Animal and Venomous Poisons: Snakebite, Insect and Marine

Snakebite is the largest single category of natural envenomation reaching Indian forensic medicine. The ICMR Million Death Study places mortality at around 58,000 lives per year, far higher than hospital reporting captures, because most deaths occur at home or on the way to a primary health centre. The WHO Snakebite Envenoming Strategy of 2019 set a target of halving global mortality by 2030, and Indian performance will determine whether that target is met.

The casework is concentrated in Uttar Pradesh, Bihar, Madhya Pradesh, Odisha, Andhra Pradesh and Tamil Nadu, peaking between June and October when paddy work brings barefoot workers into snake habitat. The most vulnerable group is people who sleep on the floor in single-room homes, where a krait foraging at night can crawl across the sleeping figure and bite if rolled on. The bite is often painless, and the victim either does not wake up or wakes hours later with a headache, droopy eyelids and difficulty swallowing.

The Big Four account for the bulk of medically important bites and define the composition of Indian polyvalent antivenom. Cobra and krait give a neurotoxic picture with paralysis and respiratory failure. The two vipers give a haemotoxic picture with consumption coagulopathy, persistent bleeding and acute kidney injury. The hump-nosed pit viper of Kerala and the Konkan falls outside the polyvalent product and is the most important gap in current Indian antivenom coverage.

The Indian cobra, Naja naja, produces a neurotoxic syndrome with significant local tissue injury. The venom is dominated by alpha-neurotoxins that bind the nicotinic acetylcholine receptor and block neuromuscular transmission. The local picture is striking swelling with blister formation and tissue necrosis. The systemic picture is descending paralysis: ptosis, ophthalmoplegia, dysphagia, diaphragmatic weakness and respiratory failure. Because the blockade is post-synaptic, antivenom can reverse the paralysis if given early.

The common krait, Bungarus caeruleus, is the species the Indian forensic toxicologist must know best because it accounts for the largest share of unexplained nocturnal rural deaths. The krait is small, slender, nocturnal, and hunts inside human dwellings. The bite is often painless and may produce only a single pin-prick mark. The venom is a pre-synaptic neurotoxin dominated by beta-bungarotoxin, which depletes neurotransmitter vesicles at the motor nerve terminal. Once the terminal is exhausted, antivenom neutralises circulating toxin but cannot regenerate function for several days. The clinical picture is morning ptosis, dysphagia, abdominal pain and progressive paralysis. Krait envenomation was misclassified as cause unknown for decades in Indian rural sudden-death series until the species was systematically identified.

Russell's viper, Daboia russelii, produces a fundamentally different picture. The venom is haemotoxic, dominated by procoagulant phospholipases and metalloproteinases that activate factor X and factor V, consume fibrinogen and platelets, and produce venom-induced consumption coagulopathy. The picture is severe local pain with rapidly progressive swelling, bleeding from bite site, gums and urinary tract, and acute kidney injury from direct nephrotoxicity and renal cortical necrosis. Capillary leak and pulmonary oedema is the late complication. Russell's viper is dominant in the agricultural districts of Maharashtra, Karnataka, Andhra Pradesh and Tamil Nadu.

The saw-scaled viper, Echis carinatus, produces a similar haemotoxic picture with prolonged INR, persistent bleeding from any wound and acute kidney injury, typically without the dramatic local swelling. It is the dominant species in arid Rajasthan, Haryana and parts of western Maharashtra. A bite victim presenting two days after the event with persistent oozing from an old injection site is the recurring picture.

The hump-nosed pit viper, Hypnale hypnale, deserves a separate note. It is endemic to Kerala, the Konkan and Sri Lanka, was formerly classed as non-venomous in older Indian texts, and falls outside the spectrum of Indian polyvalent antivenom. Its bites produce local swelling, mild coagulopathy and a high incidence of acute kidney injury. A monovalent product against Hypnale venom is in development but is not yet routinely available.

Indian polyvalent antivenom is produced by Bharat Serums and Vaccines and by VINS Bioproducts, raised in horses against pooled venom from the Big Four, purified to F(ab')2 fragments and lyophilised in 10 ml vials. Each vial is reconstituted at the bedside and given as a slow IV infusion. The initial dose is typically 10 vials titrated to clinical response, with repeats for persistent coagulopathy or neurological progression. Anaphylaxis is reported in 30 to 40 percent of patients, so adrenaline, hydrocortisone and chlorpheniramine must be drawn up before the infusion begins.

