Liz Szabo

USA TODAY

U.S. officials are gearing up for the onset of locally transmitted cases of the mosquito-borne Zika virus that is spreading rapidly throughout Latin American and the Caribbean.

The Centers for Disease Control and Prevention considers Zika to be the definitive cause of an epidemic of birth defects in Brazil and other countries with outbreaks of the virus. It also causes Guillain-Barré syndrome, a rare condition in which the body attacks its own nerve cells, causing paralysis. The agency warned the virus is "scarier than we initially thought."

The virus, largely spread by mosquitoes, can sometimes be transmitted sexually or through blood transfusions. The World Health Organization declared the outbreak a "public health emergency of international concern."

Here is the latest on what you need to know:

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Q: What is the U.S. doing to prepare for local cases?

A: Congress is still struggling to reach an agreement to provide emergency funding to battle the Zika virus, and lawmakers are worried the fight could last awhile longer, despite increasingly urgent warnings from federal health officials about the need to move quickly to prevent a U.S. outbreak of the mosquito-borne virus.

The Senate passed a bill in late May providing $1.1 billion for mosquito-extermination efforts, testing and vaccine research. But the House passed legislation providing only $622 million and redirecting money from other programs to pay for it, including some funds previously dedicated to fighting Ebola.

The two sides now must come together and reach a compromise that can pass both chambers and be signed by President Obama, who requested $1.9 billion. As an emergency measure, Obama transferred $510 million in unspent Ebola funds to the Zika fight, but public health officials said the country will need much more to prepare for and respond to Zika.

The CDC wants communities to draw up Zika action plans and has set up a model program for communities to reference. It will release millions of dollars in grants for Zika planning and response but only to states that submit a "checklist of readiness activities."

Despite the efforts, U.S. officials are warning that mosquito eradication efforts, lab tests and vaccine research may not be able to catch up with the number of cases.

Q: How do local cities and regions fight the virus?

A: Fighting mosquitoes is fundamentally a local battle led by a patchwork of 700 mosquito-control districts and more than 1,000 other programs within local governments. In some cities, mosquito control is handled by sophisticated professionals with multimillion dollar budgets. In other communities, mosquito control is more of an afterthought, tacked onto other programs, such as the parks and recreation.

Q: How many Americans have been diagnosed so far?

A: So far, nearly 600 Americans in the continental U.S. have been diagnosed with Zika after returning from visits to countries with outbreaks of the virus. Of those, more than 150 were in pregnant women and more than 10 were sexually transmitted. An additional more than 140 pregnant women from U.S. territories, where the vast majority of cases are locally acquired, have also been infected.

Bold Zika mosquitoes love to hang with humans

Q: What parts of the country could be hardest hit?

A: The potential geographic range of the mosquitoes transmitting the virus also reaches farther northward than originally thought, with the Aedes aegypti species present in all or part of 30 states, not just 12. Still, the Gulf Coast — with its steamy climate, abundant mosquitoes and international airports — could be ground zero for the virus.​ More than 60 million Americans live in the five states there — Florida, Alabama, Mississippi, Louisiana and Texas.

Parts of the U.S. could face a year-round threat from Zika, according to a map of potential hot spots for the virus. Researchers plotted the potential risk for Zika outbreaks in 50 large U.S. cities based on several factors, such as whether the locations are home to the Aedes aegypti mosquito that primarily spreads the virus.

Q: How can the risk of Zika be reduced?

A: Public health officials in the U.S. are calling on home owners to help control mosquitoes this summer by cleaning up trash and other man-made containers that can collect rain water, where the insects breed. Another way to prevent infection is to avoid mosquito bites by staying indoors when visiting an area where the virus is present, wearing long pants and long-sleeved shirts, and using mosquito repellent.

Q. Could birth defects occur in the fetuses of pregnant American women?

A. Yes. One American has already given birth to a baby with microcephaly, a condition in which babies are born with unusually small heads and incomplete brain development. In addition, two other babies have been born in the U.S. with the defect. And the fetus of an unidentified woman in Puerto Rico also tested positive for the disease. Other pregnant women had abortions after ultrasounds showed abnormalities. Some had miscarriages.

It's unclear how widespread birth defects will be in the U.S., but the CDC estimates that a fetus infected with Zika during the first three months of pregnancy has up to a 13% risk of developing microcephaly.

Q&A: What is microcephaly, the birth defect linked to Zika?

Q: Are there concerns this summer's Olympics could spread the virus wider?

A: Brazil's hosting of the Games could give mosquitoes a chance to infect people from around the world. Public health officials in Rio de Janeiro downplay the risk, saying there will be fewer mosquitoes when the sporting event opens during the cool month of August. The World Health Organization said there is "no public health justification" for postponing the Games. The statement by the Geneva-based U.N. health agency came one day after a group of doctors, scientists and bioethicists wrote a letter to the organization calling for the Aug. 5-21 Games to be postponed or moved because of concerns of the spread of Zika.

Q: How is Zika diagnosed?

