SNAKE ENVENOMATION IN ANIMALS : IT’S DIAGNOSTIC AND THERAPEUTIC OUTLOOK
Rashmi Goswami (PhD scholar, Department of Veterinary Medicine, C.V.A.Sc. G.B.P.U.A&T Pantnagar), rashugoswami0911@gmail.com
Deeksha Bharti (PhD scholar, Department of Veterinary Medicine, C.V.A.Sc. G.B.P.U.A&T Pantnagar), deekshab34@gmail.com
Damini Arya (PhD scholar, Department of Veterinary Gynaecology and Obstetrics, C.V.A.Sc. G.B.P.U.A&T Pantnagar), aryadamini07@gmail.com
SUMMARY
Snake bite envenomation is a routinely occurring life threatening emergency condition in animals in tropical countries like India. So far 300 species of snakes have been identified in India, of which 60 are known to be poisonous. Among the poisonous species, the Indian cobra (N. naja), Indian common krait (B. caeruleus), Indian Russell’s viper (D. russelii russelii), and Indian Saw-scaled viper (E. carinatus), commonly known as “Big Four” venomous snakes of India, account for the majority of snakebite deaths and morbidity in India subcontinent; therefore, they are considered as category I medically significant snakes the bite by which deserves immediate medical attention. Other than these deadly species, Indian monocled cobra (N. kaouthia), Wall’s krait (B. walli), Sind krait (B. sindanus), King cobra (Ophiophagus hannah), and several species of Pit vipers (H. hypnale, Protobothrops spp.) are also found in different parts of India and cause fatalities. Management of snake envenomation is imperative to curb the deadly effects of snake venom in the bite victim. Accurate identification of bitten species of snake, quantitation of injected venom and venom antibodies in the body fluid of patients are crucial for successful antivenom therapy. Therefore, there is a pressing need for rapid diagnostic assays for the detection of snake envenomation to be used by the clinicians in the veterinary set-ups of the tropical countries. Snake venom detection test has to be very rapid, possibly within 30 min because the first 2 h post-bite is generally considered by the clinicians as the “Golden Period” for successful antivenom treatment. If antivenom can be administered within this period then the probability of saving the life of bite victim is significantly higher. In India for the treatment of snakebite, mainly polyvalent snake antiserum is used which has activity against four medically important snakes. Indian polyvalent antivenom is a sterile preparation of equine (horse) immunoglobulin fragments F(ab)2. But, there are several other poisonous snakes in India, against which this polyvalent antivenom will be ineffective. Thus, diagnosis of the species of the snake responsible for the bite is important for optimal clinical management and for the production of specific monovalent antivenom which is currently not available in India.
INTRODUCTION
Snake envenomation is a well-known life-threatening emergency condition in tropical countries like India. Envenomation incidents are classified as Category A of neglected tropical diseases by World Health Organization since June, 2017. In India nearly 300 species of snakes inhabit across the country out of which nearly 60 are known to be venomous. Among the venomous species, the Indian cobra (Naja naja) and Indian common krait (Bungarus caeruleus) (Elapidae family); Indian Russell’s viper (Daboia russeliirusselii)and Indian Saw-scaled viper (Echiscarinatus) (Viperidae family) are collectively known as “Big Four” venomous snakes of India which account for the majority of snakebite deaths and morbidity in Indian subcontinent; therefore, they are classified as category I medically significant snakes which requires prompt medical attention. Other than these deadly venomous species of snakes, Indian monocled cobra (Najakaouthia), Wall’s krait (Bungaruswalli), Sind krait (Bungarussindanus), King cobra (Ophiophagushannah) and several species of Pit vipers (Hypnalehypnale, Protobothrops spp.) are also found in different parts of India and responsible for causing fatalities. Majority of the snake bites are caused by the non-venomous snakes and the rest of the bites which are caused by the venomous snakes many of them may be dry bite (bite by a venomous snake in which no venom is released). Management of snake envenomation is crucial to supress the deadly effects of snake venom in the bite victim. Accurate identification of biting snake species, quantitation of injected venom and venom antibodies in the body fluid of patients are crucial for successful antivenom therapy.
CLINICAL FEATURE IN SNAKE ENVENOMATION CASES
Clinical signs of Neurotoxic Bite
Some common local signs include presence of indistinct fang marks, burning pain in the bite site, swelling at the bite site and discolouration. In case of Krait bite the bite may be occult which means painless with negligible swelling, but lymphangitis and enlargement of lymph node may be seen. Systemic signs include nausea, regurgitation, emesis, colic (pre-paralytic state) and ptosis, paraesthesia, drowsiness, convulsion, paralysis of facial muscles, generalized flaccid paralysis which may progress to respiratory muscles leading to respiratory failure (paralytic stage).
