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Insecticide Poisoning

By

Ramesh C. Gupta

, DVM, MVSc, PhD, DABT, FACT, FACN, FATS, Toxicology Department, Breathitt Veterinary Center, Murray State University

Last full review/revision Oct 2020 | Content last modified Oct 2020

All pesticide labels include directions for how to properly use the product. Because regulations (and labels) change over time, it is important that label directions are always followed. Labels must also carry warnings against use on unapproved species or under untested circumstances.

Organic pesticides may have harmful effects on domestic species, fish, and wildlife. In no event should amounts greater than those specifically recommended be used, and maximal precautions should be taken to prevent drift or drainage to adjoining fields, pastures, ponds, streams, or other premises outside the treatment area.

Products stored under temperature extremes or held in partially full containers for long periods may deteriorate. Storing a chemical in anything but the original container is hazardous because its identification and label directions are then lost. Accidental contact with animals or people can then have disastrous consequences. Mixing compounds or using them in unapproved combinations can be very dangerous.

Insecticides are any substance or a mixture of substances intended to prevent, destroy, repel, or mitigate insects. Acaricides are substances that can kill ticks and mites. Poisoning by organic insecticides and acaricides may be caused by direct application, by eating feed or forage that has been treated to control plant pests, or by accidental exposure.

Carbamate Insecticides

Carbamate insecticides include aldicarb, carbaryl, carbofuran, methomyl, and propoxur. These compounds may be used more commonly because they are considered safer than organophosphates. Signs of toxicity include excessive drooling, abdominal cramping, vomiting, diarrhea, sweating, difficulty breathing, a bluish tinge to skin and mucous membranes, small pupils, muscle spasms, convulsions, buildup of fluid in the lungs, and death. Diagnosis usually depends on history of exposure to a particular carbamate and response to atropine treatment. When a history of exposure cannot be confirmed, but signs suggest carbamate or organophosphate poisoning, blood tests may help to confirm the diagnosis.

Treatment of carbamate poisoning is similar to that of organophosphate poisoning in that atropine injections are useful.

Chlorinated Hydrocarbon Compounds

Use of these agents has been drastically reduced because of issues with tissue residues and longterm toxicity. Compounds that have been used in the past but are no longer registered in the US include aldrin, DDT, dieldrin, chlordane, heptachlor, and toxaphene. Only lindane (a benzene hexachloride) and methoxychlor are approved for use on or around livestock.

Benzene hexachloride was a useful insecticide for livestock and dogs but is highly toxic to cats in the concentrations necessary for parasite control. Only lindane is a useful insecticidal agent and it should be used in preference to other benzene hexachlorides (which are stored for excessively long periods in body tissues). Extremely thin or nursing animals are more susceptible to poisoning by lindane and should be treated with extreme caution.

Methoxychlor is one of the safest chlorinated hydrocarbon insecticides and one of the few registered for use in the US. Commercial products are available for garden, orchard, and field crops and for horses and ponies.

The chlorinated hydrocarbon insecticides are general central nervous system stimulants. The most obvious signs of poisoning are tremors, convulsions, and high fever. Affected animals initially become more alert or apprehensive. Muscle spasms begin in the face and gradually spread to involve the whole body. Convulsions may last from a few seconds to several hours and lead to coma. Animals may assume abnormal postures, such as resting the chest on the ground while remaining upright in the rear or keeping the head down between the forelegs, and abnormal behaviors such as “head pressing” against a wall or fence or making continual chewing movements. Occasionally, an animal attacks other animals, people, or moving objects. Vocalization is common. Some animals are depressed, almost oblivious to their surroundings, and do not eat or drink. Usually, there is a large flow of thick saliva and an inability to control urination. Some animals have only a single convulsion and die, while others have numerous convulsions but then recover.

Chemical analysis of brain, liver, kidney, fat, and stomach contents is necessary to confirm the poisoning in dead animals. The suspected source, if it can be identified, should also be analyzed. Blood and urine from live animals may also be analyzed.

