Poisonous snakes andenvenomation inSri LankaDr. Devika IddawelaDepartment of ParasitologyFaculty of MedicinePeradeniya.Y2S2 – 09/10 batch
Objectivesto be able to- State how snakes are classified into poisonous and non-poisonous Name the poisonous snakes found in Sri Lanka Name the common non-poisonous snakes in Sri Lanka Recognize these if shown a specimen/image(to be achieved in the demonstration) State the major effects of snake venom in the differentgroups of poisonous snakes in Sri Lanka State the principles underlying the treatment andmanagement of snake bites State how snake bites can be prevented.
SNAKESFree living organismsLimbless, scaly, reptilesMedically important asbites of some cause systemic poisoning
Medically important snakes of Sri LankaSnakes are elongate, limblessreptiles with bodies covered inscalesSea snakes13 species inSri LankaLand snakes83 species inSri Lanka
SNAKE FAUNA OF SRI LANKA SEA SNAKES LAND SNAKES-Elapids-Viperids-Colubrids- ground, burrowing,arboreal,aquatic- Earth snakes (primitive)- Wart snakes (aquatic)- Constrictors (crush prey)
POISONOUS OR VENOMOUS SNAKESCephalic gland (below & behind the eye)secretes venom (poison) which is ejectedthrough a specialised tooth- the FANG
Some colubrids have small venomgland located posterior with posteriorfangs-Duvenoy’s gland
Depending on venom toxicity to humans,snakes are grouped as HIGHLY (DEADLY) venomous MODERATELY venomous MILDLY venomous
WHO , 2010Medically important snakes : twocategoriesCategory 1 – Highest medical importanceHighly venomous snakes which arecommon or widespread, cause numeroussnake bitesResulting high level of morbidity andmortality
Include: Common Krait,Ceylon cobra, Russell’s viperHump nosed viper( Hypanalehypanale)Category 2: secondary medical importanceHighly venomous snakes capable of causingmorbidity, disability and death BUT for whichexact clinical and epidemiological data arelacking or less frequently implicated becauseof their behaviour or habitat preferences
Identification of Poisonous Snakesof Sri Lanka: on their habitat SEA SNAKES LAND SNAKES
SEA SNAKES13 species in the Indian oceancases of poisoning reported in SLmost common sp. PalamisFeatures: flat, rudder –like taillaterally compressedtailbody
SCALATION- arrangement of scalesHead scales if enlarged are called SHEILDScostalssub caudalsImportant in identificationvertebralsventrals
Scalation important indifferentiating venomous from nonvenomous• head scales,• ventrals,• vertebrals and• subcaudals
kraits• The head scales and vertebralsare enlarged.• The subcaudals are single andNOT dividedvipers (except in hump nosed viper)head scales are small and equal insize.
Body form and shape: Of thepoisonous snakes elapids andvipers can be differentiated onthe shape and formElapids VipersForm:slender Thick&stoutTail: Long ShortHead: spatula shaped TriangularNeck Not distinct Distinct
ELAPIDScharacteristics:Slender body; long tail; head spatulashaped; no distinct neckScalation: head scales enlargedVertebrals enlarged, sub caudals single Ceylon Cobra Kraits- Common krait, Ceylon krait Ceylon Coral snake
CEYLON COBRANaja naja najaOnly snake in with a hood (loose foldof skin behind head)Hood has characteristic markingsdorsal‘spectacle’variations seenventral2 dark spots
common around human habitationslargest elapid in SL average length 1200 mslow moving, usually not aggressiveunlessprovoked. If provoked assumescharacteristic postureyoung cobras very aggressiveand equally poisonouscolour varies
Defense posture: raises forebody(usually 1/3) remains 5-10 minwith hood expanded and hissstrikes with raised part of the bodycobras are shy, run and hidewhen people are around.
Many snake charmers remove the fangs or thevenom sacs from their snakes, because it is toodangerous. This practice is illegal, and isconsidered inhumane to the snake.
CEYLON KRAITBangarus ceylanicussingle bands all round bellyKraits- dark banded snakesNocturnalFound in low countrywet zoneFully grown adult –2-3 feet
COMMON KRAIT -Indian kraitBangarus caeruleusnarrow double bands, clear bellyactive at night and relativelypassive during the day.
Kraits- distributionCommon krait : dry & intermediate zonesCeylon krait : Wet & parts of intermediate zoneEnters houses, usually in the night, found hidingunder furniture,mats etc.Human bites caused due to accidentalcrushing/tramplinglittle or no pain at the site of akrait bite
contain neurotoxic venomthat is 16 times more potentthan cobra venomextremely powerful andquickly induces muscleparalysis
Ceylon Coral Snake(slender coral snake)small snake , highly poisonousbut rare,Habitat: under fallen leaves,logsbites not reported in Sri Lanka
VIPERS TRUE VIPERS PIT VIPERS- loreal pit (thermoreceptor)between eye & nostrilShort tail; stout bodyHead- triangular, distinct neckHead scales usually not enlargedviviparousIt is sensitive to IR (Infrared)radiation, thus allows the snake tolocate warm-blooded prey.
