It has been claimed that Brazil is suffering from an outbreak of Microcephaly.
Several possible causes have been proposed.
The possibility that the Zika virus causes microcephaly – unusually small heads and often damaged brains – emerged only in October, when doctors in northern Brazil noticed a surge in babies with the condition.
It may be that other factors, such as simultaneous infection with other viruses, are contributing to the rise; investigators may even find that Zika virus is not the main cause, although right now circumstantial evidence suggests that it is.
However, some people are pouring doubt on this claim. For example the (Australian) ABC's Health Report radio show says:
But now there are fresh questions about the suspected link between the Zika virus and microcephaly which causes small heads in babies.
A four-year survey of over 100,000 newborn babies in north eastern Brazil has uncovered previously unrecognised patterns of microcephaly.
It suggests that the rise in cases may not be a new phenomenon, and questions whether Zika virus is actually the cause.
Another claim is that it might be caused by pyriproxyfen, a pesticide.
For example, The Ecologist reports:
With the proposed connection between the Zika virus and Brazil's outbreak of microcephaly in new born babies looking increasingly tenuous, Latin American doctors are proposing another possible cause: Pyriproxyfen, a pesticide used in Brazil since 2014 to arrest the development of mosquito larvae in drinking water tanks.
The article is based on this report by PCST ("Physicians in the Crop-Sprayed Towns", but the name is variously translated).
Is there scientific consensus around the evidence? Has there been a recent outbreak of microcephaly in Brazil, and is the cause the Zika virus, pyriproxyfen, some combination or neither?