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| March 23, 2004
Vol. 53, No. 6
cd.summary@state.or.us
www.dhs.state.or.us/publichealth/cdsummary/
AN EPIDEMIOLOGY PUBLICATION OF THE OREGON DEPARTMENT OF HUMAN SERVICES
Telephone 503/731-4024
Emergencies 503/731-4030
Fax 503/731-4798
PESTICIDE POISONING FROM SYNTHETIC PYRETHROIDS
WHEN HEALTH CARE providers
think about pesticides, organophosphates
(OPs) and their
cholinergic symptoms come to mind.
Welcome to a new generation of insecticides
—pyrethroids.
Pyrethroids are a synthetic derivative
of pyrethrins, a natural insecticide produced
from chrysanthemums. Pyrethroids
act as contact poisons, affecting the insect’s
nervous system. However, they are
not cholinesterase inhibitors like OPs;
they are, rather, dermal and respiratory
allergens. Contact dermatitis, rhinitis and
asthma have occurred following exposure.
Pyrethroids are replacing OPs in insecticides
in bugbombs, head lice treatments,
and flea sprays for pets, and are commonly
used in fruit orchards. Brand names include
Nix®, Elimite®, Dragon®, Drione®,
Pyrenon® and Pyrocide®.
Suspected pesticide-related illness and
injury have been reportable in Oregon
since 1987 (OAR 333-017-0000 through
333-019-0046). For incidents reported to
the Pesticide Poisoning Prevention Program
in the years 2000–2002, the active
pesticide ingredients associated with the
largest number of likely pesticide illness
were pyrethrins and their synthetic versions,
pyrethroids.
Pesticide poisoning in general can be
difficult to diagnose, and poisoning by
pyrethroids is no exception. Symptoms
may include headache, fatigue, peripheral
neuropathy, and vomiting. A thorough
history is generally necessary to identify
pesticides as the cause.
SYNTHETIC PYRETHROIDS AND
PARESTHESIAS
Scenario: A 58-year old adult male
with a history of well-controlled insulindependent
diabetes mellitus visits his
physician, complaining of tingling and
numbness on the fingers and dorsum of
the hands. The symptoms began 12
hours before the office visit. The patient
reports that the symptoms worsen when
he washes his hands with warm water.
He has no other symptoms. He has had
similar episodes of tingling and numbness
of the hands on 3 occasions in the
past several months. On each occasion,
the tingling and numbness occurred in
different areas of the hands. In each case,
the symptoms resolved after 12–24 hours.
On examination, the patient appears
healthy. Inspection of the hands does not
reveal rash, erythema, or edema. The
hands are warm, with good peripheral
pulses and capillary refill. Neurological
examination reveals a slight decrease in
sensation to light touch in the index
finger of the right hand and on the dorsum
of the thumb and index finger of the
left hand. When testing for temperature
sensation, the patient reports an exacerbation
of symptoms after a warm stimulus.
Neurological examination of the
lower extremities and the remainder of
the physical examination are unremarkable.
Blood work reveals a hemoglobin A1c
of 6.3% (indicating good control of blood
sugar). A dipstick urinalysis is positive
for trace levels of protein. The doc is
concerned about peripheral neuropathy,
and schedules the patient for nerveconduction
studies and a follow-up appointment
to reassess his current diabetes
treatment regimen. The patient cancels
the follow-up appointment after his
symptoms resolve within 24 hours of the
office visit.
DISCUSSION
This case demonstrates the importance
of an occupational and environmental
exposure history, as the signs
and symptoms of acute exposure to
certain pesticides can be similar to those
of other common medical conditions.
This patient was a cabbage farmer
whose skin had been exposed to the
insecticide on several occasions
throughout the growing season. When
additional questions were asked about
exposures during his farming activities,
the patient related several instances of
direct skin contact with a concentrated
insecticide in which lambda-cyhalothrin
was the active ingredient. The exposures
occurred when he was mixing and transferring
the liquid without the use of
appropriate skin protection. An expanded
occupational history led to the correct
diagnosis and an opportunity to
reduce exposure.
Lambda-cyhalothrin is an insecticide
registered for use in the US by the Environmental
Protection Agency. It is a
synthetic pyrethroid. Synthetic pyrethroids
affect the nervous system of
insects by prolonging the deactivation
of voltage-gated sodium channels,
which results in prolonged excitation of
nerve fibers.1 There is evidence that
synthetic pyrethroids, which, like lambda-
cyhalothrin, contain an alpha-cyano
group are more potent in eliciting neurotoxic
effects, compared to pyrethroids
that lack this group, e.g., permethrin1,2
(see figures).
Chemical structure of lambda-cyhalothrin
(nasty alpha-cyano group below bracket)
Year Total Cases Associated with
Cases Pyrethrins/Pyrethroids
2000 200 35
2001 213 35
2002 194 31
Reported Pesticide-Related Illness
Associated with Pyrethrins/Pyrethroids,
Oregon
Chemical structure of permethrin
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