The Health Status of Horses Used for at Least Six Complete Cycles of Loxoscelic Antivenom Production

Abstract

Antivenom production against Loxosceles venom relies on horses being immunized and bled for plasma harvest. One horse can partake in several cycles of antivenom production, which will require years of constant venom and adjuvant inoculation and bleeding. The actual impact on the health of horses that participate in several antivenom-producing cycles is unknown. Therefore, this study aimed to evaluate the general health status of horses that underwent at least six cycles of loxoscelic antivenom production. Seven crossbred horses that had partaken in six to eight complete antivenom-producing cycles were used and established as the immunized group (IG). Under the same handling and general management, eleven horses were established as the control group (CG). The horses were evaluated regarding their general clinical status and had their blood sampled, and an ECG recorded. The IG presented lower RBC and PCV, despite keeping values within inferior limits for the species. Renal function was not impaired, and liver-related enzymes were higher than those in the CG, probably due to liver exertion from immunoglobulin synthesis. ECG showed some abnormalities in the IG, such as atrioventricular block and a wandering atrial pacemaker, corroborated by an increase in CK-MB. The cardiovascular abnormalities were mainly found in the horses that participated in several antivenom-producing cycles. The overall results indicate that these horses had some impairment of their general health status. Once available, some alternative, less toxic antigens should replace the venom for immunization of horses used for antivenom production.

Keywords: antisera production; brown spider; dermonecrosis; loxoscelism; safety evaluation.

Figure 1

Multiple subcutaneous abscesses formed at infiltration sites in a horse used to produce Loxosceles antivenom.

Figure 2

ECG records from horses who had undergone from six to eight immunization cycles for Loxosceles antivenom production. (A) First-degree AV block. Note the increased PR interval (0.35 s) (black line). (B) Wandering atrial pacemaker. Notice the different P-wave morphology (arrows). (C) Second-degree AV block. Note that a P wave is not followed by a QRS complex (arrow) despite the maintenance of PP intervals. Recordings of the second deviation of the frontal plane (DII), with a velocity of 25 mm/s and amplitude 1 N.