There are no known specific antidotes. When exposure is by spraying, dipping, or dusting, a thorough and gentle bath (no brushes), using detergents and large quantities of cool water is recommended. If the poison has been eaten, flushing the stomach is recommended. Giving digestible oils such as corn oil is not recommended, although heavy-grade mineral oil plus a medication that causes emptying of the bowels can speed removal of the chemical from the intestine. Activated charcoal can help prevent absorption from the gastrointestinal tract. If the animal is excited, a sedative or anti-convulsant is recommended. Any stress, such as noise or handling, should be stopped if possible. If the animal is depressed, dehydrated, and not eating, treatment should be directed toward rehydration and nourishment either intravenously or by stomach tube.

Insecticides Derived from Plants

Most insecticides derived from plants (such as rotenone and pyrethrum) are generally considered safe for use on animals. Nicotine in the form of nicotine sulfate is an exception. Unless nicotine is used carefully, poisoning may result. Pets are exposed to tobacco by ingesting commercial tobacco products, wheres livestock may consume discarded tobacco stalks or hay contaminated with tobacco plant drippings in the barn. Affected animals show tremors, lack of coordination, difficulty breathing, paralysis, coma, and death. Treatment consists of removing the material by flushing the stomach with tannic acid, administering activated charcoal, providing artificial respiration, and treating for cardiac arrest and shock. Mildly affected animals recover rapidly without treatment in a few hours.

Pyrethrins and Pyrethroids

Pyrethrins, a group of naturally occurring compounds, are the active insecticidal ingredients of pyrethrum. Pyrethrum is extracted from chrysanthemums and has been an effective insecticide for many years. Unfortunately, certain substances, added to pyrethrum to increase its stability and effectiveness, also increase its toxicity to mammals. The pyrethroids are synthetic derivatives of natural pyrethrins that are generally more effective and less toxic to mammals but may accumulate in the environment and have detrimental effects.

Signs of toxicity may begin within a few hours of exposure. Diagnosis is based on clinical signs, history of exposure, and finding insecticide residues in body tissues and fluids. Signs are related to the nervous system and may include excessive drooling, mild tremors, incoordination, and excitability or depression. More severely affected animals can have severe tremors, seizures, and death caused by respiratory failure.

Generally, treatment is not required if a dilute pyrethrin or pyrethroid preparation has been consumed. Inducing vomiting is not usually recommended. Your veterinarian may use activated charcoal and a medication that causes emptying of the bowels. Because vegetable oils and fats promote the intestinal absorption of pyrethrum, they should be avoided. If skin exposure occurs, the animal should be bathed gently with a mild detergent and cool water. Further treatment consists of supportive care, including medications to control seizures.

d-Limonene

Extracted from citrus rind, d-limonene is used for flea control on cats and for other insect pests. At recommended dosages, the solution containing d-limonene appears to be safe. Increasing the concentration 5 to 10 times in sprays or dips increases the severity of toxic signs. These signs can include drooling, tremors, lack of coordination, and dangerously low body temperature. In dogs, ingestion of d‑limonene by mouth causes vomiting.

Organophosphates

Organophosphates have replaced the banned organochlorine compounds and leave little tissue or environmental residue. Many organophosphates have been developed for plant and animal protection. However, organophosphates vary greatly in toxicity and are a major cause of animal poisoning.

Organophosphate insecticides include azinphos-methyl (or -ethyl), chlorpyrifos, coumaphos, diazinon, dichlorvos, dimethoate, disulfoton, fenthion, malathion, methyl parathion, naled, oxydemeton-methyl, parathion, phorate, phosmet, temephos, tetrachlorvinphos (low toxicity in dogs), and trichlorfon.

Flea collars containing dichlorvos may cause skin reactions in some pets. Malathion is one of the safest organophosphates because it is highly selective (high toxicity to insects but low to mammals). Parathion (diethyl parathion) is widely used for control of plant pests such as insects (including mosquitoes) in orchards and on market garden crops. Normally, because so little is used per acre, parathion presents no hazard. However, because of its potency, care should be taken to prevent accidental exposure.

