1 - Envenomation - Snakes - Basics.pdf

21/09/2022 Envenomation – Snakes Basics •1 Locate & Review • The lymphatic system & its function • Review the nervous system, especially the neuromuscular junction • Review the clotting cascade • Review relevant articles •2 Snake Bites in Australia • 500‐3000 bites per year •  1:10 require ant...

21/09/2022 Envenomation – Snakes Basics •1 Locate & Review • The lymphatic system & its function • Review the nervous system, especially the neuromuscular junction • Review the clotting cascade • Review relevant articles •2 Snake Bites in Australia • 500‐3000 bites per year •  1:10 require antivenom •  2 fatalities per year (0.01/100,000 population) compared with 50,000‐100,000 world wide • 25‐35,000 Asia • 3‐4,000 South America •3 1 21/09/2022 Elapid vs Colubrids vs Vipers • The Elapid family are front fanged snakes and this family includes the Australian dangerous land snakes as well as the Cobras found overseas • The colubrids are a group of solid‐toothed and rear‐ fanged snakes that lack a sophisticated venom‐delivery system. Only ten species occur in Australia (all of which are found in Queensland) but this is the world’s most diverse and widespread snake family. • All viperids have a pair of relatively long solenoglyphous (hollow) fangs that are used to inject venom from glands located towards the rear of the upper jaws, just behind the eyes. There are none in Australia •4 Colubrids Snakes Elapids Vipers •5 How Venomous? • Determination of ‘lethality’ : LD50 • Dose of venom that kills 50% of mice over a 24/48h period venom •6 2 21/09/2022 Venomous Snakes in Australia • Eastern brown snake (Pseudonaja textilis), also known as the common brown snake. • Western brown snake (Pseudonaja nuchalis), also known as gwardar. • Mainland tiger snake (Notechis scutatus), also known as the common tiger snake • Inland taipan (Oxyuranus microlepidotus), also known as fierce snake or small‐scaled snake. • Coastal taipan (Oxyuranus scutellatus) • Mulga snake (Pseudechis australis), also known as King brown snake • Lowlands copperhead (Austrelaps superbus), also known as the common copperhead • Small‐eyed snake (Rhinoplocephalus nigrescens), also known as the eastern small‐eyed snake •7 Snake Venoms may Contain: • Venoms contain more than 20 different compounds, mostly proteins and polypeptides. – – – – – – – – Pain‐producing agents Enzymes Nephrotoxins Cardiotoxins Myotoxins Neurotoxins (pre‐ & postsynaptic) Haemotoxins Coagulopathy agents (anti or pro) •8 Myotoxins • Direct effect on muscle • Pain on contracting muscles against resistance • Muscle weakness (may mimic paralytic signs) • Dark urine which tests positive for blood (myoglobin) •9 3 21/09/2022 Shows necrotic tissue damage rather than, myotoxicity… but demonstrates how severe forms of tissue damage can be •10 Coagulation • May have either pro or anticoagulant activity • Ultimately both lead to reduced ability to clot •11 Defibrination Coagulopathy • Venom induced consumptive coagulopathy (VICC) Coagulation factors are activated by specific toxins Factors are exhausted Reduced ability to form clots Risk of Haemorrhage •12 4 21/09/2022 Neurotoxins Presynaptic (b-neurotoxins): elapids, vipers & crotalids ACh, CCh - response Postsynaptic ACh, CCh - No response Potassium (KCl) Should be same as initial unless muscle damage •13 Haemotoxins • Are toxins that destroy red blood cells (that is, cause haemolysis), disrupt blood clotting, and/or cause organ degeneration and generalized tissue damage. • Venoms contain enzymes and other proteins that are haemotoxic • The process by which a haemotoxin causes death is much slower than that of a neurotoxin – may be after 1 hour or days later. • A bleeding tendency occurs starting with all the mucous membranes and progress to nose bleeds, bruises, blood is found in the urine and vomiting blood. •14 Nephrotoxins • While there are no isolated nephrotoxins in any Australian snake venom, they are known from some exotic snake venoms and kidney damage is not rare in Australian snakebite. • The mechanisms are unclear, but may include both direct toxic effects on the kidney and secondary damage as a result of hypotension, myolysis or coagulopathy. • Kidney damage may develop early, is uncommon in children, but much more likely if the patient has consumed significant amounts of alcohol prior to the bite. • Key early signs include; oliguria or anuria. • Key species – any snake but particularly brown snakes, tiger snakes, mulga snakes, taipans, rough scaled snake. • Value of antivenom treatment: uncertain. •15 5 21/09/2022 Cardiotoxins • Toxins that affect the functioning of the heart. • Causes heart electrophysiology dysfunction or muscle damage. • The heart becomes weaker and is not as efficient in pumping and therefore circulating blood. • Results in heart failure •16 Any Questions •17 6