Toxicity of spiders

• Spiders use their venom toparalyze prey while they eat victim’s body fluids.
• The venom of spiders is acomplex mixture of neuroactive proteins and other chemicals.
• Toxic principle is p roteins which include protease, hyaluronidase, sphingomyelinase D and esterase.
• They have direct lytic effect on RBCs.
• The most venomous spiders in the world include Brown recluse spider, Hobo spider and Black widow spider.
• Some spider venoms can kill a mouse at a dose as low as 0.006 mg.
• The black widow species venom is made up of large proteins thought to affect the transmission of calcium ions of nervous system cells.
• The initial sting of the bite is followed by muscle cramps, sweating and possibly decreased blood pressure.
• There is no adequate treatment but the bite is seldom fatal.

Brown reculse spider , Hobo Spider  ,Black widow spider

Signs:

• The bite initially stings, then any one of the two forms may take place.

      o The cutaneous form begins as edema, progresses to an ulcerated wound.

      o The viscerocutaneous form, which is severe, produces hemolytic anemia, hemoglobinuria, icterus and hyperthermia.

• Ninety percent of the cases heal in 1 – 3 weeks. Some may need skin grafting.

 Mechanism :

Black widow:  Neurotoxin ( alpha-toxin) opens cation-selective channels and causes release of NTMs (acetylcholine and nor-ephinephrine) at NM junctions resulting in sustained muscle contractions.

Brown Recluse: Venom (proteases and phospholipases ) Sphinomyelinase D ( Potent demonecrotic toxintoxin), vasoconstrictive , thrombotic , haemolytic and necrotizing properties: commonly in face and forelegs.

• Unidentified venom component is cytotoxic to endothelial cells. This triggers intravascular coagulation and microthrombi formation within capillaries. Capillary occlusion, hemorrhage, and necrosis occur.
• Polymononuclear leukocytes and complements play important roles in potentiating the response to envenomation.

 Treatment:

• Steroids may be used to protect against systemic effects.
• Hemolytic anemia can be managed by use of fluids and bicarbonate to minimize hemoglobin deposition in renal tubules and by blood transfusion if anemia is severe enough to justify.
• Benzodiazepines relieve the symptoms of muscle rigidity and spasms.