West J Med
Copyright © BMJ Publishing Inc.
Fatal asthma in a child after use of an animal shampoo containing pyrethrin
Sheldon L Wagner
Dept of Environmental and Molecular
Oregon State University
Corvallis, OR 97331-7301
To the Editor,
An 11-year-old girl had been diagnosed with asthma at age 6 years.
She had never been hospitalized and had rarely received steroids. Her
only medication was albuterol, which was taken by inhaler as needed.
On the day of admission, she gave her pet dog a bath using a shampoo
containing 0.2% pyrethrin. She had used this shampoo 2 years earlier,
with a brief but mild increase in her asthmatic symptoms that lasted
48 hours. The dog had been in the family home for several years. She
was asymptomatic when she started to bathe the animal. Within 10
minutes, severe shortness of breath with wheezing developed, and she
was immediately transferred to a hospital. She was intubated and
treated aggressively for an acute asthmatic attack. She did not
respond to treatment and died about 2-1/2 hours after the initial
exposure to the pet shampoo.
At autopsy, there was mucous plugging of the bronchioles with an
inflammatory infiltrate composed of neutrophils and eosinophils.
There was prominent vascular congestion, and many alveolar spaces
contained homogeneous eosinophilic edema fluid. The cause of
death was listed as "respiratory arrest secondary to acute asthmatic
attack." The pathology findings were consistent with the literature
on pathologic changes in acute asthma.1
The pyrethrin class of insecticides was originally formulated from
plants of the Compositae family, which includes daisies and
chrysanthemums. Pyrethrum refers to both the crude plant extract and
the marketed formulation of insecticide. Pyrethrin is the
insecticidal chemical prepared from pyrethrum flowers, and it is also
a market name for purified pyrethrum. A third term, pyrethroid,
refers to insecticides of the same class, but these are synthetic
compounds. Pyrethrum is known to cause allergy, including asthma and
allergic skin disease. A review in 1934 warned physicians about its
allergenic properties.2 Our case is the first documented case of allergy to pyrethrin.
No cases of pyrethroid allergy have been documented.
Neither pyrethrin nor pyrethroids are currently classified as
allergens by the Environmental Protection Agency. Techniques of
extraction from the flower have greatly improved the purity of the
original pyrethrum formulations, and a recovery of 95% to 97%
pyrethrin is now achievable.3
The insecticide is, therefore, commonly marketed under the name of
Pyrethrin, but it may contain small, but still allergenic, amounts of
the impurities found in the crude extract. One suspected allergenic
impurity is oleoresin, which may have been responsible for the
allergic reaction in our case. The mechanism of allergy from
pyrethrins is poorly documented. The marketing of pyrethrin is
favored over that of pyrethrum, based on skin test studies suggesting
that it is safer.4
Although physicians have access to crude pyrethrum for skin testing,
its purified isomers or mixtures of isomers are available only in the
research laboratory. They are too expensive for practical use.
The possibility of an acute allergic reaction occurring from the
use of any currently marketed pyrethrum insecticide should be
considered in any case of respiratory or dermal allergy of unknown
cause. This case suggests that physicians should also be alert to
formulations marketed as pyrethrin. Pesticides of this class are
being used with increasing frequency in homes and are easily
available to the public. Manufacturers are not required by the
Environmental Protection Agency to state on the label that the
pyrethrum formulations are allergens.
- Roche WR. Inflammatory and structural changes in the small airways
in bronchial asthma. Am J Respir Crit Care Med1998; 157(suppl):S191
- Feinberg SM. Pyrethrum sensitization. JAMA1934; 102:1557
- Carlson DJ. Pyrethrum extraction, refining, and analysis. In:
Casida JE, Quistad GB, eds. Pyrethrum. Flowers. Production, Chemistry,
Toxicology, and Uses. New York: Oxford University Press; 1995: 97-107.
- Zucker A. Investigation of purified pyrethrum extracts. Ann
Allergy1965; 23:335 -339.