Ed. note: News is emerging that the two organizations involved with the larvicide accusations have a history of pesticide activism and Brazil's Ministry of Health says there is no scientific basis linking the chemical to the birth defect in babies. We'll continue to monitor the story and update as available.

As the World Health Organization (WHO) ramps up its fight against the Zika virus in an effort to stop the rise in microcephaly cases emerging in Brazil, a group of Argentinian and Brazilian doctors have posed a controversial question: What if the epidemic of microcephaly in South America's largest nation isn't being caused by mosquitoes, but the country's water source?

Two organizations, Physicians for Crop-Sprayed Towns (PCST) and the Association for Collective Health (ACH), are questioning the government's claim that mosquito infestations are causing thousands of babies in Brazil to be born deformed. Instead, say the organizations, the microcephaly epidemic (which is up to more than 4,000 suspected cases) is due to the government's use of a controversial larvicide, pyriproxyfen, in community drinking water sources in 2014.

The government approved the use of the larvicide in an effort to control mosquitoes in Brazil's dense population centers prior to the World Cup competition.

"A dramatic increase of congenital malformations, especially microcephaly in newborns, was detected and quickly linked to the Zika virus by the Brazilian Ministry of Health," Physicians for Crop-Sprayed Towns said in a statement on its website. The organization accused the government of overlooking several key factors that may point to the fact that the malformations aren't the result of mosquito bites, but an endocrine disruptor in the larvicide.

"[In] the area where most sick persons live, a chemical larvicide ... has been applied for 18 months," stated PCST, which notes that the larvicide reduces the number of mosquitoes by prohibiting the birth of viable larvae.

Second, the organization noted, Brazil is to-date the only country in which large numbers of microcephaly have been recorded. Many of those cases have not, as of yet, been firmly linked to Zika virus or to its "sister" virus, dengue, which is also on the rise.

"[In] other countries such as Colombia there are no records of microcephaly; [even though] there are plenty of Zika cases," the organization said. There also isn't any evidence of widespread microcephaly cases linked to previous Zika epidemics, such as the one that Brazil experienced in 2013.

The Brazil-based Association for Collective Health (ACH) is equally critical of the government's position. It maintains that pyriproxyfen's function as an endocrine disruptor and teratogenic agent (preventing the maturation of life cycle development) is the likely cause of the spike in microcephaly cases.

Poor sanitation methods in those areas hardest hit might suggest that the Zika outbreak was the cause. But ACH noted that these are also the areas in which larvicide use was concentrated in 2014.

ACH has also posed some challenging questions for the government to consider:

"[When] did the dengue cases become more serious? Between 1770 and 1950, when the similar Zika virus was discovered, dengue was 'a benign disease' that didn't cause developmental changes like microcephaly."

At least one state in Brazil is heeding the physicians' warnings. Late last week, Rio Grande do Sul banned the use of pyriproxyfen. Brazil's health minister, Marcelo Castro, criticized the decision.

“For us, there's 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," Castro told the Brazilian publication, O Globo Journal.

WHO, meanwhile, has announced an aggressive fight against the Zika virus and the aedes aegypti mosquito, which it plans to combat with increased use of genetically-modified larvicide. On Monday, the WHO announced a $51 million plan to stop the spread of the mosquito, which it sees as a "staggering" threat to combating epidemics like Zika and dengue.

The aedes aegypti, a very adept and adaptable insect, has migrated in recent years from "water collected in tree holes and the axils of plant leaves in forests," to "discarded plastic cups and bottle caps, plates under potted plants," pet bowls and other areas found in and around human population, the WHO said in a press statement. The mosquito has also adapted its feeding techniques to "sneak attacks" that help its ability to feed and can infect multiple hosts at a time.

Still, it may not be known for a few months whether the increase in microcephaly cases is really due to Zika or to the mosquito-control methods that Brazil has used in its population centers. Colombia, which has not used pyriproxyfen in its water sources, also reported an upsurge in Zika cases in recent weeks but hasn't, as of yet, reported a spike in microcephaly. Neither outcome bodes well for Brazil's population, however, which still faces a long fight against the tiny mosquito.

Image: Tony Winston/ Agencia Brasilia