BOGOTA, Colombia -- More than 2,100 pregnant women in Colombia are infected with the mosquito-borne Zika virus, the country's national health institute said on Saturday, according to Reuters.
The disease has been linked to a serious birth defect called microcephaly, which causes babies to be born with small heads and underdeveloped brains. Overall, more than 20,000 people in Colombia have developed Zika.
The virus was initially detected last year in Brazil. Dr. Margaret Chan, Director-General of World Health Organization, warned Thursday that Zika is "spreading explosively," and has quickly gone from a mild threat to one of alarming proportions.
The WHO said the virus could infect 4 million people by the end of the year.
Health officials in Brazil reported earlier this week that about 4,000 infants have been born with microcephaly, compared to fewer than 150 in 2014.
Dozens of Zika cases have been reported in the U.S., all in people who traveled outside the country.
The Centers for Disease Control and Prevention has warned that pregnant women, or those who may become pregnant, should try to avoid travel to at least 24 countries and territories, mostly in Latin America and the Caribbean, where Zika virus has been spreading.
The CDC has said that Zika is not expected to pose as much of a threat to the U.S. as it has to Brazil and other countries in the region. But officials said they do expect to see some locally-transmitted cases occur in the United States.
"We will see mini-outbreaks like in Florida and in Texas that can be well controlled with mosquito vector control," said Dr. Anthony Fauci, director of the U.S. National Institutes of Health's National Institute of Allergy and Infectious Diseases.
"You have multiple countries in South America and in the Caribbean, so by anybody's definition that would be considered a pandemic," Fauci said.
Health officials are also concerned about a spike in a rare, sometimes-paralyzing syndrome that could be linked to the Zika virus.
A health official said Saturday Colombia has now recorded 41 cases of Guillain-Barre syndrome that appear to be linked to Zika. It had detected 12 such cases a week ago.
Venezuelan Health Minister Luisana Melo said her country has seen 255 cases of Guillain-Barre, apparently as part of its effort to fight Zika, though she did not specify the link or the time frame.
Former Health Minister Jose Oletta said Venezuela normally sees 30 to 40 cases of Guillain-Barre a month and said the large number now indicates that Zika infections are far greater than the roughly 4,500 suspected cases than officials acknowledge.
On Monday, the WHO will gather its Emergency Committee for about three to six hours in a "virtual" meeting, spokesman Christian Lindmeier told CBS News' Pamela Falk on Friday.
The committee will draft a recommendation to Chan, who will make a determination next week whether to declare Zika a "public health emergency of international concern," or PHEIC. WHO would then help coordinate an international emergency response.