As part of CDC recommendations, how long should quarantined rats be held before reintroduction if negative?

• A. 2 weeks
• B. 4 weeks
• C. 6 weeks
• D. 8 weeks

Answer: (B)

Quarantine is used to separate new animals and monitor them for illness so they don’t introduce infections into the rest of the colony. For rats, a four-week period is used because it aligns with the time it can take for many pathogens to reveal themselves or become detectable after exposure, even if initial screens are negative. Holding for four weeks gives multiple chances to observe for subtle or late-developing signs and, if testing is done, to confirm that residual infections aren’t present before reintroduction.

Going shorter, like two weeks, risks missing infections with longer incubation or latent periods. Extending beyond four weeks generally isn’t needed given standard surveillance and testing practices and would add unnecessary cost and stress. During this quarantine, maintain separate housing and equipment, monitor for clinical signs, and perform follow-up testing as indicated before reintroducing the rats to the main colony.