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The Zika virus, a flu-like virus transmitted by mosquito bites and sex that can cause severe birth defects, has quickly spread since the start of last year's outbreak — first in Brazil, and then through Latin America and elsewhere, eventually reaching some U.S. territories and Florida.

Because the virus can cause birth defects, including microcephaly — an abnormally small head and brain size — the Centers for Disease Control and Prevention (CDC) has been regularly posting travel alerts, including advice for pregnant women to avoid travel to areas where Zika is active: Miami-Dade County, as well as 59 countries or territories in the Americas, the Pacific Islands, Africa, and Asia.

The Florida Department of Agriculture and Consumer Services reported in September that the first mosquitoes to test positive for Zika in the state had been identified in the Miami Beach area. As of October 19, the CDC's guidance for travel, testing, and other matters relating to the Zika virus was extended to all of Miami-Dade County.

The number of people now known to be infected with Zika by local mosquitoes in Florida is 180, according to the state's department of health, which believes local spread is limited to certain areas in Miami-Dade county.

Here are the facts about the Zika virus:

1. The Zika Virus Is Spread by Mosquito Bites and by Sex

Zika is a virus related to the West Nile, yellow fever, and dengue viruses that's passed on primarily by the bite of an infected Aedes mosquito. “A person bitten by a mosquito that has the virus then becomes viremic. They get bitten by another mosquito, which then passes the virus along,” explains Peter Jay Hotez, MD, PhD, dean of the National School of Tropical Medicine at the Baylor College of Medicine in Houston.

The Zika virus can also be sexually transmitted, notes the CDC. Men infected with Zika have passed it on to both female and male partners, and the CDC’s Morbidity and Mortality Weekly Report noted in July that “the first reported occurrence of female-to-male sexual transmission of Zika virus” appeared to have occurred in New York City.

If your partner has or had Zika, or traveled to an area where Zika is spreading, condom use is advised for 8 weeks to 6 months, depending on the circumstances.

CDC guidelines recommend that pregnant women coming back from areas where Zika is active get tested for the virus, and that men who have a pregnant partner use condoms for the duration of the pregnancy if they live in or travel to areas with Zika infection. As of October 20, the Zika Pregnancy Registry noted 953 U.S. cases of possible Zika infection in pregnant women, and an additional 2,027 in U.S. territories.

If you're pregnant and your partner had or has Zika, or has been exposed to mosquitoes in regions that have Zika, the CDC recommends that you speak with your doctor and also consider using condoms or abstaining from sex throughout the pregnancy.

As a safety measure to protect the blood supply and transplant recipients from Zika, the Food and Drug Administration (FDA) recommends not donating blood, tissue, or organs if, within the last six months, you've:

Been diagnosed with the Zika virus

Been in an area with active Zika virus

Had sex with a man who's had the virus

Banned donations include blood, organs, semen, oocytes, umbilical cord blood, placenta, corneas, bone, skin, and heart valves. Deceased organ or tissue donors are also no longer eligible if they had been diagnosed with Zika within six months of their death.

2. Symptoms of Zika Virus Infection Are Usually Mild

Eighty percent of people who become infected never have symptoms. In those who do, the most common Zika virus symptoms are fever and rash; it can also cause muscle and joint pain, headache, pain behind the eyes, and conjunctivitis (itchy, red eyes), according to the World Health Organization (WHO).

Health experts at the WHO Regional Office for the Americas note that symptoms generally last two to seven days. Rare complications can include internal bleeding, which caused the first U.S. Zika-related death in Puerto Rico in April. Nine deaths have been attributed to Zika virus in the current epidemic, and in one case, the infection was passed on to a caregiver — possibly through contact with the patient's infected sweat and tears, according to a September 28 letter to the New England Journal of Medicine.

Research points to a possible connection to higher rates of Guillain-Barré syndrome — a condition in which the immune system attacks nerves following an infection, causing muscle weakness and paralysis — in adults with Zika infection.

No effective treatment is available for Zika infection, but over-the-counter fever or pain medication can be helpful for symptom relief.

3. Unborn Babies Are Most at Risk From Zika Virus Complications

When pregnant women are infected with Zika, the unborn child is at risk, says Dr. Hotez. “We’re seeing illness when it strikes women who are pregnant, and it’s producing a horrific effect of microcephaly,” he says. “We don’t know when in pregnancy the consequences are greatest.”

Microcephaly may cause mental retardation, as well as delays in speech, movement, and growth, according to the Mayo Clinic.

The CDC's February 26 Morbidity and Mortality Weekly Report noted that the Zika virus in nine pregnant U.S. travelers they studied was associated with two early pregnancy losses, two elective terminations, the birth of a baby with severe microcephaly, two healthy births, and two continuing healthy pregnancies. The CDC has established a registry to track pregnant U.S. women who have a lab-confirmed Zika virus infection, as well as infants born with Zika-related birth defects and pregnancy losses from birth defects.

