Reply to Vikrant and Verma about “Monitor Lizard Envenoming”

We read with concern the case report by S. Vikrant and B.S. Verma (Renal Failure online early DOI: 10.3109/0886022X.2013.868223), claiming a bite from a monitor lizard caused systemic envenoming and fatal renal failure. In the patient’s location a variety of venomous snakes exist, including Russell’s viper (Daboia russelii), envenoming by which would certainly be able to cause the constellation of effects and outcome experienced by this patient. Snakebite causes at least an estimated 45,000 fatalities in India every year1 and Russell’s viper is a leading contributor to this toll. Being bitten by this snake while performing agrarian chores is a classic cause of such bites. The rapid development of coagulopathy is typical of envenoming by this snake, as is the local hematoma formation and development of AKI.2 The treating doctors decided to give Indian polyvalent snake antivenom, likely a fortunate choice, but then the antivenom was stopped because of the identification of the supposed culprit as a monitor lizard. However, even if this was a case of D. russelii envenoming, administration of further antivenom may have been unsuccessful in altering the outcome of such a late and life-threatening presentation, in the absence of hemodialysis available for an extended period. The rhabdomyolysis in this case is also a documented problem with some Russell’s viper bites. The combination of renal failure due to AKI and hyperkaliemia inadequately controlled by peritoneal dialysis is a known cause of fatal cardiac events in snakebite.2^,3 Thus, this case is entirely consistent with snakebite, and relevantly, particularly with D. russelii envenoming.

In contrast there is contentious research describing the presence in some monitor lizards (especially the Komodo dragon; Varanus komodoensis) of genes, or their transcripts, encoding toxins that are found in snake venoms; shared among some squamate reptiles and these may be expressed in oral secretions,4 but there are no confirmed cases of clear envenoming associated with monitor bites including by the Bengal monitor (V. bengalensis). To date, there are no “venom” studies on oral secretions of V. bengalensis specifically that confirm the presence of toxins such as those reported from oral secretions of V. komodoensis or V. varius (lace monitor), let alone studies demonstrating any such toxins have potent procoagulant, nephrotoxic, hemolytic, or myotoxic activities, and that these might be delivered in medically significant volumes/concentrations. In the absence of such information it is, in our opinion, absolutely inappropriate to claim, as Vikrant and Verma do, that this lizard can cause such systemic envenoming effects in humans. It is both surprising and disconcerting that such a claim passed by the peer review process, and was retained in the published paper.

At most, this case could have been presented as a case of fatal envenoming where the causation was unknown, but there was a temporal association with a possible bite by V. bengalensis. The author’s bold assertions that their case demonstrates that “monitor lizard venom is capable of producing intravascular hemolysis, coagulopathy, and rhabdomyolysis” is scientifically unsound and without merit. This species of monitor has been widely kept in captivity for many decades, with numerous bites occurring and there are no reports, either in the scientific or medical literature, consistent with medically significant envenoming by this or any other monitor lizard species.5 We are aware of two anecdotal reports describing non-specific “toxic” effects after bites by the desert monitor, V. griseus;6^,7 these reports do not, in our opinion, meet appropriate standards for peer reviewed scientific or medical papers, nor can they be characterized as clearly medically significant envenoming.

Can we even be sure of the identity of the culprit in this case? Can we be sure that only the allegedly witnessed culprit was responsible for any bite(s)? The answer in both cases is likely “no”. For such an extraordinary case, it is incumbent on the authors to ascertain with the highest degree of assurance, the identity of the culprit and validity of the proffered history. They offer no evidence they have undertaken such scientific rigor. It is worth noting that one of the regional vernacular names for V. bengalensis mentioned by Vikrnat and Verma, “goh”, is a contraction of “gohera” or “ghorpad”, and is quite similar to “ghonas” and “gunas”, local names for D. russelii.

Finally, it is important to emphasize that we are not claiming that envenoming by some varanid lizards could not happen. We are asserting the need for careful documentation and verified confirmation of the envenoming animal’s identity before assigning a fatal bite to any species for which there is no previous evidence for such lethal potential. Such assignment carries serious and indelible medical, biological and legal ramifications that cannot be ignored or dismissed and so must be supported by substantial quality evidence. We contend that the case report by Vikrnat and Verma does not meet this standard.

Declaration of interest

The authors declare no conflicts of interest. The authors alone are responsible for the content and writing of this article.