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In Response to How Not To Train Your Dragon: A Case of Komodo Dragon Bite, by Borek and Charlton

2015; Elsevier BV; Volume: 26; Issue: 4 Linguagem: Inglês

10.1016/j.wem.2015.04.003

1545-1534

Scott A. Weinstein, Julian White,

Amphibian and Reptile Biology

We read with interest the article by Borek and Charlton1Borek H.A. Charlton N.P. How not to train your dragon: a case of Komodo dragon bite.Wilderness Environ Med. 2015; 25: 196-199Abstract Full Text Full Text PDF Scopus (6) Google Scholar that described the uncomplicated lacerations that resulted from a Komodo monitor (Varanus komodoensis) bite. In their article, Borek and Charlton1Borek H.A. Charlton N.P. How not to train your dragon: a case of Komodo dragon bite.Wilderness Environ Med. 2015; 25: 196-199Abstract Full Text Full Text PDF Scopus (6) Google Scholar document the mild local trauma induced by the described bite; bites from any varanid lizard, especially V komodoensis, are rarely formally documented, and thus the report has notable value. However, the authors then discuss the recent classification of these lizards as venomous without critically balancing the premature use of this term, or considering the current lack of sufficient evidence supporting the use of venom by V komodoensis in prey capture. It must be noted that the current, traditional, synthesized definition of venom with emphasis on snake venoms does not include any reference to possible medical effects in humans, as we are not natural prey or predators of venomous snakes (for a discussion of the definition of venom, see Weinstein et al2Weinstein S.A. Keyler D.E. White J. Replies to Fry et al. (Toxicon 2012, 60/4, 434–448). Part A. Analyses of squamate reptile oral glands and their products: a call for caution in formal assignment of terminology designating biological function.Toxicon. 2012; 60: 954-963Crossref PubMed Scopus (19) Google Scholar; Fry et al3Fry B.G. Casewell N.R. Wüster W. Vidal N. Young B. Jackson T.N. The structural and functional diversification of the Toxicofera reptile venom system.Toxicon. 2012; 60: 434-448Crossref PubMed Scopus (100) Google Scholar; Jackson et al4Jackson T.N. Casewell N.R. Fry B.G. Response to “Replies to Fry et al. (Toxicon 2012, 60/4, 434–448). Part A. Analyses of squamate oral glands and their products: a call for caution in formal assignment of terminology designating biological function.”.Toxicon. 2013; 64: 106-112Crossref PubMed Scopus (4) Google Scholar; Weinstein et al5Weinstein S.A. White J. Keyler D.E. Kardong K.V. Response to Jackson et al. (2012).Toxicon. 2013; 64: 116-127Crossref PubMed Scopus (6) Google Scholar). Also, although Borek and Charlton1Borek H.A. Charlton N.P. How not to train your dragon: a case of Komodo dragon bite.Wilderness Environ Med. 2015; 25: 196-199Abstract Full Text Full Text PDF Scopus (6) Google Scholar note the theoretical nature of the possible roles of varanid lizards’ oral products, as asserted by some authors,3Fry B.G. Casewell N.R. Wüster W. Vidal N. Young B. Jackson T.N. The structural and functional diversification of the Toxicofera reptile venom system.Toxicon. 2012; 60: 434-448Crossref PubMed Scopus (100) Google Scholar, 6Fry B.G. Wroe S. Teeuwisse W. et al.A central role for venom in predation by Varanus komodoensis (Komodo dragon) and the extinct giant Varanus (Megalania) priscus.Proc Natl Acad Sci U S A. 2009; 106: 8969-8974Crossref PubMed Scopus (91) Google Scholar they cited without critical consideration an arguably flawed published clinical report7Vikrant S. Verma B.S. Monitor lizard bite-induced acute kidney injury—a case report.Ren Fail. 2014; 36: 444-446Crossref PubMed Scopus (12) Google Scholar of a reportedly fatal outcome of a presumed envenomation by the Bengal monitor (Varanus bengalensis). That report has been challenged8White J. Weinstein S.A. Reply to Vikrant and Verma about “Monitor lizard envenoming.”.Ren Fail. 2015; : 1-2Crossref PubMed Scopus (5) Google Scholar because it lacks essential information such as the verified identity of the envenoming animal and any biomedical or clinical information that supports the likelihood of a fatal bite delivered by a V bengalensis. The unfortunate victim in that report exhibited a clinical course very similar to that of a life-threatening envenoming by Russell’s viper (Daboia russelii), a species that is a major cause of snakebite-inflicted morbidity and mortality in the region where the bite reportedly occurred.8White J. Weinstein S.A. Reply to Vikrant and Verma about “Monitor lizard envenoming.”.Ren Fail. 2015; : 1-2Crossref PubMed Scopus (5) Google Scholar Furthermore, there is contentious research describing the presence of genes or their transcripts encoding toxins that are found in snake venoms, which may be expressed in oral secretions, in some squamate reptiles, including some monitor lizards (especially V komodoensis)9Fry B.G. Vidal N. Norman J.A. et al.Early evolution of the venom system in lizards and snakes.Nature. 