Brazilian health officials are denying the allegations from an Argentine group of doctors who say the recent uptick in cases of microcephaly could be caused by a larvicide, instead of by the mosquito-borne Zika Virus.

The Brazilian Health Ministry released a clear statement saying "the association between the use of pyriproxyfen and microcephaly has no scientific basis", noting that "some localities that do not use pyriproxyfen also had reported cases of microcephaly".

Pyriproxyfen is a larvicide used to control the Aedes Aegypti mosquito, which spreads Zika, Dengue, and other viral nasties.  The group calling itself Physicians in the Crop-Sprayed Towns says introduced to Brazil's drinking water in 2014 in regions affected by the increased cases microcephaly - a birth defect that results in under-sized, malformed skulls and impeded brain development.

"In the area where most sick persons live, a chemical larvicide producing malformations in mosquitoes has been applied for 18 months, and that this poison (pyroproxifen) is applied by the state on drinking water used by the affected population," according to the report from the Argentinian doctors group, which has not been peer-reviewed.  It added that the increase of microcephaly cases was "not a coincidence" and accused the Brazilian Ministry of Health of "ignoring its responsibility". 

Officials in Rio Grande do Sul state even suspended the use of pyroproxifen on Saturday "until we have a position from the ministry of health"; although they still urge people to do everything they can to knock down mosquito populations by eliminating standing water where they breed. 

Now, localities have that official position from Brasilia.  Although Zika has not been positively proven to cause microcephaly, officials have reams of circumstantial evidence including "the presence of the virus in samples of blood, tissue and amniotic fluid".  This week, researchers confirmed the presence of Zika in brain samples taken from microcephalic babies that died shortly after birth. 

But the Argentinian doctors aren't the first to question the link from Zika to microcephaly.  Last week, a Brazilian cardiologist reviewed earlier cases and found that the increase in microcephaly predated the current Zika outbreak by three years.  I'm no researcher, but by my count this increase also appears to predate the use of pyriproxyfen as well.