What is the Zika virus?

The World Health Organisation has rejected calls from health experts to postpone the Rio Olympics because of the threat posed by the Zika virus.

But what exactly is the Zika virus and how is it spread?

• What is Zika?

Zika is a mosquito-borne virus. It was first identified in the rhesus monkeys in Uganda in 1974, and moved to humans in Uganda and the United Republic of Tanzania in 1952.

• How is Zika transmitted?

It is spread by the Aedes mosquito, which usually bites during the day.

The virus can also be spread from person to person through sexual contact, but other forms transmission - such as blood transfusion - are being investigated.

• What does Zika do?

The main concern for Zika is the threat to unborn babies.

Zika is a known cause of microcephaly, where babies heads are abnormally small due to the fact their brains haven't developed properly.

In some cases, microcephaly can cause serious developmental problems and death.

• What are the symptoms?

Symptoms include fever, itching, conjunctivitis, red and sore eyes, headaches, rashes and joint pain.

However the majority of people show no signs of infection.

• How can you protect yourself?

There is currently no vaccine against Zika.

Mosquitoes are attracted to still and stagnant water - such as ponds and buckets - to lay their eggs.

Official health advice says people should use insect repellents, cover up with long-sleeved clothing and keep windows and doors closed.

• Which countries are effected?

Outbreaks of the virus have been recorded in Africa, the Americas, Asia and the Pacific.

So far, 64 countries and territories have reported occurrences of the virus since 2007.

"Increasing or widespread transmission" has been recorded in much of Central and South America - including Brazil.

• What is the travel advice?

Pregnant women should postpone non-essential travel to countries with active or established Zika transmission until after pregnancy.

Furthermore, women should avoid becoming pregnant while travelling in areas with active Zika virus, and for 28 days after their return.