Data on hamster LD50 from Leptospira and its impact on Title 9, Codified Federal Regulations Sections 113.102-113.103 test validity.

These data and analyses support the research article "Re-evaluating the LD50 requirements in the codified potency testing of veterinary vaccines containing Leptospira serogroups Icterohaemorrhagiae and Canicola in the United States" (Walker et al., 2018). Validity and disposition requirements submitted to the Center for Veterinary Biologics (CVB) are provided for serials (numbered lots) of commercial product potency tested for serogroups Canicola and Icterohaemorrhagiae in support of the Virus-Serum-Toxin Act (VSTA). Time course data for hamster loss after challenge with various concentrations of Leptospira during codified potency testing are also presented. The dose of Leptospira lethal to 50% of hamsters (LD50) was calculated by the Dragstedt-Behrens method for the in vivo data collected, and the equation is described here.

Re-evaluating the LD50 requirements in the codified potency testing of veterinary vaccines containing Leptospira (L.) serogroup Icterohaemorrhagiae and L. serogroup Canicola in the United States.

Approximately one-third of the reportable USDA Category D and E laboratory animals in the United States are expended on the potency testing of leptospiral vaccines by the codified hamster vaccination-challenge assay. Valid tests require ≥80% of challenge controls to succumb to disease and an LD50 between 10 and 10,000. This work evaluates the risk associated with the removal of LD50 limits; thereby, eliminating back-titration hamsters from in vivo potency assays for Leptospira (L.) serogroups Canicola and Icterohaemorrhagiae. The impact was assessed through 1) retrospective analysis of industry and CVB serial release data from July 2011-April 2015 and 2) evaluation through vaccination-challenge assays. For the initial vaccination-challenge assays (n = 3/serogroup), one group received potent bacterin (PB) and six groups received subpotent bacterins (SB1-SB6). PB and SB1 were challenged with a single dilution of Leptospira between 10 and 10,000 LD50. SB2-SB6 received serial dilutions of more concentrated challenge. Based on the retrospective analysis and in vivo assays, 80% of the challenge controls succumbing to disease reasonably ensured the minimal LD50 was administered. Subpotent vaccines were not at increased risk for being deemed potent when challenged with >10,000 LD50, but potent vaccines were at risk of being deemed subpotent when challenged with >10,000 LD50.