Imagine this clinical scenario: a client has brought in their dog that has a suspected snakebite. The patient has two wounds that are consistent with fang marks, and the owner has reason to suspect that their pet has been in contact with a snake.
You are aware that infection is possible due to bacteria present on snake fangs but don’t want to prescribe antimicrobials unless it is necessary. You want to know whether there is evidence that the use of antimicrobials in this case will improve the clinical outcome by reducing wound infection.
The evidence
Seven papers were critically reviewed. Five of the papers were retrospective case series studies. These were Pritchard et al. (2014), Hackett et al. (2002), Kim et al. (2022), McCown et al. (2009) and Witsil et al. (2015), all of which retrospectively studied the cases of dogs that were presented to veterinary hospitals across multi-year periods. The studies looked at 52, 100, 70, 218 and 272 dogs, respectively. All of the studies contained patients who had been treated with antibiotics and patients who had not, and all studied the treatment received and the clinical outcomes. Other outcomes studied were: complications (Hackett et al., 2002), clinical signs and examination records (Kim et al., 2022) and type of antibiotic used (Witsil et al., 2015).
The other two studies were prospective studies: a prospective observational case series (Carr and Schultz, 2015) and a prospective case series (Lervik et al., 2010). The studies looked at 102 and 53 dogs over a period of 13 and 6 months, respectively. In both studies, some patients were treated with antibiotics, while others were not; the percentages of patients treated with antibiotics were 82 percent (Carr and Schultz, 2015) and 18.8 percent (Lervik et al., 2010). Carr and Schultz (2015) studied the following outcomes that were relevant to the question: treatment, mortality and incidence of wound infection. None of the outcomes studied by Lervik et al. (2010) were relevant to the question.
Limitations of the evidence
All of the studies were case series, which means they have limited evidentiary power, have a high likelihood of bias and cannot reliably prove causation
None of the papers studied directly addressed the question by directly comparing antimicrobial treatment to no antimicrobial treatment in dogs that had snakebites. Some studies either did not study wound infection at all (Lervik et al., 2010; Pritchard et al., 2014) or did so in a manner that weakened the quality of the findings (Hackett et al., 2002; Kim et al., 2022; McCown et al., 2009).
Additionally, study design was poor. Five of the studies were retrospective case series studies (Hackett et al., 2002; Kim et al., 2022; McCown et al., 2009; Pritchard et al., 2014; Witsil et al., 2015), while one was a prospective observational case series (Carr and Schultz, 2015), and the other was a prospective case series (Lervik et al., 2010). All of the studies were case series, which means they have limited evidentiary power, have a high likelihood of bias and cannot reliably prove causation.
The studies also had relatively low sample sizes. These numbers are even lower when you consider how many dogs studied received antimicrobials, and there are insufficient cases of patients receiving antimicrobials against those that did not to make a significant comparison.
A further complicating factor is that the studies looked at bites from a variety of different snake species, and each patient would have been afflicted with varying amounts of venom. For example, Lervik et al. (2010) studied snakebites from the common European viper, Carr and Schultz (2015) and Hackett et al. (2002) both studied snakebites from rattlesnakes and McCown et al. (2009) studied snakebites from crotalids.
Further studies with larger cohorts and better study design – such as randomised controlled trials – that directly study the impact of antimicrobial administration on canine snakebite wound infections would help in providing stronger evidence relating to the research question.
A further complicating factor is that the studies looked at bites from a variety of different snake species, and each patient would have been afflicted with varying amounts of venom
Summary of findings
There is weak evidence to suggest that the administration of antimicrobials does not significantly affect the incidence of wound infection. However, this must be considered in conjunction with the limitations outlined above.
Lervik et al. (2010), Carr and Schultz (2015) and Pritchard et al. (2014) all looked at the incidence of wound infection following a snakebite. They reported that zero, one and one of the patients studied experienced infection, respectively. None of these recorded whether the patients experiencing infection received antibiotics, and Carr and Schultz (2015) found that the infection they recorded was not consistent with the oral flora of a snake.
McCown et al. (2009), Kim et al. (2022) and Witsil et al. (2015) evaluated survival and mortality in dogs that had been bitten by snakes. Four percent, 12 percent and 2.9 percent of patients in each study died, respectively. McCown et al. (2009) did not provide data on which fatalities had received antimicrobials. Kim et al. (2022) revealed a correlation between antibiotic use and survival but could not prove causation. Of the eight fatal cases (2.4 percent of a cohort of 272) reported by Witsil et al. (2015), three had received antibiotics and five had not.
Hackett et al. (2002) found no significant association between antimicrobial treatment and any outcome variables.
Conclusion
The papers studied suggest that administration of antimicrobials may not have a significant effect on the incidence of wound infection or outcome of survival in dogs that have been bitten by snakes
The papers studied suggest that administration of antimicrobials may not have a significant effect on the incidence of wound infection or outcome of survival in dogs that have been bitten by snakes. However, it must be noted that the quality of evidence was poor to low, and not directly applicable to the clinical scenario outlined above. Further research, directly applicable to this question and with good study design, is required to strengthen the quality of evidence.
| The full Knowledge Summary can be read in RCVS Knowledge’s open access journal Veterinary Evidence. |
Disclaimer
The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise; patient’s circumstances and owner’s values; country, location or clinic where you work; the individual case in front of you; and the availability of therapies and resources.
Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.
