The Zika virus which has caused thousands of birth defects in Latin America has also spread to Europe, as most recently, a Danish tourist has caught the virus.
It was “deeply concerning” that the virus has now been detected in many countries in the Americas, said the WHO Director-General Margaret Chan, quoted on the official web site of the Organisation.
"The situation today is dramatically different. Last year, the virus was detected in the Americas, where it is now spreading explosively. As of today, cases have been reported in 23 countries and territories in the region, she said.
“The level of alarm is extremely high. Arrival of the virus in some cases has been associated with a steep increase in the birth of babies with abnormally small heads” she added.
Zika is a virus with no cure or vaccine in the current situation, and its symptoms are linked with microcephaly, a serious defect involving abnormally small heads among newly born babies.
Governments have been warning especially pregnant women against travelling to areas where Zika has been detected.
The level of alarm is extremely high.
Arrival of the virus in some places had been associated with a steep increase in the birth of babies with abnormally small heads and in cases of Guillain-Barre syndrome, she said. "A causal relationship between Zika virus infection and birth malformations and neurological syndromes has not yet been established, but is strongly suspected."
"The possible links, only recently suspected, have rapidly changed the risk profile of Zika, from a mild threat to one of alarming proportions. The increased incidence of microcephaly is particularly alarming, as it places a heart-breaking burden on families and communities" she added.
WHO's Regional Office for the Americas (PAHO) has been working closely with affected countries since May 2015. PAHO has mobilized staff and members of the Global Outbreak and Response Network (GOARN) to assist ministries of health in strengthening their abilities to detect the arrival and circulation of Zika virus through laboratory testing and rapid reporting.
"The aim has been to ensure accurate clinical diagnosis and treatment for patients, to track the spread of the virus and the mosquito that carries it, and to promote prevention, especially through mosquito control" said the WHO in a statement.
The Organization is supporting the scaling up and strengthening of surveillance systems in countries that have reported cases of Zika and of microcephaly and other neurological conditions that may be associated with the virus, it said.
"Surveillance is also being heightened in countries to which the virus may spread. In the coming weeks, the Organization will convene experts to address critical gaps in scientific knowledge about the virus and its potential effects on fetuses, children and adults" the WHO said.
WHO will also prioritize the development of vaccines and new tools to control mosquito populations, as well as improving diagnostic tests.