A: Diagnosing Zika is difficult because its symptoms can mimic those of other mosquito-borne diseases, and there are is just one commercially available test. Until the Food and Drug Administration granted emergency approval for the first commercial test for Zika, doctors didn't have access to an off-the-shelf test to quickly diagnose patients with the disease. Instead, physicians sent blood samples to state public health labs or the CDC in Atlanta.

Urine tests for Zika more accurate than blood

Q. What advice do U.S. agencies give for couples trying to conceive and pregnant women?

A. The Centers for Disease Control and Prevention says couples trying to conceive should use condoms every time or abstain for six months if the man had confirmed illness or Zika symptoms and was in an outbreak area. If the male partner was in a Zika outbreak area but didn’t get sick, they should abstain or use condoms for eight weeks.

The agency also warns pregnant women to avoid traveling to areas with Zika outbreaks. The WHO issued similar guidance. Women who cannot avoid traveling should consult their doctors and take steps to avoid mosquito bites, such as wearing long sleeves and pants. Women thinking of becoming pregnant should also consult their doctors before traveling to outbreak zones.

Study: Zika may affect babies even in later stages of pregnancy

Q. How serious is the risk of sexual transmission?

A. The WHO says sexual transmission of Zika is more common than previously thought, but scientists still have questions about the first mosquito-borne disease known to spread through sex, including how long it lasts in semen. Doctors aren't sure if a person needs to be sick with obvious symptoms in order to spread the virus through semen.

Q: What does research show about the birth defects Zika causes?

A: The type of microcephaly seen in babies affected by Zika is particularly severe. Babies affected by the virus appear to have "fetal brain disruption sequence," which occurs when normal growth in a fetus is interrupted by a destructive virus or parasite.

In addition to microcephaly and brain abnormalities, babies with Zika infections also have had eye problems that could cause blindness, extra scalp skin, clubfoot and arthrogryposis, a condition in which newborns' joints are stuck in either a flexed or extended position.

Ultrasounds found major abnormalities in 29% of the fetuses from 88 pregnant women in Brazil who tested positive for Zika, according to a study published in The New England Journal of Medicine. The defects included microcephaly. The fetuses from women not infected with Zika showed no abnormalities.

A separate study uncovered evidence that the Zika virus specifically targets developing brain cells, leading to stunted brain development. The findings, which eventually could identify drugs that treat the virus when it first infects, were published in the scientific journal Cell Stem Cell. The research found the virus affects neural stem cells, which develop into much of the nervous system in fetuses, slowing their growth.

Q: Where is the virus currently spreading?

A: Zika is now active in at least 39 countries and territories, mainly in Latin America and the Caribbean. The virus is spreading locally in the U.S. Virgin Islands, American Samoa and Puerto Rico, which the CDC warned could see hundreds of thousands of cases.

Q: How does it spread?

A: The Aedes mosquito spreads Zika. Unlike the flu, it does not spread from person to person. Mosquitoes that bite an infected person can spread it to future victims.

Q. What are the symptoms of Zika?

A. Four out of five people infected by Zika have no symptoms. Those who do usually have mild symptoms lasting two to seven days, such as fever, rash, headaches, joint pain, muscle pain, lack of energy, weakness and pink eye. It typically takes three to 12 days for illness to develop after a mosquito bite.

Q: Is it deadly?

A: Not usually, but people with pre-existing health problems can develop fatal complications.

Q: Are Americans well informed about Zika?

A: Turns out they're not. Although Zika infections are rarely fatal, 42% of those surveyed thought people infected with the virus are "very likely" or "somewhat likely" to die, according to a survey by the Annenberg Public Policy Center. About 44% said those infected with Zika would know it because the virus always produces noticeable symptoms, according to the survey. In fact, 80% of people with Zika infections display no symptoms, according to the CDC. A separate survey found nearly one in three people mistakenly believe the virus can be spread by coughing or sneezing, like a cold.

Q: Why are people concerned?

A: The virus causes serious birth defects. Seven countries have reported microcephaly cases related to the outbreak, with more than 1,300 confirmed cases in Brazil, according to the World Health Organization.

Children with microcephaly may have facial distortions, developmental disabilities, short stature, difficulties with balance and coordination, speech problems and seizures.

Q: What populations are at greatest risk of Zika?

A: People who live in poverty are at greatest risk because they live in environments where mosquitoes thrive: trash-strewn neighborhoods with lots of standing water, where mosquitoes breed, in homes without air conditioning or even window screens to keep the mosquitoes out. Although cities in Latin America and the Caribbean often meet these conditions, many impoverished communities along the Gulf Coast in the USA are also at risk.

Q: How long does Zika last in blood or semen?

A: Scientists largely conclude that Zika stays in the blood for about a week. Mosquitoes can only pick up the virus if they bite someone during this time. Scientists don't know how long Zika can live in semen.

The virus could linger months longer in the blood of pregnant women than other patients, according to a report published in The New England Journal of Medicine. One pregnant woman's blood tested positive for Zika for 10 weeks after being infected. Doctors can't say for sure why the woman harbored Zika in her blood for so long, in spite of having developed antibodies against the virus.

