When performing leptospira PCR, when should the test be run?

• A. Before starting antibiotic treatment
• B. After starting antibiotic treatment
• C. Only after serology is positive
• D. Only in vaccinated animals

Answer: (A)

PCR for Leptospira is most informative during the early infection when the bacteria are circulating in the blood. Doing the test before antibiotic treatment maximizes the chance of detecting leptospiral DNA, because antibiotics promptly reduce bacterial load and can lower PCR sensitivity. Serology tends to become positive later, after the immune response develops, so waiting for serology would miss the window when PCR works best. Antibiotics after onset can still show positive PCR, but with reduced sensitivity, so the ideal timing is before starting treatment. Vaccination does not guarantee absence of infection or bacteremia, so PCR isn’t restricted to unvaccinated animals.