Clinical signs of Haemotoxic bite
Some common local signs include rapid swelling, blistering, discolouration, prolonged bleeding from fang marks and traumatic bleeding from recent wounds. Systemic signs include epistaxis, haematemesis, haematuria, haemorrhages, renal failure, rectal bleeding or melena and beeding into mucosae, skin and retina.
DIAGNOSIS
Diagnosis of snake envenomation/ snake venom is very important for the detection of the envenoming species so that serotherapy can be given to the snake bite patient as it is the only approved method to treat snakebite cases, thus to ensure that most specific antivenom is administered to the snake bite victim. It is seen in various studies that monovalent antivenoms, if available, have superior target specificity and venom clearance potential than polyvalent antivenoms which can cause various immunological complications making them the preferable choice in potentially fatal snake bite instances. It is need of hour to develop field applicable venom detection devices.
Some of the popular classical methods for detection of snake envenomation in animals include: description of the snake provided by the owner or witnesses, examination of the bite site/ fang marks, local symptoms of envenomation and various laboratory test results.
Clinical signs alone do not differentiate envenomation syndromes with other illnesses because of the overlap in clinical manifestations. Local knowledge of snake species and the relevant history, together with information gathered from laboratory testscan aid in diagnosis.
Fang marks: Depending on the species, two puncture wounds separated by a distance ranging from 8mm to 4cm. A single swipe may result in a single puncture, whereas multiple bites may result in numerous fang marks. Fang marks are typical for venomous snakes whereas in case of non-venomous snakes two carved rows of small teeth may be present with no specific fang marks as non-venomous snakes doesn’t have fangs.
Examination of local symptoms of envenomation like abdominal pain, weakness, bleeding, neurological symptoms etc.
20-min whole blood clotting test (20WBCT): It is a popular bed side test for initial assessment of snake envenomation. It is an indicator of the extent of snake envenoming by determining the clinically significant coagulopathy. In this test few milliliters of freshly sampled venous blood is placed in a clean and dry glass test tube and is left undisturbed for 20 minutes. The test tube is gently tilted to discover if the blood clots. If there is no formation of clots then it is positive. Snake bites by Viperidae family shows coagulopathy, therefore this test is applicable only against Viperidae bites.
MANAGEMENT OF SNAKE BITE
The management protocol of snake bite includes various step, namely:
- First aid treatment
First-aid treatment is carried out immediately or as soon as possible after the bite, before the patient reaches a veterinary hospital or a clinic. Recommended first aid methods include immobilizing the patient’s body by laying down and immobilize the bitten limb with a splint or sling. Any movement or muscular contraction, will increase absorption and spread of venom by squeezing veins and lymphatics.
The pressure-pad immobilization method is preferred and recommended which was developed in Australia in 1974 by Sutherland which includes immobilizing the bitten limb using crepe bandage and splint. The condoned methods include: application of tight tourniquet as it doesn’t stop venom from entering the bodybut may lead to local damage, gangrenous extremities, respiratory failure, embolism. Cutting and suction at the wound site should be avoided as it may lead to severe bleeding, infection and local necrosis. Vigorously washing the wound should be avoided as it increases lymphatic circulation and venom absorption.
- Antivenom therapy
First two hours post bite are considered the golden period for successful antivenom treatment. In India for the treatment of snakebite, mainly polyvalent snake antiserum is used which has activity against four medically important snakes i.e. Indian cobra, Indian common krait, Indian Russell’s viperand Indian Saw-scaled viperwhich are collectively responsible for the largest number of snakebite deaths in India. For this reason, these snakes are also called the “Big Four”.
Indian polyvalent antivenom is a sterile preparation of equine immunoglobulin fragments F(ab’)2. Each milliliter of reconstituted antivenom has the potency to neutralize the venom of the following snakes: 0.6 mg of dried Indian cobra venom, 0.6 mg of dried Russell’s viper venom 0.45 mg of dried saw-scaled viper venom and 0.45 mg of dried common krait venom. But, there are several other poisonous snakes in India, against which this polyvalent antivenom will be ineffective. Snake antivenom may be supplied in a liquid form or lyophilized (freeze-dried) form. The freeze-dried antivenom is reconstituted in 10 ml of sterile water for injection. It can be administered by slow intravenous (IV) injection (2 ml/min) or by infusion after dilution in isotonic saline or glucose over a period of 1 hour with close monitoring
Dosage of antivenin to be administered may vary from 1 vial to upto 10 vials of reconstituted antivenom depending on the severity of the clinical symptoms shown by the patients or amount of venom injected into the body of animal. But the animals receiving greater amount of antivenins were more likely to die due to secondary complications.
