The World Health Organization view that the microcephaly outbreak in Brazil's impoverished northeast is caused by the Zika virus has, so far, received few challenges.

Brazil's Health Minister, Marcelo Castro, has gone so far as to say that he has "100% certainty" that there is a link between Zika and microcephaly, a birth defect in which babies are born with small heads.

The view is widely supported in the medical community worldwide, including by the US's influential Center for Disease Control. But there is no hard evidence of the link, rather a mixture of epidemiological indications and circumstantial evidence.

One of the key scientific papers, by A S Oliveira Melo et al in the journal Ultrasound in Obstetrics & Gynecology, found Zika virus in the amniotic fluids and other tissues of the affected babies and their mothers. But only two women were examined, far too small a number to establish a statistically significant link.

The New York Times also reported on 3rd February on the outcome of analyses by Brazil's Health Ministry: "Of the cases examined so far, 404 have been confirmed as having microcephaly. Only 17 of them tested positive for the Zika virus. But the government and many researchers say that number may be largely irrelevant, because their tests would find the presence of the virus in only a tiny percentage of cases."

And last weekend, the most powerful indicator yet that the microcephaly may have another cause altogether was announced by Colombia's president, Juan Manuel Santos, as reported by the Washington Post. Colombian public health officials, stated Santos, have so far diagnosed 3,177 pregnant women with the Zika virus- but in no case had microcephaly been observed in the foetus.

Argentine doctors: it's the insecticide

Now a new report has been published by the Argentine doctors' organisation, Physicians in the Crop-Sprayed Towns (PCST), [1] which not only challenges the theory that the Zika virus epidemic in Brazil is the cause of the increase in microcephaly among newborns, but proposes an alternative explanation.

According to PCST, the Ministry failed to recognise that in the area where most sick people live, a chemical larvicide that produces malformations in mosquitoes was introduced into the drinking water supply in 2014.

STOP PRESS - Brazilian state Rio Grande do Sul bans Pyriproxyfen for use in controlling Zika virus mosquitos.

This pesticide, Pyriproxyfen, is used in a state-controlled programme aimed at eradicating disease-carrying mosquitos. The Physicians added that the Pyriproxyfen is manufactured by Sumitomo Chemical, a Japanese 'strategic partner' of Monsanto. - a company they have learned to distrust due to the vast volume of the company's pesticides sprayed onto Argentina's cropland.

Pyriproxyfen is a growth inhibitor of mosquito larvae, which alters the development process from larva to pupa to adult, thus generating malformations in developing mosquitoes and killing or disabling them. It acts as an insect juvenile hormone or juvenoid, and has the effect of inhibiting the development of adult insect characteristics (for example, wings and mature external genitalia) and reproductive development.

The chemical has a relatively low risk profile as shown by its WHO listing, with low acute toxicity. Tests carried out in a variety of animals by Sumitomo found that it was not a teratogen (did not cause birth defects) in the mammals it was tested on. However this cannot be taken as a completely reliable indicator of its effects in humans - especially in the face of opposing evidence.

The PCST commented: "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."

They also noted that Zika has traditionally been held to be a relatively benign disease that has never before been associated with birth defects, even in areas where it infects 75% of the population.

Brazilian doctors also suspect pyriproxyfen

Pyriproxyfen is a relatively new introduction to the Brazilian environment; the microcephaly increase is a relatively new phenomenon. So the larvicide seems a plausible causative factor in microcephaly - far more so than GM mosquitos, which some have blamed for the Zika epidemic and thus for the birth defects.

The PCST report, which also addresses the Dengue fever epidemic in Brazil, concurs with the findings of a separate report on the Zika outbreak by the Brazilian doctors' and public health researchers' organisation, Abrasco. [2]

Abrasco also names Pyriproxyfen as a possible cause of the microcephaly. It condemns the strategy of chemical control of Zika-carrying mosquitoes, which it says is contaminating the environment as well as people and is not decreasing the numbers of mosquitoes.

Instead Abrasco suggests that this strategy is in fact driven by the commercial interests of the chemical industry, which it says is deeply integrated into the Latin American ministries of health, as well as the World Health Organization and the Pan American Health Organisation.

Abrasco names the British GM insect company Oxitec as part of the corporate lobby that is distorting the facts about Zika to suit its own profit-making agenda. Oxitec sells GM mosquitoes engineered for sterility and markets them as a disease-combatting product - a strategy condemned by the Argentine Physicians as "a total failure, except for the company supplying mosquitoes."

Both the Brazilian and Argentine doctors' and researchers' associations agree that poverty is a key neglected factor in the Zika epidemic. Abrasco condemned the Brazilian government for its "deliberate concealment" of economic and social causes: "In Argentina and across America the poorest populations with the least access to sanitation and safe water suffer most from the outbreak." PCST agrees, stating, "The basis of the progress of the disease lies in inequality and poverty."

Abrasco adds that the disease is closely linked to environmental degradation: floods caused by logging and the massive use of herbicides on (GM) herbicide-tolerant soy crops - in short, "the impacts of extractive industries."

The notion that environmental degradation may a factor in the spread of Zika finds backing in the view of Dino Martins, PhD, a Kenyan entomologist. Martins said that "the explosion of mosquitoes in urban areas, which is driving the Zika crisis" is caused by "a lack of natural diversity that would otherwise keep mosquito populations under control, and the proliferation of waste and lack of disposal in some areas which provide artificial habitat for breeding mosquitoes."

Community-based actions

The Argentine Physicians believe that the best defence against Zika is "community-based actions". An example of such actions is featured in a BBC News report on the Dengue virus in El Salvador.

A favourite breeding place for disease-carrying mosquitoes is storage containers of standing water. El Salvadorians have started keeping fish in the water containers, and the fish eat the mosquito larvae. Dengue has vanished along with the mosquitoes that transmit the disease. And so far, the locals don't have any Zika cases either.

Simple yet effective programmes like this are in danger of being neglected in Brazil in favour of the corporate-backed programmes of pesticide spraying and releasing GM mosquitoes. The latter is completely unproven and the former may be causing far more serious harm than the mosquitoes that are being targeted.

Claire Robinson is an editor at GMWatch.

This article was originally published by GMWatch. This version includes additional reporting by The Ecologist.

Notes

1. 'Report from Physicians in the Crop-Sprayed Towns regarding Dengue-Zika, microcephaly, and mass-spraying with chemical poisons'. 2016. Physicians in the Crop-Sprayed Towns.

2. 'Nota técnica e carta aberta à população: Microcefalia e doenças vetoriais relacionadas ao Aedes aegypti: os perigos das abordagens com larvicidas e nebulização química - fumacê'. January 2016. GT Salud y Ambiente. Asociación Brasileña de Salud Colectiva. ABRASCO.