The Zika virus, linked to thousands of birth abnormalities in Latin America, could spread rapidly across the globe to parts of Asia, sub-Saharan Africa and potentially southern Europe, a senior World Health Organisation expert has warned.

Dr Anthony Costello, a British paediatrician who is the WHO’s head of child health, said scientists were racing to plug gaps in their knowledge about the impact of the illness, which causes only mild symptoms in adults but appears to have devastating effects on unborn children by causing microcephaly, abnormally small heads.

Brazil, one of the worst-hit countries, has announced a nationwide assault on the mosquito responsible for transmitting the virus and President Dilma Rousseff vowed to “win this war” against the insect.

Zika Virus

In a sign of the growing concern at Zika’s global spread, Public Health England last night advised men to use condoms for at least a month if they had returned from one of the 23 countries in the Americas where the virus is now present if their partner was pregnant, or at risk of becoming so. PHE said the risk of sexual transmission was very low but condoms should be used as a precaution.

As the WHO prepares to decide on Monday whether to declare an international health emergency, experts warned the “explosive” movement of the virus across the Americas meant it has the potential to spread further.

Dr Costello told The Independent: “We are seeing a very rapid spread of the Zika virus across Latin America. One very significant concern is that it seems possible it could move into other parts of the world with vulnerable populations. “These are places within the tropical belt and beyond – sub-Saharan Africa, Southeast Asia, southern parts of the United States and southern Europe.”

He warned that a vaccine may take years to develop, and added that experts dealing with the dramatic rise in Zika cases in Latin America were being hampered by the lack of a commercially available diagnostic test as they try to track and investigate the virus.

The Brazilian President, Dilma Rousseff, has warned that her country was losing the battle against the mosquito responsible for spreading Zika, which is suspected of being the cause of a dramatic increase – up to 4,000 cases – in the number of babies born with abnormally small heads. The condition, known as microcephaly, can cause developmental issues and lifelong disability.

With the Olympics in Rio de Janeiro just seven months away, Ms Rousseff demanded a national effort to eradicate the insect. Brazil has said it will deploy 220,000 troops to help to eliminate the Aedes aegypti mosquito from its breeding groups in puddles and standing water.

Dr Costello echoed the concerns of WHO’s director general, Dr Margaret Chan, who warned this week that Zika is spreading “explosively” across the Americas. Since the first cases in Brazil early last year, the virus has spread to 23 countries and territories, prompting epidemiologists to warn of up to four million cases a year across the continent.

Dr Costello, renowned for his work on improving survival rates among newborns in developing countries, told The Independent that medics were concerned that the speed of Zika’s spread since its last outbreak on a group of Pacific islands in 2007 means it will jump to other continents.

Speaking from WHO’s headquarters in Geneva, he said: “It seems possible that the virus could move back into other parts of the world with vulnerable populations, places within the tropical belt and beyond – sub-Saharan Africa, South-east Asia, southern parts of the United States and southern Europe. Some of these places will be better able to deal with that threat than others.”

Researchers warned last year that parts of the Italian, French and Spanish Mediterranean coasts are suitable for the survival of the Aedes aegypti mosquito. The insect also carries the dengue and chikungunya viruses, both from the same family of microbes as Zika.

The Zika virus - in pictures Show all 5 1 /5 The Zika virus - in pictures The Zika virus - in pictures A three-month-old, who has microcephaly, in Recife, Brazil. A rise in microcephaly cases is thought to have been caused by the spread of the Zika virus in affected countries Getty Images The Zika virus - in pictures A mother holds her baby who has microcephaly Getty Images The Zika virus - in pictures A five-month-old baby, who has microcephaly, in Recife, Brazil Getty Images The Zika virus - in pictures A pediatric infectologist examines a two-month-old baby, who has microcephaly, in Recife, Brazil Getty Images The Zika virus - in pictures A baby affected with microcephaly

But while surveillance systems and advanced healthcare mean that any outbreak could be rapidly isolated in Europe or the US, experts fear that developing countries in Africa and Asia would be vulnerable. Unlike malaria-carrying mosquitoes, the two Zika-carrying varieties feed in daylight, so the arrival of the virus would require a sea change in prevention habits.

WHO, which was blamed for failing to act quickly in the early stages of the Ebola outbreak, is to meet on Monday to decide whether the Zika outbreak should be declared an international health emergency.

Unlike Ebola, the new virus, first discovered in Uganda in 1947, causes relatively mild symptoms and is not readily transmitted by human-to-human contact. While some might experience a fever and a rash, 75 per cent of sufferers have no symptoms at all.

However, public health experts are concerned by its catastrophic effects on pregnancy and its ability to spark a rare immune response that can leave some adults paralysed.

Scientists have yet to prove conclusively that Zika is the direct cause of the rise in microcephaly cases, saying only that there is strong circumstantial evidence of a link between the two. Doctors want to investigate whether mothers were also infected with dengue or chikungunya to see if a cocktail of viruses is to blame.

Dr Costello said WHO medics were nonetheless operating on the assumption that Zika is the cause and are racing to plug gaps in their knowledge. It is not known what percentage of mothers infected with the virus give birth to children with abnormalities.

The Independent understands that WHO figures suggest there has been at least a 10-fold increase in expected rates of microcephaly in Brazil.

Dr Costello said: “A really big issue is establishing the scale of the microcephaly problem and the damage it is doing to babies’ brains at the most vulnerable point in their development... At the moment, we don’t know if a pregnant woman has a 90 per cent or 5 per cent risk of her child developing microcephaly if she is infected.”

Among the priorities for those dealing with the virus is a cheap, commercially available diagnostic test in place of time-consuming laboratory tests. A vast effort to eliminate the disease-carrying mosquitoes will be made while the search for a vaccine gets under way.

Dr Costello said the best solution would be a vaccine that could be made available to girls in much the same way as the rubella jab. But he warned that while a vaccine can take just 12 months to develop, the reality may be a wait of years. “We have done years of research on a vaccine for dengue but we don’t yet have one.”