P yrethrum is extracted from the flowers of Chrysanthemum cinerariifolium (botanic family of Compositae) ( 1). The active components of pyrethrum are esters of chrisanthemic and pyrethric acids (i.e., pyrethrins, cinerins, and jasmolins), which are collectively referred to as pyrethrins. Pyrethrum and pyrethrins have been used since the early 19th century for control of indoor insect pests as well as for direct application to man and animals. Synthetic analogs, termed the pyrethroids (e.g., permethrin, allethrin, tetramethrin, and permethrin), have been developed to enhance insecticidal activity and photostability.
A 47-year-old man had been working for 6 years in a firm involved in the extermination of indoor insect pests. He sprayed various insecticide formulations containing organophosphorus compounds and pyrethroids. About 6 years after starting employment, he experienced asthma at work. He noticed that his symptoms were related to the use of pyrethroid-based insecticides. About 1 year later, he had to leave his job, because his asthma symptoms worsened despite treatment. Inhalation challenges were carried out 6 years later. At that time, he was treated with inhaled fluticasone dipropionate 500 μg b.i.d. and inhaled salbutamol when required. He had smoked 10 cigarettes a day for 15 years. Baseline spirometry showed FEV1 of 2.70 l (75% predicted value) with an FEV1/FVC ratio of 74%. Histamine PC20 was 0.125 mg/ml. After a control challenge with a paint diluent, the subject sprayed an insecticide formulation containing 0.2% tetramethrin and 0.1% fenitrothion, which resulted in a dual asthmatic reaction ( Fig. 1, upper graph). Five months later, the subject was challenged with pure tetramethrin powder (diluted 1/10 in lactose) ( Fig. 1, lower graph). Exposure to tetramethrin provoked a 31% fall in FEV1. The subject refused further challenge with pyrethrins or other pyrethroids. Skin prick testing with common inhalant allergens and tetramethrin (diluted 1/1000, 1/100, and 1/10 in saline) gave negative results.
To our knowledge, this is the first account of asthmatic reactions provoked by tetramethrin, although it remains unknown what mechanisms were responsible for the induction of these reactions. Pyrethrins do not exhibit anticholinesterase activity; they act directly on axons by altering transmembrane sodium conductance ( 1). Several reports have documented asthmatic reactions ( 2–5), as well as a hypersensitivity pneumonitis-like syndrome ( 6), in subjects exposed to insecticides containing pyrethrum or pyrethrins. Skin tests with pyrethrum extracts were positive in some of the reported subjects ( 2, 3, 6), although these reactions could have been caused by allergenic impurities derived from C. cinerariifolium. The respiratory effects of an aerosol insecticide containing a mixture of pyrethrins and tetramethrin have been prospectively evaluated in seven asthmatic subjects who reported a history of chest tightness on exposure to sprayed insecticides ( 4). Although exposure to the insecticide spray produced respiratory symptoms in all subjects, significant changes (>20%) in FEV1 were documented in only one of them. This report indicates that the impact of pyrethroids on respiratory health deserves further investigation.