Yoda was a 10 year old male castrated Yorkshire terrier that presented to the Emergency and Critical Care service for possible rattlesnake bite. He was given a rattlesnake vaccination earlier in the year.
On presenting physical exam, she was noted to be tachycardic (170bpm) and tachypnic (50bpm) with a normal temperature. He was noted to have bleeding puncture wounds over the proximal hind limb. Yoda was given an injection of methadone for pain control initially.
Prior to performing lab work, Yoda was given 1 vial of IV over 1 hour and then started on IV fluids. His vital parameters were monitored every 5 – 15 minutes during administration and he was noted to remain stable. He was then continued on IV fluids and Fentanyl CRI.
Lab work checked after administration of anti venom included a CBC, chemistry, and PT. CBC revealed an unremarkable hemogram, leukogram and platelet count. Chemistry revealed mild elevation in ALT (536u/L; RR 10- 125u/L), hyperbilirubinemia (2.7mg/dl; RR 0- 0.9mg/dL), and hyperglobulinemia (4.6g/dL; RR 2.5-4.5g/dL). PT was within normal limits at 12s (RR 11-17s).
Overnight, the edema and swelling of the wound worsened, with extension from the flank to the hock with ventral ecchymoses being evident. A second vial of Venom Vet Antivenom was administered IV with no changes to vital parameters during administration.
After completion of the second vial of antivenom, the wound was stable and non painful on examination. He was willing to eat, was transitioned to gabapentin, discontinued fentanyl and discharged with oral pain medications. His case was lost to follow up so information after discharge was not known.
Pit viper envenomation tends to be the first thought when anyone thinks of Texas. It is an unfortunate, but completely appropriate association.
Clinical signs for dogs tend to be worse than in cats, as cats seem to be more resistant to pit viper envenomation. There are a lot of factors that seem to play a role in the severity of the envenomation, including species, age, size, location of the bite, post bite excitability, and the health status of the parties involved. Concurrent medications may affect the severity the clinical signs. The quantity and toxicity of the snake venom injected is influenced by the season, the time since last discharge of venom, age and
size of snake, and the motivation of the snake.
Venom carries multiple components, including toxins that cause tissue necrosis and damage, hemolytic toxins, anticoagulase toxins, metalloproteinase, collagenase, hyaluronidase, phospholipases, etc.
The local wound tends to be edematous, be severely painful, have ecchymoses, and discoloration. Shaving the hair in the area can help with finding the strike marks. In the absence of pain and swelling, potentially the pet received a dry or non poisonous bite.
Many of the systemic signs can include hypotension, shock, cardiac arrhythmias, bleeding disorders, ptyalism, nausea, vomiting, respiratory distress, and confusion. Most of the clinical signs reliably occur in the first 30 minutes from the bite.
Diagnostic recommendations include lab work, wound evaluation, and clotting factor evaluation. Some patients additionally require continuous ECG or blood pressure monitoring. In some patients that are at a higher risk of acute renal failure, from shock, myoglobinuria, defibrination syndrome, or hemoglobinuria, also require urine testing and urine production monitoring.
Hematologic abnormalities are noted in 81% of the cases, with coagulation changes in 56% of cases (McCown, et al) and thrombocytopenia in 88% of cases (Hackett, et al).
Antivenom is the key component for treatment of the more severe pit viper envenomations. Not all envenomated patients require antivenom treatment. The choice to administer is based on the clinical aspects of the patient. The four most common indicators for antivenom include 1) rapid progression of swelling, 2) significant coagulopathy, defibrination or thrombocytopenia, 3) neuromuscular toxicity; and/or 4) shock.
Antivenom does not prevent all effect of venom, including myotoxins, and if not administered in a short time frame, metalloproteinases. Antivenom is very beneficial in reversing most systemic effects including coagulation deficits, fluid loss, neurologic signs, and cardiac dysrhythmias.
In addition to antivenom, IV fluid therapy and pain management are the mainstays of management. In general, non-steroidal anti inflammatory medications are not recommended for patients at risk for impaired platelet aggregation or acute kidney injury. Glucocorticoids are also controversial in management both in human and veterinary medicine.
Prognosis is dependent on the severity of envenomation as well as the promptness of appropriate medical management.