazilian scientists say.

The finding does not mean the virus can be readily transmitted through these bodily fluids.

Meanwhile, the US has advised men to abstain from sex or use condoms after visiting affected countries, if their partner is pregnant.

The US Centers for Disease Control believes a recent case of Zika was spread through sex.

While Zika is normally mild, the infection has been linked to thousands of suspected birth defects.

The updated advice says avoiding mosquitoes remains the best way to prevent infection, but advises men returning from affected countries to "correctly use condoms during sex or abstain from sexual activity for the duration of the pregnancy".

In another development the governor of Puerto Rico has declared a public health emergency over Zika. The US territory has 22 confirmed cases.

Transmission

The main method of infection is via mosquito bites.

But scientists say tests on two patients have revealed Zika can be found in other body fluids.

Paulo Gadelha, the head of Brazil's Fiocruz Institute which is part of the Ministry of Health, said: "The presence of the active Zika virus has been found in saliva and urine.

"But that does not mean there is a capacity for transmission through saliva and urine."

Traces of Zika's genetic material was detected in saliva and urine during the 2013 outbreak in French Polynesia, but the Brazilian authorities say this is the first time "active" virus has been detected.

Wilson Savino, from Oswaldo Cruz Institute said: "It means the virus is active, capable of infecting a cell so this is completely different, it means that the virus is functional."

More on the Zika crisis:

What you need to know Key questions answered about the virus and its spread

Key unanswered questions The many things we do not know about Zika

Travel advice Countries affected and what you should do

The mosquito behind spread of virus What we know about the insect

Abortion dilemma Laws and practices in Catholic Latin America

Prof Jonathan Ball, a virologist at the University of Nottingham, told the BBC: "Because we can detect a virus in a particular body fluid it does not mean that it will become an important source of virus for transmission to humans.

"At the peak of virus replication in the blood, virus can often be detected in other body fluids, but the levels of virus are often much lower and there is no obvious or efficient means for the virus to get from that bodily fluid into another person's bloodstream."

The risks of different modes of infection are still unclear.

But experts say that the million-plus suspected cases in the Americas have been contained to areas where the mosquito is found, suggesting it does not spread easily through other means.

Brazil has seen 4,783 suspected cases of babies born with small brains, although only 404 have been confirmed, 709 have been rejected and 3,670 are still being investigated.

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