Insecticides by virtue of their actions are toxic or lethal poisons and it is important that the manufacturers instructions are followed when using them. Furthermore most of these chemicals are absorbed through the skin and therefore become potentially hazardous to the operator. Take note of the detailed recommendations for use, particularly when handling the concentrate. Poisoning in pigs from insecticides may arise from incorrect application, pigs eating contaminated feed or accidental exposure. Insecticides are available as four different chemical types; carbamate, chlorinated hydrocarbons, pyrethrins and organophosphorus compounds (OPs).

All insecticides act on the nervous system and the general symptoms are similar. These include muscle tremors, hyperactivity and ultimately convulsions and death.

Carbamates

The most common of these are carbaril and methomyl which are often used to destroy worms and other insects. They act by blocking the transmission of nervous impulses at nerve muscle junctions and act in a similar manner to organophosphorus compounds. The antidote is atropine sulphate by injection and veterinary advice should be sought.

Chlorinated Hydrocarbons

These include aldrin, benzene hexachloride (BHC), lindane, chlordane, dieldrin, methoxychlor and toxaphene. They are highly effective against insects, but due to their side effects and toxicity to humans a number of them are now prohibited. BHC is still used in large animals and dogs and lindane is the best known proprietary name used in pigs. Most hydrocarbons are restricted to use on crops.

Clinical signs

All chlorinated hydrocarbons stimulate the central nervous system and signs include twitching of the muscles of the face, generalised muscle trembling and shivering, followed by fits coma and death. Some pigs may stand with heads pressed against the wall continually licking and chewing, others show loss of leg function (ataxia). Symptoms appear within 24 hours. The chlorinated hydrocarbons are absorbed by the body fat.

Diagnosis

Whilst the history assists in indicating the type of poison, a laboratory analysis of the brain, kidney, liver and fat tissues is required for confirmation. Pseudorabies and salt poisoning (water deprivation) can give similar signs.

Treatment and control

• There are no known antidotes but severe nervous signs can be controlled by barbiturates.
• Chlorinated hydrocarbons are excreted slowly from the body over a long period of time and suspected carcasses should be destroyed and not used as food.

Pyrethrins

Pyrethrins are naturally occurring substances found in the chrysanthemum plant and have a powerful knock down effect on insects. Synthetic compounds are manufactured that have similar effects. Toxicity is relatively low and it is unlikely to be seen unless massive doses are either absorbed through the skin or taken in by mouth. All compounds have an effect on the central nervous system causing excitation, convulsions, coma and death. Marked muscle trembling and paralysis may also be seen. Most pigs die from respiratory failure.

Treatment

• Pigs usually recover naturally and none is required. Activated charcoal or attapulgite given by stomach tube will reduce absorption.

Organophosphorus Compounds (OPS)

These groups of medicines are widely used as insecticides and pesticides. OPs and similar carbonate insecticides affect the chemical transmitters that control the nerve endings in muscles. The result is over activity causing muscles to go into a continual spasm.

Clinical signs

The continual and excessive stimulation of the muscles in acute poisoning causes excessive salivation, the passing of faeces and urine and a very stiff awkward gait. This may be followed by vomiting, diarrhoea and muscle tremors of the face and body. Death can be fairly rapid, within 1 to 4 hours and is caused by respiratory failure.

Diagnosis

A history of exposure to OPs gives rise to a suspicion and together with the clinical signs point to a diagnosis. The insecticides will be identified in the stomach or in the suspect material such as feed, but detection is unlikely in body tissues.

Treatment and control

• The antidote is atropine sulphate at 0.5mg/kg bodyweight by intramuscular injection. The response is usually seen within 3 to 5 minutes. Consult your veterinarian immediately.
• Move affected pigs to well bedded hospital pens.
• Give activated charcoal or attapulgite by mouth if possible to absorb the insecticide.