Allergies: 35 Million in US Affected

The body's immune system is normally pretty good at its job, which is to defend against invaders such as bacteria and viruses. In those who suffer from some form of allergy, though, the immune system is most often responding to "false alarms" that don't bother most people. A broad range of otherwise harmless substances called allergens trigger these immunological responses.

Allergic diseases are major causes of illness and disability in the US, afflicting more than 35 million people with upper respiratory symptoms. Pollen allergy (hay fever) is one of the most common chronic diseases. Airborne allergens can also provoke the respiratory symptoms of asthma, which is rising rapidly in incidence among younger Americans and affects 15 million people in the US by the most conservative estimates. Worldwide, airborne dust causes the most problems for people with allergies.

"Allergies can represent many different things," said Asriani M. Chiu, MD, Medical College of Wisconsin Assistant Professor of Pediatrics and Medicine (Allergy). "In general, what's going on is the individual is eliciting a hypersensitive response to a particular protein. The protein can be airborne pollen, or dust mite, or it can be something like a food protein such as in peanuts, for example. Dr. Chiu practices both at the Children's Hospital of Wisconsin Asthma and Allergy Center and the Zablocki VA Medical Center.

"The types of symptoms that you can get from these allergens can range from something as simple as hay fever, where commonly many people develop itchy, watery eyes, nasal symptoms of sneezing, watery nose, post-nasal drainage. Or you could also elicit more of an asthmatic reaction, with lower respiratory symptoms consisting of cough, wheezing, chest tightness or difficulty breathing.

"In the most severe reactions, you can actually have those respiratory symptoms plus others including cardiovascular symptoms and shock. This can potentially be life threatening. Those types of reactions tend to be more related to the food protein allergies or even to something like an insect sting."

Why Don't We All Have Allergies?
Research has shown that some people inherit a general tendency to be allergic, increasing the likelihood that their immune system will react to one or more allergens. Children are much more likely to develop allergies if one or both of their parents have allergies, although they probably do not inherit a tendency to be allergic to any specific substance. A parent allergic to pollen, for example, can pass along genetic traits to a child who then develops a different allergy.

Exposure to allergens at certain times when the body's defenses are lowered or weakened, such as after a viral infection or during pregnancy, seems to contribute to the development of allergies. "After you have the genetic predisposition," said Dr. Chiu, "then you need to have the environmental exposure, whether it be to animal dander or dust mite or to the food protein. Usually what happens is the person's exposed for the first time to the particular protein and they get what we call 'sensitized', which means that a specific allergy antibody is elicited.

"Then, when they're re-exposed to that protein, because that allergy antibody is present in their system, it can cause a kind of chemical reaction where all those allergy antibodies then cross-link and they essentially 'explode' and release all the chemical mediators like histamines that make us have the symptoms of allergy.

"So you have to have a genetic predisposition and prior exposure in order to develop a reaction. Interestingly, that's why many times a pediatrician will say to a family that 'the child's too young to develop allergies'. What they're trying to say, for example for an infant under two years old, is that they're probably too young to develop seasonal allergies because they wouldn't have seen enough seasons to be exposed and then have that sensitization. But it's not uncommon to have kids even under one year old to have some kind of reaction to those other daily environmental exposures, like dust or pet dander."

Diagnosing Allergic Diseases
People with common allergy symptoms may at first suspect they have a cold, but the "cold" lingers on. It is important to see a doctor about any respiratory illness that lasts longer than a week or two. When it appears that the symptoms are caused by an allergy, the patient should see a physician who understands the diagnosis and treatment of allergic diseases.

Allergy diagnosis has not changed much in recent years, said Dr. Chiu. A medical history is taken to try to determine if the condition is seasonal in nature and determine which allergens are the likely culprits. Mucous membranes, which often appear swollen and pale or bluish in persons with allergic conditions, are examined.

Skin tests using extracts from allergens common to the area in which the patient lives are used to determine whether a patient has IgE antibodies in the skin that react to a specific allergen. Positive reactions to skin tests can give the physician important diagnostic clues, but a positive reaction does not always prove that a particular allergen is the cause of the patient's symptoms. A test reaction may indicate that IgE antibody to a specific allergen is present in the skin, but respiratory symptoms do not necessarily result, so clinical correlation is important.

Skin testing is the most sensitive and least costly way to identify allergies, but these should not be used to test patients with eczema or if they have taken medications that can interfere with the testing. For those patients there are other diagnostic tests that use blood samples from the patient to detect levels of IgE antibody to a particular allergen.

Treatment Advances Center on Medications
"I think we've made a lot of headway in allergy treatment in the last couple of years," said Dr. Chiu. "We now have very effective and safe medications that can be used once or twice daily depending on the drug. These range from intra-nasal steroids, to take care of the inflammation in the nasal passages, to non-sedating antihistamines like Allegra that can be taken once daily. So the medications are safe, effective, and easier to use with less frequent dosing.

"Probably the most truly significant new treatment that's out there is reserved right now for moderate to severe allergic asthma, not just allergy nasal symptoms or rhinitis. It is a drug called Xolair (omalizumab). Omalizumab is actually an antibody to the allergy antibody. What it's doing is like "soaking up" the IgE that's in a person's system so that it can hopefully decrease the reactions."

The Medical College of Wisconsin and Children's Hospital of Wisconsin participated in clinical trials for Xolair use in the pediatric and adult population, before the US Food and Drug Administration approved it. The drug has greatly improved the lifestyle of many patients who were once on multiple medications or may have had to visit the emergency room when there's a high mold count, said Dr. Chiu. It is now also being studied for people who are peanut allergic, not as a cure but as a useful treatment in cases of accidental exposure to decrease the severity of their reaction.

"It was amazing because during the trials, patients that had what we call the 'allergy triad' with nasal symptoms plus asthma plus eczema, had all 3 conditions get better, and they were able to get off their other medications" said Dr. Chiu. "Unfortunately, it's still relatively expensive compared to inhalants or antihistamines for less severe conditions. It's an injection given once or twice a month depending on the IgE levels, and it's not a cure. Once the injections are stopped the symptoms recur and the allergy antibody comes back. So this treatment is different from an allergy injection that would act like a vaccine to change the immune response.

"What's exciting about this field is the current research is focusing on how we can change the allergic response to a protective response, which is great. I think we still have a way to go, but that's what we're trying to do now - prevent problems from recurring."

Dan Ullrich
HealthLink Contributing Writer

This article includes information from the National Institute of Allergy and Infectious Diseases, National Institutes of Health.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.