Ehrlichia ewingii Infection in White-Tailed Deer
Two closely related zoonotic ehrlichiae, Ehrlichia chaffeensis and E. ewingii, are transmitted by Amblyomma americanum, the lone star tick. Because white-tailed deer (Odocoileus virginianus) are critical hosts for all mobile stages of A. americanum and are important vertebrate reservoirs of E. chaffeensis, we investigated whether deer may be infected with E. ewingii, a cause of granulocytotropic ehrlichiosis in humans and dogs. To test for E. ewingii infection, we used polymerase chain reaction and inoculation of fawns with whole blood from wild deer. Of 110 deer tested from 20 locations in 8 U.S. states, 6 (5.5%) were positive for E. ewingii. In addition, natural E. ewingii infection was confirmed through infection of captive fawns. These findings expand the geographic distribution of E. ewingii, along with risk for human infection, to include areas of Kentucky, Georgia, and South Carolina. These data suggest that white-tailed deer may be an important reservoir for E. ewingii.
Ehrlichia ewingii, one of the causative agents of canine granulocytotropic ehrlichiosis, has been reported in dogs in several U.S. states, including Oklahoma, North Carolina, and Virginia. Human infections with E. ewingii have been reported from Missouri, Oklahoma, and Tennessee; the clinical disease, similar to that caused by other Ehrlichia spp., is characterized by fever, headache, and thrombocytopenia, with or without leukopenia. Experimentally, the lone star tick (Amblyomma americanum) has been shown to be a competent vector; however, natural infection of two other tick species, Rhipicephalus sanguineus and Dermacentor variabilis, has been reported in Oklahoma.
The white-tailed deer (Odocoileus virginianus) is an important host for all three mobile stages of A. americanum, and deer and lone star ticks serve as the major reservoir and vector, respectively, for E. chaffeensis. Because E. ewingii is closely related to E. chaffeensis and shares the same vector, our goal was to determine if white-tailed deer are naturally infected with E. ewingii. In some human and canine infections with E. ewingii, cross-reactions with E. chaffeensis antigens have been reported; however, not all infections with E. ewingii result in positive serologic tests to E. chaffeensis antigen. Because E. ewingii has not been isolated in culture and because serologic test reagents are not readily available, we used several techniques to detect infections, including 1) testing serum samples for antibodies reactive with E. chaffeensis antigen, 2) testing leukocytes or whole blood by polymerase chain reaction (PCR) with primers specific for E. ewingii and E. chaffeensis, and 3) injecting captive white-tailed fawns with whole blood from deer collected in an A. americanum-endemic area.
Two closely related zoonotic ehrlichiae, Ehrlichia chaffeensis and E. ewingii, are transmitted by Amblyomma americanum, the lone star tick. Because white-tailed deer (Odocoileus virginianus) are critical hosts for all mobile stages of A. americanum and are important vertebrate reservoirs of E. chaffeensis, we investigated whether deer may be infected with E. ewingii, a cause of granulocytotropic ehrlichiosis in humans and dogs. To test for E. ewingii infection, we used polymerase chain reaction and inoculation of fawns with whole blood from wild deer. Of 110 deer tested from 20 locations in 8 U.S. states, 6 (5.5%) were positive for E. ewingii. In addition, natural E. ewingii infection was confirmed through infection of captive fawns. These findings expand the geographic distribution of E. ewingii, along with risk for human infection, to include areas of Kentucky, Georgia, and South Carolina. These data suggest that white-tailed deer may be an important reservoir for E. ewingii.
Ehrlichia ewingii, one of the causative agents of canine granulocytotropic ehrlichiosis, has been reported in dogs in several U.S. states, including Oklahoma, North Carolina, and Virginia. Human infections with E. ewingii have been reported from Missouri, Oklahoma, and Tennessee; the clinical disease, similar to that caused by other Ehrlichia spp., is characterized by fever, headache, and thrombocytopenia, with or without leukopenia. Experimentally, the lone star tick (Amblyomma americanum) has been shown to be a competent vector; however, natural infection of two other tick species, Rhipicephalus sanguineus and Dermacentor variabilis, has been reported in Oklahoma.
The white-tailed deer (Odocoileus virginianus) is an important host for all three mobile stages of A. americanum, and deer and lone star ticks serve as the major reservoir and vector, respectively, for E. chaffeensis. Because E. ewingii is closely related to E. chaffeensis and shares the same vector, our goal was to determine if white-tailed deer are naturally infected with E. ewingii. In some human and canine infections with E. ewingii, cross-reactions with E. chaffeensis antigens have been reported; however, not all infections with E. ewingii result in positive serologic tests to E. chaffeensis antigen. Because E. ewingii has not been isolated in culture and because serologic test reagents are not readily available, we used several techniques to detect infections, including 1) testing serum samples for antibodies reactive with E. chaffeensis antigen, 2) testing leukocytes or whole blood by polymerase chain reaction (PCR) with primers specific for E. ewingii and E. chaffeensis, and 3) injecting captive white-tailed fawns with whole blood from deer collected in an A. americanum-endemic area.
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