Lead

Source:-

• Licking of lead paint containing objects.
• Ingestion of lead pencil or lead batteries.
• Lead contaminated pastureland.
• Use of lead containing insecticide.(Lead arsenate)
• Water supply through lead pipe . White lead and red lead are used by plumbers, used in the manufacture of linoleum, golf-balls, roofing felt etc.
• Acidic food kept in lead coated vessels.
• Lead acetate (sugar of lead) is an important soluble salt of lead used in the preparation of white lotion.
• Petrol contains tetraethyl lead as contaminant.

Factors affecting the lead toxicity:-

• Age:- Young animals are considerably more sensitively than older one.
• Species variation;- Goat, swine, and chickens are more resistant than others.
• General body condition:- Poorly nourished, debilitated and parasitized animals are more susceptible.
• Pregnancy:- Pregnancy is more susceptible than non pregnant one.
• Forms of lead:- Soluble salts are readily absorbed.
• Presence of ingesta in intestine or stomach may delay or reduce the rate of absorption.
• Previous exposure may reduce or delay the toxic effect.
• Intravenous route of administration is more effective than others.

Absorption and Fate :Lead almost always enters the body through mouth.  Only a small portion of lead is absorbed and over 98% is excreted in faeces. lead binds to haemoglobin in the RBCs and serum albumin. Only 1% of absorbed lead is in free form. Absorbed lead is stored mainly in the bones after redistribution and its subsequent mobilization is similar to that of calcium. • Lead crosses both the blood brain barrier and the placental barrier.

Mechanism of action:-

• Lead particularly inhibits the conversion of heme precursor D-amino lavaevulinic acid resulting the inhibition of heme synthesis. Due to the inhibition of heme synthesis anemia starts to develop.
• Interfere with GABA & dopamine uptake which ultimately inhibits neurotransmission.

Acute Symptoms :-

Gastrointestinal disorders:- Diarrhoea, abdominal pain, salivation, vomition.

Nervous sign:- Bellowing, jaw champing, rolling of eyes, twitching of ears, aimless jumping or jumping over the wall or any objects.

 Head is pushed against the wall or objects; excitement, blindness, staggering gait,  muscular spasm, titanic convulsion and death

Chronic Symptoms :-

• Gastro-intestinal disorders:- Anorexia, lack of appetite, black color faeces, transient constipation followed by diarrhoea, abdominal pain (lead pain or lead colic).
• Neuro-muscular symptoms:-
  • Wrist drop
  • Foot drop.
  • In co-ordination.
  • Muscular weakness.
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• CNS symptoms:-
  • Disturbance of vision.
  • Vertigo/feeling dizziness.
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 PM lesions:

• No observable gross lesions.
• Ingested lead containing material may be found in the stomach and intestines.
• There may be gastritis, hyperemia, petichae on various organs and brain edema.
• In horses there may be aspiration pneumonia secondary to laryngeal paralysis.

Diagnosis:

Diagnosis is based on history, clinical symptoms, post mortem lesions and presence of a source of lead and the lead content of the blood and faeces in a living animal.

• Measurement of ALA dehyratase in blood.
• Urine ALA is increased. Level of lead >4 ppm in the liver, 0.2 ppm in whole blood δ indicates lead poisoning.

Treatment:-

• Use of atropine sulphate during salivation.
• Use of sedatives to release from excitement and convulsion.
• Use of dextrose in case of dehydration.
• Di sodium calcium edentate can be used as an antidote for lead poisoning. This chelates lead to make it non-toxic and the complex lead EDTA so formed is rapidly excreted. This itself is nephrotoxic. This drug is administered in cattle and horses 110 mg/kg i/v or s/c two doses at 6 hours interval every other day for three treatments. • In dogs 110 mg/kg subcutaneously as a 1% solution diluted with 0.9% saline or dextrose divided into four doses every other day for three treatments is recommended.
• Intestinal lavage or a cathartic can be administered to eliminate the unabsorbed lead.
• Thiamine 2 – 4 mg/kg subcutaneously in cattle with sodium calcium edentate is found to be useful.
• BAL increases lead excretion in urine and removes lead from the parenchymatous organs. •