Zika Virus Outbreak Updates: Florida Expands State of Emergency to 7th County

— -- As the Zika virus outbreak continues, including in wide swaths of Central and South America, concerns are growing, especially for pregnant women, because the mosquito-borne virus has been linked with a serious birth defect called microcephaly, characterized by an abnormally small head and brain.

Here are the latest updates about the outbreak, which the World Health Organization has deemed a "global health emergency."

Florida Expands Public Health Emergency to Seven Counties

New cases of people diagnosed with the Zika virus in Florida has prompted government officials to expand a state of emergency to two additional counties, for a total of seven counties.

The Florida Surgeon General and Secretary of Health Dr. John Armstrong announced Monday that 16 people in total have been diagnosed with the Zika virus. The counties now under a public health emergency are Broward, Hillsborough, Lee, Miami-Dade, Osceloa, Santa Rosa and St. Johns.

Armstrong urged residents to help stop mosquito activity by draining "standing water weekly, no matter how seemingly small. A couple drops of water in a bottle cap can be a breeding location for mosquitoes."

US 'Better Prepared' for Zika Virus, NIH Official Says

The U.S. is "better prepared" for an outbreak of the Zika virus compared to last year, according to Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health.

Fauci said health agencies have responded "rapidly" to the Zika virus threat.

"I think we are clearly better prepared for an outbreak like Zika then [we] were, let's say, a year or so ago," Fauci told reporters on Monday. "I think that's testified by the fact that we have responded very, very rapidly to this. We had the President of the United States involved in a very thorough briefing and briefings of this very early on."

Unlike the Ebola outbreak, where the outbreak was not identified for weeks to months, the response to the Zika virus outbreak has been swift, Fauci said.

Zika Virus Leads CDC to Activate Highest Level of Emergency Operations

The U.S. Centers for Disease Control and Prevention announced Monday that its Emergency Operations Center has been moved to Level 1, the agency's highest level, due to the risk of Zika virus transmission in the U.S.

The Level 1 activation is "reflecting the agency’s assessment of the need for an accelerated preparedness to bring together experts to focus intently and work efficiently in anticipation of local Zika virus transmission by mosquitoes," the agency said in a statement.

The highest level activation means the CDC staff will work around the clock to combat a critical emergency. The three other Level 1 activations have been to combat Ebola, to combat H1N1 influenza in 2009, and after Hurricane Katrina.

What Does the Virus Do?

Common symptoms of the Zika virus include fever, rash, joint pain and conjunctivitis, according to the CDC. Approximately one in five people infected with the virus show symptoms. Severe complications from the virus that require hospitalization are rare, according to the CDC.

The virus has also been associated with a rise of microcephaly birth defect cases.

The CDC is also investigating if a rare paralysis syndrome called Guillain-Barre is related to the virus. The syndrome is an immunological reaction that can also occur after other viral or bacterial infections.

How Is It Transmitted?

The virus is transmitted mainly through the bite of the Aedes aegypti species of mosquito. This is the same type of mosquito that spreads dengue fever. The Aedes albopictus species has also been identified as a potential carrier.

Before the current outbreak, the virus had been found mainly in tropical settings in Africa, Southeast Asia and the Pacific Islands. An outbreak of the disease in Brazil led to an alert by the Pan American Health Organization last May.

Health officials have also reported rare cases of transmission through blood transfusions and through sexual contact, including one case in Dallas, Texas.

Get real-time updates as this story unfolds. To start, just "star" this story in ABC News' phone app. Download ABC News for iPhone here or ABC News for Android here.