Snake bite cases are often encountered in humans and animals but still it’s a neglected health issue as listed by WHO in “Neglected tropical disease” list. Animals usually encounter snakes during grazing in fields, hunting or playing in garden. Snake bite cases are mostly reported in dogs and horses¹. Mortality due to snake bite is more commonly reported in dogs as compared to other domestic animals may be due to the small size of dogs². Canines and felines are most often bitten around the head and limbs. The major venomous snake species found in India are cobra or Naja naja, krait or Bungarus caeruleus, Russell's viper or Vipera russelli and saw-scaled viper or Echis carinatus³. Snake Venom induces inflammatory, neurotoxic and hemotoxic effects. Neurotoxicity is exhibited by flaccid and respiratory paralysis. However, the hemotoxins are released in the blood and cause thrombosis, necrosis of blood vessels, hemorrhage and coagulopathy⁴. Therefore, snake bite in human as well as animals requires rapid examination and critical care for proper treatment. The present study describes the pathological changes in various body organs of a female Beagle dog due to viper snake bite.

A female Beagle dog of five-year-old was presented for necropsy at Department of Veterinary Pathology, College of Veterinary and Animal Science (CVAS), Navania, Udaipur with a history of snake (Viper) bite after a fight with snake. The snake was identified by its external features. The dog had no history of previous illness. A thorough postmortem examination was conducted and tissue samples of lung, heart, liver, spleen, intestine, stomach, kidney and skin at the site of bite mark were collected in 10% neutral buffered formalin for histopathological examination. The tissues were processed for paraffin wax embedding technique and sections of 3-4μm thickness were cut. The sections were stained with Haematoxylin and Eosin (H&E) stain as per standard procedure described by Bancroft and Gamble (2008)⁵. External examination of the dog revealed good general condition of the Beagle dog. Injury marks of 2-3mm diameter were present above the upper lip and on head (Fig. 1). At the site of bite, haemorrhages and mild swelling were present. It has been reported that frequent site of snake bite in dogs is head, muzzle, tongue and lips⁶. The swelling might be attributed to the enzymatic action of hyaluronidase present in the snake venom, which acts as a spreading factor⁷.

Internal examination revealed congestion and haemorrhages in almost all the visceral organs. Haemorrhages seen in different organs of the dog could be due to altered vascular permeability of the vessels and endothelial lining damage due to action of venom⁸. Increase in vascular permeability and damage to blood vessel wall result in fall in blood pressure leading to shock and death^9,10. Baldo et al. (2010) explained that haemorrhagic toxins accumulate near the blood vessel walls and hydrolyze preferable collagen IV of the basement membrane leading to disturbed hemostasis and necrosis of surrounding tissue¹¹. Moreover, Chauhan (2010) reported that snake venom contains hyaluronidase, phosphodiesterase and peptidase which are responsible for vascular changes, hemolytic anemia, hemoglobinuria, cardiac irregularities, and fall in blood pressure, shock and neurotoxicity¹².

Lungs were severely congested, haemorrhagic and dark red in colour (Fig. 2 a). Blood was oozing out from cut section of lung. Coronary vessels of the heart were congested. Liver was severely congested and dark brown in colour along with petechial haemorrhages on all the lobes (Fig. 2 b). The gall bladder revealed haemorrhages on the mucosa (Fig. 2 c). Spleen revealed focal ecchymotic haemorrhages. Kidneys were congested and haemorrhagic (Fig. 2 d). Mucosa of stomach and intestines was congested alongwith severe congestion of mesenteric blood vessels. Similar findings of multi-visceral congestion or edema and petechial haemorrhages have been reported earlier¹³.

Histopathological examination of lungs revealed congestion, haemorrhages, mild pulmonary oedema and an inflammatory reaction comprising of neutrophils and a few lymphocytes and macrophages (Fig. 3). Similar findings have been observed in mice and humans^14,15. It has been reported that damage to micro blood vessels occurs due to rapid accumulation of neutrophils around these vessels which eventually damages the surrounding pulmonary tissue¹⁶. This is because leukocytes produce inflammatory mediators which enhance the inflammation resulting in edema, congestion, haemorrhages and increased cellular infiltration. This inflammatory reaction blocks the alveolar airspaces and disrupts gaseous exchange in lungs resulting in respiratory failure.

The heart revealed myocardial congestion and haemorrhages. Liver revealed dilated portal vein, sinusoidal congestion, hepatocellular degeneration, cytoplasmic vacuolation, disarrangement of hepatic cords and individualization of hepatocytes alongwith fatty changes and signet ring appearance in few hepatocytes (Fig. 4 and 5). Necrosis of hepatocytes was evident near the periportal area; the necrotic changes might have occurred due to the action of phospholipases present in the venom that hydrolyzes the phospholipid cell membrane of hepatocytes. Congestion of blood sinusoids and central vein was evident. Kupffer cells number was increased in liver which might be in response of increased haemorrhages⁸. Liver injury is also reported in sheep who also observed karyolysis and karyorrhexis of hepatocytes⁸. These changes might be due to action of snake venom on the mitochondrial and microsomal function of the hepatocytes leading to the disruption of lipoproteins and lipid accumulation in the cells⁸. Mild congestion is noticed in stomach and intestine. This may be due to circulation of the venom with the blood flow to the stomach and intestine.

In kidneys, there was acute tubular injury characterized by dilated tubules with necrosis and separation of epithelial cells from the basement membrane (Fig. 6). Hyaline casts were seen in few tubules, haemorrhages, and mild infiltration of inflammatory cell was noticed in interstitial space. There was loss of cytoplasmic eosinophlia in tubular epithelial cells. Glomeruli were hypercellular. Similar findings of inflammatory cell infiltration, shrinking of glomeruli and degeneration of the proximal and distal tubules in the kidney was reported in mice due to Naja naja envenomation and in humans^14,17. In humans, acute kidney injury is major cause of death due to snake envenomation as reported earlier¹⁸. This could be due to the cytotoxic effect of the venom, the release of bradykinin and circulatory collapse, arteriolar vasoconstriction leading to reduced renal blood flow¹⁴,¹⁹. The toxic substances reach the kidney along with the circulating blood so it is observed that kidney injury is common in snake envenomation¹⁴. It has been reported that probably the venom phospholipases are responsible for tissue injury by disorganizing the lipid bilayer of the cell membrane and reduction in Na-K ATPase activities resulting in change in the ionic gradient across the cell membrane leading to destruction of the cell membranes and finally death of the cell²⁰.

The main histological findings of myocardial haemorrhages, pulmonary edema and congestion, diffuse alveolar damage, tubular and/or glomerular necrosis, acute interstitial nephritis, intestinal injuries, pituitary hemorrhage/necrosis and adrenal gland hemorrhage were also observed in humans and rabbits as reported earlier¹³.

Thus it is concluded that viper snake venom causes vascular changes in the visceral organs of dog and damages particularly the pulmonary and renal tissue. Therefore, further research needs to be carried out to find anti-venom related drugs that can reduce damage produced at cellular and microvascular level.

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