antivenom

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Antivenoms Against Malaysian Poisonous Snakes
Prof Tan, Nget Hong
Department of Molecular Medicine
Faculty of Medicine, University of Malaya
Kuala Lumpur, Malaysia

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Abstract:
Protection Against Malaysian Snake Envenomations: Comparative Potency of Some Commercial and Laboratory-prepared Antivenoms

The protective effects of several commercial antivenoms against venom poisoning by common Malaysian snakes were investigated using animal experiments.
Commercial Calloselasma rhodostoma (Malayan pit viper) antivenom effectively neutralized the lethality of C.rhodostoma venom but was effective only against the lethal effect of some Trimeresurus venoms. It could, however, neutralize the thrombin-like activity of all the Trimeresurus venoms tested, though not the local necrotizing and hemorrhagic effects. Thus, C.rhodostoma antivenom may be of some benefits in the treatment of systemic Trimeresurus venom poisoning particularly when specific Trimeresurus antivenom is not available.
Both the monovalent and polyvalent Trimeresurus antivenoms exhibited broad cross-reactivity against heterologous Trimeresurus venoms (except T.wagleri) and were generally very effective in neutralizing both the local and systemic effects of the venoms. These antivenoms, however, could not neutralize the lethal toxicity or thrombin-like activity of C.rhodostoma venom in mice but were effective in neutralizing the local necrotizing and hemorrhagic activities of C.rhodostoma venom.
Monovalent cobra antivenom was effective in neutralizing the lethal toxicity of Naja kaouthia (Monocellate cobra) and Ophiophagus hannah (king cobra) venoms but was only moderately effective against the Naja naja sputatrix (Malayan spitting cobra) venom. It also failed to neutralize any of the Bungarus (krait) venoms tested.
Monovalent Bungarus fasciatus (banded krait) antivenom was only effective in neutralizing the lethal toxicity of the homologous venom and failed to neutralize cobra venoms or venoms from the other two common Malaysian kraits, B.candidus and B.flaviceps.
Monovalent king cobra antivenom could effectively neutralize both the homologous venom and N.kaouthia venom. It could not neutralize N.n.sputatrix nor any of the Bungarus venoms tested.
A commercially available polyvalent elapid antivenom raised from Naja naja atra (Taiwan cobra) and Bungarus multicinctus (Many banded krait) was found to be very effective against the venoms of all the six common Malaysian elapids (N.kaouthia, N.n.sputatrix, O.hannah, B.candidus, B.fasciatus and B.flaviceps). The results suggest that polyvalent elapid antivenom might be useful in the treatment of Malaysian elapid envenomation particularly when accurate diagnosis of the biting species could not be made.
Poisonous Snakes and Snakebites in Malaysia

Snakebite is a serious medical problem in Malaysia. During the period 1958-1980, as many as 55000 cases of snakebites were admitted to the hospitals in Malaysia. While the mortality rate of snakebite in Malaysia is only 0.3 per 100000 population, the local necrotic effects of some venoms can cause prolonged morbidity or crippling deformity.
In Malaysia and the coastal waters of the region, there are at least 18 different species of venomous front fanged land snakes and more than 22 different species of sea snakes. These venomous snakes belong to the following five subfamilies:
a) Crotalinae: the genera Calloselasma (C.rhodostoma) and Trimeresurus (at least seven known species);
b) Elapinae: the genera Naja, Bungarus, Ophiophagus, Maticora and Calliophis
c) Subfamilies Laticaudinae, Hydrophiini and Ephalophiini: the sea snakes.
Only a few of the Malaysian venomous snakes can be regarded as of medical importance. Epidemiological studies showed that snakebites in Malaysia were mainly due to four species of land snakes: Calloselasma rhodostoma (Malayan pit viper), Trimerusurus purpureomaculatus (shore pit viper), Naja naja (Asian common cobra) and Trimeresurus wagleri (Wagler’s pit viper). Other venomous snakes indigenous to Malaysia that are potentially dangerous to human include Bungarus candidus (Malayan krait), Bungarus fasciatus (banded krait), Ophiophagus hannah (king cobra), Trimeresurus sumatranus (Sumatran pit viper) and the sea snakes.
Antivenom therapy is the most effective treatment of systemic snake venom poisoning. At present, monospecific antivenoms are available only against the three common types of Malaysian poisonous snakes (anti-Malayan pit viper, anti-Malayan cobra and anti-Enhydrina schistosa). Also, in Malaysia in the majority of snakebite cases, the diagnosis is conjectural based mainly on clinical observations. Immunodiagnosis of snakebite using ELISA technology has been successfully developed but is not used in the field. In view of these, we carried out animal neutralization experiments to examine the effectiveness of some commerical antivenoms in protection against the common Malaysian poisonous snakes as well as investigating the cross-reactivity of some monovalent antivenoms.

