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The World Health Organisation issued a "global emergency" after a worldwide epidemic of the Zika virus was linked to a huge rise in babies being born with abnormally small heads.

The UK is busy spraying planes from affected areas to kill the carrier mosquitos, British tourists have been warned against unprotected sex and women have been told to avoid getting pregnant in a bid to halt Zika's spread.

Brazil – where more than 4,000 cases of the birth defect called microcephaly have been reported since October – has even faced calls to postpone the Rio 2016 Olympics this summer.

But experts have now cast doubt on the link between Zika and microcephaly.

And a bid to wipe out the mosquitos that carry Zika may be making things worse – much, much worse.

(Image: GETTY)

Two independent teams of doctors now believe pyriproxyfen – a pesticide used to kill mosquitos – may be the real cause of microcephaly.

The researchers – from Brazil and Argentina – point out that in 2014 the government started adding pyriproxyfen to the drinking water supply in the area of Brazil where the majority of microcephaly cases have been reported.

Pyriproxyfen targets baby mosquitos – known as larvae.

It stunts their development – such as stopping them from growing proper wings and genitalia.

This bears a shocking correlation with microcephaly, in which babies' heads fail to develop properly.

Their skull stays small – keeping their heads abnormally little and limiting their brain's development.

**CLICK HERE TO READ THE INSIDE STORY FROM FAMILIES OF BABIES WITH MICROCEPHALY**

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(Image: EPA)

The researchers point out that Zika has spread across Africa, Asia, Micronesia since it was discovered in 1947 and epidemics have been reported across the globe without any associated outbreak of microcephaly.

Zika is normally a relatively harmless virus that causes little more than a rash and no birth defects have been reported in some areas where as many as three in four people have it.

The virus has been present in Brazil for a number of years, but the outbreak of microcephaly was only reported in April 2015 – several months after pyriproxyfen was added to the water supply.

So far 3,177 pregnant women have contracted Zika in Colombia – but none of the babies have developed microcephaly.

Brazil may be overstating the number of microcephaly cases linked to Zika.

More than 4,100 cases of Zika-related microcephaly cases have been reported there since October.

But experts double-checking the reports claim as many as half of the children either don't have microcephaly or the Zika virus.

Physicians in the Crop-Sprayed Towns, an Argentine doctors' organisation, said: "Malformations detected in thousands of children from pregnant women living in areas where the Brazilian state added pyriproxyfen to drinking water are not a coincidence – even though the Ministry of Health places a direct blame on the Zika virus for this damage."

The group claims international chemical companies – who have strong links to WHO and health ministries in South America – may be trying to shift the blame for microcephaly onto Zika.

WHO lists pyriproxyfen as having "low acute toxicity" and its manufacturer claims it didn't cause birth defects in mammals during tests.

But this is not a fail-safe indicator of its effect on humans.