Arsenic

The second most important pollutant for livestock.
Source:
v Inorganic form is used in paints.
v Pasture near smelters may be contaminated.
v Industrial effluents released into nearby water body.
v Insecticides (arsenic trioxide, lead arsenate).
v Herbicides (Sodium arsenite, lead arsenate)
v Rodenticides (arsenic trioxide) all can kill non-target species. (As arsenic is poisonous, all such products are being replaced with safer substances).
v Milk from affected dams poisons the calves.
v Arsenical preparations (Sodium thiacetarsamide for blood parasites, acetylarsan as a skin toxic) cause toxicity.
v Arsenic is used as a growth promoter in pigs and poultry. This form causes peripheral nerve demyelination that differs from inorganic arsenic toxicity.
Ex: - Roxarsone in poultry, Arsanilic acid in pigs.
Mechanism of action: Arsenic irrespective of route of absorption affects tissues rich in oxidative enzymes like intestine, liver and kidney. It crosses the placental barrier but does not seem to cross BBB. Excreted in faeces, bile, milk, saliva and sweat.
At cellular level Arsenic mainly causes relaxation of capillaries and increases capillary permeability. Increased capillary permeability causes oedema in gastric sub mucosa and overlying mucosa is disshelved.
At molecular level inhibits SH group of enzymes of lipoic acid, which is essential for glycolysis and citric acid cycle.
At local level Arsenic causes corrosion of the gastro intestinal mucosa.
Clinical Signs
Per acute cases – animal found dead or sudden and severe colic, staggering, collapse, paralysis and death are seen.
Acute cases - Severe colic, staggering, weakness, trembling, salivation, vomiting, thirst, projectile watery diarrhoea (rice water stools in humans), dysentery, rapid and weak pulse, prostration, normal or sub-normal temperature, death in 1-3 days.
Sub-acute cases - Same as acute toxicity except for partial paralysis of hind limbs, cold extremities, stupor, hematuria and convulsions.
Chronic cases - rare as the metalloid is excreted very fast. The symptoms could be wasting, poor condition, haemorrhagic dermatitis in buffaloes and humans as arsenic accumulates in skin, nails and hair. (tissues rich in thiol groups). Polyuria and anuria, haematuria, weak irregular pulse, brick red m.m.
Lesions are quite prominent except in per acute cases. Congestion and haemorrhages in abomasal or duodenal mucosa and sub mucosal oedema resulting in sloughing of the duodenal mucosa or perforation of gut wall. The intestinal contents are fluid; foul smelling, bloody with shreds of intestinal mucosa. Liver soft and yellow. Lungs oedematous and congested. Haemorahages on heart, peritoneum, kidneys and liver.
Swine: Inflamed and oedematous fauces, which extends to larynx and trachea causing asphyxia.
Poultry: Intense inflammation of proventriculus and gizzard, horny lining of gizzard may slough because of underlying gelatinous exudates. Duodenal mucosa is congested.
Differential Diagnosis: Pesticides, urea and lead show colic and other GI signs but watery diarrhoea with blood and mucous and foul smell, severity and the sudden onset, is only seen in arsenic.
Irritant plants, certain insects that harbour on plants too cause severe diarrhoea.
Rx
Arsenic binds to dithiol groups in the body; hence BAL (dimercaprol) is the drug of choice to revive inhibited enzyme activity. But caution is to be exercised and the treatment schedule be maintained strictly as BAL itself is toxic.
Large animals
1). BAL 3 mg/kg I/M 5% solution (in 10% of benzyl benzoate in peanut oil).
Repeat every 2 hours for first 2 days, every 6 hours 3rd day, 12 hours for the next 10 days till recovery.
2). Sodium thiosulfate
20-30 gm in 300 ml water orally. Also 8-10 gm. In 10-20% solution I/V.
Or
30-40 mg/kg. I/V 2-3 times a day until recovery.
60-80 mg/kg orally.
Small animals
1. BAL 2.5-5 mg/kg. 10% solution in arachis oil.
Dosage intervals same as for large animals. Use 5 mg/kg on the first day in acute cases only.
2. Sodium thiosulfate 5-6 gm in 60 ml water orally,
2-2.5 gm in 10-20 % solution I/V.
Symptomatic Therapy
I/V fluids and electrolytes. Antibiotics, analgesics and demulcents.
Mercury