The head of the CDC announced new findings Wednesday that further support the connection between Zika and a serious birth defect called microcephaly - babies born with abnormally small heads and affected brain development.
Researchers identified markers of the virus in two babies who died of the condition in Brazil.
"This is the strongest evidence to date that Zika is the cause of microcephaly, but it's still not definitive," said CDC Director Dr. Tom Frieden.
Protecting pregnant women remains the top priority.
There are now 66 cases of Zika virus in the United States, including two women in Pennsylvania and one in Delaware.
All but one of the total cases were acquired outside the U.S in areas where the virus is spreading.
Health officials in Pennsylvania say the women had mild symptoms. They have not released if either was pregnant.
In Delaware, it's confirmed the woman infected is not pregnant.
Zika is predominantly spread through mosquitoes. The type which carries the virus is not common in our area, but is found in other parts of the country.
Another type of mosquito has the potential to carry the virus, but, so far, that has not been found.
Once spring hits, local health officials say they'll be on alert.
"We will be looking to see if there is any transmission of this virus during our mosquito season here in Delaware," said Dr. Karyl Rattay, Delaware Division of Public Health.
At hearings today on Capitol Hill, Dr. Freiden said, "We are quite literally discovering new things about Zika every single day."
Frieden and Dr. Anthony Fauci of the National Institute of Allergy and Infectious Disease told a congressional subcommittee there are reports the Aedes Aegypti mosquito which carries Zika virus is resistant to some insecticides.
Tests are underway in Puerto Rico to determine which products work and which don't.
There is hope that the biological control agent Bti, Bacillus thuringiensis serotype israelensis, may be successful in killing the mosquito larva.
Bti is a bacteria which is harmless to people, pets, and birds.
They said controlling Aedes egyptyi mosquitoes with conventional methods is difficult.
Outdoor spraying doesn't work very well.
The insect bites indoors, and can hide in closets or under tables for long periods.
One mosquito can also bite 4 or 5 people for one blood meal, infecting more people than mosquitoes common in our area.
Dr. Frieden said his agency is looking at "targeted indoor spraying," a technique which Australia has used.
Another question to be answered is the role malnutrition and poverty may play in microcephaly.
Mother's nutrition is an important factor in neural and brain development in developing fetuses.
CDC: New findings support Zika virus link to birth defect
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