 -- 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 to what the World Health Organization has deemed a global health emergency.

Reported Case of First Zika Virus Infection Via Blood Transfusion

Brazil is reporting the first case in this outbreak of the virus being transmitted via a blood transfusion, according to Reuters. A man was infected after he was given blood while being treated for gunshot wounds.

While the Zika virus is primarily transmitted via mosquitoes, in rare cases it has been reported to spread through blood transfusion or sexual contact.

The American Red Cross issued new guidelines on Wednesday in the face of the Zika outbreak asking for prospective donors who have visited a Zika-affected area to wait 28 days before donating blood.

Brazil's President Calls Zika a 'Real Threat'

President Dilma Rousseff said in a televised address on Wednesday that the virus has moved from a "distant nightmare" to a "real threat." She told residents that the government is working on a vaccine, but that right now mosquito prevention is the best course of action.

Hundreds of thousands of soldiers and health care workers were called up to help stop the Zika outbreak. Soldiers have been going door to door in hard-hit areas to look for standing water where mosquitoes could breed. More than a million people in Brazil are believed to have been infected with the virus since it was first found in the country last year.

This week, the popular Carnival festival will start across Brazil, bringing in many tourists to the country.

At Least 51 People Sickened by Zika Virus in the U.S.

There are at least 51 people sickened by the Zika virus in the U.S. Nearly all cases were contracted while outside the U.S., health officials said. In just one case, the virus was transmitted within the U.S. when an infected person transmitted the disease to a partner through sexual contact, according to Dallas health officials.

Texas and Florida are the two states with the largest number of infected people. Texas has at least 10 people infected with the virus and Florida has at least nine.

The mosquito species that spread the Zika virus are present in the U.S., but in winter the mosquito activity is generally lower.

Florida Declares a State of Emergency in Five Counties

Florida Gov. Rick Scott expanded the state of emergency to a fifth county today where the Zika virus has been diagnosed. Although none of the residents were infected in the U.S., Scott said he wanted to be prepared for the upcoming mosquito season.

The five counties are Broward, Miami-Dade, Hillsborough, Lee and Santa Rosa.

"Although Florida’s current nine Zika cases were travel-related, we have to ensure Florida is prepared and stays ahead of the spread of the Zika virus in our state," Scott said in a statement on Wednesday as he announced a state of emergency in four counties. "Our Department of Health will continue to be in constant communication with all county health offices, hospitals and the Federal Centers for Disease Control and Prevention (CDC). We know that we must be prepared for the worst even as we hope for the best.”

Scott's executive order allows the commissioner of agriculture to issue a "mosquito declaration" in the affected counties to reduce populations of the insects that can spread the disease.

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.

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