In January 2001, a homeowner contacted Flagstaff Animal Control about a dead skunk. Although no human had been exposed to the skunk, tissues were submitted to the Arizona State Health Laboratory, where rabies was diagnosed. This skunk was the first rabid terrestrial wild carnivore reported from the area. The Texas Department of State Health Services subsequently identified an RABVV associated with bats in tissues sent for antigenic characterization. From January through April, 14 more skunks, dead or exhibiting abnormal behavior, were found throughout a large residential subdivision within 4 km of the initial case. All were infected with the same bat RABVV. From April through July, 4 more skunks infected with bat RABVV were identified ≈9 km west of the initial focus (). Control measures included prohibiting relocation of nuisance skunks, comprehensive public education, pet rabies vaccine clinics, and a 90-day emergency quarantine requiring pets to be leashed or confined and vaccinated (). Additionally, 217 urban skunks were vaccinated and marked with ear tags during a 6-month phased program of trap, vaccinate, and release.
Figure 1 Temporal and geographic distribution of rabies outbreak in Flagstaff, Arizona. A) Timeline and control measures. TVR: trap, vaccinate, release program. B) Geographic location of rabid skunks (dark gray dots = subclade 1, light gray dots = subclade 2). (more ...)
In Flagstaff and the surrounding county, during the decade before this epizootic, 2 rabid bats, on average, were reported each year. During the epizootic, 218 animals were submitted for rabies testing (). Rabies was confirmed in 19 (13%) of 145 tested skunks and 2 (9%) of 22 tested bats. Although most (18 [95%]) of the rabid skunks were identified and reported by lay citizens, no contact between these skunks and humans or domestic animals was reported.
Animals from Flagstaff submitted for rabies diagnosis, January–July, 2001
Local baseline population estimates were not available to indicate whether skunk demography affected disease attributes. Synchronous with this outbreak, independent epizootic activity caused by well-established skunk RABVV was documented in southern Arizona, which suggests that regional skunk epizootiologic dynamics were similarly affected. Skunks' seasonal behavior may have contributed to transmission events. This epizootic was initially recognized when a dead skunk appeared in a snow-covered backyard, during a season when skunks are in communal dens. Given an incubation period of 2 months, most transmission would have occurred between late autumn (when skunks are in their dens) and late winter (when they are mating).The Flagstaff epizootic peak coincided with nationwide seasonal trends of rabid skunks (1
). Enhanced postepizootic surveillance in Flagstaff did not detect additional rabid terrestrial mammals for the next 3 years. However, in 2004, a total of 5 skunks found in the initially affected east Flagstaff neighborhood and 1 fox 28 km south of Flagstaff were infected with the same bat RABVV (10
Viruses isolated from the rabid skunks exhibited monoclonal antibody patterns similar to RABVV associated with big brown (Eptesicus fuscus
) and Myotis
bats in the western United States (11
). These are among the most abundant bat species in Arizona and often roost in houses and outbuildings; however, no bat colonies were found in association with any of the rabid skunks. Restriction digests of PCR amplicons from the rabid skunks did not match patterns known for RABVV from North American terrestrial reservoirs (12
). Phylogenetic analysis of a 300-bp region of the N gene showed that the Flagstaff skunk RABVV was identical (100%) to Arizona bat RABVV (, A), and differed by 22% from skunk and gray fox RABVV. A monophyletic clade (clade A) of 8/8 big brown, 5/14 Myotis
, and 1/6 southern yellow (Lasiurus ega
) bats shared >95% identity with Flagstaff skunk RABVV. An additional 44 samples, representing 11 bat species, differed by >8% from Flagstaff skunk RABVV.
Figure 2 A) Phylogenetic tree of the 19 rabid skunk isolates and representative samples of known rabies virus variants (RABVV) from Arizona based on 300 bp of the nucleoprotein (N) gene (GenBank accession no. AY170226–304). B) Detailed analyses of clade (more ...)
An analysis of clade A, which incorporates N and G genes, indicated that the Flagstaff skunk RABVV were more closely related to 2 bat RABVV (E. fuscus from Coconino County, M. velifer from Maricopa County) collected in 1999 and 1997 than to the 2 bat RABVV collected locally during the outbreak. In clade B, subclade 1 RABVV were collected from January through early April from the northeastern region of the outbreak, whereas subclade 2 RABVV were collected from early March through July from the southeastern and western regions of the outbreak (). However, phylogenetic data do not support a wavelike spread from northeast to west because this would require nesting of subclade 1 within subclade 2. In contrast, both subclades exhibit independently derived mutations. East-to-west epizootic movement of RABVV within subclade 2 (sk16–19 form a monophyletic clade nested within subclade 2) during April is supported by the data and may be related to dispersal of infected skunks along river corridors or translocation by humans. One person reported trapping, moving, and releasing a skunk before the outbreak was known in the community. Alternatively, apparent shifts may be an artifact of intensified public awareness and reporting. Lack of sampling in the uninhabited forest between the eastern and western foci limits our ability to discriminate among these hypotheses.