Florida, July 30 : Florida authorities stepped up \"aggressive\" investigations after health officials reported the first local transmission of the Zika virus in the country, a media report said on Saturday.

Governor of Florida Rick Scott reported on Friday that four persons in southern Florida likely contracted Zika through local mosquito bites, even though no insect trapped and tested in the state has proven positive for the virus so far, The Guardian reported.

\"This morning we learned that four people in our state likely have the Zika virus as a result of a mosquito bite. This means Florida has become the first state in our nation to have local transmission,\" Scott said.

\"These are the first cases of locally transmitted Zika virus in the continental US,\" said Tom Frieden, Director for the Centers for Disease Control and Prevention (CDC).

\"As we have anticipated, Zika is now here,\" Frieden added.

Although there have been over 1,600 cases of the virus confirmed by health officials in nearly all 50 states, every patient save the four reports in Florida contracted the disease either travelling abroad or through sexual transmission.

According to the CDC, at least 50 pregnant women a day are affected in the US.

In Puerto Rico, over 4,500 cases of the virus, virtually all contracted through mosquitoes, was reported.

\"This is a silent epidemic that is rapidly spreading through Puerto Rico,\" Frieden said.

Florida announced on Thursday that blood donations were suspended in the affected area until all current samples could be tested.

Two of the cases suspected of local transmission were in Miami-Dade County, and two were in Broward County, Scott said. The patients included one women and three men, and none needed hospitalisation.

Health officials believe that the infections occurred in a very small area, north of Miami. Officials were also going door to door in the area offering to test the public, and Scott said that they would be \"aggressively testing people\".

\"All the evidence we have seen indicates that this is mosquito-borne transmission that occurred several weeks ago in several blocks in Miami,\" Frieden added.

Earlier in July, authorities began investigating the possible first local transmission of Zika, but Scott\'s near-confirmation on Friday amounted to a serious development of the feared health crisis.

There have been 386 cases of Zika reported in Florida so far, mostly in Miami-Dade and Broward counties. Fifty-five pregnant women have been affected.

The Orlando area is teeming with an influx of tourists , attending the cluster of theme parks in the area such as Disney World, Universal Studios and SeaWorld. Officials fear local transmission because local mosquitos could spread the disease far more rapidly than isolated travel or sex, The Guardian reported.

There is no treatment or preventive vaccine for Zika. The disease produces mild symptoms for most, such as headache, feverishness and red eyes, and 80 per cent of healthy people who become infected suffer no symptoms.

But for expectant mothers, infection with the Zika virus can lead to infants born with serious brain defects and developmental abnormalities, especially an abnormally small head in a condition called microcephaly.

Florida Senator Marco Rubio has bucked his party\'s line and pleaded for funding. Earlier this month he called the Zika threat a \"full-blown health crisis\" for the US, allying himself with California Senator Barbara Boxer, a Democrat, who said, \"we need to act now.\"

Zika virus: Florida steps up investigation after first local transmission