Protection against Malayan pit viper (Calloselasma rhodostoma)

In Malaysia, Calloselasma rhodostoma (Malayan pit viper) is confined only to the northern states of Kedah, Perlis and Penang. It is the commonest cause of snake bite in Peninsular Malaysia. Fortunately, only 10% of those bitten developed severe poisoning and death rate is less than2%. Swelling always follows Malayan pit viper venom poisoning. Local necrosis occurred in 11% of the patients and in 15% of the cases there was an overt hemorrhagic syndrome. The principal characteristics of systemic Malayan pit viper venom poisoning was systemic bleeding characterized by defibrination and thrombocytopenia.
Monovalent Malayan pit viper antivenom (Thai Red Cross Society) of equine origin was effective against Malayan pit viper venom. Both the polyvalent Trimeresurus antivenom (National Institute of Preventive Medicine, Taiwan, rasied against T.mucrosquamatus and T.stejnegeri venoms) and monovalent Green pit viper antivenom (Thai Red Cross Society, raised against T.albolabris) failed to neutralize the lethal toxicity of C.rhodostoma venom in mice. However, the polyvalent Trimeresurus antivenom was effective in neutralization of the hemorrhagic and necrotizing activities of C.rhodostoma venom but failed to neutralize the thrombin-like activity of the venom.

Protection against Malaysian lance-headed pit vipers

The Trimeresusus are pit vipers in which all the scales on the top of the head are small and irregularly arranged. There are at least seven known species of Trimeresurus in Malaysia. Snakebite cases by T.wagleri and T.purpuromaculatus have been reported but they rarely resulted in serious poisoning. T.sumatranus is considered a dangerous species as the snake is reported to be aggresive. Bites from other Malaysian Trimeresurus are rare.
We examined the effectiveness of three Trimeresurus antivenoms: the polyvalent Trimeresurus antivenom (NIPM, Taiwan), the monovalent Green pit viper venom and a laboratory-prepared monovalent T.purpureomaculatus antivenom. All three Trimeresurus antivenoms were effective in neutralization of the lethality of venoms of four common Southeast Asian Trimeresurus: T.purpureomaculatus, T.sumatranus, T.popeorium and T.albolabris. The cross-neutralziation potency of the NIPM polyvalent Trimeresurus antivenom (the most potent Trimeresurus antivenom tested) was further examined and the results show that it was effective in neutralization of the lethality, thrombin-like, hemorrhagic and necrotizing activities of a wide range of Trimeresurus venoms, except T.elegans, T.macrops and T.wagleri venom.
The results indicate that Trimeresurus antivenoms exhibit broad cross-reactivity against heterologous Trimeresurus venoms. The polyvalent Trimeresurus antivenom is shown to be potent also in the neutralization of the local and systemic effects of the venoms. While it is true that clinical efficacy may not correlate well with laboratory results, the use of the polyvalent Trimeresurus antivenoms should be considered in patients biten by rare or little-known Trimeresurus for whose venoms there is usually no monospecific antivenom available.
Monovalent Malayan pit viper antivenom (Thai Red Cross Society) of equine origin failed to neutralize the lethality of Trimeresusus purpureomaculatus venom, was partially effective against T.sumatranus, T.popeorium and T.wagleri venoms, but effective against T.albolabris venom. The antivenom, however, could effectively neutralize the thrombin-like activity of all the Trimeresurus venoms but not the hemorrghic activity. Since thrombin-like enzyme activity is usually the major factor causing prolonged coagulation defect in Southeast Asian Trimeresurus bite, C.rhodostoma antivenom may be of some benefits in the treatment of systemic Trimeresurus venom poisoning particularly when Trimeresurus antivenom is not available.

