A dispute has broken out in Brazil over whether the Zika virus is responsible for a rise in cases of microcephaly after a report by Argentinian doctors claimed a larvicide used in drinking water was instead to blame.
Brazilian health officials were forced to address claims that the larvicide pyriproxyfen, which is used to control the Aedes aegypti mosquito, could be associated with a surge in babies born with the condition after one state said it was suspending use of the chemical.
A report last week by Argentinian group Physicians in Crop-Sprayed Towns suggested pyriproxyfen might be causing the deformity, which impairs foetal brain development.
The organisation said the substance had been introduced into drinking water supplies since 2014 in affected areas of Brazil.
"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," the report said.
It added that cases of microcephaly being found in areas where pyriproxyfen was used was "not a coincidence" and said the Brazilian Ministry of Health was "ignoring its responsibility".
The report also pointed out that there had been no cases of microcephaly in other countries affected by Zika, such as Colombia, which has the highest incidence of the virus after Brazil.
In response, the local government in Rio Grande do Sul, a state in the south of Brazil, suspended the use of pyriproxyfen on Sunday. "We decided to suspend the use of the product in drinking water until we have a position from the Ministry of Health, and so, we reinforce further still the appeal to the population to eliminate any possible mosquito breeding site," said Joao Gabbardo dos Reis, state health secretary in Rio Grande do Sul.
It's important to state that some localities that do not use pyriproxyfen also had reported cases of microcephaly.
However, the federal Government dismissed the fears, insisting there had been no scientific study that linked pyriproxyfen to microcephaly. "Unlike the relationship between the Zika virus and microcephaly, which has had its confirmation shown in tests that indicated the presence of the virus in samples of blood, tissue and amniotic fluid, the association between the use of pyriproxyfen and microcephaly has no scientific basis," it said. "It's important to state that some localities that do not use pyriproxyfen also had reported cases of microcephaly."
The Government said it only used larvicides recommended by the World Health Organisation (WHO).
Some experts have raised questions over what is behind the Brazilian spike in microcephaly, particularly due to the absence of a similar surge in cases in other areas hit by the virus. Others have also suggested that it has been grossly over-reported in Brazil. The country has registered a total of 3852 suspected cases, but of the roughly 1200 investigated so far, just 462 have been confirmed. Evidence of Zika infection was found in just 41 of the affected babies.
Last week, a report by researchers in Paraiba, one of the worst hit areas, found that the state had been seeing high numbers of microcephaly cases since 2012, with the condition more common in 2014 than last year, when Zika virus was first recorded in Brazil.
But the WHO says a definitive link between the disease and the condition is within weeks of being confirmed. Two separate studies last week also found evidence of Zika virus in the brain tissue of aborted foetuses or babies who died soon after birth, who had microcephaly. Scientists around the world are racing to develop a vaccine for the virus, with clinical trials expected within a year to 18 months.
Health Minister Marcelo Castro told journalists in Brazil: "For us, theres no doubt at all that the microcephaly epidemic is a consequence of the epidemic of Zika virus, which did not exist in the Americas before."