What’s causing microcephaly in Latin American newborns?

A group of Argentinian doctors have now claimed that the recent increase of microcephaly has been caused by pesticide use rather than Zika. Other experts, however, remain skeptical.

The Fight Against Pesticide

Supposedly pyriproxyfen — an insecticide used to prevent mosquito growth — has been used to prevent other prominent diseases such as dengue in many of the same towns which are now affected by Zika. The Brazilian government began using pyriproxyfen in 2014.

According to the report published by Physicians Against Fumigated Towns:

[quote_box_center] 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. However, they fail to recognise that 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 (pyroproxyfen [sic]) is applied by the State on drinking water used by the affected population.[/quote_box_center]

Their argument is moreover based on the observation that previous Zika outbreaks did not seem to cause birth defects. They also point out that other Latin American countries — like Colombia — have reported numerous cases of Zika, but few to no cases of microcephaly.

Argentinian Dr. Medardo Avila Vazquez, author of the report, admits:

[quote_center]“It’s a hypothesis, a probability.”[/quote_center]

Nevertheless, he also adds, “For us, it’s more likely…”

Scientific Disagreement

Other scientific leaders disagree. In fact, the U.S. National Institutes of Health (NIH) call the Physicians Against Fumigated Towns’ report “sketchy.”

While some argue that pyriproxyfen’s ability to inhibit mosquito larvae development suggests the possibility of a similar effect in human children, Bruce Gordon of the World Health Organization (WHO)’s Water, Sanitation, Hygiene and Health group says:

[quote_center]“There’s absolutely no concerns for reproductive effects that have been raised for this chemical.”[/quote_center]

As Gordon explains, pyriproxyfen mimics an invertebrate hormone for development that is completely unrelated to mammalian processes.

Furthermore, the amount of insecticide used by Brazilian states and cities to manage mosquitoes is far less than than WHO’s published threshold for safe drinking water. “You’d have to drink hundreds of liters of water to get anywhere near potentially risky levels,” says Gordon.

NPR’s Rae Ellen Bichell reports:

[quote_box_center]Toxicologists have fed the chemical to guinea pigs, dogs, mice, lactating goats, laying hens, and pregnant rats and rabbits. At very high doses, it gave some animals mild anemia and liver and kidney problems. When given to the goats and hens, extremely small amounts of pyriproxyfen were found in their milk and egg yolks. (You can read about the toxicology studies here.)[/quote_box_center]


Both sides of the pesticide-Zika debate present intriguing arguments. Even so, there is at least one statement everyone can agree on. As epidemiologist and former Pan American Health Organization employee, Dr. Gustavo Bretas declares: “We need more information.”

Dr. David Morens of the NIH’s Institute of Allergy and Infectious Diseases adds in:

[quote_box_center]“I can say that what we’ve heard about these cases of microcephaly and the epidemic of Zika, and now the possible chemical or pesticide exposure, are claims and statements that don’t yet have scientific backing… My sense is that even some scientists are confused … What we really need is more scientific information that looks at cause and effect, rather than just association.”[/quote_box_center]

What Can Be Done?

Bretas’s current employer, the Brazilian Association of Collective Health (a.k.a. ABRASCO), believes the country should minimize the use of pesticides and refocus their attention on improving access to potable water.

Many people throughout Latin America have limited access piped water and therefore use tanks or buckets to store water. These latter methods, however, can become breeding places for mosquitoes — bearers of Zika, dengue and all sorts of other tropical diseases

In terms of finding more information about the possible cause of microcephaly, South Korea has pledged to contribute roughly $2.4 million (USD) for Zika research. The U.S. has also announced a partnership with Brazil to find a vaccine against Zika. Meanwhile, WHO seeks a grand sum of $56 million (USD) for Zika research.

With all these world powers investing to find answers, one can only hope this speculation will soon be replaced by evidence-based facts.