Browsing by Author "Dissanayake, D.S.B."

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An Evaluation on Factors Influencing Venom Yield in Spectacled Cobra (Naja naja) in Sri Lanka
(Faculty of Graduate Studies, University of Kelaniya, 2015) Dissanayake, D.S.B.; Rajapakse, R.P.V.J.; Kularatne, S.A.M.
Snake venom contains medically important toxic proteins. Proteroglyphous snakes of the family Elapidae: Naja naja is the only recognized species of cobra in Sri Lanka and is responsible for a considerable number of envenomation and deaths due to snake bites. The dose of antivenin depends upon the amount of venom inflicted by the snake and the kinetics of venom distribution in the whole body. Although several studies have been conducted regarding this subject, the amount of venom ejecting per bite is still under investigation. The current study investigated whether the body size, sex and other morphological characteristics of N. naja have any influence on venom yield when milked manually. For milking, small-sterilized beakers that are tightly covered with parafilms layers were used. The head of each milking snake was held and venom was extracted to the prepared beakers by applying a gentle pressure to the venom glands. After that, the volume of wet venom of each snake was measured using graduated pipets and these volumes were used for statistical analysis. N. naja The average wet venom volume in 40 adult cobra (mean total length 1698 ± 161mm; mean body weight 1466 ± 287g) ranges from 200-1500μl (mean 485.15 ± 178.9μl) and 10 juvenile snakes (mean total length 632 ± 95mm and body weight 420 ± 93g) were 15-70μl. The venom yield positive correlated with the length and body weight of the snakes. Even though males hold slightly high volume of venom than females, this volume difference is not significant. In summary, we found that the venom yield is more correlated to the body size and total length than the sex and other morphological characters of snakes. Further studies are necessary to find out whether venom yield differs due to geographic variations or other related ecological factors.
Molecular Phylogeography and Clinical manifestations of Russell’s viper (Daboia russelii) in Sri Lanka
(Faculty of Graduate Studies, University of Kelaniya, 2015) Dissanayake, D.A.; Dissanayake, D.S.B.; Bandara, K.B.A.T.; Kularatne, S.A.M.; Karunathilake, D.G.K.J.K.; Rajapakse, R.P.V.J.
The Russell‘s viper, Daboia russelii has a relict distribution over large areas of Indian Sub Continent, Taiwan and the Lesser Sunda islands. Russell‘s viper is distributed with varying densities and occurrence throughout many natural and modified habitats in Sri Lanka. Bite of this species is associated with a high incidence of morbidity and mortality in Sri Lanka. There is scanty of information available about Russell‘s viper in Sri Lanka. Thus, preliminary study was carried out using clinical data obtained from the twenty eight patients admitted due to Russell‘s viper bite in General Hospitals in the Gampaha District. Further, thirty five DNA samples were collected from the tail tip of specimens of the Russell‘s viper from Gampaha, Kandy, Rathnapura, Galle, Anuradhapura and Kurunagala districts for molecular phylogeny. Then fragment of mtDNA sequencing fragments of cytochrome b genes were amplified. PCR and products were subjected. DNA sequencing for molecular analysis using raxmlGUI software. Results revealed that the clinical features following Russell‘s viper envenomation are follows; local swelling 86%, local necrosis 7%, coagulopathy 75%, neurotoxicity 32%, nephrotoxicity 14% and cardiac effects 3%. Mortality of Russell‘s viper bites are caused by complications like renal failure, neurotoxicity, respiratory failure, disseminated intravascularcoagulation, heart failure and other cardiotoxic effects. Alignment of Sequences of Cytochrome-b gene by maximum likelihood analysis revealed that two strongly supported monophyletic clades corresponding to Sri Lanka and the Indian subcontinent. However, Sri Lankan Russell‘s viper was nested within the clade of Indian Russell‘s viper group. There was genetic divergence (2%) between the Indian clades and the Sri Lankan clade. However, these haplotypes do not show any geographically significant pattern. Thus, it could be suggested that Indian and Sri Lankan Russell‘s viper are genetically closely related and origin may be India or Sri Lanka. Further studies are being carried out on morphometric, molecular taxonomic and venomous differences in different geographic location within the Sri Lanka and Asian region.