Discussion
North central Florida is a unique geographic area home to five indigenous venomous pit vipers including water moccasins, and eastern diamondback, timber and pygmy rattlesnakes. The amount of venom injected varies according to the species, snake size, time lapse since the last venom delivery, and degree of threat sensed prior to venom delivery.10–12 Adult dogs might pose more of a threat to the snake compared to the playful and naive nature of puppies which would cause the snake to release more venom into the adult victim.10 This might be a contributing reason to explain why all five puppies in this series survived.
All five of the puppies were taken to the emergency hospital within a two-hour period following their likely snake encounter. Four of these were fortunate to maintain stable vital signs upon presentation. Case two was on the threshold of decompensating, but readily stabilized with emergency treatment. In envenomated children, their small size has traditionally been thought to predispose them to a greater amount of venom per square meter area, thus exposing more cells to the adverse effects of the venom.13,14 In Parish’s study dating as far back as 1965, the majority of children did well so long as they received antivenom.13 In LoVecchio’s study of 66 envenomated children over a 10-year period, 38% of children developed a hypersensitivity to whole IgG antivenom and there were five cases of morbidity, but all survived.14 These reports of increased rather than decreased survival is likely due to the availability of antivenom and its use in children during the 1960’s and after. The same guarded prognosis was assumed with this young canine population, but all puppies in this report survived as well with timely antivenom and medical management.
These five puppies are the first cluster of canine pediatric snake bite victims, aged 11 to 20 weeks old, in the United States to be described. The clinical signs in this particular group were similar to those seen in many adult dogs in the same region.15,16 Two of the four had prolonged activated clotting times, with bleeding restricted to the bite site. The ACT was selected to monitor coagulopathy because of the small amount of blood required for this test, its relative low cost, proximity of the machine to the emergency room, and its proven clinical benefits as a point-of-care test when managing snake bite victims with coagulopathies.17
Three of the five puppies were bitten in the face while two were bitten in the limbs which is similar to that seen in adult dogs.15 The snake bite severity scores ranged from 1 to 10 with all values reverting to minor status by day two following treatment.
The amount of antivenom administered to each puppy paralleled its SSS whereby those with scores < 2 receiving 1-2 vials, and the most severely affected puppy (case two) with a presenting score of 10 receiving proportionally more antivenom (nine total vials). None of the puppies in this case series developed a hypersensitivity reaction to the F(ab)2 antivenom§. In children, hypersensitivity reactions to equine-derived IgG antivenom is common (38%)14, while less common (2.8%)7when administered ovine-derived F(ab) antivenom. As this is a small case series, it is likely that equine derived F(ab)2antivenom has the potential to cause hypersensitivity reactions in puppies, similar to adult dogs.15
Fluid overload in children weighing less than 10 kg and those with physiologic concerns for fluid overload, such as congestive heart failure, chronic lung disease, and renal insufficiency is a concern in human medicine when multiple doses of antivenom are administered as their protocols typically dilute antivenom in 250 mL 0.9% saline.7 Puppies in this study ranged from 4.3 to 15.2 kilograms, and the same risk for fluid overload should be considered when treating pediatric dogs requiring multiple doses of antivenom. In this series, antivenom was diluted in 50 to 100 mL 0.9% saline at the clinician’s discretion, and no reported complications from fluid overload occurred.
The small number of puppies included in this case series limits statistical analysis to determine prognostic factors. In addition, due to the retrospective nature of this case series and medical record system at the author’s institution, cases were obtained by searching invoice items for pit viper antivenom and age of six months or less in dogs. As such, puppies presenting to the emergency room with a snake bite, but did not receive antivenom, due to lack of clinical need or owner financial restrictions, would have been overlooked in data collection. Therefore, prospective studies to enroll all pediatric dogs with a witnessed or suspected pit viper envenomation are warranted to determine morbidity and mortality.