SOURCES: Feb. 23, 2016, news release, U.S. Centers for Disease Control and Prevention; Feb. 19, 2016, Morbidity and Mortality Weekly Report; Feb. 17, 2016, The Lancet Infectious Diseases; U.S. Food and Drug Administration, news release, Feb. 16, 2016; Associated Press
TUESDAY, Feb. 23, 2016 (HealthDay News) -- Fourteen U.S. cases of possible sexual transmission of the Zika virus are now under investigation by the U.S. Centers for Disease Control and Prevention, the agency announced on Tuesday.
The cases highlight the still-evolving understanding of how the virus might transmit between couples, and the potential danger to the fetus, the CDC said.
Babies born to mothers infected with the Zika virus can develop microcephaly, a condition where infants have smaller heads and the potential for long-term developmental issues.
Transmission of Zika via a mosquito bite has been thought to be the primary mode of infection, but sexual transmission may also occur, the CDC said.
"In two of the new suspected sexual transmission events, Zika virus infection has been confirmed in women whose only known risk factor was sexual contact with an ill male partner who had recently traveled to an area with local Zika virus transmission," the CDC noted in a news release. "Testing for the male partners is still pending," they added.
For the other 12 suspected cases of sexual transmission, four have been supported in preliminary lab tests but depend on other tests to confirm a Zika infection, while eight more cases involve an "ongoing" investigation, the CDC said.
"In all events for which information is available, travelers were men and reported symptom onset was within 2 weeks before the non-traveling female partner's symptoms [of Zika infection] began," the agency said.
On Feb. 5, the CDC issued an advisory on the potential sexual transmission of Zika after laboratory confirmation of the first such case in the continental United States.
The CDC stressed that, "although sexual transmission of Zika virus infection is possible, mosquito bites remain the primary way that Zika virus is transmitted."
However, the CDC advises that men who live in or have recently traveled from a Zika-endemic area should abstain from sex or use a condom with a pregnant or non-pregnant partner.
How long would these precautions be warranted? The CDC is not yet sure. "The science is not clear on how long the risk should be avoided," the agency said. "Research is now underway to answer this question as soon as possible. If you are trying to get pregnant, you may consider testing in discussion with your health care provider."
In the meantime, the quest to answer important questions about Zika continues. Teams of American and Brazilian scientists will travel on Tuesday to areas of Brazil hit hard by the Zika virus, in hopes of confirming a link between Zika and microcephaly.
Brazil has already recorded more than 4,100 cases of the birth defect, and while links to prenatal exposure to the Zika virus are strong, they have yet to be confirmed.
According to the Associated Press, the new research initiative is a partnership between Brazil's Health Ministry and the U.S. Centers for Disease Control and Prevention. Researchers plan to compare infants born with microcephaly and their mothers against infants born without the birth defect.
Eight teams, comprised of one CDC expert plus three Brazilian health workers, will go door to door to randomly selected families with new babies living in Paraiba, a state on Brazil's northeast coast. They hope to recruit at least 130 babies with microcephaly and compare them to almost triple that number of infants without the condition, the AP said. All will undergo blood tests looking for infection with Zika and another mosquito-borne virus, dengue.
"If we can provide some basic information or show a potential association [between a virus and microcephaly], that will allow us another avenue of how do we prevent this and what do we need to do next," Erin Staples, a Colorado-based epidemiologist who heads the CDC contingent in Paraiba, told the AP.
The study's launch comes a day after President Barack Obama asked Congress for $1.9 billion to help stem the spread of the Zika virus.
Since it first surfaced last spring, the virus has spread to over 32 countries and territories in Latin America and the Caribbean. The World Health Organization now estimates there could be up to 4 million cases of Zika in the Americas in the next year.
Meeting Monday with the nation's governors, Obama said he hoped to work with them in guarding against an outbreak of the disease in the United States.
Obama said the money he is requesting would be used for research into new vaccines and better diagnostic tools, the AP reported. He added that the money would also go toward more support for Puerto Rico and territories where there are confirmed cases, and to help pay for mosquito-control programs in southern states, such as Florida and Texas, at risk for the Zika virus.
Obama also asked for the flexibility to use some of $2.7 million that was approved to fight the 2014 Ebola outbreak in West Africa but was never used. House Republicans have said that would be the best way to fund a fight against Zika, the AP said.
Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, and Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, appeared before a Congressional panel earlier this month to lobby for Zika funding.
Although first discovered in Uganda in 1947, the Zika virus was not thought to pose serious health risks until last year. In fact, approximately 80 percent of people who become infected never experience symptoms.
But the recent increase in both cases and severe brain birth defects among thousands of newborns in Brazil has prompted health officials to reassess their thinking about Zika and pregnant women.
Last Friday, the CDC advised that healthy newborns of women who traveled in an area affected by the Zika virus within two weeks of delivery, or whose mothers show signs of Zika infection, be checked for infection.
According to the U.S. Food and Drug Administration, people considered at risk for Zika infection include those who have:
There have been no reports to date of Zika virus entering the U.S. blood supply, the FDA has said. But, the risk of blood transmission is considered likely based on the most current scientific evidence of how Zika and similar viruses are spread.
The American Red Cross has also asked potential blood donors who have traveled to Zika-affected areas to wait 28 days before giving blood.
For more on Zika virus, and where the virus is endemic, head to the U.S. Centers for Disease Control and Prevention.
To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.