- Management of pain and inflammation
- Corticosteroids: The use of steroids in snake bite cases is still debated; while some say they have no specific role but their administration does provide some help to the patient. Steriods reduce the inflammatory process and the use of corticosteroid prior to the polyvalent snake antivenom also reduces the chances of serum sickness.
- Opioid analgesics like tramadol and fentanyl can be used for pain management.
- Neostigmine test
Neostigmine is an anticholinesterase that prolongs the life of acetylcholine and can therefore reverse respiratory failure and neurotoxic symptoms. It is particularly effective for post-synaptic neurotoxins such as those of the Cobra. In the case of neurotoxic envenomation neostigmine test can be done. The neostigmine dose is 0.05 mg/kg IV and atropine @ 0.04 mg/kg may be given by continuous infusion. The patient should be closely observed for 1 hour to determine if the neostigmine is effective. Check for regaining of normal breathing pattern and disappearance of ptosis.
- Reaction to anti snake venom
Since it is an animal protein, it may cause immediate or delayed immune response which may be type III and Ig E type of hypersensitivity reaction.
Immediate type of reactions: They occur within 10-180 minutes of antivenom administration. There may be signs such as fever, urticaria, pruritus, vomiting, bradycardia, hypotension, respiratory distress. In such cases Antivenin must be immediately withdrawn and adrenalin 1:1000, antihistamines and corticosteroids are recommended to be administered. Delayed type of reactions: It includes serum sickness which may occur 1 – 12 days after the snake bite and include symptoms such as urticaria, arthralgia, myalgia, fever, lethargy, lymphadenopathy and proteinuria. In such cases antihistamines and corticosteroids can be administered.
- Management of complications
- Hypotension and shock: For this a selective vasoconstrictor such as Dopamine can be given as constant rate infusion.
- Coagulopathy:Antivenom is effective for neutralization of unbound procoagulant toxins but once procoagulant venom components are bound, antivenom is not able to remove them from the prothrombinase complex that leads to venom induced consumptive coagulopathy. Due to the time lag required for resynthesis of clotting factors and increased levels of circulating fibrin degradation products, clotting times take many hours to return to normal in animals that have suffered from venom-induced consumption coagulopathy.
- Myopathy: IV fluid therapy until CK concentration starts to come down and their urine normalizes in colour. Urine output should be maintained at more than 1 mL/kg/h and renal function should be monitored regularly.
- Renal failure: Haemodialysis or peritoneal dialysis can be performed for management of renal impairment.
- Persistent bleeding: There should be repeated administration of anti-snake venom at an interval of 1 hour if the bleeding doesn’t stop. Blood transfusion may be performed in case of severe bleedings. Ethamsylate can be administered although its administration in contraindicated in some texts.
- Sepsis: As the contaminated snake mouth may harbour many bacteria and may introduce tetanus spores into animal body through bite thus antibiotics such as ampicillin, amoxicillin, enrofloxacin, cephalosporins etc. and tetanus toxoid administration provides protection against it.
Drugs that are contraindicated in cases of snake envenomation
Heparin, botropase, antihistaminics and NSAID’s are contraindicated as they may cause complications such as bleeding, prolongation of coagulation, impair platelet aggregation, nephropathy and gastrointestinal ulcers.
CONCLUSION
Snake-bites are well-known veterinary emergencies in many parts of the world, especially in rural areas of India. Majority (80%) of the snake bites are caused by non-venomous snakes and out of these 50% are dry bites. Due to lack of snake venom detection kit in developing countries, the clinicians are still dependent on their skill, experience to deal with snakebite, and of course, the classical methods of detection of venomous snakebite. Most of the traditional first-aid methods should be discouraged as they do more harm than good. Any interference with the bite wound should be avoided and immediate veterinary help should be sought. Anti-venom treatment is the only specific antidote to snake venom. Diagnosis of the species of the snake responsible for the bite is important for optimal clinical management. Community education about venomous snakes and snake-bite is, therefore, strongly recommended as the method most likely to succeed in preventing bites.
There is a need to standardize the treatment protocol and training about the snake bites cases should be provided to the veterinarian. There is need to develop early diagnostic tests, increase the production of antisnake venom, development of monovalent antisnake venom, public awareness campaign about the snake bites and identification of species of snakes.
https://www.pashudhanpraharee.com/treatment-of-snakebite-cases-in-cattle-in-india/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4052258/
