The Zika virus is a mosquito-borne virus sweeping Latin America, usually lasts less than a week, except when it derails a whole life.
Zika, which resembles a light case of the flu, is often so mild that people don't realise they have it.
But health officials in Latin America say the tropical fever is linked to neurological problems and a surge in microcephaly, a condition in which babies are born with abnormally small heads. The defect can cause brain damage and death.
Read: Surge of Brazilian babies born with small heads
The outbreak has led authorities in some countries to urge couples not to get pregnant, while the US Centres for Disease Control (CDC) has warned pregnant women to avoid traveling to 22 affected countries.
Here are some questions and answers on the virus.
The virus was first identified in a monkey in Africa in 1947. Its name comes from a forest in Uganda where the first infected rhesus monkeys were found. Within several years the virus had jumped to humans in Uganda and Tanzania, according to the World Health Organisation (WHO).
Like dengue fever and chikungunya, two similar diseases, Zika is transmitted by mosquito species found in tropical and sub-tropical regions: Aedes aegypti and Aedes albopictus, or tiger mosquitoes.
Read: 7 things worth knowing about mosquitoes
How do I know if I have it?
In 70 to 80 percent of cases, the disease goes unnoticed. The symptoms resemble a mild case of the flu headache, muscle and joint pain, and mild fever plus a rash.
Symptoms usually last two to seven days.
Why are experts worried?
The disease is suspected of causing two serious complications: neurological problems and birth defects in babies born to infected women. But while there appears to be a connection with Zika, researchers have not definitively confirmed a causal link.
The main neurological complication is Guillain-Barre syndrome, a disorder in which the immune system attacks the nervous system, causing weakness and sometimes paralysis.
Most patients recover, but the syndrome is sometimes deadly. Cases linked to Zika have been reported in Brazil and French Polynesia.
Read: Our expert on microcephaly
Microcephaly and other brain deformities in newborns have also been reported, particularly in Brazil. Microcephaly cases in the giant South American country surged from 163 per year on average to 3,893 after the Zika outbreak began last year. Forty-nine of those babies have died.
What's the treatment?
There is no vaccine for Zika, and no specific treatment patients simply take pain-killers and other medication to combat the symptoms.
The virus is transmitted through mosquito bites, so prevention entails fighting mosquitoes and avoiding contact with them. Health officials recommend covering up, using insect repellent and keeping windows closed or screened.
Authorities have responded to the outbreak by fumigating and cleaning up the standing water where mosquitoes breed.
Authorities in Brazil, Colombia, Ecuador, El Salvador and Jamaica have advised couples to avoid pregnancy for the time being.
In Brazil, authorities have announced a crackdown on mosquito breeding grounds ahead of the Olympics, which will bring hundreds of thousands of travelers from around the world to Rio de Janeiro in August.
Where is Zika now?
The virus was first reported in Africa, Asia and the Pacific before leaping to the Americas last year.
It is now spreading locally in some 20 Latin American and Caribbean countries, as far north as Mexico. Brazil has been the hardest hit.
Read: Zika virus spreads to more tropical destinations
Travelers have also brought it back to the US states of Florida, Hawaii and New York. A woman in Hawaii gave birth to a baby with microcephaly after traveling to Brazil.
So far there have been no locally transmitted US cases reported, though the Aedes aegypti mosquito's habitat stretches into the United States.
The European Centre for Disease Prevention and Control (ECDC) says on its website that "there is no evidence of transmission (of) Zika virus in Europe to date and imported cases are rare".
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Surge of Brazilian babies born with small heads
Brazil sees a growth in microcephaly cases
Image: Mosquito on a leaf from iStock