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Allergy incidence rising, but questions remain about why
Allergy is hereditary, but the offending allergens can vary from generation to generation.
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The prevalence of allergy has risen during the past 20 years, but little is known about why allergies manifest when they do and why their effect varies among families.
“Nobody has a good answer. It’s a combination of things. One of them is that because there’s a genetic component, there are more people being born with the allergy marker. People are also more aware of allergies than ever before,” said Mike Tringale, MSM, director of marketing and communications for the Asthma and Allergy Foundation of America.
The incidence of allergy is difficult to track because allergies vary by season and region. Although the environment may play a role in the development of allergy, the incidence is distributed proportionally among the population, Mr. Tringale told Ocular Surgery News.
“It gets even more gray because people usually have more than one allergy. There’s a lot of overlap in allergy prevalence based on the type. Approximately 50 million people in the United States have allergies,” he said.
In the general population, 4% have ocular allergy as their primary allergy. The overall incidence is difficult to calculate because many people have more than one allergy, Mr. Tringale said.
“Further complicating the whole issue of ocular allergy is what causes them and their symptoms,” he said.
The large population affected by allergy has triggered massive advertising campaigns by the major pharmaceutical companies, Mr. Tringale noted. As a result, more people are aware of allergies, and they either self-diagnose and self-treat with over-the-counter therapies or contact their physicians about their condition.
“Allergies have never had a higher profile. It’s a major ad theme, and it’s such a huge population. People are simply more aware,” he said.
Inherited disease
Allergy is an inherited disease of the immune system, Mr. Tringale said. A child has a 7-in-10 chance of developing an allergy if both of his parents have allergies. However, that child may be sensitive to different allergens than his parents. The variation is what makes allergy so difficult to understand, he said.
“Allergic parents are passing along the atopic possibility that the offspring will be allergic. It’s more complicated than what people think,” he said.
People with the genetic predisposition for allergy have an abnormal immune response when they come in contact with an allergen, Mr. Tringale said.
“It’s an extreme response from the immune system that interprets the allergen as an invader, much like a virus or bacteria. It should just be a reflex, though. That’s why it’s a disease. The body is acting inappropriately to something that’s not normally harmful in other people,” he said.
Types of ocular allergy
Overall, allergy affects an estimated 8% to 20% of the population, said Esen Karamursel Akpek, MD, of Johns Hopkins University. She said there are four basic types of ocular allergy: allergic conjunctivitis, giant papillary conjunctivitis, atopic keratoconjunctivitis and vernal keratoconjunctivitis.
“The incidence is different depending on the season and the region. In developed countries, the incidence is getting higher probably because of environmental pollution and a decrease in the incidence of infection,” she said.
Allergic conjunctivitis is the most common form of ocular allergy, affecting adults and children, Dr. Akpek said. The incidence rate varies between 5% and 25% based on age, region and time of year, she said.
| Day care centers a source for indoor allergens |
| Day care centers are an important source of exposure to indoor allergens, according to a study by researchers at the National Institute of Environmental Health Sciences. In investigations in 89 day care facilities in North Carolina, researchers detected animal dander, fungi, dust mites and mouse allergen. Many of the allergens were found in carpets at the facilities. Samuel J. Arbes, DDS, MPH, PhD, and colleagues, surveyed and collected the specimens from carpet and hard surfaces in the rooms where children spent most of their time, according to a press release from the American Academy of Allergy, Asthma & Immunology (AAAAI). The study found that the highest concentrations were for fungus, American dust mite allergen and dog and cat allergens. Dog and cat allergens were found in 97% and 100% of the facilities respectively, even though the animals were not present in most of the facilities. The lowest concentrations found were cockroach allergen, European dust mite allergen and mouse allergen, the researchers said. “Carpeted surfaces had significantly higher levels of dog, cat and dust allergens, indicating that carpets provide a reservoir for these allergens,” the press release said. The study was published in the online version of the Journal of Allergy & Clinical Immunology, the peer-reviewed journal of the AAAAI. |
Giant papillary conjunctivitis is typically associated with contact lens wear, although it can be caused by irritation from an ocular prosthesis or sutures, Dr. Akpek said.
Atopic keratoconjunctivitis is rare, affecting 0.3% of the population, Dr. Akpek said. Among those affected, 29% to 40% will have clinically diagnosable eye disease stemming from the allergy, she said. The condition is associated with atopic dermatitis or eczema. Patients may develop keratitis, which can cause decreased visual acuity from corneal scar formation, in addition to the conjunctivitis, she said.
Vernal keratoconjunctivitis is a seasonal condition. It primarily affects children in warm climates such as the Middle East and Africa, Dr. Akpek said. In Africa, vernal keratoconjunctivitis is the primary cause of acquired blindness among children, she said.
When, why allergy appears
Researchers do not know why some allergies occur early or late in life, Dr. Akpek said. Several factors are related to the development of allergy, she noted. Patient age, the type of allergen and the patient’s immune status are among these factors. The younger the patient, the more susceptible he is to allergy.
There is little physicians can do to eliminate allergy, and people are not always able to avoid the environmental factors that cause it, Dr. Akpek said. Fortunately, Dr. Akpek said, the available treatments are effective in relieving allergic symptoms.
“There may be some allergens we may be able to avoid. If a patient is allergic to something metallic or a type of food, it’s easily avoidable. House dust mites are harder to avoid, but you can recommend filters and elimination of carpets that may alleviate the severity,” she said.
The method in which the allergen enters the system also makes a difference, Dr. Akpek said. An allergen may be fatal if ingested but harmless otherwise, she said.
Allergists use patch tests to determine what allergens affect patients, Dr. Akpek noted. Without performing such extensive testing, she said, ophthalmologists can treat symptoms empirically and see whether the patient responds to the treatment. If symptoms persist, she recommended that patients should be referred to get a patch test.
“If they don’t get better with antiallergy medications, or if the cornea or symptoms like hay fever and sinusitis are involved, then I recommend a patch test. Half of the time, they’re allergic to everything; others may be allergic to more specific things,” she said.
In some cases, an irritant may be causing the patient’s symptoms. The physician should try to determine what might be causing irritation, Dr. Akpek said.
“Try to eliminate what could be irritating the ocular surface like make-up, moisturizers, soaps, etc. Treat the allergy with medications and recommend artificial tears for the eye surface,” she said.
For Your Information:
- Mike Tringale, MSM, can be reached at 1233 20th St. NW, Suite 402, Washington, DC 20036; 202-466-7643 ext. 272; fax: 202-466-8940; e-mail: mike@aafa.org; Web site: aafa.org.
- Esen Karamursel Akpek, MD, can be reached at The Wilmer Eye Institute at Johns Hopkins University, 600 North Wolfe St., Woods 474, Baltimore, MD 21287-9235; 410-955-5494; fax: 410-614-2816; e-mail: esakpek@jhmi.edu.
- Jeanne Michelle Gonzalez is an OSN Staff Writer who covers all aspects of ophthalmology, specializing in practice management, regulatory and legislative issues. She focuses geographically on Latin America.