Potential effect of prior raccoonpox virus infection in raccoons on vaccinia-based rabies immunization.

BACKGROUND: The USDA, Wildlife Services cooperative oral rabies vaccination (ORV) program uses a live vaccinia virus-vectored (genus Orthopoxvirus) vaccine, Raboral V-RG (V-RG), to vaccinate specific wildlife species against rabies virus in several regions of the U.S. Several naturally occurring orthopoxviruses have been found in North America, including one isolated from asymptomatic raccoons (Procyon lotor). The effect of naturally occurring antibodies to orthopoxviruses on successful V-RG vaccination in raccoons is the focus of this study. RESULTS: Overall, raccoons pre-immunized (n = 10) with a recombinant raccoonpox virus vaccine (RCN-F1) responded to vaccination with V-RG with lower rabies virus neutralizing antibody (VNA) titers than those which were not pre-immunized (n = 10) and some failed to seroconvert for rabies VNA to detectable levels. CONCLUSION: These results suggest that the success of some ORV campaigns may be hindered where raccoonpox virus or possibly other orthopoxvirus antibodies are common in wildlife species targeted for ORV. If these areas are identified, different vaccination strategies may be warranted.

Use of infrared thermography to detect signs of rabies infection in raccoons (Procyon lotor).

Infrared thermography was evaluated as a technique to determine if raccoons (Procyon lotor) experimentally infected with rabies virus could be differentiated from noninfected raccoons. Following a 10-day adjustment period, raccoons (n = 6) were infected with a virulent rabies street strain raccoon variant by injection into the masseter muscle at a dose of 2 x 10(4) tissue-culture infectious dose (TCID50) in 0.2 ml (n = 4) or 10(5) TCID50 in 1 ml (n = 2). Five of the six raccoons developed prodromal signs of rabies 17 to 22 days postinoculation (PI) and distinctive clinical signs of furious rabies between 19 and 24 days PI. At the time of euthanasia, which occurred 2 days after the onset of clinical signs of rabies, these five raccoons tested positive for rabies virus in brain tissue. Infrared thermal images of each raccoon were recorded twice daily during the preinoculation and PI periods. No apparent differences were identified among thermal temperatures compared among days for the eye, average body surface, and body temperature recorded from subcutaneous implants throughout the experiment for any of the six raccoons. However, increases in infrared surface temperature of the noses and differences in the visual thermal images of the noses were detected when animals began showing clinical signs of rabies. Differences were detected among the mean infrared nose temperatures for the disease progression intervals (F3.12 = 70.03, P < 0.0001). The mean nose temperature in the clinical rabies stage (30.4 +/- 3.5 degrees C) was significantly elevated over the prodromal stage (F1,12 = 151.85, P < 0.0001). This experiment provides data indicating that infrared thermography can be used in an experimental setting to detect raccoons in the infectious stage and capable of exhibiting clinical signs of rabies.