Cross-Reactivity against Naja sumatrana (Black Spitting Cobra) Envenoming from the Haffkine Antivenom in a Mouse Model

Naja sumatrana is the dominant cobra species in Malaysia, Singapore, Borneo, and Sumatra, and it does not have specific antivenom. The Haffkine antivenom has been advocated instead. This study aims to determine the efficacy of this antivenom against Naja sumatrana envenoming using a mouse model. Methods. Male Swiss albino mice were used. Intravenous LD50 was first determined separately for Naja naja and Naja sumatrana venom. ED50 was determined by preincubating antivenom with each venom at 2.5 LD50 before administering the mixture into the tail vein. Validation was carried out using a challenge test. Each mouse received 111？μg of Naja sumatrana venom intramuscularly followed by intraperitoneal administration of dilute Haffkine antivenom. Survival was recorded 24 hours after envenoming. Results. The LD50 of Naja naja venom was 78.13？μg, standard error (SE) 13.3？μg. The ED50 of the Haffkine antivenom against Naja naja venom was 45.9？mg, SE 7.5？mg. The LD50 and ED50 of Naja sumatrana venom were 55.5？μg, SE 12.0？μg; and 73.9？mg, SE 12.0？mg, respectively. The intra-peritoneal ED50 against 111？μg intramuscular Naja sumatrana venom was 136.95？mg, SE 36.74？mg. Conclusion. The Haffkine polyvalent antivenom exhibited cross-neutralisation against Naja sumatrana venom when used at a higher dose. 1. Introduction 1.1. Background and Importance Naja sumatrana, commonly known as the black spitting cobra or Equatorial spitting cobra, is the dominant cobra species in Peninsular Malaysia, Singapore, Borneo, and Sumatra [1]. It was estimated that the highest burden of snake bites exists in South Asia, Southeast Asia, and sub-Saharan Africa [2]. Cobra bites are common in Peninsular Malaysia and require significant medical intervention [3, 4]. However, snake bites are considered uncommon in largely urban Singapore [5, 6]. Unfortunately specific antivenom therapy against the Naja sumatrana does not exist. The Haffkine antivenom was arbitrarily advocated as an antivenom. It is an equine polyvalent antivenom raised against the Indian binocellate cobra (Naja naja), common krait (Bungarus caeruleus), Russell’s viper (Vipera russelli), and saw-scaled viper (Echis carinatus) [7]. However, these species of snakes are not normally found in Southeast Asia. The antivenom composition of the Haffkine was chosen for the treatment of black spitting cobra snake bites due to the empirical belief that cobras are originated from the Naja naja. These species are, however, considered to be separate now. It is unknown if the Haffkine product has any effective paraspecific activity against the