The World Health Organization is convening an emergency committee on Monday to decide if the Zika virus outbreak should be declared an international health emergency.

At a special meeting Thursday in Geneva, WHO Director-General Dr. Margaret Chan said the virus — which has been linked to birth defects and neurological problems — was “spreading explosively.”

Chan said although there was no definitive proof that the Zika virus was responsible for a spike in the number of babies being born with abnormally small heads in Brazil, “the level of alarm is extremely high.” She also noted a possible relationship between Zika infection and Guillain-Barre syndrome, which can cause temporary paralysis.

“The possible links, only recently suspected, have rapidly changed the risk profile of Zika from a mild threat to one of alarming proportions,” Chan said.

Zika virus was first detected in 1947 and for decades only caused mild disease. But Chan noted that “the situation today is dramatically different.” According to the U.S. Centers for Disease Control, the Zika virus is now in more than 20 countries, mostly in Central and South America.

Chan cited four main reasons why WHO is “deeply concerned” about Zika: The possible link to birth defects and brain syndromes, the prospect of further spread, a lack of immunity in populations in the newly affected areas and the absence of vaccines, treatments or quick diagnostic tests for the virus.

Still, convening an emergency committee does not guarantee that a global emergency will be declared — WHO has held 10 such meetings to assess the Middle Eastern respiratory syndrome coronavirus and no emergency has been announced.

Declaring a global emergency is akin to an international SOS signal and usually brings more money and action to address an outbreak. The last such emergency was announced over the 2014 devastating Ebola outbreak in West Africa; polio was declared a similar emergency the year before.

Marcos Espinal, WHO’s director of infectious diseases in the Americas region, said Brazil is conducting studies to determine if there is scientific evidence that Zika virus causes birth defects and neurological problems. He said they are hopeful Brazil may have data to share in a couple of months.

Brazil’s Zika outbreak and the spike in microcephaly have been concentrated in the poor and underdeveloped northeast of the country, though the prosperous southeast, where Sao Paulo and Rio de Janeiro are located, are the second hardest-hit region. Rio de Janeiro will host the Aug. 5-21 Olympic games.

Earlier this week officials in Rio ramped up their fight against the mosquitoes that spread Zika, dispatching a team of fumigators to the Sambadrome, where the city’s Carnival parades will take place next month.

There is no specific treatment or vaccine for Zika, which is related to dengue — scientists have struggled for years to develop a dengue vaccine but have failed to create an effective shot so far.

(AP)