Menge T. B. B. Pharm; M.Sc (Pharmacology & Toxicology) UPDATES ON VACCINES ANTISNAKE VENOM

2 EPIDEMIOLOGY There are about 3000 species of snakes worldwide About 300 are of medical significance (i.e. venomous). Africa: 400 snake species most are relatively harmless. Approximately 100 species are medically important 30 species have been known to cause death.

3 EPIDEMIOLOGY It has been estimated that about 1,000,000 snake bites occur annually around the world, 40,000 of which result in deaths. In Africa: Nigeria, recent statistics show that 80% of all hospital admissions in some districts are due to snake bites, South Africa, hospital admissions per 100,000 persons are due to snake bites. In India 30,000 deaths occur annually due to snake bites. Malindi District Hospital records. Jan Aug Total No. of cases = 76 Treated with antivenom = 21 (but query on 3 cases) Fatalities = 1

Bioken, Watamu, Kenya Nov Nov Species DangerousPuff adders33 (2 fatal) Cobras17 (3 fatal) Black mamba5 (2 fatal) Green mamba6 Boomslang2 (1 fatal) Twig snake1 Venom in eyes11 Non - lethalMole vipers61 Green night adder2 Harmless-29 Others20 TOTAL Antivenom provided: 94

5 CLASSIFICATION OF SNAKES Medically important snakes can be divided into four families The Colubridae A very large group of snakes Non-venomous: sand snakes, egg eaters, mole snakes (blind snakes), house snakes and bush snakes. Medically significant snakes in this group are the Boomslang and the Vine (Twig) snake Their venom is haemotoxic. The Elapidae This group includes cobras, mambas and coral snakes. have large hollow fangs at the front of the jaw The venom of these snakes is neurotoxic Some cobra spit venom that is cytotoxic as well.

6 CLASSIFICATION OF SNAKES cont’ The Viperidae This group covers adders. They have hollow hinged fangs on the front of the jaw. The venom of this group is mostly cytotoxic; some species have neurotoxins. The Hydrophidae This group is composed of sea snakes. The venom is neurotoxic (and especially myotoxic), Most bites are not associated with serious envenomation because of their low venom output and short fangs.

7 VENOM COMPOSITION AND FUNCTION Snake venom is one of the most biochemically and pharmacologically complex toxins known. The most important venom components that cause serious clinical effects are pro-coagulant enzymes, cytolytic or necrotic toxins, haemolytic and myolytic phospholipases A 2, pre- and postsynaptic neurotoxins, and haemorrhagins.

8 VENOM COMPOSITION AND FUNCTION cont’ Snake venoms vary in their composition from species to species but also within a single species: (i) throughout the geographical distribution of that species, (ii) at different seasons of the year, (iii) as the snake grows older (ontogenic variation). This contributes to the enormous and f ascinating clinical diversity of snakebites

9 FUNCTION OF VENOM 1.To immobilize prey 2.To digest prey 3.To defend from harm

10 MECHANISM OF TOXICITY AND ROUTES OF POISONING The predominant mechanisms are; Cytotoxicity, Haemotoxicity, Neurotoxicity Myotoxicity. Venom excretion occurs primarily through the kidneys Some of the complications of envenomation are due to nephrotoxicity.

11 CLINICAL PATTERNS OF ENVENOMING Cytotoxic envenoming This is characterized by painful and progressive swelling with blood- stained tissue fluid leaking from the bite wound, hypovolaemic shock, blistering and bruising. The victim will complain of severe pain at the bite site and throughout the affected limb and painful and tender enlargement of lymph glands draining the bite site. resulting from cytolysis, ischaemia, blood extravasations and direct proteolytic activity, irreversible death of tissue may occur (necrosis/gangrene).

12 CYTOTOXIC symptoms

13 CYTOTOXIC EFFECTS

CLINICAL PATTERNS OF ENVENOMING Neurotoxic envenoming This is characterized by moderate or absent local swelling, progressive descending paralysis starting with drooping eyelids (ptosis) and paralysis of eye movements causing double vision. There may be painful and tender enlargement of lymph glands draining the bite site. The patient may vomit, the saliva may become profuse and stringy, and eventually there may be difficulties with swallowing and breathing. Species involved include black and green mambas and non- spitting cobras

15 CLINICAL PATTERNS OF ENVENOMING NEUROTOXICITY/MYOTOXICITY Neurotoxic venoms cause paralysis due to their effects on the nervous system. predominantly associated with Elapids and Hydrophids There are two types of neurotoxins: 1. Neurotoxins of hydrophids bind to post synaptic acetylcholine receptors resulting in paralysis. Respiratory paralysis is the primary cause of immediate death. 2. Neurotoxins of Elapids (cobras and mambas) have pre-synaptic action which inhibits the release of acetylcholine at myeneural junction.

16 Neurotoxic Effects

Neurotoxic effects Neurotoxicity from Berg adder Bitis atropos bite: The patient is contracting the (forehead) frontalis muscle in an attempt to open his eyes despite bilateral ptosis

Neurotoxicity Black mamba bite (Dendroaspis polylepis) showing ptosis, external ophthalmoplegia and facial paralysis recovering on the day after the bite

CLINICAL PATTERNS OF ENVENOMING Haemorrhagic envenoming This is characterized by bleeding from the gums; gastro-intestinal and genito-urinary tracts; recent and partly healed wounds. Species involved include saw-scaled/carpet vipers, puff adders, Gaboon and rhinoceros vipers, boomslang, and vine snakes.

