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Aerial Mosquito Spraying Linked To Autism

University of California - Riverside

Mosquitos and similar pests are a major source of concern around the world, especially marshy areas like eastern North Carolina. These organisms can leave painful bite marks and harmful diseases, including yellow fever and the Zika virus.

But a recent study discovered a possible link between certain pesticides, the way they’re administered, and developmental delays in children.

Chris Thomas has this report.

If you’ve got standing water or trash around your property, you may be a popular destination for mosquitos this summer.

James Gardner is director of the Vector Control Program in Pitt County.

“If you drive around and look and most people tend not to see the trash that creates the largest problems with mosquitos. It’s very easy to go out and ride two or three blocks and you’ll find, if you’re looking really hard, you’ll find tires or buckets or whatever and mosquitos love those. That’s the best breeding place in the world for them.

We reached out to a dozen counties and of the responders, only four – Beaufort, New Hanover, Onslow, and Pitt – have vector control programs. You may see them spraying a misty substance from their trucks in your neighborhood over the next few months.

One of the more common kinds of ingredients used for pesticides are called pyrethroids – a synthetic class of chemical that’s been on the consumer market for the past two decades.

Pitt County uses two pyrethroid based insecticides – Biomist 3+15 and Flit.

“They’re effective with probably the least side effects.”

These programs tend to be expensive and are relatively rare on the county and municipal level. Property owners more often apply their own treatments or contract private firms.

But a recently published study pointed toward a connection between aerial applications of pyrethroid based insecticides and the increased risk of Autism Spectrum Disorder (or ASD) and other developmental delays in children.

The study was led by Dr. Steven D. Hicks, a pediatrician at Pennsylvania State University’s Hershey Medical Center and was inspired by a similar one done on the west coast in 2014.

At the time, Dr. Hicks was practicing at a hospital in upstate New York.

“They found that a specific type of pesticide known as pyrethroids, could lead to increased rates of autism, especially if they were exposed to mothers during the third trimester of their pregnancy and we realized that same kind of pesticide, pyrethroids, were being sprayed over a swampy area near our medical center in Syracuse.”

According to an outline of the study, first presented at a national pediatrician’s symposium on April 30th, Dr. Hicks and his team identified an area in Central New York that administers pyrethroid pesticides aerially and compared it to surrounding areas that use earthbound methods, like the ones most commonly seen in eastern North Carolina.

They lined those figures up with estimates of the number of children diagnosed with disorders on the autism spectrum and other developmental delays.

The results? An increased risk of ASD when exposed to pyrethroid pesticides from aerial application.  

“I honestly was a bit surprised that we were able to replicate some of the findings of that previous large study. Not so much because I didn’t believe the results but because I wasn’t confident that the power of our study would allow us to see statistically significantly differences.”

The study’s outline did not specify why aerial application seems to have this effect, only that there seems to be a correlation between it and developmental delay in children.

Hicks advises caution on the part of the general public upon hearing the results of the study. It is the first of several planned throughout the nation and should not be considered a magic key that opens the, still confounding, lock facing the Autism Spectrum Disorder community.

That key, or keys, may not be found for a while yet, since disorders on the spectrum vary immensely.

“I think that, unlike many of the monogenic disorders that are out there – that is, diseases caused by a single gene change – there are a lot of genes that are implicated in autism. They account for about 50 percent of autism cases, but there are also cases out there without a genetic explanation.”

Furthermore, the study didn’t find a connection between pregnancy term and exposure to pyrethroids.  

Dr. Hicks stresses that it isn’t a particular kind of pyrethroid, but the way in which it’s administered – aerially – that made the difference. It is not a common method throughout the state, including eastern North Carolina.

His suggestion to concerned individuals – don’t panic.

“These results are preliminary and they’re not sufficient yet to cause major changes to public health policy.”

Depending on a number of factors – including rainfall – mosquito spraying will continue from now until the end of the summer, and perhaps into autumn in eastern North Carolina.

Mr. Gardner said he wasn’t familiar with the study and declined to comment on it, but offered several suggestions to lessen the effect of mosquito bites.

“The biggest thing people can do is do a survey of their yard, find where mosquitos may breed, and eliminate that source if possible. If not, there are some products on the market, if someone has water that cannot be dumped or they want to use it on their garden or whatever.”  

Mosquitos, and the pesticides used to control their population, are a source of concern the world over, and rightfully so. But with new scientific discoveries made about both attracting headlines, it’s important to remember responsible scientific studies almost always take lots of time – decades in some cases – and numerous trials in a variety of environments.

The study done in upstate New York is an initial one and only shows, for now, correlation, not causation.