Urticaria

Acute and chronic urticaria and angioedema can result from exposure to a number of agricultural products. They may be caused by immunologic and nonimmunologic histamine releasers. Immunologic mechanisms involve type I (immunoglobulin G [IgG]-mediated), type II (cytotoxic antibody-mediated), or type III (immune complex-mediated) reactions. Nonimmunologic mechanisms usually involve substances such as aspirin that directly incite the release of histamine and other mediators from mast cells. Medications, foods, food additives, and the bites of insects and snakes have been implicated. Common food allergies include shellfish, fish, eggs, nuts, chocolate, berries, tomatoes, cheese, and milk (27).

Figure 18.1. Allergic contact dermatitis from garlic in a production worker. (Photo by Dr. James E. Lessenger.)

There are four categories of urticaria:

1. Localized: a wheal and flare only where the chemical or substance touched

2. Angioedema: a generalized urticaria over the entire body

3. Pulmonary: manifested by wheezes

4. Anaphylaxis: manifested by a sudden onset of shock

Treatment for urticaria includes antihistamines, tricyclics, and systemic steroids (27).

Latex Allergies

Most of the use of natural rubber latex (NRL) is in the medical field where use increased dramatically as a response to the increased need for bloodborne pathogen control in the AIDS epidemic. Natural rubber latex is also used in worldwide agriculture to protect the hands of workers, especially for research, artificial insemination, and veterinary services (28-30).

The principal nonrubber components of NRL are proteins; 60% by weight of protein is bound to rubber, and 40% exists in a free aqueous phase. The product that arrives on the shelves in the form of gloves may have as many as 16 natural polypeptides with the ability to bind IgE antibodies (28-30).

Latex hypersensitivity reactions are categorized into two main types: (1) type IV or delayed (cell-mediated) hypersensitivity reactions, and (2) type I or immediate (IgE-mediated) anaphylactic reactions. Risk of sensitization is dependent on the frequency and intensity of NRL exposure. Atopy is a risk factor, as are allergies to foods such as banana, kiwi, avocado, and chestnut, which contain allergens that cross-react with antibodies to latex proteins. Typically the dermatitis is localized to the hand where the gloves are worn and is manifested by a polymorphic, erythemic rash with edema and vesicles. Chronic rashes may progress to maceration or lichenification with fissures. Along with hand dermatitis, the symptoms of asthma, rhinoconjunctivitis, hand urticaria, and general urticaria are seen in allergic individuals (28-30).

Patch and prick tests and a serum antibody test are available, but the diagnosis is primarily made by the clinical presentation. Prevention of occurrences entails offering alternative gloves of vinyl or nitrile to workers with a history of atopy or allergies to key foods. Treatment for the acute dermatitis consists of moist compresses and topical steroids. Research has documented that the purchase of powder-free NRL examination gloves significantly reduces the incidence of new cases of latex allergic dermatitis (28-30).

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