The Zika virus outbreak in Latin America could be a bigger threat to global health than the Ebola epidemic that killed more than 11,000 people in Africa.

That is the stark claim of several senior health experts ahead of an emergency meeting of the World Health Organisation on Monday which will decide whether the Zika threat – which is linked to an alarming rise in cases of foetal deformation called microcephaly – should be rated a global health crisis.

“In many ways the Zika outbreak is worse than the Ebola epidemic of 2014-15,” said Jeremy Farrar, head of the Wellcome Trust. “Most virus carriers are symptomless. It is a silent infection in a group of highly vulnerable individuals – pregnant women – that is associated with a horrible outcome for their babies.”

There is no prospect of a vaccine for Zika at present, in contrast to Ebola, for which several are now under trial. “The real problem is that trying to develop a vaccine that would have to be tested on pregnant women is a practical and ethical nightmare,” added Mike Turner, head of infection and immuno-biology at the Wellcome Trust.

Jeremy Farrar, head of the Wellcome Trust Photograph: the Guardian

With at least 80% of those infected showing no symptoms, tracking the disease is extremely difficult. The mosquito species that spreads Zika, Aedes aegypti, has been expanding its range over the past few decades. “It loves urban life and has spread across the entire tropical belt of the planet, and of course that belt is expanding as global warming takes effect,” added Farrar.

Only extreme measures are likely to contain the Zika threat, said Turner. These could include the use of DDT to eradicate Aedes aegypti as quickly as possible. “We have to balance the risk posed to the environment by DDT with the terrible impact this virus is having on the unborn.”

Britain is unlikely to be affected because Aedes aegypti cannot survive the cold of UK winters. However, couples returning from south or central America have been warned not to try for a baby for at least a month in case they have become infected.

Public Health England said that the risk of sexual transmission of Zika was low, but it had been recorded in a limited number of cases.