Zika virus has spread to more than 20 countries in the Americas.
The unprecedented and explosive outbreak of the mosquito-borne disease is causing fear in the affected regions.
While the effects are generally mild, the greatest concern is about a strongly suspected link with brain defects in babies.
There have been no travel bans, but what advice is there for people visiting the regions?
Which countries are affected?
The Pan American Health Organization is publishing updates on the affected countries.
But the virus is expected to spread throughout North, Central and South America, except Canada and Chile, and people should check for the latest advice before travelling.
Should I go?
Only pregnant women have been advised to reconsider their plans to visit countries affected by Zika.
It is thought that within the female body the virus can travel across the placenta and affect the health of an unborn baby.
There has been a surge in microcephaly - in which the baby's brain does not develop properly - in Brazil.
The UK's National Travel Health Network and Centre says pregnant women should reconsider their travel plans, and that any traveller should seek advice from a health professional before departing.
And it adds that pregnant women who have to travel should take "scrupulous" measures to avoid being bitten by mosquitoes.
The US Centers for Disease Control says women trying to get pregnant should "talk to your doctor about your plans to become pregnant and the risk of Zika virus infection [and] strictly follow steps to prevent mosquito bites during your trip."
Is it safe to get pregnant after visiting?
The CDC says Zika lingers in the blood for approximately a week.
And: "The virus will not cause infections in a baby that is conceived after the virus is cleared from the blood.
"There is currently no evidence that Zika virus infection poses a risk of birth defects in future pregnancies."
How to avoid mosquito bites?
Zika is spread by the Aedes aegypti mosquito which is most active during the day.
People are advised to:
- Cover up with long-sleeved shirts and trousers
- Use insect repellents such as those containing DEET or picaridin
- Apply sunscreen before using applying insect repellent
- Keep doors and windows closed and to use air conditioning
What about men?
It is thought the virus can persist in semen for two weeks after a man recovers from an infection.
Public Health England is taking a safety-first approach after two suspected cases of sexual transmission.
The organisation says the risk of spreading the virus through sex is "very low".
But it recommends using condoms if you have a pregnant partner or one who might become pregnant.
This should be done for 28 days after coming home if you have no symptoms, and for six months if Zika symptoms do develop.
The US Centers of Disease Control advises either giving up sex or using condoms for the duration of a pregnancy.
What are the symptoms?
Most infections do not result in symptoms, but they may include:
- joint pain
- conjunctivitis or red eyes
- muscle pain
- eye pain
If you have Zika?
If you have symptoms such as fever, a rash, joint pain or red eyes, which develop either on holiday or when you return, then you should speak to a doctor.
The US Centers for Disease Control says:
- Take medicine, such as acetaminophen or paracetamol, to relieve fever and pain
- Do not take aspirin, products containing aspirin, or other nonsteroidal anti-inflammatory drugs such as ibuprofen
- Get lots of rest and drink plenty of liquids
- Prevent additional mosquito bites to avoid spreading the disease
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