14 heartbreaking images of the untreatable Zika virus, which is causing one of the biggest public health crises in Brazil's history

The Centers for Disease Control (CDC) has urged pregnant women not to travel to countries that have reported cases of the Zika virus, an untreatable, mosquito-borne disease.

The Zika virus has recently been linked to a neurological disorder that causes babies to be born with small craniums and limited brain development, a condition called microcephaly.

In 2014, there were 146 cases of microcephaly in Brazil. In 2015, the rate of babies born with microcephaly grew to be 20 times the normal rate.

Since the outbreak of the Zika virus in April 2015, there have been close to 4,000 cases in newborn babies from women who were infected during their pregnancy.

The Zika virus is transmitted through the Aedes aegypti mosquito, and the symptoms - which include a low-grade fever, small rashes, joint pains, and red eye - are relatively mild, which is why it did not cause much alarm when the outbreak started in Brazil early last year.

Below are shocking images of the birth defect caused by the Zika virus.