Media playback is unsupported on your device Media caption The BBC's James Cook goes inside the high-security lab trying to find a cure

American scientists studying the Zika virus have warned that it could be a decade before a vaccine is publicly available.

The virus is linked to shrunken brains in unborn children, leading to severe brain damage or death.

It has spread to more than 20 countries, and has caused panic in Brazil where thousands of people have been infected.

There is currently no vaccine or cure, and diagnostic testing is difficult.

The search for a vaccine is being led by scientists at the University of Texas Medical Branch.

They have visited Brazil to carry out research and collect samples, and are now analysing them in a suite of high-security laboratories in Galveston.

But they warn that although a vaccine could be ready for testing in two years, it may be another decade for it to be approved by regulators.

Access to the building is tightly controlled by police and the FBI.

Speaking to the BBC inside the facility, Professor Scott Weaver, director of the Institute for Human Infections and Immunity, said people were right to be frightened by the virus.

"It's certainly a very significant risk," he said, "and if infection of the foetus does occur and microcephaly develops we have no ability to alter the outcome of that very bad disease which is sometimes fatal or leaves children mentally incapacitated for the remainder of their life".

The Zika virus was discovered in monkeys in 1947 in Uganda's Zika Forest, with the first human case registered in Nigeria in 1954 but for decades it did not appear to pose much of a threat to people and was largely ignored by the scientific community.

It was only with an outbreak on the Micronesian island of Yap in 2007 that some researchers began to take an interest.

In the past year the virus "exploded" said Prof Weaver, sweeping through the Caribbean and Latin America "infecting probably a couple of million people".

The symptoms in adults and children are similar to those for dengue fever but generally milder, including flu-like aches, inflammation of the eyes, joint pain and rashes although some people have no symptoms at all.

In rare cases the disease may also lead to complications including Guillain-Barre syndrome, a disorder of the nervous system which can cause paralysis.

There is some evidence that Zika can be transmitted through saliva and semen although this does not appear to be common.

"We think that sexual transmission can occur but we don't know how often or what the risk is to an individual man who becomes infected," said Prof Weaver.

The main concern is for unborn babies and - because Zika is difficult to diagnose - it can be late in a pregnancy before expectant mothers are informed of the risk, if they are informed at all.

Image copyright US CDC Image caption Aedes aegypti

What is the Zika virus:

Spread by the Aedes aegypti mosquito, which also carries dengue fever and yellow fever

mosquito, which also carries dengue fever and yellow fever First discovered in Africa in the 1940s but is now spreading in Latin America

Scientists say there is growing evidence of a link to microcephaly, that leads to babies being born with small heads

Can lead to fever and a rash but most people show no symptoms, and there is no known cure

Only way to fight Zika is to clear stagnant water where mosquitoes breed, and protect against mosquito bites

Zika: What you need to know

'The worst day of my life'

Work on a vaccine only began a few months ago but the scientists in Galveston say they are not starting from scratch.

Zika is a member of the flavivirus family, which includes the viruses which cause dengue fever, yellow fever, Japanese encephalitis and West Nile disease, and the team intends to use existing vaccines for those conditions as a platform for its work.

Image caption Prof Nikos Vasilakis

Nikos Vasilakis, an assistant professor in the university's pathology department who works in the Centre for Biodefence and Emerging Infectious Diseases in Galveston, said they could have a vaccine ready for testing within a year or two, although he warned that winning approval from regulators could take much longer.

"What would take the longest time would be the process of passing it through the FDA (US Food and Drug Administration) and other regulatory agencies to allow it for public use and that may take up to 10 to 12 years," said Prof Vasilakis.

Vaccine research is also going on in Brazil, where scientists say one could be ready in five years.

Scientist Shannan Rossi has recently returned from Brazil with Prof Vasilakis where they saw the devastating effects of the virus first hand.

She is now inspecting samples of human and animal tissue as well as studying mosquitoes to answer a number of questions such as which animals it infects and how long it stays in humans.

"Right now we're really at the beginning stages," said Dr Rossi.

In the meantime, the worry is that the disease will continue to spread.

Image copyright Getty Images Image caption The military has been deployed in Brazil to inform the public about the virus' risks

"It's now in our doorstep in Mexico," said Prof Vasilakis, who is based on Galveston Island which looks out across the Gulf of Mexico.

"About 25 to 30 million people are at risk of exposure here in the southern United States if we have a local transmission of Zika," he added.

By this he means not just that humans arrive in the US with Zika, which has already happened in several states including Texas, but that they are then bitten by a mosquito which can carry the disease on to other people.

"The biggest traffickers of viruses globally are infected humans," he said, adding that the majority of infected people do not show any symptoms of the disease, making it difficult to detect.

In the absence of a vaccine or treatment, the best way to reduce the risk of infection, says the Texan team, is to use insect repellent and fumigate homes to get rid of mosquitoes.

Image copyright Getty Images Image caption Fumigation is being used to try and prevent the spread of the virus in San Salvador

Combating infection will be easier in the United States than in poorer countries, they say, because of the widespread use of air conditioning and window screens, which means mosquitoes are less likely to come into contact with human skin.

Working with insects which can carry such a dangerous virus is not without risks.

Deep inside the University of Texas Medical Branch building, the mosquitoes which are deliberately infected with Zika and other viruses so they can be studied are kept in a secure facility, inside cages, behind screens and double air-locked doors.

Prof Saravana Thangamani is the director of the Insectary Services Core.

"In this insectary we keep about 23 different strains of mosquitoes for all researchers within our campus and we have Aedis Egypti from 12 different countries," he said.

Image caption Prof Saravana Thangamani handling mosquitoes

Aedes Aegypti is the main species of mosquito which passes the virus from person to person, according to researchers.

Unlike mosquitoes which spread malaria it is mostly active during the day and is found in countries throughout the Americas, except for Canada and Chile where it is too cold for it to survive.

Prof Scott Weaver described the disease as frightening people in countries across Latin America and the Caribbean.

Image copyright Getty Images

So were they right to be frightened, especially pregnant women?

"Absolutely," answers Prof Weaver, without hesitation. "If I had a daughter of child-bearing age who was planning a spring break vacation to the Caribbean in the next few months I would strongly urge her not to go there at this point."

Sadly for millions of women living in the infected countries, that is not an option.