The bedside diagnostic test is the 20-minute whole blood clotting test. A few millilitres of fresh venous blood are drawn into a clean dry glass tube, left undisturbed for 20 minutes, and gently tilted. A firm clot indicates intact coagulation. A liquid result indicates consumption coagulopathy from a viper bite, and antivenom is indicated regardless of species. The 20WBCT can be repeated every six hours to track response and detect recurrence from a venom depot at the bite site.

The bedside neurological screen rests on three findings. Ptosis is the earliest and most sensitive sign. The neck flexion test, in which the patient cannot lift the head off the pillow, marks significant neuromuscular blockade. The single breath count falls from 30 to 40 towards single digits as diaphragmatic weakness progresses, with a count below 20 as the trigger for intubation.

When the patient is dead and the question is whether envenomation occurred and which species was responsible, the forensic toxicologist relies on three layers of evidence. The first is the scene and the body: photograph fang marks, swab the puncture for residual venom, document local swelling or necrosis, and preserve tissue from the bite site, the regional lymph node, the liver and the kidney. The fang mark pattern is informative: two distinct deep punctures suggest a viper, a pin-prick or a pair of small marks suggests an elapid.

The second layer is venom enzyme-linked immunosorbent assay. Species-specific antibodies raised against Big Four venoms are used in a sandwich ELISA to detect residual antigen in serum, urine, bite-site exudate or homogenised tissue. The Indian Institute of Science Bangalore, the Liverpool School of Tropical Medicine and the antivenomics group at the Instituto Clodomiro Picado in Costa Rica have contributed validated protocols. Sensitivity is best in bite-site tissue, where venom proteins concentrate locally and remain detectable for days.

The third layer is lateral-flow immunochromatographic detection, the rapid point-of-care equivalent of ELISA, in field evaluation in West Bengal and Tamil Nadu for bedside species identification. PCR adds a fourth layer when the snake is unavailable: a swab from the bite site can contain trace snake DNA from salivary residue, and cytochrome b DNA barcoding against an Indian reference database can yield a species call from a few nanograms of template. This closes the loop in a homicidal bite case where species matters legally and the snake has been disposed of.

Indian arthropod envenomation is dominated by the Indian red scorpion, Mesobuthus tamulus, locally called lal bichhu. The species is endemic to the Konkan, parts of Karnataka and Kerala, and inland Madhya Pradesh and Saurashtra. The venom is an alpha-toxin that binds voltage-gated sodium channels and prolongs the action potential, producing massive neurotransmitter release from autonomic nerve terminals. The clinical picture is the autonomic storm: an initial cholinergic phase of vomiting, sweating, priapism, salivation and bradycardia, followed by an adrenergic phase of severe hypertension, tachycardia, ventricular arrhythmias, pulmonary oedema and acute myocarditis. Children under twelve are at highest risk.

The Bawaskar protocol transformed the outcome. Himmatrao Bawaskar, working from a rural practice in Maharashtra, demonstrated that oral prazosin at 30 micrograms per kilogram every three hours blocks the adrenergic phase and dramatically reduces mortality from pulmonary oedema and myocarditis. The protocol is now standard at every district hospital in the scorpion belt, and the ICMR has incorporated prazosin as the first-line agent. Anti-scorpion venom serum from the Haffkine Bio-Pharmaceutical Corporation in Mumbai is adjunctive in cases progressing despite prazosin.

The black scorpion (Heterometrus) is a less potent species seen across southern and eastern India, producing severe local pain but rarely systemic toxicity. Centipede bites from Scolopendra cause local pain and transient swelling, treated with wound care, tetanus prophylaxis and analgesia.

Hymenoptera envenomation from bees, wasps and hornets is the third arthropod category. Apitoxin contains phospholipase A2, hyaluronidase and melittin. A single bee sting in a sensitised individual can trigger fatal anaphylaxis within minutes, treated with intramuscular adrenaline, antihistamines, hydrocortisone and oxygen. Massive multiple envenomation, above 50 stings in an adult or 20 in a child, produces systemic toxicity even in non-allergic individuals with rhabdomyolysis, haemolysis and acute kidney injury. The Indian hornet (Vespa) produces particularly severe multi-sting envenomation in agricultural workers who disturb a nest. Ants of the genus Pachycondyla deliver a formic-acid sting treated symptomatically.

