Is the Zika threat overhyped?

A new report challenges the theory of Zika virus causing microcephaly among newborns in Brazil and claims pesticide-laced drinking water is to blame

CAUSE AND EFFECT: “The alternative theory has also found support from the Brazilian Association for Collective Health, which named Pyriproxyfen as a likely cause of the birth defects and has condemned the strategy of chemical control of Zika-carrying mosquitoes.” Picture shows a four-month-old child born with microcephaly in Brazil.

With direct causality between Zika virus and microcephaly, a congenital brain development anomaly, yet to be established, Latin American doctors have come up with an alternative explanation: that a pesticide, Pyriproxyfen, was “introduced into the drinking water supply in 2014”.

The six-page report from an Argentine doctors’ organisation, Physicians in the Crop-Sprayed Towns (PCST), has challenged the theory of Zika virus causing microcephaly among newborns in Brazil. The report comes days after the World Health Organization (WHO) had said that the causality (of Zika virus leading to microcephaly and Guillain-Barre syndrome) could be confirmed in the next few weeks.

According to the PCST, “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 report adds that the Brazilian Health Ministry has “failed to recognise that in the area where most sick persons live, a chemical larvicide producing malformations in mosquitoes has been applied for 18 months”.

The article (http://goo.gl/OfrLUP) first appeared on GM Watch, run by an eponymous independent organisation, which comments on genetically modified (GM) foods and crops. In the past two months, Brazil has become the epicentre of the Zika outbreak which has now spread to more than 30 countries.

The alternative theory has found support from the Brazilian Association for Collective Health (ABRASCO), which named Pyriproxyfen as a likely cause of the birth defects on newborns and has condemned the strategy of chemical control of Zika-carrying mosquitoes.

Pyriproxyfen is used in a state-controlled programme aimed at eradicating disease-carrying mosquitoes. The PCST report states, “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 physicians also note that Zika outbreaks in the past have traditionally been relatively benign and never associated with birth defects — even in areas where it infects 75 per cent of the population.

“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 mosquitoes, which some have blamed for the Zika epidemic and thus for the birth defects. There is no sound evidence to support the notion promoted by some sources that GM mosquitoes can cause Zika, which in turn can cause microcephaly. In fact, out of 404 confirmed microcephaly cases in Brazil, only 17 (4.2%) tested positive for the Zika virus,” reads the PCST report.

Note of caution

The report comes at a time when British medical journal The Lancet in its latest issue stated that the numbers need to be interpreted with caution. Between mid-2015 and January 30, 2016, 4,783 suspected cases of microcephaly were reported. Of these, 1,103 cases have completed clinical, laboratory, and imaging examinations, and 404 (36.2 per cent) were classified as confirmed cases of microcephaly.

Among the confirmed cases, brain abnormalities were detected by imaging in 387 babies and the Zika virus was detected in 17 babies: 709 cases were discarded and 3,670 suspected cases of microcephaly remain under investigation.

In a commentary on the subject, The Lancet states: “This temporal increase in suspected cases of microcephaly could also be distorted given both raised awareness, with more children than usual being measured and reported, and changing definitions of microcephaly over time. The possibility of over-reporting and misdiagnosis was recently raised by the Latin American Network of Congenital Malformations, 4 and their report led to speculation in the international scientific press on the magnitude of the increase in microcephaly cases.”

Meanwhile, the Brazilian Health Ministry issued fresh figures on February 12, with the latest number of suspected Zika cases at 4,314, up from 4,074 on February 2.

vidya.krishnan@thehindu.co.in

Published - February 14, 2016 01:33 am IST