2006; 439: 584-588Crossref PubMed Scopus (441) Google Scholar; however, there are no confirmed cases of clear envenoming associated with monitor bites, including by the Bengal monitor (V bengalensis). The synthesized traditional consensus definition of venom is “a complex substance produced in a specialized gland and delivered by an associated specialized apparatus that is deleterious to other organisms in a given dosage and is actively used in the subjugation and/or digestion of prey and/or in defense.”2Weinstein S.A. Keyler D.E. White J. Replies to Fry et al. (Toxicon 2012, 60/4, 434–448). Part A. Analyses of squamate reptile oral glands and their products: a call for caution in formal assignment of terminology designating biological function.Toxicon. 2012; 60: 954-963Crossref PubMed Scopus (19) Google Scholar Biological function—that is, how it is used—is a crucial defining factor that is the essence of the definition. Although the oft-repeated hypothesis of a role of oral, pathogenic bacteria in V komodoensis predation has no objective supporting evidence and is likely incorrect, there is likewise currently no clear evidence of a “venom” function; those advocating this function3Fry B.G. Casewell N.R. Wüster W. Vidal N. Young B. Jackson T.N. The structural and functional diversification of the Toxicofera reptile venom system.Toxicon. 2012; 60: 434-448Crossref PubMed Scopus (100) Google Scholar, 6Fry B.G. Wroe S. Teeuwisse W. et al.A central role for venom in predation by Varanus komodoensis (Komodo dragon) and the extinct giant Varanus (Megalania) priscus.Proc Natl Acad Sci U S A. 2009; 106: 8969-8974Crossref PubMed Scopus (91) Google Scholar state that V komodoensis “seem incapable of bringing down an adult water buffalo” and assign as a proposed cause of death possible life-threatening sepsis in retreating, bitten buffalos that occurs as a consequence of extended submersion in fecally contaminated water.3Fry B.G. Casewell N.R. Wüster W. Vidal N. Young B. Jackson T.N. The structural and functional diversification of the Toxicofera reptile venom system.Toxicon. 2012; 60: 434-448Crossref PubMed Scopus (100) Google Scholar As we have opined elsewhere, given the most parsimonious evidence available, animals bitten by V komodoensis most likely succumb from massive blood loss and hypovolemic shock.2Weinstein S.A. Keyler D.E. White J. Replies to Fry et al. (Toxicon 2012, 60/4, 434–448). Part A. Analyses of squamate reptile oral glands and their products: a call for caution in formal assignment of terminology designating biological function.Toxicon. 2012; 60: 954-963Crossref PubMed Scopus (19) Google Scholar V komodoensis possess large, serrated teeth, and significant bites inflict serious damage to large blood vessels. There is no current evidence that V komodoensis bites cause coagulopathy or precipitous hypotension, aside from that associated with hypovolemic shock from trauma, in bitten prey animals. There is also no convincing evidence whether toxins detected in V komodoensis oral secretions might be delivered in volumes or concentrations significant enough to cause the death of a prey animal or produce medically significant effects in a bitten human. Although not subjected to formal medical review, there have been one or two V komodoensis bites described that also featured uncomplicated, mild-to-moderate local effects resulting from physical trauma.10Auffenberg W. The Behavioral Ecology of the Komodo Monitor. University of Florida Press, Gainesville, FL1981: 406Google Scholar Other varanid species (including V bengalensis) have been popular in private collections 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. We are aware of 2 anecdotal reports (see White and Weinstein8White J. Weinstein S.A. Reply to Vikrant and Verma about “Monitor lizard envenoming.”.Ren Fail. 2015; : 1-2Crossref PubMed Scopus (5) Google Scholar) describing nonspecific “toxic” effects after bites by the desert monitor, Varanus griseus; these reports do not, in our opinion, meet appropriate standards for peer-reviewed scientific or medical papers, nor can they be characterized as consistent with medically significant envenoming. Finally, it should be noted that we are not claiming that envenoming by some varanid lizards could not happen. We are asserting the need for independent confirmation of the biological function of purported “venom” before the term is applied, and careful documentation and verified confirmation of the envenoming animal’s identity before assigning a medically significant bite to any species for which there is no previous evidence for such. The patient bitten by a captive V komodoensis in the case documented by Borek and Charlton1Borek H.A. Charlton N.P. How not to train your dragon: a case of Komodo dragon bite.Wilderness Environ Med. 2015; 25: 196-199Abstract Full Text Full Text PDF Scopus (6) Google Scholar experienced only mild, uncomplicated trauma. Any assignment of venomousness accompanied by suggested or implied medical significance carries serious and indelible medical, biological, and legal ramifications that cannot be ignored or dismissed, and so must be supported by substantial quality evidence.8White J. Weinstein S.A. Reply to Vikrant and Verma about “Monitor lizard envenoming.”.Ren Fail. 2015; : 1-2Crossref PubMed Scopus (5) Google Scholar Currently, the implied venom functions of varanid oral secretions are not supported by available evidence, nor is the presumptive assignment of any clinical significance of varanid oral toxins or their transcripts.