Gorgas Case 2022-04 |
The following patient was seen on the inpatient ward of Cayetano Heredia Hospital in Lima by the 2022 Gorgas Course participants. History: A 53-year-old woman was bitten by a snake in the 4th digit of the right hand while washing the dishes outside. Immediately, there was intense stabbing pain in the finger, radiating to the hand; the area around the bite started swelling and becoming red. She poured kerosene and gasoline over her entire arm and went to the nearest health center, where she was referred to our institution, arriving two hours after the bite. Epidemiology: She was born in Huarochirí, Lima, and currently lives in Yangas, elevation 915 meters, in Canta province in the highlands of Lima, 40 km northeast of UPCH. She works as a housekeeper. Physical Examination: T 36°C, BP 120/70 mmHg, HR 65 bpm, RR 17 rpm, Sat 98% (FiO2 0.21) Patient appeared unwell. On the 4th finger of the right hand, the skin was darkened and blistering (Image A). The right arm was swollen up to the axilla, with petechiae and ecchymoses (Image B). Spontaneous systemic bleeding was detected from the gums. Swelling increased in the following days. Local lymphadenopathy was not detected. The rest of the physical exam was unremarkable. Laboratory: Hematocrit: 34%. Hemoglobin:11.6 g/dl. WBC: 5.75 (0% bands, 86.5% segmented, 0% eosinophils), Platelets 192. Creatinine: 0.4 mg/dl. Urea: 35 mg/dl. INR: 1.8 (normal less than 1.2), PT: 24.3 (normal 11-13.5 seconds), aPTT: 70.6 (normal 25-35 seconds), CK 483. mcg/l. Urine Exam: density 1030, 0-2 leu/field, 4-6 RBC/field, sparse epithelial cells.
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Diagnosis: Mild envenoming by desert lance-headed pit viper (Bothrops pictus or B. roedingeri) Discussion: Species diagnosis: After being bitten, the patient killed the snake and took a picture of it with her mobile phone (Image C), which allowed us to identify it as a desert lance-headed pit viper (Bothrops pictus or B. roedingeri) (“jergón de la costa”, or “víbora”), approximately 30 cm in total length. These are the only venomous species found in the Lima area. [Campbell, JA, Lamar, WW. (eds.) The Venomous Reptiles of the Western Hemisphere. Ithaca, Comstock Cornell University, 2nd Ed 2004]. B. pictus and B. roedingeri are endemic Peruvian species (Images D and E) found on the western slopes of the Andes, and throughout the coastal foothills and mountains at altitudes between sea level and 2,300 m, from the south of Ancash Ancash to Arequipa. They also occur in some of the drier inland valleys and mountains, such as Chillón and Canta, and cerros in the Cono Norte of metropolitan Lima. These two species are superficially similar in appearance, have been widely confused and, indeed are, according to some authorities, merely subspecies (http://reptile-database.reptarium.cz/species?genus=Bothrops&species=pictus). B. roedingeri differs from B. pictus in being longer and more slender (up to 100cm in total length compared to 60cm), having fewer dorsal scale rows and more ventral scales, and inhabiting lower altitudes closer to the coast as far North as La Libertad [Campbell, JA, Lamar, WW. (eds.) The Venomous Reptiles of the Western Hemisphere. Ithaca, Comstock Cornell University, 2nd Ed 2004]. Evolution of envenoming: After receiving a bite on the 4th finger of her right hand, our patient developed, over the next few days, progressive pain, dysfunction, swelling and bruising of the entire arm, axilla and right side of her trunk (Image B) which largely resolved over the next few days. Evidence of mild systemic envenoming was gingival bleeding, ecchymoses and petechiae, associated with abnormal PT, INR and aPPT, attributable to venom procoagulant toxins and endothelial-damaging metalloproteinase hemorrhagins. Literature reports and local snake-bite experts in the Lima area have not distinguished bites by B. pictus from those by B. roedingeri. A study of 23 patients with presumed B. pictus bites admitted to Cayetano Hospital in 1990-1998 described local swelling, erythema, bruising (sometimes extensive), and blistering as the commonest features [Folia Dermatol Perú 1998;.9: 41-48]. Coagulopathy was detected in 6 of 8 cases and one developed acute kidney injury. 75% were treated with INS antivenom and there were no fatalities. Envenoming is not inevitable after a bite by a venomous snake even when there are visible puncture marks on the skin. The phenomenon of “dry bite” has been well documented in about 50-80% of snake-bite victims [Toxicon 2017;133:63-67]. It was well illustrated by a patient seen in the ED of Cayetano Hospital on a previous edition of the Gorgas Course. Despite fang marks and identification of the causative snake as a desert lancehead, he developed no symptoms or signs of envenoming. Mechanism of hemorrhage: The venom of B. pictus contains an array of toxic proteins and peptides typical of Viperidae, but compared to some other Peruvian pit vipers, such as the notorious B. atrox of the Amazon region (see case 2, 2014), it has a higher proportion of hemorrhagins [J Proteomics 2012;75(7):2181-95]. These are large molecular weight P-III snake venom metalloproteinases (SVMPs) that possess an N-terminal Zn 2+ - dependent catalytic domain, disintegrin-like domain and C-terminal cysteine-rich region. They degrade matrix proteins in the capillary basement membrane, resulting in spontaneous systemic hemorrhage, a dangerous effect of envenoming [Toxins (Basel) 2016;8(4):93]. A variety of venom toxins, including SVMPs, and an L-amino acid oxidase from B. pictus venom, can inhibit platelet agglutination [Toxicon 2017;139:74-86]. Although our patient did not develop thrombocytopenia, her platelet function may have been impaired, contributing to the extent of local bleeding. Mechanism of hemorrhage: The venom of B. pictus contains an array of toxic proteins and peptides typical of Viperidae, but compared to some other Peruvian pit vipers, such as the notorious B. atrox of the Amazon region (see case 2, 2014), it has a higher proportion of hemorrhagins [J Proteomics 2012;75(7):2181-95]. These are large molecular weight P-III snake venom metalloproteinases (SVMPs) that possess an N-terminal Zn 2+ - dependent catalytic domain, disintegrin-like domain and C-terminal cysteine-rich region. They degrade matrix proteins in the capillary basement membrane, resulting in spontaneous systemic hemorrhage, a dangerous effect of envenoming [Toxins (Basel) 2016;8(4):93]. A variety of venom toxins, including SVMPs, and an L-amino acid oxidase from B. pictus venom, can inhibit platelet agglutination [Toxicon 2017;139:74-86]. Although our patient did not develop thrombocytopenia, her platelet function may have been impaired, contributing to the extent of local bleeding. We would like to thank Professor David Warrell, Emeritus Professor at Oxford University, for providing insightful case discussion. |