Echis carinatus, commonly known as the Saw-scaled Viper, is a highly venomous snake species found across a wide geographic range, including parts of the Middle East, Central Asia, and particularly the Indian subcontinent. It is recognized as one of the “Big Four” snakes in India, a group responsible for the majority of snakebite incidents and fatalities in the region. Its widespread distribution and severe venom effects make it a public health concern. Frequent human encounters occur due to its inconspicuous nature and presence in populated areas.
Identification and Habitat
The Saw-scaled Viper is a relatively small snake, typically measuring between 38 and 80 cm in total length. Its head is distinct from its neck, with a short, rounded snout and elliptical pupils. Its stout body is covered in small, rough, keeled scales, aiding camouflage.
Coloration varies, including pale buff, grayish, reddish, olive, or pale brown, often with whitish spots edged in dark brown. A whitish trident-type pattern may be on its head, and a faint stripe can extend from the eye to the jaw. Its rough scales produce a characteristic rasping or sizzling sound when rubbed together, serving as a warning. It primarily moves by sidewinding, an efficient locomotion method well-suited for sandy habitats.
Echis carinatus is highly adaptable, inhabiting deserts, scrublands, grasslands, and rocky outcrops, and is often found near human settlements. It avoids marshy areas, thriving in hot, dry climates. These vipers are mostly crepuscular and nocturnal, seeking refuge during the day in deep mammal burrows, rock fissures, fallen logs, or by burying themselves in sand with only their heads exposed. They are frequently active after rains or on humid nights. In some areas, up to 80% of adults may climb into bushes and shrubs, sometimes as high as 2 meters, during rainfall.
Venom and Its Effects
The venom of Echis carinatus is potent and complex, containing a mixture of toxins, primarily hemotoxins and cytotoxins. On average, the snake produces about 18 mg of dry venom, with a maximum of 72 mg. It can inject up to 12 mg per bite, and the estimated lethal dose for an adult human is as low as 5 mg.
The venom’s primary action involves disrupting the body’s blood coagulation system. It directly activates prothrombin, leading to a severe depletion of clotting factors such as fibrinogen, and an increase in fibrin degradation products. This results in incoagulable blood and a significant risk of spontaneous systemic bleeding, which can manifest as bleeding from the gums, nose, or internal organs like the gastrointestinal tract or urinary system. Hemorrhage and coagulation defects are prominent systemic symptoms, potentially leading to hypovolemic shock.
Beyond blood clotting issues, Echis carinatus venom also causes local tissue damage at the bite site. Within minutes of a bite, localized swelling and pain develop, spreading rapidly, sometimes up the entire affected limb within 12 to 24 hours. Blistering and necrosis (tissue death) can occur, complicating recovery.
The venom also contains phospholipase A2 (PLA2) and snake venom metalloproteinases (SVMPs), which contribute to muscle necrosis, inflammation, and hemorrhagic activity by hydrolyzing the basement membrane of capillary blood vessels. Other physiological processes, such as complement activation and hemoglobin metabolism, are also affected. Severe envenomation can lead to acute kidney failure, sometimes requiring dialysis, often due to intravascular hemolysis or disseminated intravascular coagulation.
Medical Management of Bites
Immediate medical attention and rapid transport to a healthcare facility are important following a suspected Echis carinatus bite. Swift medical intervention impacts the outcome. The primary treatment for envenomation by this snake is the administration of antivenom. Antivenom, derived from antibodies of animals exposed to snake venom, works by binding to and neutralizing toxins.
The dose of antivenom is carefully controlled, often guided by monitoring the patient’s blood coagulability through simple clotting tests. This helps ensure an adequate neutralizing dose and prevents unnecessary use of the expensive antivenom. While antivenom is effective in reversing systemic effects, particularly coagulation defects, its efficacy against local tissue damage may vary. Supportive care is also provided, which includes managing pain, addressing any complications like kidney failure, and preventing secondary infections at the bite site. Patients are monitored for signs of ongoing bleeding or other systemic effects until blood coagulability is restored, which can take several hours after the initial antivenom dose.
Prevention Strategies
Minimizing the risk of Echis carinatus bites involves adopting precautions, particularly in prevalent areas. Wearing appropriate footwear, such as sturdy closed-toe shoes or boots, and long trousers can provide a physical barrier against bites. This is important when walking through grassy or rocky terrain, or in agricultural areas.
Caution is advisable when walking at night, as these vipers are primarily nocturnal. Using a flashlight can help illuminate pathways and identify any snakes that might be present on the ground. Avoiding disturbing rocks, logs, or piles of debris is also recommended, as these are common hiding spots for the snakes during the day. Maintaining awareness of surroundings and refraining from direct contact with any snake are effective prevention measures.