Jan. 23, 2016, 9:24 a.m.
The Zika virus, an alarming and disturbing infection that may be linked to thousands of babies being born with underdeveloped brains, is spreading through the Americas.
Some areas have declared a state of emergency, doctors have described it as "a pandemic in progress" and some are even advising women in affected countries to delay getting pregnant.
Identified in Uganda in 1947, previous outbreaks were confined to a few small areas in Africa, South East Asia and the Pacific Islands.
But, in May 2015, it was reported in Brazil.
And it has since been reported in:
"Its current explosive pandemic re-emergence is, therefore, truly remarkable," the US National Institutes of Health said.
How does it spread?
If Aedes aegypti mosquitoes, found throughout the Americas, drink the blood of an infected person they can then infect subsequent people they bite.
They also spread dengue and chikungunya virus.
And, unlike the mosquitoes that spread malaria, they are mostly active during the day, so bed nets offer limited protection.
How dangerous is it?
Deaths are rare and only one in five people infected is thought to develop symptoms.
There is no vaccine or drug treatment, with patients advised to rest and drink plenty of fluids.
But the biggest concern is the impact it could have on babies developing in the womb and the surge in microcephaly.
What is microcephaly?
It is when a baby is born with an abnormally small head, as their brain has not developed properly.
The severity varies, but it can be deadly if the brain is so underdeveloped that it cannot regulate the functions vital to life.
Children that do survive face intellectual disability and development delays.
It can be caused by infections such as rubella, substance abuse during pregnancy or genetic abnormalities.
Brazil had fewer than 150 cases of microcephaly in the whole of 2014, but there have been about 4,000 since October.
The link with Zika has not been confirmed, but some babies who died had the virus in their brain and no other explanation for the surge in microcephaly has been suggested.
As there is no treatment, the only option is to reduce the risk of being bitten.
Health officials advise people to:
The mosquitoes lay their eggs in standing water, so people are also being told to empty buckets and flower pots.
The US Centers for Disease Control has advised pregnant women not to travel to affected areas.
The Brazilian Health Minister, Marcelo Castro, has said a new testing kit is being developed to identify infections quickly.
He also said more money was being put into the development of a vaccine.
Some scientists are also trialling the use of genetically modified sterile mosquitoes that appear to reduce mosquito populations by 90%.
Meanwhile, efforts are under way to kill the mosquitoes with insecticide.
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