The World Health Organization Assistant Director-General Bruce Aylward speaks during a news conference at the European headquarters of the United Nations in Geneva, Switzerland, Feb 19, 2016. Aylward said here Friday it could still take months to determine for certain that the Zika virus causes the serious birth defect microcephaly, but said evidence was growing. [Photo/Xinhua]

BEIJING -- While the Zika virus is spreading explosively in the Americas, where an increasing number of microcephaly cases are being reported, rumors about the virus and microcephaly are also swirling.

The World Health Organization (WHO) on Friday issued a statement, dispelling the four biggest rumors around the mosquito-borne virus and microcephaly.

Rumor Number One: Microcephaly in babies is caused by vaccines.

There is no evidence that vaccines cause microcephaly in babies, the WHO said.

The statement added that there is no evidence linking any vaccine to the increase in microcephaly cases that were observed first in French Polynesia during the 2013-2014 outbreak and more recently in northeastern Brazil.

Meanwhile, an extensive review of the literature published in 2014 found no evidence that any vaccine administered during pregnancy resulted in birth defects. The Global Advisory Committee on Vaccine Safety reached a similar conclusion in 2014.

Rumor Number Two: Pyriproxyfen insecticide causes microcephaly

A team of WHO scientists found no evidence that pyriproxyfen affects the course of pregnancy or the development of a fetus, after they recently reviewed data on the toxicology of pyriproxyfen.

The U.S. Environmental Protection Agency and EU investigators reached a similar conclusion when they carried out a separate review of the product.

Pyriproxyfen, one of the 12 larvicides that WHO recommends to reduce the development of mosquitos, has been used since the late 1990s without being linked to microcephaly.

In places with no piped water, people tend to store drinking water in outdoor containers, which serve as ideal breeding grounds for mosquitos.

Larvicides are often used in those containers to kill the mosquito in its larval stage.

When people drink water from containers that have been treated with pyriproxyfen, they are exposed to the larvicide -- but in tiny amounts that do not harm their health.

Moreover, 90-95 percent of any larvicide ingested is excreted into the urine within 48 hours.

Rumor Number Three: The Zika outbreak and recently increasing microcephaly cases in Brazil are linked to the release of genetically modified (GM) mosquitoes in the country.

The WHO said there is no evidence that the Zika virus disease or microcephaly in Brazil is caused by GM mosquitoes. The transgenic practice is a new means to control mosquitoes, in which the genes of male mosquitoes are modified and their larval offspring cannot survive after they mate with female mosquitoes.

Currently, the WHO encouraged affected countries to boost the use of current mosquito control interventions and judiciously test the new approaches that could be applied in the future.

Rumor Number Four: Sterilized male mosquitoes contribute to the spread of Zika

The WHO noted that the sterilized mosquito is also a technique to control the spreading of diseases by mosquitoes. It uses low doses of radiation to sterilize male mosquitoes and the eggs laid by their female mating partners cannot survive.

The organization said that there is no evidence that the technique has been associated with increases in microcephaly cases or other human anomalies or defects.