Since discontinuing exposure to fenthion, both individuals who were most severely affected have gradually improved. In very limited studies, neurotoxicity has been demonstrated in hens. In humans and in experimental animals, chronic exposure to organophosphates has been shown to cause various forms of nerve damage. The mixed sensory-motor neuropathy usually begins in the legs, first causing burning or tingling sensations, then weakness of the lower legs and feet. The thighs and arms also become involved.
Severe cases proceed to complete paralysis, impaired respiration, and death.
Confusion, headache, disorientation, and altered mental and emotional states have also been reported. The nerve damage of organophosphate-induced delayed neuropathy is usually permanent. Therefore, because of the above investigation, it would appear prudent to add fenthion to the list of agents thought capable of producing this syndrome. An estimated 30,000 veterinarians are in private practice in the United States, and they employ an additional 45,000 support personnel. It is not known how many use fenthion or other organophosphate insecticides in the manner described here.