Eritania Maria, who was six months pregnant, is seen in front of her house at a slum in Recife, Brazil, on Feb. 2, 2016. (Reuters/Ueslei Marcelino) 
 
 Scientists have discovered that three existing drugs — used for cancer, hepatitis C and for parasitic infections — appear to be promising against the Zika virus. 
 
 The experiments that led to the discovery were conducted only in lab-grown human cells in petri dishes, but the results were dramatic. Zika is so devastating that the damage it does has been thought to be irreversible. But the researchers said some of the tested compounds allowed cells not only to live longer in the face of infection but also in some cases to fully recover. 
 
 The news, reported in Nature Medicine on Monday, is an exciting but only a very preliminary step toward a treatment. The researchers will have to test the drugs in animal models to see if they can replicate the results. If these tests are successful, they will have to start the long process of testing the drugs’ effectiveness in humans. 
 
 [U.S. warning: Zika could spread to Gulf states, persist for one to two years] 
 
 Co-author Hongjun Song, director of the stem cell program at Johns Hopkins, said that the drugs “are very effective against Zika in the dish, but we don’t know if they can work in humans in the same way.” 
 
 He said, for instance, that it’s unknown whether niclosamide, which is used to treat patients with parasites in the gut, can even penetrate the central nervous system to get to an unborn baby’s brain. 
 
 The researchers also don’t have any idea whether the drugs could treat the whole spectrum of damage done by the virus, from microcephaly (abnormally small heads) in infants to paralysis of the gastrointestinal tract. Scientists also have not yet determined whether the drug can treat the brain cells targeted by Guillain-Barré syndrome, one of the results of Zika infection in adults. 
 
 The identification of the drugs was based on a large-scale screening of 6,000 drugs. Given that it can take decades for scientists to come up with and test medications, looking at those that are already approved by regulators or in clinical trials can cut the development time a great deal. This technique has also been used in the hunt for an Ebola treatment. 
 
 [Heartbreaking images show how Zika destroys babies' brains] 
 
 The three drugs identified are PHA-690509, which is investigational and is being used on cancer patients; emricasan, which is being used in clinical trials to determine whether it might be able to help reduce liver damage from the hepatitis C virus; and niclosamide. 
 
 The experiments were conducted in what the researchers described as “two- and three-dimensional cell cultures called ‘mini-brains,’ ” which share some structures with the human brain. They measured indicators of cell death and found that there seemed to be two classes of drugs with potential to help stop or hinder the virus. The first group includes neuroprotective drugs, which might stop cell death, and antiviral drugs, which might slow or stop infection or replication of the virus in the brain. 
 
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 US scientists have urged the World Health Organisation to take urgent action over the Zika virus, which they say has "explosive pandemic potential". 
 
 Writing in a US medical journal, they called on the WHO to heed lessons from the Ebola outbreak and convene an emergency committee of disease experts. 
 
 They said a vaccine might be ready for testing in two years but it could be a decade before it is publicly available. 
 
 Zika, linked to shrunken brains in children, has caused panic in Brazil. 
 
 Thousands of people have been infected there and it has spread to some 20 countries. 
 
 The Brazilian President, Dilma Roussef, has urged Latin America to unite in combating the virus. 
 
 She told a summit in Ecuador that sharing knowledge about the disease was the only way that it would be beaten. A meeting of regional health ministers has been called for next week. 
 
 Writing in the Journal of the American Medical Association, Daniel R Lucey and Lawrence O Gostin say the WHO's failure to act early in the recent Ebola crisis probably cost thousands of lives. 
 
 They warn that a similar catastrophe could unfold if swift action is not taken over the Zika virus. 
 
 Image copyright Getty Images Image caption Alice Vitoria Gomes Bezerra, three months old, was born in Brazil with microcephaly 
 
 "An Emergency Committee should be convened urgently to advise the Director-General about the conditions necessary to declare a Public Health Emergency of International Concern," Mr Lucey and Mr Gostin wrote. 
 
 They added: "The very process of convening the committee would catalyze international attention, funding, and research." 
 
 White House spokesman Josh Earnest said on Wednesday the US government intended to make a more concerted effort to communicate with Americans about the risks associated with the virus. 
 
 No cure 
 
 There is no cure for the virus and the hunt is on for a vaccine, led by scientists at the University of Texas Medical Branch. 
 
 The researchers have visited Brazil to carry out research and collect samples and are now analysing them in a suite of high-security laboratories in Galveston, Texas. 
 
 Access to the building in Galveston 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". 
 
 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 
 
 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. 
 
 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'
– The good news: Three drugs that already exist appear to be successful at fighting the Zika virus. The bad news: Scientists aren't yet sure if the drugs will actually work on humans who have the Zika virus, the Washington Post reports. The drugs—PHA-690509, a drug currently being tried on cancer patients; emricasan, a drug currently being tried on patients with liver damage from hepatitis C; and niclosamide, which is used for gut parasites—"are very effective against Zika in the [petri] dish, but we don’t know if they can work in humans in the same way," says the co-author of the study that led to the discovery. The study, which screened 6,000 existing drugs, used the drugs on lab-grown human cells; the three aforementioned drugs allowed those cells to live longer when faced with Zika infection—and sometimes even recover completely, though Zika damage was previously thought to be impossible to reverse. The next step is to test the drugs in animal models, then, if the results are replicated, test them on humans. Meanwhile, in addition to the problems Zika is already linked to in unborn babies, USA Today reports that the virus is now also linked to hearing loss.