Daboia (Vipera) palaestinae Envenomation in 123 Horses: Treatment and Efficacy of Antivenom Administration

Abstract

Envenomation by venomous snakes is life threatening for horses. However, the efficacy of available treatments for this occurrence, in horses, has not yet been adequately determined. The aim of this study was to describe the treatments provided in cases of Daboia palaestinae envenomation in horses and to evaluate the safety and efficacy of antivenom administration. Data regarding 123 equine snakebite cases were collected over four years from 25 veterinarians. The majority of horses were treated with procaine-penicillin (92.7%), non-steroidal anti-inflammatory drugs (82.3%), dexamethasone (81.4%), tetanus toxoid (91.1%) and antivenom (65.3%). The time interval between treatment and either cessation or 50% reduction of local swelling was linearly associated with case fatality (p < 0.001). The overall mortality rate was 20.3%. Treatment with procaine-penicillin was significantly associated with reduced mortality (OR = 0.11). Three horse-derived antivenom products were available during the study period, of which the horses were administered different brands of varying dosages. Administration of the recommended dosage of any of the aforementioned products led to a significant decrease in mortality (p = 0.014), even in severe cases (scoring 2 or greater on the equine snakebite severity scale). No adverse reactions were reported. The results of this study show that species-specific D. palaestinae antivenom administered at the manufacturer-recommended dosage is effective in significantly reducing mortality in cases of envenomation in horses.

Keywords: Daboia palaestinae; Vipera palaestinae; antivenom; envenomation; horse; snakebite.

Figure 1

Frequencies of administration of different treatments following Daboia palaestinae envenomation displayed as percentage of 123 horses. [n/a = not available].

Figure 2

Mortality rates of horses treated with different products and dosages of antivenom following Daboia palaestinae envenomation.

Figure 3

Mortality rates of horses treated for Daboia palaestinae envenomation, in relation to (a) cessation of progression of clinical signs (local swelling), and (b) improvement of clinical signs (50% reduction of local swelling), as subjectively assessed by the attending veterinarian. The percentage of fatal cases within each group appears in bold above each bar.

Figure 4

Mortality rates of horses treated with the recommended dosage of species-specific antivenom (10 mL/1000 PD₅₀ Vipera palaestinae antiserum or 20 mL/500 PD₅₀ Viper-stat^®) in comparison to horses receiving no antivenom, or treated with less than the recommended dose (underdose) or with a non-specific antivenom product following Daboia palaestinae envenomation. The percentage of fatal cases within each group appears in bold above each bar.