Twenty-three babies have been born in the United States with confirmed Zika-related birth defects, and as of October 20, the CDC had confirmed five pregnancy losses in which the fetuses had birth defects.

After considering mounting evidence, researchers concluded in an April special report in The New England Journal of Medicine that Zika virus infection during pregnancy can cause microcephaly, as well as other severe brain abnormalities.

Healthcare workers in Brazil were stunned to learn that, from November 2015 to July 2016, there were 1,709 congenital microcephaly cases confirmed to be related to Zika infection — higher than the total number of microcephaly cases from any cause in prior years.

4. Research Is Underway for a Zika Vaccine

“There’s going to be a need to accelerate a Zika vaccine,” says Hotez. “I think the world got caught by surprise at the congenital infections. Now there’s going to be a lot of interest in a vaccine for women of reproductive age, like the rubella vaccine [to prevent birth defects]."

The FDA has given approval to Inovio Pharmaceuticals in Plymouth Meeting, Pennsylvania, to go ahead with tests of an experimental Zika vaccine in people.

5. Zika Began in Africa and Spread Rapidly

The virus, originally named ZIKV, was first discovered in 1947 in a rhesus macaque in the Zika forest in Uganda. Researchers there found that it lived in mosquitoes, and they learned through experimentation that it could also infect mice.

Outbreaks were reported from 1951 to 1981 throughout Africa and Asia, and in 2007 in Polynesia, where 73 percent of the population was infected. But since the first cases were discovered in Latin America in 2014, the virus has quickly spread. In December 2015, the Pan American Health Organization/World Health Organization (PAHO/WHO) recommended Latin American countries start gearing up to screen for Zika and prepare for demands on the healthcare systems due to the severe health problems it's causing in newborns.

6. Zika Has Reached Florida's Mosquitoes

As of October 26, Florida had reported 180 cases of locally-transmitted Zika infection.

“Puerto Rico reported the first locally-acquired Zika virus case in the United States” in December 2015, according to Benjamin Haynes, a CDC spokesperson. Current case numbers are at 28,111 and increasing.

“I think we have to proceed along a worst-case scenario that the Gulf Coast is at risk. We’re vulnerable,” says Hotez. “I'm not an alarmist. But I am worried about a Zika outbreak on the Gulf Coast.” That includes areas around Houston, New Orleans, and Tampa-St. Petersburg, Florida, which are all potential hot zones for tropical diseases because mosquitoes thrive there.

7. U.S. Travelers Bring Zika Back With Them

“The first travel-associated Zika virus disease case among U.S. travelers was reported in 2007,” says Haynes. “From 2007 to 2014, a total of 14 returning U.S. travelers had positive Zika virus testing performed at the CDC.” The numbers have risen dramatically in 2015 and 2016.

To date, the CDC has reported 3,951 travel-associated cases of Zika in U.S. states, and 28,627 locally acquired cases in U.S. territories.

8. Travelers Probably Don’t Bring Infected Mosquitoes Along

“It’s extremely unlikely that mosquitoes would be carried back to the United States by citizens traveling abroad,” says Jim Fredericks, PhD, chief entomologist and vice president of technical and regulatory affairs for the nonprofit National Pest Management Association in Fairfax, Virginia.

“As adults, mosquitoes are a relatively fragile insect that doesn’t travel very well. In addition, since only a fraction of the total mosquito population in Zika-endemic areas carries the virus, it’s even less likely for an infective mosquito to be brought back alive,” he says.

The bigger concern is that a person infected with the virus can pass it along by having sex, or to local mosquito populations through mosquito bites.

RELATED: Mosquito Repellents That Offer Safe Protection From Zika

9. Using Insect Repellents Helps Prevent Zika

If you're in areas with a current Zika outbreak, take steps to avoid catching the virus. “The best way to avoid mosquito bites is to use a repellent containing picaridin, oil of lemon-eucalyptus, at least 20 percent DEET, or IR3535 when venturing outdoors, especially near dawn and dusk when mosquitoes are most active,” says Dr. Fredericks.

Here are some examples of mosquito-fighting repellents:

Cutter Lemon Eucalyptus Spray, from $8, Amazon.com

All Terrain Herbal Armor Spray for Kids, $11.13, Amazon.com

You can find more of the most effective products in Consumer Reports' insect repellent ratings. “Whenever possible, it also makes sense to wear long sleeves and pants when outside during these times,” he says.

10. Mosquito Control Can Help Prevent Zika

Controlling the insect vector by cutting down on mosquito breeding is one way to prevent spread of Zika and other mosquito-borne viruses.

Breeding sites include water-filled habitats like plant containers and toilets inside the home, and puddles, birdbaths, and pooled water outdoors. Chemical pesticides can kill mosquitoes, but use them carefully to prevent contamination that could be harmful to your health, notes the CDC.