Antivenom cross neutralisation in a suspected Asian pit viper envenoming causing severe coagulopathy

There is evidence of cross-neutralisation between common toxin groups in snake venoms and therefore the potential for antivenoms to be effective against species they are not raised against. Here we present a 49 year old female bitten by an unknown pit-viper in Nepal. She developed a venom induced consumption coagulopathy with an unrecordable international normalised ratio and undetectable fibrinogen. On return to Australia 5 days post-bite she was treated successfully with one antivenom raised against Malayan pit viper and green pit viper venoms (Haemato-polvalent antivenom from Thailand) and then subsequently with another antivenom raised against American pit-viper venoms (Antivipmyn). Presumed pit viper venom was detected in patient sera with an enzyme immunoassay against Hypnale hypnale venom. There was increased absorbance before antivenom compared to non-envenomed control samples, which then decreased after the administration of each antivenom. The recurrence of venom detected by enzyme immunoassay between antivenom doses was accompanied by a recurrence of the coagulopathy. Cross reactivity between the unknown venom and both antivenoms was supported by the fact that no venom was detected in the pre-antivenom samples after they were incubated in vitro with both antivenoms. This case and investigation of the venom and antivenoms suggest cross-neutralisation between pit vipers, including pit vipers from different continents.