Haemorrhagic envenoming Saw-scaled viper Echis ocellatus bite, showing bleeding from gingival sulci Saw-scaled viper Echis ocellatus bite, showing bleeding from gingival sulciand into floor of mouth

Haemorrhagic envenoming Saw-scaled viper Echis ocellatus bite, persistent profuse bleeding from multiple incisions at the site of bite inflicted 18 hours earlier Saw-scaled viper Echis ocellatus bite on foot 36 hours previously, persistent bleeding from incision made to attach black “snake stone”

22 CLINICAL PATTERNS OF ENVENOMING COAGULOPATHIES These are the most significant most unpredictable systemic manifestations Snakes from all families have been implicated Both anti coagulant and pro coagulant properties have been described

23 SYSTEMIC EFFECTS…. Haematotoxicity ANTICOAGULATION Results from: i) Interference of activation of clotting factors ii) Fibrinolytic and fibrinogenolytic activity. iii) Direct or indirect activation of plasminogen PRO-COAGULATION i) Direct action on phospholipids. ii) convert prothrombin to thrombin by cleaving appropriate peptides THROMBOCYTOPENIA Occurs with or without other coagulopathies and may result from intravascular clotting and consumption of platelets sequestration of platelets by the venom. The degree of thrombocytopenia may directly correlate with the severity of envenomation. DISSEMINATED INTRAVASCULAR COAGULATION Snake venom constituents may interact at various points of coagulation cascade to activate clotting factors or prothrombin directly. Significant amounts of thrombin like enzymes have also been identified

24 MANAGEMENT OF SNAKE BITES Snake venom is primarily intended to assist the snake in capturing prey digestion. Its effects are therefore far more effective in overcoming prey (e.g. rodents) than humans

ANTIVENOMS Antivenoms are the only effective specific treatments or antidotes for snakebite. They are raised in large domestic animals (usually horses, donkeys or sheep) by hyperimmunizing them against a single snake venom (producing a monovalent/monospecific antivenom) or against venoms of several species of snakes whose bites are common and frequently lead to severe envenoming in the geographical area where the particular antivenom is intended to be used (producing a polyvalent/polyspecific antivenom).

PRODUCTION OF ANTIVENOMS The venom of a single species of snake may vary in composition and antigenicity. As a result, pooled venom from many (20-50) individual specimens of each snake species should be used for antivenom production. These individuals should come from different parts of the geographical range and should include some younger (smaller) specimens to take these factors into account.

PRODUCTION OF ANTIVENOMS After animals have completed the immunization schedule, plasma is collected, preferably by plasmapheresis (so that the red blood cells can be returned to the donor animal) and is passed through several processes designed to produce either refined whole IgG antibodies or IgG antibody fragments such as F(ab')2 or Fab, which are free of other plasma proteins such as albumin, fragments such as Fc, aggregates (a major cause of antivenom reactions), pyrogens and microbes. It is then either lyophilized or stored as a liquid.

28 USE OF ANTIVENIN Antivenom neutralizes a fixed amount of venom. Since snakes inject the same amount of venom into adults and children, the same dose/volume of antivenom must be administered to children as to adults. Antivenom can be effective as long as venom is still active in the patient’s body causing symptoms of systemic envenoming. These may persist for several days or even weeks after the bite (e.g. incoagulable blood and bleeding after saw-scaled viper bites).

29 INDICATIONS FOR ANTIVENOM When used correctly, antivenin can effectively reverse systemic poisoning Antivenin should not be administered routinely in all cases of snake bites as it can cause severe acute reactions or fatality.

Indications for antivenom treatment after bites by African snakes Systemic envenoming 1. Neurotoxicity 2. Spontaneous systemic bleeding 3. Incoagulable blood (20MWBCT) 4. Cardiovascular abnormality: hypotension, shock, arrhythmia, abnormal electrocardiogram Local envenoming by species known to cause local necrosis* 1. Extensive swelling (involving more than half the bitten limb) 2. Rapidly progressive swelling 3. Bites on fingers and toes *Bitis, Echis, Cerastes, Macrovipera spp. and spitting cobras

Sources of antivenom There is great concern about the supply of antivenom for Africa. Several Indian producers, including Serum Institute of India (SII), Vins Bioproducts and Bharat Serum and Vaccines Ltd. (Asna Antivenom), export antivenoms to Africa. The clinical efficacy and safety of these antivenoms needs to be established. Confirm that the venoms used for their production are from African and not Asian snake species. Beware of misleading labelling implying that they have activity against African rather than Asian cobra and saw- scaled viper venoms

Resolutions from Dakar Conference (April 2011) 1. Snake and scorpion bites exist and need to be handled urgently and competently. 2.Need for Epidemiological Surveys. 3.Training of Health Workers (Inclusion in the Medical Curriculum). 4.Need for individual country capacity building. 5. Address the issue of FAKE and unsuitable antivenoms. 6. Joint procurement by countries in a given regional block from one regional producer to ensure price reduction. 7. Feedback meetings. 8. Intense Pharmacovigilance by relevant government authorities. 9. Funding for production or purchase of antivenoms through subsidies. 10. Collaboration with Traditional Healers and more research into their Herbal preparations