Experimental Transmission of Ehrlichia chaffeensis (Rickettsiales: Ehrlichieae) Among White-Tailed Deer by Amblyomma americanum (Acari: Ixodidae)

Abstract

Ehrlichia chaffeensis Anderson, Dawson & Wilson, causative agent of human (predominantly monocytic) ehrlichiosis, was successfully transmitted experimentally by Amblyomma americanum (L.) to white-tailed deer, Odocoileus virginianus (Zimmerman). Deer were needle-exposed intravenously to E. chaffeensis in tissue-culture canine macrophage (DH82) cells, and 11 d later were exposed to laboratory-reared A. americanum larvae, nymphs, and adults for acquisition feeding. Three months after this feeding, naive deer and dogs were exposed to recently molted nymphs and adults. Attempted reisolation of the pathogen by way of tissue culture was successful from one needle-exposed deer but not from the tick-exposed deer or dogs. Based on serologic evidence and polymerase chain reaction data, both nymphal and adult ticks transmitted E. chaffeensis to naive deer but not to dogs.

Experimental Infection of White-tailed Deer (Odocoileus virginianus) with Ehrlichia chaffeensis by Different Inoculation Routes

“…Other experimental studies also detected E. chaffeensis inconsistently in needle-inoculated deer over time (Dawson et al, 1994b;Ewing et al, 1995). Similar findings were observed in this study for deer, regardless of inoculation route.…”

“…An obligate intracellular bacterium, E. chaffeensis is the causative agent of human monocytic ehrlichiosis (HME). Ehrlichia chaffeensis is transmitted via the lone star tick, Amblyomma americanum; white-tailed deer (Odocoileus virginianus) serve as the principal vertebrate reservoir host (Dawson et al, 1994b;Ewing et al, 1995). White-tailed deer were first identified as a potential reservoir host for E. chaffeensis in 1994, when anti-E. chaffeensis antibodies were detected in 43% of deer from 17 states and experimental infection was demonstrated through PCR and seroconversion (Dawson et al, 1994a, b).…”

“…To our knowledge, intravenous (IV) inoculation has been the only route used in needle inoculation of deer with E. chaffeensis (Dawson et al, 1994b;Ewing et al, 1995;Kocan et al, 2000;Davidson et al, 2001). Because E. chaffeensis is naturally transmitted through the bite of a lone star tick, intravenous injection of organism directly into blood may not suitably illustrate the true course of infection.…”

“…Because E. chaffeensis is naturally transmitted through the bite of a lone star tick, intravenous injection of organism directly into blood may not suitably illustrate the true course of infection. Experimental transmission by feeding E. chaffeensis infected ticks on deer has been successfully accomplished (Ewing et al, 1995), but captive deer are difficult to handle and controlled tick-feeding studies are challenging and often impracticable compared to needle inoculation. Subcutaneous (SQ) and intradermal (ID) inoculations are also easy to administer, but unlike IV inoculation, SQ and ID routes may more closely mimic transmission via tick feeding because they do not introduce organisms directly into a major vein, but rather near the surface of the skin.…”

Characteristic peripheral blood findings in human ehrlichiosis

“…Initially recognized in the early 20th century as a zoonotic infection in ruminants and dogs, human infection by several different species has been described. [1][2][3][4][5] E. chaffeensis is transmitted by Amblyomma americanum 6 and primarily infects monocytes and produces human monocytic ehrlichiosis. 7 Another species similar to E. phagocytophilia and E. equi is transmitted by Ixodes scapularis and infects granulocytes, and produces human granulocytic ehrlichiosis in patients in the midwest and northeast.…”