There are two common species of Asiatic cobras in Malaysia: the monocellate cobra (Naja kaouthia) and the black, spitting Malayan cobra (Naja naja sputatrix). King cobra, which belongs to a different genus, is also common. For the Asiatic cobras, local necrosis is the main feature of venom poisoning while the main systemic effects are myoneural curare-like (neurotoxic) effect and cardiovascular effect. The main systemic effect of king cobra venom bite appears to be neurotoxic poisoning. We examined the effectiveness of the following antivenoms: Monovalent cobra antivenom (Thai Red Cross Society), Monovalent Bungarus fasciatus antivenom (Thai Red Cross Society), Monovalent king cobra antivenom (Thai Red Cross Society); Polyvalent elapid antivenom (National Institute of Preventive Medicine, Taiwan, raised against Bungarus multicinctus and Naja naja atra venoms):
The monovalent Cobra antivenom was very effective against N.kaouthia venom and also effective against King cobra venom, but only moderately effective against N.n.sputatrix venom. The Bungarus fasciatus antivenom could not neutralize any of the Malaysian cobra venoms. It is interesting to note that against king cobra venom, the neutralizing capacity of monovalent King Cobra antivenom was approximately the same as that of the monovalent Cobra antivenom (which was raised against N.kaouthia venom). It is also note that the monovalent King Cobra antivenom exhibits paraspecific protection against N.kaouthia venom, but not against N.n.sputatrix venom. The Polyvalent Elapid Antivenom appears to be very effective against N.kaouthia venom and effective against N.n.sputatrix and king cobra venoms.
Protection against Malaysian kraits

There are three species of krait in Malaysia: B.fasciatus (banded krait), B.candidus (Malayan krait) and B.flaviceps (Redheaded krait). The reported incidence of krait bite is low but mortality is high. Bites by krait are usually characterized by neurotoxic poisoning.
The monovalent Cobra and King Cobra antivenoms were not effective in the neutralization of the lethality of Malaysian Bungarus venoms. The monovalent B.fasciatus antivenom was moderately effective only against the homologous B.fasciatus venom. However, the polyvalent Elapid Antivenom was very effective in the neutralization of B.candidus and B.flaviceps venoms, and moderately effective in neutralizing B.fasciatus venom. In the absence of monovalent Bungarus antivenoms it appears that the polyvalent Elapid Antivenom is a good alternative in antivenom treatment of Bungarus envenomation in Malaysia.
Protection against Common Sea Snake

There are more than 18 species of sea snake in the costal waters of Malaysia. The commonest species is Enhydrina schistosa (beaked sea snake) which is also the most aggresive species. The venom has a powerful myotoxic effect in human and envenomation results in myonecrosis that causes generalized muscle movement pains and myoglobinuria. Sea snake envenomation is not very common in Malaysia. Monovalent Enhydrina schistosa antivenom was reported to be very effective in combating common sea snake venom poisoning. Australian workers reported that Monovalent Notechis scutatus antivenom was also effective.

Sources of Antivenoms Monovalent Malayan pit viper antivenom, Monovalent Green Pit Viper antivenom, Monovalent King Cobra Antivenom, Monovalent Bungarus fasciatus antivenom: Thai Red-Cross Society (Queen Saovabha Memorial Institute, Thai Red Cross Society, Rama IV Road, Bangkok, Thailand)
Monovalent Enhydrina schistosa antivenom and Monovalent Notechis schtatus antivenom: Commonwealth Serum Laboratory, Parkville, Victoria, Australia. http://www.csl.com.au/
Polyvalent elapid antivenom and Polyvalent Trimeresurus antivenom National Institute of Preventive Medicine, DOH, Taiwan. 161, Kunyang Street, Nankang, Taipei, Taiwan, ROC. Tel: 886-2-27839723

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