Zika is the virus that health experts have cited as reason to postpone this summer's Rio Olympics.
Some 150 leading scientists have signed an open letter to the World Health Organisation and International Olympic Committee (IOC) asking for the Games to be rescheduled "in the name of public health".
But what exactly is the disease, and how can people stay safe?
What is Zika?
Zika is a mosquito-borne virus which was first identified in rhesus monkeys in Uganda in 1947 and moved to humans in Uganda and the United Republic of Tanzania in 1952.
How is the virus transmitted?
It is spread by the Aedes mosquito, which usually bites during the day, and can be transmitted from person to person through sexual contact.
Other modes of transmission, such as blood transfusion and perinatal transmission, are currently being investigated.
What does Zika do?
The main concern from Zika is the threat to babies in the womb. Zika is now known to be a cause of microcephaly, where babies are born with abnormally small heads due to the fact their brains have not developed properly.
Microcephaly can cause serious developmental problems and death in some cases.
What are the symptoms of Zika?
The majority of people show no sign of infection and for those who do display symptoms they are usually mild and last two to seven days.
Symptoms include fever, itching, conjunctivitis, red and sore eyes, headaches, rashes and joint pain.
A disorder of the nervous system known as Guillain-Barre syndrome has also been linked to the infection.
What can people do to protect themselves?
There is currently no vaccine against Zika. The best protection is to take steps to avoid being bitten by mosquitoes.
Official health advice says people should use insect repellents, cover up with long-sleeved clothing and keep windows and doors closed.
Still water and stagnant water such as in buckets and ponds also attracts mosquitoes to lay their eggs.
Which countries are affected?
Outbreaks of the disease have been recorded in Africa, the Americas, Asia and the Pacific, with 64 countries and territories reporting occurrences since 2007.
There is currently widespread transmission in much of Central and South America, including Brazil which has "increasing or widespread transmission".
What is the current travel advice?
Pregnant women should postpone non-essential travel to countries with an active and established Zika virus transmission until after pregnancy.
Women should avoid becoming pregnant while travelling in an area with active Zika virus transmission, and for 28 days after their return.