Q: What other ailments are linked to Zika?

A: Zika can cause Guillain-Barre, a rare immune system disorder that can cause temporary paralysis. WHO reported a number of countries with Zika are also seeing a rise of Guillain-Barre.

The virus is linked to a second type of autoimmune disorder called acute disseminated encephalomyeltis, which is similar to multiple sclerosis. The condition causes swelling of the brain and spinal cord that affects the myelin, the coating around nerve fibers.

Another study found the virus may also be associated with a deadly type of brain inflammation. Researchers found the Zika virus in the spinal fluid of an 81-year-old man with meningoencephalitis, a dangerous inflammation of the membranes that surround the brain, according to a report from French researchers in The New England Journal of Medicine.

Q: Can Zika spread through urine and saliva?

A: Scientists in Brazil found the virus can be "active" in the saliva and urine of infected people, but that isn't proof transmission via those routes can occur. More research is needed to confirm a possibility of infection through those fluids.

Q: What are sperm banks doing to keep Zika out of their supplies?

A: U.S. fertility associations have not issued guidelines yet on Zika virus. The British Fertility Society recommends people who have traveled to areas with Zika outbreak should not try to conceive naturally, donate sperm or eggs or undergo fertility treatments for 28 days.

Some sperm banks and fertility societies are taking steps to keep the Zika virus out of supplies of donor sperm to avoid infecting women trying to get pregnant. California Cryobank won't accept sperm donations from men who have traveled to countries with Zika outbreaks in the past month or who have had sex with someone who has traveled there within the past month

Q: Can you get Zika through a blood transfusion?

A: Yes. Brazil has reported that two people have gotten Zika through a blood transfusion. However, the risk of contracting Zika from a blood transfusion in the continental USA is extremely low because the virus is not spreading among local mosquitoes.

The Food and Drug Administration announced it will allow blood centers to screen blood with an experimental test for the Zika virus. The test means that blood donation and collection can resume on Puerto Rico, which had stopped collecting blood in early March because there was no way to test donations for Zika.

Q: Are blood banks taking precautions?

A: Yes. The American Red Cross is asking people to avoid donating blood if they've traveled to Zika-affected areas in the past 28 days. The American Association of Blood Banks issued a similar recommendation. Canadian Blood Services is barring people from giving blood within 21 days of traveling outside Canada, the continental USA and Europe.

Q: How can people reduce the risk of sexual transmission?

A: Using condoms and practicing safe sex reduces the risk of sexual transmission of Zika. The Centers for Disease Control and Prevention issued new recommendations that men who have live in or have traveled to an outbreak area should wear condoms or abstain from sex if they have a pregnant sexual partner.

Q: What is WHO doing to fight the virus?

A: The organization is asking nations around the world for $56 million to fight the Zika virus through the end of June, but the agency has only received $3 million so far.

Q: What are outside organizations doing?

A: The World Bank offered $150 million to fight the Zika outbreak and provide medical care. The institution said more funds could be made available if needed in the future.

Q: When did Zika emerge?

A: Zika virus appeared for the first time in 1947 in Uganda. For decades, health experts considered it a minor-league virus that, until recently, was limited to a narrow belt of equatorial Africa and Asia.

Q: When and where did this current outbreak begin?

A: Zika was first detected in Brazil in May. ​Researchers suspect the virus may have arrived in South America during the 2014 World Cup Games that drew millions of fans to Brazil. However, a new study suggests it may have reached the county between May and December 2013.

Q: Why did some nations advise women to postpone pregnancy?

A: The spike in birth defects in Brazil prompted Colombia, Ecuador, El Salvador and Jamaica to recommend women delay pregnancy until doctors understand more about the virus. El Salvador issued the strongest warning, urging women not to conceive for two years.

However, scientists have no idea how long the Zika virus will pose a risk to pregnant women. Health officials in El Salvador believe that people could develop immunity to the virus over time.

The U.N. High Commissioner for Human Rights called on Zika-affected nations to repeal restrictive laws that limit access to contraception and abortion, saying advice to delay pregnancy "ignores the reality that many women and girls simply cannot exercise control over whether or when or under what circumstances they become pregnant."

About half of pregnancies are unplanned.

Q: What actions is the travel industry taking?

A: All three of the USA's biggest airlines are allowing some customers to cancel or postpone their trips if they’re ticketed to fly to areas affected by Zika. Hilton Worldwide and Hyatt hotels are waiving cancellation fees in affected areas. Marriott International and Wyndham Hotels and Resorts are addressing cancellation requests on a case-by-case basis but being liberal in waiving fees.

Q: What treatments or vaccines are available for Zika virus?

A: There are no approved treatments or vaccines for Zika.

Q: How is microcephaly treated?

A: There's no treatment for microcephaly. Dozens of Brazilian babies have died. Although some children have normal intelligence and development, their heads remain small, according to the Mayo Clinic.