Mosquitos carrying the Zika virus have reached mainland U.S., with more than a dozen reported cases of Zika infections from local mosquitos in Miami.

The news led to a historic travel warning on Aug. 2 from the U.S. Centers for Disease Control and Prevention, which advised pregnant women and their partners not to travel to the small Miami community where Zika is actively circulating. This is the first time CDC officials recall recommending people avoid travel to an American neighborhood over infectious disease concerns.

The mysterious tropical virus has caused global worry due to its link to microcephaly, a birth defect marked by a small head size and severe developmental problems in babies. The virus has now affected nearly 50 countries and territories and even raised alarm about the 2016 Olympics set in Brazil where the microcephaly outbreak began.  

There still many unknowns, but maternal fetal medicine expert Marjorie Treadwell, M.D., director of the fetal diagnostic center at the University of Michigan, answers some questions about Zika.

How do the Florida cases affect recommendations for pregnant women?

Treadwell: We had anticipated eventually seeing homegrown Zika cases in southern parts of the country like Florida and Texas as the weather warmed and during mosquito season. The virus is spread by the Aedes aegypti mosquito, which is reportedly a very difficult mosquito to control.

The CDC is advising that pregnant women avoid travel to the Miami neighborhood where people have been infected with Zika from local mosquitos. Pregnant women should regularly check the CDC's list of places to avoid and also protect themselves from mosquito bites in general.

That being said, most Zika cases are still from travel outside of the U.S., or sex with someone who was infected with Zika from traveling to a Zika-affected area outside of the country. 

What is your advice for patients?

Treadwell: We are telling pregnant patients not to travel to any areas where the CDC has confirmed active cases of transmission, and not to have unprotected intercourse with a partner who may have been exposed.

Especially during this season, pregnant women should avoid mosquito bites in general, especially if they live in an area where the Aedes mosquitos are found.

CDC guidelines recommend that those who have traveled to affected areas and are trying to conceive should wait at least eight weeks after potential exposure before trying to get pregnant. Men with Zika should wait at least six months after symptoms began to try to conceive. Patients should be aware that these recommendations may change as we learn more about how long the virus remains in serum and semen. They should continue to check the CDC website for up to date information.

Men who cannot avoid travel to areas where the Zika virus is found should also take precautions to protect themselves from mosquito bites to avoid exposing partners to risks.

What do we know about risks to babies born to women infected with Zika?

Treadwell: Research is ongoing, so we still can't say with certainty what the chance is that a pregnant woman with Zika will have a baby with microcephaly. Experts have put the risk anywhere between 13 and 80 percent, but that could change as we learn more. We believe that the earlier a woman is infected during pregnancy, the greater the risks to the fetus. Unfortunately, we can't say any time in pregnancy is a safe zone for a Zika infection.

We also don't yet understand the full spectrum of potential outcomes. There may be less obvious, mild or long-term effects on babies born to mothers who contracted Zika during pregnancy. We don't know if children who have normal sized heads at birth are not impacted, or if it will just be a delay until we realize the impact.

We also don't know if the infection behaves differently in the presence of other influences like nutritional state or environmental factors.  

Newborn deaths, stillbirths and miscarriages have also been reported in association with the virus.

How can someone get Zika?

Treadwell: Zika is a mosquito-borne virus related to dengue, yellow fever and the West Nile virus.  The most common means to get this infection is from a mosquito bite in a region where the virus is currently being spread. Sexual intercourse with someone who has contracted Zika is also a known risk.

In January, the World Health Organization declared Zika a global health emergency. What have we learned about the virus since then?

Treadwell: When the outbreak began, we thought the microcephaly was associated with Zika, but couldn't say for sure. We have now seen several studies supporting that Zika was indeed the cause of slowed brain development in unborn fetuses of infected mothers. Although a relatively small number overall, there continue to be more babies born with birth defects from the Zika virus.

We also know that not only can Zika be transmitted through mosquito bites, it is sexually transmitted, and the virus seems to be present in urine and semen longer than in blood.

What are the risks of Zika to people who are not pregnant or have pregnant partners?

Treadwell: For symptomatic people, the Zika virus usually causes only a brief, mild flu-like illness; 80 percent of people infected have no symptoms at all. The most common symptoms are usually mild, including fever, rash, joint pain or conjunctivitis (eye irritation).

What should you do if you're pregnant and think you've been infected with Zika?

Treadwell: Families should contact their primary health provider about a possible Zika virus diagnosis during pregnancy. If you have traveled to an affected region during pregnancy and are concerned, your doctor will help determine best next steps and possibly recommend diagnostic and fetal testing to evaluate your baby's health and development.

How should pregnant women protect themselves if they are in a Zika-infected area?

Treadwell: Pregnant women should take all possible precautions to protect themselves and their unborn babies if they are in a Zika-affected territory. Use insect repellent, wear long sleeves and long pants, and stay inside with air conditioning and window screens as much as possible. All travelers should check with their primary care provider for travel recommendations, and visit the CDC Travelers' Health site for the most updated information.

Is there any way to treat Zika?

Unfortunately at this time, there isn't a vaccine to prevent Zika. There is also no treatment for those infected. Prevention is key. 

For more information and updates about the Zika virus, visit the CDC's website.

This post was originally published on June 9, 2016, and was updated on Aug. 3, 2016.