As many as 4 out of 5 people infected with the Zika virus have no signs or symptoms. When symptoms do occur, they usually begin two to seven days after a person is bitten by an infected mosquito. Signs and symptoms of the Zika virus most commonly include:

• Mild fever
• Rash
• Joint or muscle pain

Other signs and symptoms may include:

• Headache
• Red eyes (conjunctivitis)

Most people recover fully, with symptoms resolving in about a week.

The Zika virus is transmitted primarily through the bite of an infected aedes species mosquito, which can be found throughout the world. The virus was first identified in the Zika Forest in Uganda in 1947, but outbreaks have since been reported in southeastern and southern Asia, the Pacific Islands and the Americas.

When a mosquito bites a person infected with the Zika virus, the virus enters the mosquito. When the infected mosquito then bites another person, the virus enters that person's bloodstream.

The virus can also spread to the fetus during pregnancy.

Spread of the virus through sexual contact and blood transfusion have been reported.

Factors that put you at greater risk of developing the Zika virus include:

• Living or traveling in countries where there have been outbreaks. Being in tropical and subtropical areas increases your risk of exposure to the virus that causes the Zika virus. Especially high-risk areas include several islands of the Pacific region, a number of countries in Central, South and North America, and islands near West Africa. Because the mosquito that carries the Zika virus is found worldwide, it's likely that outbreaks will continue to spread to new regions.

The mosquitoes that carry the Zika virus are found in some parts of the United States. Most cases of the Zika virus infection in the U.S. have been reported in travelers returning to the U.S. But local transmission has been reported in certain areas of the U.S. and in Puerto Rico.

• Having unprotected sex. The Zika virus can spread to another person through sex. If male sex partners or a couple that includes a male and female partner travel to an area with a Zika risk, the CDC suggests using condoms or avoiding sex for three months. If female partners travel to an area with a Zika risk, the CDC suggests using condoms or avoiding sex for at least two months. Also, the CDC advises abstinence from sexual activity during pregnancy or condom use during all sexual contact for a pregnant woman or her partner who have traveled to or lived in an area of active Zika virus transmission.

Zika virus infections during pregnancy have been linked to miscarriage and microcephaly, a potentially fatal congenital brain condition.

The Zika virus may also cause congenital Zika syndrome, which includes these birth defects:

• Severe microcephaly with a partly collapsed skull
• Brain damage and reduced brain tissue
• Eye damage
• Joint problems, including limited motion
• Reduced body movement due to too much muscle tone after birth

The Zika virus also may cause other neurological disorders such as Guillain-Barre syndrome.