Friday, November 26, 2010

Ecology and Bites of the Humped-nosed Viper

The Western Ghats of southwestern India is a biodiversity hot spot. The western slopes of the mountains experience heavy annual rainfall (with most precipitation occurring from June to September) but the eastern slopes are drier. Rainfall also varies from north to south producing a wide variation in rainfall patterns and thus a pattern of vegetation that ranges from scrub forest to tropical rainforest. Sawant et al. (2010a) examined the distribution and abundance of pit vipers in five wildlife sanctuaries in Goa using seasonal and day-night transects to determine habitat use in three pit vipers: the Bamboo Pit Viper (Trimeresurus gramineus), the Malabar Pit Viper (Trimeresurus malabaricus) and the Humped-nosed Pit Viper (Hypnale hypnale). They found specific habitat preferences for each species and note snake abundance changes with the seasons. The Malabar Pit Viper, Trimeresurus malabaricus, predominantly occupied tropical semi-evergreen forests and rarely used moist deciduous forests while the Bamboo Pit Viper, Trimeresurus gramineus and the Humped-nosed Viper, Hypnale hypnale were mostly in cane brakes, wet bamboo brakes, tropical semi-evergreen, and moist deciduous forests. Unexpectedly, the Hump-nosed Viper made a remarkable change in their habitat use. After the monsoon and into the winter they occupy the cashew plantations adjoining the wildlife sanctuaries. Hump-nosed Vipers are terrestrial and semi-arboreal and Sawant et al (2010b) examined its ecology, threats, and conservation. This little pitviper prefers cool and moist microhabitats. Females using the cashew plantations were more susceptible to human activity. The authors point out that this preference for a particular micro-habitat emphasizes the need for conservation despite the fact most suitable habitat in the Western Ghats, for this species is included in areas already protected.

Bites from the Humped-nosed Vipers are also turning out to be a more serious problem than previously thought. Hypnale hypnale and H. nepa can cause renal failure and haemostatic dysfunctions. Several fatalities due to H. hypnale envenoming, for which there is no specific antivenom, have been reported in India and Sri Lanka. One reason the bites are particularly troublesome is that the snakes are frequently misidentified as Saw-scale Vipers (E. carinatus) in Kerala, India. Consequently, many H. hypnale bite victims end up receiving ineffective antivenom (Alirol et al. 2010; Joseph, et al. 2007). Tan et al. (in Press 2010) report clinical studies indicate the locally available polyvalent antivenoms produced in India are not effective against Hump-nosed Pit Viper venom. Therefore, there is a need for an effective antivenom. Tan et al. examined the ability of the Malaysian Pit-Viper, Calloselasma rhodostoma, monovalent antivenom and the Hemato polyvalent antivenom, both produced by Thai Red Cross Society (TRCS) to neutralize the lethality and toxic effects of H. hypnale venom. They chose this antivenom because C. rhodostoma is considered a sister of H. hypnale. In vitro neutralization studies of Hemato polyvalent antivenom effectively neutralized the lethality of H. hypnale venom (1.52 mg venom/ml antivenom), as well as the hemorrhagic, procoagulant and necrotic activities of the venom. The monovalent C. rhodostoma antivenom also neutralize the lethality and toxic activities of the venom, but the potency was lower. Experiments with Hemato polyvalent antivenom effectively protected mice from the lethal and local effects of H. hypnale venom. Thus the Hemato polyvalent antivenom may be beneficial in the antivenom treatment of H. hypnale envenoming.

Alirol, E., S. K. Sharma, H. S. Bawaskar, U. Kuch, and F. Chappuis. 2010. Snake Bite in South Asia: A Review. PLoS Neglected Tropical Diseases 4(1): e603. doi:10.1371/journal.pntd.0000603.

Joseph J. K., I. D. Simpson, N. C. Menon, M. P. Jose, and K. J. Kulkarni. 2007. First authenticated cases of life-threatening envenoming by the hump-nosed pit viper (Hypnale hypnale) in India. Transactions of the Royal Society of Tropical Medicine and Hygiene 101: 85–90.

Sawant, N.S., T. D. Jadhav and S. K. Shyama 2010a. Distribution and abundance of pit vipers (Reptilia: Viperidae) along the Western Ghats of Goa, India. Journal of Threatened Taxa 2(10): 1199-1204.

Sawant, N. S., T. D. Jadhav and S. K. Shyama . 2010b. Habitat suitability, threats and conservation strategies of Hump-nosed Pit Viper Hypnale hypnale Merrem (Reptilia: Viperidae) found in Western Ghats, Goa, India. Journal of Threatened Taxa 2(11): 1261-1267.

Tan, C. H., P. K. Leong, et al. 2010. Cross neutralization of Hypnale hypnale (hump-nosed pit viper) venom by polyvalent and monovalent Malayan pit viper antivenoms in vitro and in a rodent model. Acta Tropica In Press, Accepted Manuscript;doi:10.1016/j.actatropica.2010.11.001

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