Brown snake envenomation in cats: are two antivenom doses better than one?
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Snake bite poisoning is a common emergency seen in cats at our veterinary hospital and at veterinary clinics in many parts of Australia.
Brown snakes (Pseudonaja spp.) are the most common snake causing poisoning in Australian dogs and cats. The snake venom causes severe nervous system damage leading to progressive paralysis. In addition, snake venom causes a blood clotting disorder leading to spontaneous bleeding or excessive bleeding from minor wounds.
Intravenous administration of brown snake antivenom is the mainstay of treatment for brown snake envenomation. The survival rate of cats and dogs treated with antivenom is significantly higher than those not treated, but severely affected animals still have a high risk of death.
A major unanswered question is how to judge the number of doses of antivenom to administer to an animal. This is important to know since antivenom is expensive, and pet owners’ decisions on what treatment to allow for their animals are best informed by both financial and outcome data.
Over the summer of 2018-2019 we developed a scoring system to assess snake bitten cats as soon as they were admitted to the hospital. Those cats with a score ≥7 turned out to have a 50% probability of dying despite supportive care and one dose of antivenom, which was the standard treatment at that time. This scoring system was developed by analysing a relatively small number of cats.
To follow up, we collected data on additional cats over the summer of 2019-2020. This data needs to be thoroughly analysed, but preliminary analysis supports the conclusion that cats with a score of ≥7 have a 50% probability of dying despite standard treatment.
- To firmly establish a classification scheme for accurately predicting outcome after treatment with one vial of brown snake antivenom and supportive care, to be applied at initial clinical presentation of cats envenomated by brown snakes (Pseudonaja genus). This aim will be accomplished by thorough analysis of existing clinical records.
- To prospectively compare the clinical outcomes of a cohort of envenomated cats with poor prognostic features treated with one vial versus a cohort treated with two vials of snake antivenom. We have funding from the Australian Companion Animal Health Foundation to provide a second dose of antivenom at no cost to owners of animals with severe clinical signs. Data from these cases will need to be collected between October 2020 and March 2021, and analysed for comparison with the cohorts treated with only one dose of antivenom.
- To better understand the incidence, diagnosis, treatment and outcomes of brown snake envenomated cats in general practice, we propose to analyse electronic clinical records from general practices, in collaboration with colleagues from the University of Queensland. We will make use of the data collected by VetCompass Australia from several hundred veterinary practices throughout Australia.
- On the basis of our preliminary data from 2018-2019, we hypothesise that cats with initial clinical scores ≥ 7 in our classification system and that are treated with only one vial of antivenom and supportive care after brown snake bites will have a 50% death rate.
- The corollary of this hypothesis is that the survival rate will be higher than 50% for cats with initial clinical scores ≥ 7 that receive two vials of antivenom in addition to supportive care.