Washington: Mosquito-borne Zika virus has infected over 2,100 pregnant women in Colombia, the country's national health institute said on Saturday.

It is notable that this disease is linked to a serious birth defect called microcephaly, which causes babies to be born with small heads and underdeveloped brains. According to Colombia's national health institute, over 20,000 people in the country have developed Zika.

Zika virus was first detected in Brazil last year. Dr. Margaret Chan, Director-General of World Health Organization, warned Thursday that Zika is "spreading explosively," and has now transformed from a mild threat to one of alarming proportions. The WHO said around 4 million people would be infected by this virus by the end of the year.

Earlier this week, health officials in Brazil said that about 4,000 infants have been born with microcephaly, compared to fewer than 150 in 2014. Some cases of Zika have been reported in the US too but all these cases are related to people who traveled outside the country.

The Centers for Disease Control and Prevention has issued a warning saying 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, however, remarked that Zika would not pose as much of a threat to the U.S. as it has to Brazil and other countries in the region. "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 added.