Sunday, April 26, 2015

On "the nocebo effect" and spraying for gypsy moths

This week my inbox has been flooded by emails about the decision by our Ministry of the Environment to spray for gypsy moths in parts of Surrey and Delta. For those of you outside the British Columbia lower mainland you might not know about gypsy moths. As a province dependent on the export of both agricultural and forest products British Columbia is particularly sensitive to the presence of European and Asian gypsy moths. Both are invasive species that can devastate deciduous trees (read destroy fruit trees) and the presence of gypsy moths can result in our wood products being banned for export. Based on these concerns our government has an integrated program including ministries ranging from the Ministry of Agriculture, to the Ministries of Forests and Environment. This program includes trapping moths, identification of outbreaks and, if necessary, spraying. While the gypsy moth can cause devastation to our economy, it is possible to control it using a safe and effective, non-toxic, aerial spray called Btk. The best thing about Btk is it is the essence of a directed, organic response to infestations. You see Btk is not a chemical pesticide but rather is a formulation of naturally occurring bacteria mixed in a non-toxic solution appropriate for aerial dispersal. As anyone familiar with our environment knows bacteria exist throughout our environment. Each and every one of us carry three to four pounds of bacteria in and on our bodies. Without our natural gut bacteria we would be unable to digest certain foods and people who lose these bacteria either need a transplant or they become extremely ill and in rare cases can die. Due to our interactions with bacteria, our bodies are well suited to their presence and bacteria are similarly adapted. While some bacteria can make you sick, other bacteria (like Btk) cannot. There are literally thousands of studies demonstrating that Btk is harmless to people and pets. More details here. Ironically Btk can’t even hurt adult gypsy moths, their eggs or their pupae. It only works when ingested during the caterpillar stage of their life cycle at which point it gets into their guts, infects them and kills them. I simply lack the space to write about how safe this spraying is which brings us to the topic of this post: The nocebo effect.

So what is the “nocebo effect”? Well let’s start with something everyone knows: the “placebo effect”. The placebo effect is a long understood effect where, in the absence of an active ingredient, a “placebo” (often a sugar pill) has the same effect as if an actual pharmaceutical had been used. The placebo effect has been long understood, heck I first saw it discussed in a MASH episode back in the late 1970’s. Research on the placebo effect is both thorough and extensive. In a review article from 2012 over 2200 studies were identified (ref) demonstrating or discussing trials demonstrating the existence of the effect. The scientific basis of the placebo effect is also well-understood. Human perceptions are driven by our neurochemistry and human neurochemical responses are understood to vary with mood and perceptions. Interestingly enough even the simple act of smiling can cause a biochemical response improving one’s mood (ref). Convince a person with a minor illness that the sugar pill you are giving them will make them feel better and often that is all it takes. As everyone knows, the placebo effect does not work on everyone, nor does it work every time. All that is certain is that on a small percentage of people, in a small number of circumstances, it can have a real effect.

Let’s get back to the “nocebo effect”, it is essentially the placebo effect’s less attractive younger sibling. You could say it is Stephen Baldwin to the placebo effect’s Alec Baldwin. In keeping with the Baldwin theme, while Alec Baldwin is well known for being a liberal-Democrat Stephen is known as an ardent Republican. So while the placebo effect has the ability to help you feel better in the absence of any active ingredients, the nocebo effect has the ability to make a person feel poorly in the absence of any active stimuli. As described in this review paper the nocebo effect is not as well studied as the placebo effect but it has been demonstrated to be real. It is important to recognize a couple things about the nocebo effect. First and foremost, people who “feel bad” or claim to be “sick” via the nocebo effect are neither lying nor are they fakers, rather they are doing one of two things. They are either associating actual symptoms from other causes to the “nocebo” or they are having phantom symptoms based on their minds playing tricks on them. Think about this in your daily lives. Every parent of young children dreads the arrival of the “pink sheet” from your elementary school. For those of you without young children, the “pink sheet” is the warning announcement the schools send home to tell families that one of the children in their child’s class has been diagnosed with lice. The sheet asks parents to check their kids for lice. Try watching a group of parents when their kids hand them the “pink sheet” and watch as virtually every parent in the group starts itching their heads. You would think someone had spread a dose of itching powder into the group. This is the nocebo effect in action. An itchy head is no longer just something you get from life; it is now all about lice. Until you have had a chance to check your kids and yourselves every itch is a sign that you are one of the unlucky ones. There are any number of celebrated cases where people have be shown that their “illnesses” were all in their minds but by far the most entertaining one is described in this article from Daily Tech. In that case a community complained about health issues associated with radio towers even though the radio towers had been turned off during the time the community members claimed they were being made ill by the towers. I have neither the time, nor the space to talk about fears of WiFi in this article, but I think we can all agree that any case where a transmission tower is turned off and people still complain it is making them sick is an example of the nocebo effect.

So let’s go back to the gypsy moth spraying. When a mother on television claims that following the spraying for gypsy moths she felt a sore throat, it could be that she didn’t look at the pollen count for the morning and woke up with a sore throat from exposure to high levels of pollen or it could be that she simply had a dry throat that on any other day would be solved with a glass of water. In either case once the “sore” throat is associated with the Btk spraying in a person’s mind, it will be that factor that makes it the cause of the “illness” thereafter. Regardless of the amount of research that shows otherwise, every time a community is told that there is going to be aerial spraying you will get a dozen or so people who claim to have symptoms of various indistinct illnesses all of them “caused” by the spraying. Ironically, the illnesses are indeed associated with the spraying but not in the way you would expect. It is not the spray itself but rather by the simple fact that spraying is occurring that caused people to display their symptoms.

This brings us back to a topic of a previous post “On Science Communication and the Difficulty Relaying Scientific Information to the Public” which introduced the concept of “dread risk”. As I describe in my previous post: dread is a term used by Dr. Paul Slovic in his seminal article on risk communication called "Perceptions of Risk". For those of you without access to journal articles Dr. Roger Pielke discusses the topic in a blog posting. I have previously suggested that any reader who wants a non-technical but compelling read on the subject of Risk should get the book by Dan Gardner of the same name. For those of you not interested in too long a read, dread risks are risks associated with factors that cannot be seen or felt using our normal senses and can have serious or life-threatening consequences, often a long time after the initial exposure. In this the aerial spraying for Btk has features associated with dread risk. The spray, once released, is invisible to the touch, cannot be smelled [author's correction: the Foray 48B formulation has a very minor odour associated with one of the ingredients used to hold the Btk in suspension] but can sometimes leave a minor residue on surfaces. This makes it an ideal source of dread risk. The problem is that based on all the existing science Btk does not cause any short-term, medium term or long-term risk to humans, animals or anything that is not a caterpillar. Unfortunately, as is the case in many other endeavours, a solid basis in science is never enough to calm all the fears in a population that is mostly science-blind. All our regulators can do is to continue spraying, all the time trying to educate the population about the fact that the spraying does not represent a real risk to human health.


  1. You seem to use BTK and "the spray" interchangeably; however, BTK is just one ingredient of "the spray".

    ARTICLE: "The spray, once released, is invisible to the touch, cannot be smelled"
    FACT: The spray does smell and the smell lasts for several hours.

    ARTICLE: "Btk is not a chemical pesticide but rather is a formulation of naturally occurring bacteria mixed in a non-toxic solution appropriate for aerial dispersal."
    FACT: Perhaps BTK may be a safe naturally occurring bacteria... but more than 80% of the ingredients are listed as "other". The actual ingredients used for aerial dispersal are not listed.

    What are the "other" ingredients Blair? Perhaps something that smells? Or are people making that up too?

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