Mosquitoes: "The most murderous animal on Earth"

Concerns continue to grow over the mosquito-borne Zika virus, which is spreading rapidly through Central and South America and has been linked to birth defects and neurological problems.

The disease usually causes only mild illness and many of those infected do not experience symptoms at all, but Zika is considered a major threat to pregnant women. Health officials in Brazil believe the virus is responsible for a spike in the number of babies being born with abnormally small heads, a condition called microcephaly, which often results in brain damage.

Some people infected with Zika have also developed Guillain-Barré syndrome, an autoimmune condition which can cause at least temporary paralysis.

WHO is warning that there could be 3 to 4 million cases of Zika in the Americas over the next year.

So far the CDC reports there have been 31 cases in the United States, all in travelers who contracted it abroad, and more are likely. However, Fauci said he said that he did not expect to see a major Zika epidemic in the U.S.

“If Zika acts like the other types of viruses that are mosquito-borne that we’ve had experience with, like dengue and chikungunya, we will see mini-outbreaks like in Florida and in Texas that can be well controlled with mosquito vector control. Hopefully we will not see anything worse than that, but we have to be very vigilant,” Fauci told “CBS This Morning.”