Crotoxyphos is of rather low toxicity as used to control external parasites of cattle and pigs, although Brahman cattle are more susceptible than European breeds. Ethyl 4-nitrophenyl phenylphosphonothioate (EPN) is related to parathion and is about one-half as toxic when applied externally; when ingested by mouth, it is about equally toxic. Tetraethyl pyrophosphate (TEPP) is one of the most severely toxic insecticides. It is not used on animals, but accidental exposure occurs occasionally, and deaths can occur within 40 minutes.

In organophosphate poisoning, certain nerve cells are overstimulated. Signs usually begin within hours after exposure but may be delayed for more than 2 days. Initial signs include excessive drooling, small pupils, frequent urination, diarrhea, vomiting, colic, and difficulty breathing, followed by muscle spasms and weakness, and finally nervousness, lack of coordination, apprehension, and seizures. Severity and course of poisoning is influenced mainly by the dosage and route of exposure. In sudden and severe poisoning, the primary signs may be breathing distress and collapse followed by death.

Blood tests can be an important diagnostic aid. Unfortunately, the results of the test do not necessarily correlate with the severity of the poisoning. Analyses performed after exposure may be negative because organophosphates do not remain long in tissues.

Specific treatment consists of atropine and the antidote pralidoxime (also called 2‑PAM) to reverse signs of organophosphate poisoning. Removing the poison from the animal should also be attempted. If the organophosphate exposure was on the skin, the animal should be gently washed with detergent and water. Vomiting should be induced if the animal ingested the organophosphate less than 2 hours previously. Vomiting should not be induced if the animal is depressed. Mineral oil given by mouth decreases absorption from the gastrointestinal tract. Activated charcoal is also helpful. Artificial respiration or administration of oxygen may be required. Tranquilizers should not be given.

Pesticide Potentiating Agents

Piperonyl butoxide is used in many pesticide formulations including pyrethrins, pyrethroids, and d-limonene to make them more effective. It decreases breakdown of the chemical in the animal or insect’s body. This makes the pesticide more toxic to the insect—but also to the host animal. Animals that are debilitated or cannot metabolize drugs well become more susceptible to the pesticide. Species affected include cats, dogs, rats, and people. Cimetidine (a drug used to reduce stomach acid) and chloramphenicol (an antibiotic) have the same potentiating effect.

Solvents and Emulsifiers

Solvents and emulsifiers are required to make most liquid insecticides. Usually they have low toxicity, but they must be considered as possible causes of poisoning. Treatment is the same as for petroleum product poisoning.

The main signs of acetone poisoning are gastrointestinal irritation, unconsciousness, and kidney and liver damage. Treatment consists of flushing the stomach, providing supplemental oxygen, and feeding a low-fat diet. Additional supportive treatment can lessen signs.

Signs of poisoning by isopropyl alcohol include gastrointestinal pain, cramps, vomiting, diarrhea, dehydration, dizziness, stupor, coma, and death. The liver and kidneys are affected but may recover. Pneumonia may develop. Vomiting can be induced or the stomach flushed by your veterinarian, followed by providing respiratory support, and giving milk by mouth.

Methanol poisoning causes vomiting, abdominal pain, heightened reflexes, muscle spasms causing backward arching of the neck and spine, convulsions, fixed pupils, and inflammation of nerves. Large overdoses can lead to blindness. Treatment should include medications that cause vomiting followed by flushing of the stomach, saline laxatives, oxygen treatment, intravenous sodium bicarbonate, and pain relievers. Intensive and prolonged treatment is required, and the prognosis is poor.

Sulfur and lime-sulfur are 2 of the oldest insecticides. Elemental sulfur has practically no toxicity. Lime-sulfur may cause irritation, discomfort, or blistering. Death is rare. Treatment consists of removing residual material, applying bland protective ointments, and providing supportive measures.

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