VipersTrue vipers Pit vipersBased on the presence or absence of a loreal pit, one onEach side of the head between the nostril and the eyeTVRussell’s viperSaw-scaled viperPVGreen pit viperHump-nosed viper
widely distributedin all climatic zonesthick snake averagelength of 900 mmsluggish, nocturnalAttacks readily in defensehisses loudly, strikesfrom a coiled position,hurling whole body
Saw scaled viper- Echis carinatusBird’s foot or dagger marking on headScales saw- like edgeHabitat: under sand, coastal areasGrating noise due to scales rubbingagainst each otherSmallest viper –200 mmActive, very aggressiveConfined to Jaffnapeninsula
PIT VIPERSGREEN PIT VIPERm<d fm<.darboreal, common in highland areasmedium/large snake, 750- 1300 mm
Stout snakearboreal,nocturnalsluggishwell camouflagedwith the surroundingsGrouped as highlyVenomous
HUMP NOSED VIPERcommon, Viperine head with enlarged headScales,snout acutelypointed & upturned- 300 mmHypnale hypnale; H h nepal+klgQjd" fmdf<dka f;,siaidHuman bites from thissnake is common andfatal bites have beenreported in Sri Lanka.
COLUBRIDS Non poisonous-majority Mildly poisonous(11 species)Duvernoy’s gland & rear,grooved fangsvertebrals NOT enlarged,sub caudals -biserial (twinned)comprise the majority of snakesArboreal,aquatic,land, burrowing
CAT SNAKE (Mapila )Pupil slit vertical, head triangular shapemildly poisonous, several colour variationsno human fatalities causedWrongly identified asa hump nosed viperbut can bedifferentiated by theabsence of a loreal pitand humped snout
Polmal karawala- flying snaketree snakeCommon in dry zone, can glide, back -fangedWATER SNAKE- dog-faced water snakeosh nßhd
CONSTRICTORSKills pray by coiling aroundpray and constrictingPython, Sand boaQuadrate markings on bodymsUQrd" je,s msUQrd
Poison (venom)composition complexMYOTOXIN-myalgia, myoglobinuriaNEUROTOXIN- ptosis, dysarthria,alteration inlevel of conciousness, respiratory failureVASCULOTOXIN- non clotting of bloodhaemotytic, haemorrhagicintravascular thrombosis
Sea snakes: neurotoxin+ myotoxinnecrosis of muscle Loss of myoglobinmuscle enzymespotassiummyalgia, myoglobinuriaKraits: post synaptic + pre synaptic toxinminimal local reaction,muscle paralysismortality highCobra:Post synaptic neuro toxins;local reaction+muscle paralysis
Enzymes:Russell’s viper venom- proteasesactivate mammalian blood clotting cascadeHyaluronidases- spread of venom in tissueProteolytic enzymes- local changes in vascularpermeability oedema, blisters, necrosisSri lankan russell’s viper: bothvascular and neuro toxins
Systemic effectsEarly effects –specific symptoms & signsvary with the type of snakeViper bites – blood stained sputum,ecchymoses,bleeding from gums and bitewound, prolonged clotting time, ptosis,dysphagia, external ophthalmoplegia,dysarthriaElapid bites -ptosis, dysphagia, dysarthria,mental confusion, respiratory failureSea snake bites – myalgiamyoglobinuria, respiratory failure
Severe envenomation – rapid death afterelapid bitesMost protracted after viper bitesManagementTrivial envenoming – Aches, stiffness, painin limbs , neck• No treatment needed.• In doubt – admit, observeSerious envenoming –• Respiratory failure• Electrolyte disturbances –hypokalaemia• Renal failure
FIRST AID Treat shock & fright, reassure Wash wound with soap and water/clean clothto prevent/limit entry of pathogens Immobilise as for fracture (if limb)to minimize dissemination (spread) of poison Remove rings, bangles etc. on bitten limbto minimize tissue damage that could arise from effects ofenvenomation Paracetamol for pain no alcohol,aspirin, narcotic drugsor nasal instillations Transport patient to hospital? Venous tourniquet if available.
Transport victim to the nearesthospital• Send killed snake to hospital foridentification• avoid - alcohol, aspirin, incision,suction, cauterizationdo not panic. It is better to donothing than to do harm
Specific antiseraPolyvalent antivenin(VINS Bioproducts Ltd. India in current use)Not effective againstsea snakes/ hump nosed viperSea snake antivenin-CommonwealthSerum Laboratories, AustraliaSupportive therapy:Tetanus toxoid,antibioticsrenal./respiratory failure
PREVENTION use bright light in the dark use foot wear look where you tread& warnthem by treading heavily assnakes are relatively deaf but areSensitive to ground vibrationSnakes bite only in defensewhen & if provoked.
Do not handle or keep snakesunless you are an expertSnakes are cold blooded and anapparently dead snake may well bealive. Reflex biting can occur
Do not put your hand intoant hills, cavities in treesand thick under growth andunder logsKeep your dwelling free ofrats, mice, frogs, lizardswhich attract snakes
Information on snake bites: incidencemorbidity, case fatality not very accurateOnly 30-40% seek hospital careBased on few hospital based studies confined togeographical areas.Very important health problem in Sri Lanka2002- 37,200 treated at governmenthospitalsHambantota District 10thleading cause ofhospitalization
Over 80 land snakes in Sri Lanka only6 are known to cause fatalities.Only ½ snake bites are by deadlypoisonous snakes and only ¼ of thesecause systemic poisoningRussell’s viper-30%Cobra 17%Kraits 15%Recent studies: Hump nosed viper bites 27%of the snake bites and 2% fatality reported
Take home massageNot All snakes biteNot all snake bites arevenamousNot all venamous snakebites are fatal