What virus may not be clinically apparent but may cause an increased death rate during anesthesia in rats?

• A. Sendai virus
• B. Lymphocytic choriomeningitis virus
• C. Parvovirus
• D. Sialodacryoadenitis virus

Answer: (D)

The concept here is that some rat viral infections can be hidden or subclinical, yet stressors like anesthesia can reveal their harmful potential by increasing mortality risk. Sialodacryoadenitis virus is a coronavirus that commonly causes mild or no obvious illness in rats. Because the infection can be clinically silent, routines may miss it. However, under anesthesia, the respiratory system is already under stress, and SDA can contribute to airway and gland inflammation that worsens respiratory function or overall stress tolerance, leading to higher death rates during anesthesia. That combination of being often subclinical and still elevating anesthesia risk makes this virus the best fit.

Other viruses listed are more likely to produce overt signs in many rats (for example, respiratory symptoms with Sendai virus), are less commonly associated with anesthesia-specific mortality when subclinical, or are notable for zoonotic concerns or different disease patterns that don’t align as closely with the anesthesia-related risk described here.