Marine toxins reach the Indian forensic toxicologist through coastal casework and the occasional aquarium exposure. They are biologically active at picomolar concentrations, which makes them invisible to routine alkaloid screens.

Tetrodotoxin (TTX) is the dominant entity in pufferfish poisoning. Produced by symbiotic bacteria in the puffer gut, it accumulates in liver, ovaries and skin and is a potent voltage-gated sodium channel blocker. Numbness of lips and tongue appears within 30 minutes, followed by ascending paralysis and respiratory failure within 6 to 24 hours. Indian cases are reported from the Andamans and coastal Goa and Karnataka.

Ciguatera poisoning is caused by ciguatoxin from the dinoflagellate Gambierdiscus toxicus, concentrated up the reef-fish food chain into grouper, snapper and barracuda. The picture is gastrointestinal symptoms followed by cold-reversal paraesthesia, in which cold objects feel painfully hot, lasting weeks. Indian cases are reported from Lakshadweep, the Andamans and parts of the Kerala coast.

Saxitoxin is the principal toxin of paralytic shellfish poisoning, produced by Alexandrium and Pyrodinium dinoflagellates during red tide blooms and concentrated by filter-feeding mussels and clams. The picture mirrors tetrodotoxin: perioral tingling, ascending paralysis, respiratory failure. Indian events are episodic along the Gujarat coast during algal bloom seasons.

Palytoxin from Palythoa soft corals is an aquarium-handler exposure in urban India, often from aerosolised material during tank cleaning, producing rhabdomyolysis and respiratory distress. Cone snails (Conus) deliver peptide neurotoxins to divers and shell collectors. Scombroid poisoning, from histamine in poorly stored tuna and mackerel, responds to antihistamines. The Andaman coast has reported box jellyfish stings with severe systemic toxicity.

Tetrodotoxin and saxitoxin are detected by liquid chromatography tandem mass spectrometry at low picogram sensitivity, with the National Institute of Oceanography in Goa and the Central Marine Fisheries Research Institute in Kochi providing reference support to state forensic laboratories.

The Indian envenomation casebook has been dominated by accidental snakebite, but a small and growing subset involves deliberate envenomation as homicide. The pattern documented in Kerala is to drug or restrain the victim, induce a captive snake to bite, and present the death as a natural snakebite.

The Sooraj Suresh case from Kerala, in which the accused was convicted in October 2021 of murdering his wife Uthra by causing a captive Indian cobra to bite her while she slept, became the landmark case. The investigation included reconstruction of bite mechanics, forensic herpetological consultation, retrieval of the snake, and chemistry showing the victim had been sedated before the bite. The methodology now informs any suspicious snakebite death in which the history does not fit the findings.

A separate pattern of homicidal krait poisoning has been documented in Kerala, in which relatives placed a live krait on a sleeping victim to simulate a rural snakebite. These cases are difficult because krait fang marks are small, local signs are mild, and the family is the only witness. Suspicion is raised by an unusual indoor location, multiple bite marks suggesting the snake was handled, sedation on toxicology, and inconsistency between the family account and the findings.

Forensic confirmation rests on the same three layers as natural envenomation: photographic documentation of fang marks, ELISA detection of venom in serum and bite-site tissue, and species identification by DNA barcoding. The additional element in the homicidal case is a parallel sedative screen for benzodiazepines, opioids and ketamine.

Current law brings such cases under the Bharatiya Nyaya Sanhita 2023. BNS Section 125 covers acts endangering life through administration of poison, including induced envenomation, and BNS Section 100 covers culpable homicide. The earlier IPC Sections 328 and 302 served the same function before the BNS.

Routine snakebite management is decentralised, with polyvalent antivenom stocked at every primary health centre and 20WBCT performed at the bedside. The forensic confirmation pathway is concentrated at a smaller number of referral laboratories.

Venom ELISA on post-mortem tissue is offered by the Centre for DNA Fingerprinting and Diagnostics in Hyderabad, the Indian Institute of Science in Bangalore, and academic snakebite groups, with the Liverpool School of Tropical Medicine providing a reference panel. LC-MS/MS for marine toxins is available at the National Institute of Oceanography in Goa and the Central Marine Fisheries Research Institute in Kochi. Snake DNA barcoding is performed at the Centre for Cellular and Molecular Biology in Hyderabad and the Wildlife Institute of India in Dehradun. ELISA against Mesobuthus tamulus venom is available at the Haffkine Institute and the National Institute of Virology in Pune.