January 2019

Big, Bad, Bulging, Bug Bites … is There a Hay Fever Connection?

Author: Dr. Thomas Beller

Spring is coming, and that means warmer weather is right around the corner. It also means the return of mosquitoes and other bothersome insects, which are more active during warmer months. For most of us, these insects are nothing more than a minor annoyance. For others, they are a much more significant nuisance because of the way the body overreacts to their bites. For these unlucky people, a walk in the park or a nice spring picnic can result in a collection of inflamed mounds on the exposed skin. In some cases, the inflammatory response can be severe enough to cause noticeable swelling of an entire foot or other body part.

Why do some people react so severely to insects when others hardly react at all? The purpose of this article is to present a theory that environmental allergy (sometimes called hay fever) is the underlying cause. To understand this, first, we have to understand why our bodies react to insects in the first place. Some insects sting us with venom in a manner that is designed to cause pain and inflammation as a warning to get away. Others are actually biting us because they are feeding on our blood. We react to both, for different reasons.
Stinging insects inject venom that triggers a toxic response, resulting in swelling and inflammation. Some people can develop allergy to venom, resulting in severe allergic reactions. Biting insects cause swelling for another reason. It’s not because of venom, nor because the body cares about what the insect took from us, and it is almost never because of an allergic reaction to the insect. Rather, biting insects cause swelling because historically their saliva contained parasites and other infectious organisms. The immune system is responding to the bite in an effort to defend itself from the invasion of these organisms.

In our society today, hygiene and medications have allowed us to eradicate many of the organisms that biting insects used to carry. So, why do we still react to them? And why do some of us react so dramatically? It appears that evolution has allowed our immune systems to recognize the association between insect saliva and these organisms. Today, insect saliva alone is enough to trigger the inflammatory response, acting as a surrogate signal for parasites based on their strong historical association. In other words, there is an “assumption” that parasites and other organisms may be present, even when they are not. To understand why some people overreact we have to understand the nature of allergy.

Allergies have a significant relationship to parasites. The more we have eliminated parasites from our society, the more problematic allergies have become. Parasites were such a common part of our lives in the past that virtually everything humans ate and drank for millions of years contained them. It was also more common for biting insects to carry them in their saliva. Today, we have a much different scenario, and this scenario has changed fairly rapidly.

The elimination of parasites has occurred primarily because of two factors: cooking our food and chlorinating our water supply. Chlorinating the water supply may be the most important factor. There is evidence that we started cooking food over a million years ago, leaving the water supply as our last remaining major source of parasitic exposure. We only started chlorinating the water a little more than 100 years ago, and this is when our exposure to parasites went to nearly zero.

Medications have also helped eliminate parasites from people as well as domesticated animals and animals in the food chain. Fewer infections also means fewer insects with parasites, since insects pick up parasites from their victims who harbor them.

It is theorized that our immune systems continue to search for parasites and even amplify this search since they are virtually absent, resulting in mistakes. It turns out that parasites and allergens have similarities in their protein structure, making it easy for the immune system to mistake allergens as parasites. It has long been known that parasites have protein patterns that we call pathogen associated molecular patterns (PAMPs) or sometimes danger associated molecular patterns (DAMPs). Recently PAMPs and DAMPs have also been discovered on pollen, dust mites, pet dander and other allergens. The sharing of PAMPs and DAMPs makes it easy for the immune system to mistake allergens for parasites. When the immune system makes this mistake, it attacks allergens using the same immune pathways and mediators that it uses for parasites. Allergens can therefore be thought of as false parasites. This theory is called the “old friends” hypothesis, a subset of the broader “hygiene” hypothesis. Simply put, the cleaner our society has become, the more our immune system has to search for things to kill, resulting in mistakes.

The immune system of a person with environmental allergies is constantly defending the body from what it perceives to be a massive invasion of parasites. In the same way that war can prompt the need for production of weapons, allergy can amplify anti-parasitic pathways and the production of anti-parasitic mediators of the immune system. Severe allergy sufferers can easily over-produce these mediators in a dramatic way. These anti-parasitic pathways and mediators are the same as those used in the skin when the body reacts to the saliva of insects after a bite. These mediators are so abundant in the skin that even a single insect bite can cause a dramatic inflammatory response. This completes the connection.

If this theory is true, can anything be done about it? Antihistamines can help, but only if they are taken before the bites occur. Once the swelling is present, histamine has already performed its duty. Steroid creams are modestly helpful to reduce swelling, and oral steroids are very helpful but come with side effects. The best approach for those who are severely affected by this issue may be to start allergen immunotherapy for environmental allergies, a treatment referred to as “allergy shots.” Benefits of immunotherapy are well established for typical nasal/ocular allergies and for asthma, but are not yet proven to help with large local reactions to insects. However, in my experience, immunotherapy typically reverses this issue whether administered as shots or as sublingual drops under the tongue. So, as the weather gets warm, enjoy the outdoors, but if you are significantly affected by big, bad, bulging, bug bites, go see an allergist.

Dr. Thomas Beller is a board certified specialist in adult and pediatric allergy, asthma, and immunology. For more information, visit www.hiltonheadallergy.com.

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