Assessing the Efficacy of First-Aid Measures in Physalia sp. Envenomation, Using Solution- and Blood Agarose-Based Models

Abstract

Stings from the hydrozoan species in the genus Physalia cause intense, immediate skin pain and elicit serious systemic effects. There has been much scientific debate about the most appropriate first aid for these stings, particularly with regard to whether vinegar use is appropriate (most current recommendations recommend against vinegar). We found that only a small percentage (≤1.0%) of tentacle cnidae discharge during a sting event using an ex vivo tissue model which elicits spontaneous stinging from live cnidarian tentacles. We then tested a variety of rinse solutions on both Atlantic and Pacific Physalia species to determine if they elicit cnidae discharge, further investigating any that did not cause immediate significant discharge to determine if they are able to inhibit cnidae discharge in response to chemical and physical stimuli. We found commercially available vinegars, as well as the recently developed Sting No More^® Spray, were the most effective rinse solutions, as they irreversibly inhibited cnidae discharge. However, even slight dilution of vinegar reduced its protective effects. Alcohols and folk remedies, such as urine, baking soda and shaving cream, caused varying amounts of immediate cnidae discharge and failed to inhibit further discharge, and thus likely worsen stings.

Keywords: Portuguese man o’ war; bluebottle; cnidaria; first aid; hydrozoa; jellyfish; marine envenomation; sting.

Figure A1

Two methods for estimation of dactylozooid bead surface area for calculation of percent cnidae discharge during a sting event. As both methods produced similar results, 1.54 mm² was used as the bead surface area.

Figure 1

Estimation of cnidae discharge during a sting event. Cnidae visualized (A) before and (B) after stinging in the blood agarose model (N = 4); an estimated 5.2 ± 1.5% of the tentacle’s cnidae sloughed off and remained adherent to the agarose, which are shown in (C,D). Panel (C) shows adherent cnidae after the 10-minute sting, while (D) shows the increased discharge of adherent cnidae after the application of site pressure. In both, examples of undischarged cnidae are indicated with black arrows, while discharged cnidae are indicated with white arrows. Site pressure led to about three times as much discharge from adherent cnidae.

Figure 2

Microscope images of P. utriculus tentacles 10 min after exposure to: (A) seawater; (B) vinegar; (C) urine; (D) ethanol; (E) Sting No More^® Spray; or (F) 30 s of pressure in the TSA. Discharged cnidae appear empty (lighter than the background or even white), though the extended tubule is not always visible (white arrows), while undischarged cnidae are darker than the background with a coiled tubule visible (black arrows). No discharge was seen in (A,B,E); moderate discharge is visible in (C); and maximal discharge is seen in (D,F).

Figure 3

Size of venom-induced hemolytic zone over time using the TBAA model when stings were treated with hot packs, cold packs, or kept at room temperature for: (A) P. utriculus stings of human blood agarose or (B) P. physalis stings of sheep’s blood agar plates. Significant differences between the treatments were found for both (Kruskal–Wallis Test, p < 0.0001 for P. physalis and one-way ANOVA, p = 0.0097 for P. utriculus). Cold packs resulted in significantly larger hemolytic zones after 24 h when compared to hot packs (post-hoc Fisher’s LSD; p = 0.0034 and p < 0.0001 for (A,B), respectively).

Figure 4

Size of venom-induced hemolytic zone over time using the TBAA model: (A) when P. utriculus tentacles were doused halfway through the sting with seawater (dark blue), soda (brown), ethanol (red), freshwater (light blue), or urine (yellow), or were pretreated with vinegar for 30 s (orange) using the human blood agarose, or (B) when P. physalis tentacles were pretreated with seawater (dark blue), ethanol (red), vinegar (orange) or Sting No More^® Spray (green) and tested using sheep’s blood agar. Significant differences between the treatments were found for both (Kruskal–Wallis Test, p = 0.0162 for P. physalis and one-way ANOVA, p < 0.0001 for P. utriculus). The addition of soda, freshwater and ethanol increased the size of the hemolytic area of P. utriculus stings after 24 h (p = 0.0007, = 0.0065, and = 0.0791 respectively compared to the no solution control in Fisher’s LSD post-hoc analyses), while pretreatment with vinegar led to a smaller area of lysis (Fisher’s LSD, p = 0.1259). Pretreatment with vinegar also reduced the lysis for P. physalis, particularly when compared with pretreatment with ethanol (p = 0.0285 in Dunn’s multiple comparison test).