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USDA is committed to reducing the use of live animals in testing and experimentation. Vaccines used in controlling animal disease frequently undergo testing in animal models to ensure they are effective. The USDA Center for Veterinary Biologics (CVB) enforces the Virus Serum Toxin Act, which requires animal vaccines to be safe, potent, and effective. From 2013-2018, CVB developed alternatives to the codified Leptospira vaccine potency test to help reduce the number of hamsters used for this test. Hamsters are used because of their sensitivity to the Leptospira organism. Approximately 40 total hamsters per serogroup are required for potency testing each leptospiral fraction. This number encompasses 10 vaccinated animals, 10 unvaccinated control animals, and additional unvaccinated animals used to determine the LD50 of the challenge strain. A valid test that confirms sufficient vaccine potency requires 80% survival in the vaccinated animals and 80% mortality in unvaccinated control animals after administering a standardized dose of leptospiral challenge.
In order to reduce the number of animals used in this testing, CVB provided options to veterinary biologics manufacturers. An ELISA was developed by CVB to eliminate live animal potency testing after appropriate validation for a particular product line. In cases where the ELISA was not yet a reasonable option for a product line, CVB allowed back-titration hamsters to be removed from the codified test. A company that wishes to use these options must request and receive an exemption from CVB.
A separate group of hamsters is also required to propagate and maintain virulent strains for the codified test and developmental needs associated with regulated vaccines. Over 2,500 hamsters per year per facility are estimated to be used for propagation of virulent Leptospira. As a result, the CVB developed a cryopreservation protocol for the commonly used leptospiral strains and provides cryopreserved virulent Leptospira upon request.
From 2013 to 2018, the USDA Animal Care program monitored the number of hamsters listed under Category E on the annual reports from six companies that conduct Leptospira vaccine potency testing. Category E includes instances in which pain or distress, or potential pain or distress, is not relieved with anesthetics, analgesics, and/or tranquilizer drugs. Facilities that use animals for research, teaching, and testing are required to submit to the USDA an annual report on animal usage under the Animal Welfare Act. In 2013, the Category E designations indicated approximately 35,767 hamsters were used in total for Leptospira vaccine potency testing. Monitoring revealed a steady decline in animal numbers over five years such that 20,099 hamsters were used in 2018 demonstrating a 38% reduction.
CVB believes the findings indicate that these options significantly contributed to the downward trend in hamster use. The options remain available and can be found on the CVB website. At this juncture, the USDA will continue annual monitoring of hamster use in Leptospira vaccine potency testing and also explore other areas where the 3Rs (replacement, reduction, or refinement of animal use) can be applied.