“Rickettsia amblyommii” andR. montanensisInfection in Dogs Following Natural Exposure to Ticks

Abstract

To determine the risk of canine infection with spotted fever group (SFG) Rickettsia spp. following natural tick exposure, 10 dogs determined to be free of evidence of exposure to or infection with tick-borne disease agents were exposed to ticks via weekly walks in a wooded area in north-central Oklahoma. After each walk, dogs were examined and the number and species of ticks present were recorded. The dogs were then returned to outdoor kennels to allow the infestations and subsequent transmission of any pathogens to proceed. Serum samples and whole blood were collected from each dog twice weekly for 121 days and evaluated via indirect fluorescence antibody (IFA) for antibodies reactive to Rickettsia rickettsii, R. montanensis, and "R. amblyommii," and by PCR for evidence of Rickettsia spp. Dogs became infested with a total of 57-108 ticks over the entire 8-week infestation period (weekly average tick infestation=12.0±4.1). The great majority of the ticks present were Amblyomma americanum (90.5%), with a small number of Dermacentor variabilis and A. maculatum also identified. All (10/10) dogs seroconverted to R. rickettsii, R. montanensis, and "R. amblyommii," with mean maximum inverse titers of 1176, 1448, and 6654, respectively, for all dogs in the study. Maximum inverse titers to "R. amblyommii" ranged from 4096 to 16,384 and were higher in 9/10 dogs than maximum inverse titers to R. rickettsii or R. montanensis. Sequence-confirmed SFG Rickettsia spp. (R. montanensis and "R. amblyommii") were occasionally, but not consistently, identified from whole blood by PCR. Taken together, our data suggest that, in areas where A. americanum is common, antibodies reactive to R. rickettsii in dogs may be due instead to infection with "R. amblyommii" or other, closely related SFG Rickettsia spp.

Serologic evidence of the exposure of small mammals to spotted-fever Rickettsia and Rickettsia bellii in Minas Gerais, Brazil

“…In fact, antigenic cross-reactivity among Rickettsia of different species occurs [38]. In this regard, it is important to note that several Rickettsia species may be present at one location and even in the same tick, and thus animals may be exposed to more than one species simultaneously or over time with an unknown effect on seroreactivity [6].…”

The Biological Survey of Canada: A Personal History

“…This patient developed an afebrile rash illness four days after being bitten by a D. variabilis tick that tested positive for R. montanensis (McQuiston 2012). A study in dogs naturally exposed to A. americanum, A. maculatum, and D. variabilis ticks suggested that several SFG rickettsia species may cause infections in canines, including R. montanensis and R. amblyommii (Barrett et al 2014).…”

Human Infections by Multiple Spotted Fever Group Rickettsiae in Tennessee

“…Dogs were naturally infected with R. amblyommii and R. montanensis after tick exposure. 24 Clinical evaluations of patients with specific reactivities to R. amblyommii indicated that these patients commonly experienced fever, headache, and myalgia, while anemia, thrombocytopenia, rash, and the presence of eschar occurred < 50% of the time. Previously thought to be nonpathogenic, there is increasing evidence that R. amblyommii infection in humans may be symptomatic or may cause a mild illness after a tick bite.…”