Viral RNA in the bloodstream suggests viremia occurs in clinically ill rabies-infected mice

Data regarding the occurrence of a viremia during rabies virus infections are contradictory. Here, we attempted to clarify the dissimilar results using a qualitative TaqMan PCR assay to detect viral RNA in blood of mice that had been injected intramuscularly with rabies virus. Viral RNA was detected at two different intervals. Initially, RNA was present in blood of 30/32 (94%) mice, from 1 h to 2 days after injection of virus. The RNA in the blood at this time most likely resulted from trauma to blood vessels at the injection site and leakage of the inoculated virus into the circulation. Thereafter, from 3 to 30 days, viral RNA was undetectable in the blood of 37 mice that remained free of clinical disease. However, and more importantly, viral RNA was detected again in 21/25 (84%) mice that became clinically ill and were exsanguinated 2–4 days after the onset of paralysis. The presence of viral RNA in blood of the clinically ill mice might have been due to an escape of virus into the bloodstream as a result of viral replication induced injury in the central nervous system and other tissues. Anti-rabies virus neutralizing antibody was detected in sera of 11/21 (52%) clinically ill mice whose blood was positive for rabies viral RNA. The presence of viral RNA in the bloodstream of mice that developed clinical rabies suggested that a viremia might occur in rabies-infected mice. Thus, the current opinion that a viremia does not occur in experimental or natural rabies infections of other species might need to be re-evaluated.