Ehrlichia chaffeensis Infection in the Reservoir Host (White-Tailed Deer) and in an Incidental Host (Dog) Is Impacted by Its Prior Growth in Macrophage and Tick Cell Environments

Abstract

Ehrlichia chaffeensis, transmitted from Amblyomma americanum ticks, causes human monocytic ehrlichiosis. It also infects white-tailed deer, dogs and several other vertebrates. Deer are its reservoir hosts, while humans and dogs are incidental hosts. E. chaffeensis protein expression is influenced by its growth in macrophages and tick cells. We report here infection progression in deer or dogs infected intravenously with macrophage- or tick cell-grown E. chaffeensis or by tick transmission in deer. Deer and dogs developed mild fever and persistent rickettsemia; the infection was detected more frequently in the blood of infected animals with macrophage inoculum compared to tick cell inoculum or tick transmission. Tick cell inoculum and tick transmission caused a drop in tick infection acquisition rates compared to infection rates in ticks fed on deer receiving macrophage inoculum. Independent of deer or dogs, IgG antibody response was higher in animals receiving macrophage inoculum against macrophage-derived Ehrlichia antigens, while it was significantly lower in the same animals against tick cell-derived Ehrlichia antigens. Deer infected with tick cell inoculum and tick transmission caused a higher antibody response to tick cell cultured bacterial antigens compared to the antibody response for macrophage cultured antigens for the same animals. The data demonstrate that the host cell-specific E. chaffeensis protein expression influences rickettsemia in a host and its acquisition by ticks. The data also reveal that tick cell-derived inoculum is similar to tick transmission with reduced rickettsemia, IgG response and tick acquisition of E. chaffeensis.

Vector potential and population dynamics for Amblyomma inornatum

“…E. chaffeensis is frequently isolated from A. americanum (Nair et al 2014), and has also been detected in A. mixtum and A. maculatum (Williamson et al 2010). The latter two ticks are also present in the study area.…”

Amblyomma americanum ticks infected with in vitro cultured wild-type and mutants of Ehrlichia chaffeensis are competent to produce infection in naïve deer and dogs

“…The first group of ticks included an E. chaffeensis transposon mutant (Ec_0480) which is known to persist similar to wild-type E. chaffeensis (Cheng et al, 2015) and the second group of ticks received five equal molar mixed transposon mutants containing two mutants which persist in deer (Ech_0284 and Ech_0480) and three mutants which clear rapidly (Ech_0202, Ech_0379, and Ech_0660) in deer and dogs (Cheng et al, 2013; Cheng et al, 2015). We performed a tick-transmission experiment to test if the needle-infected ticks cause similar infections as those seen with natural transmission in deer (Nair et al, 2014). For deer infestations, we used 20 ticks (10 females and 10 males; for dog infestations, we used fifty ticks per dog (25 females and 25 males).…”

Attenuated Mutants of Ehrlichia chaffeensis Induce Protection against Wild-Type Infection Challenge in the Reservoir Host and in an Incidental Host

“…Host cell-free E. chaffeensis lysate was prepared and used for enzyme-linked immunosorbent assay (ELISA) (13). Plasma samples from deer or dogs collected prior to infection and several days following infections were assessed by ELISA for the presence of the E. chaffeensis-specific IgG (13).…”

“…Vaccine development is complicated due to limited understanding of the pathogen antigens involved in stimulating protective immunity (12). Deer, dog, and A. americanum tick infection studies are ideal for mapping genes essential for E. chaffeensis growth and persistence, as they are the recognized reservoir host, an incidental host, and the tick vector, respectively (13). The canine host is an ideal incidental host model that is similar to that of humans in acquiring E. chaffeensis infections from A. americanum ticks (14).…”

“…The canine host is an ideal incidental host model that is similar to that of humans in acquiring E. chaffeensis infections from A. americanum ticks (14). We recently reported that E. chaffeensis infections in deer and dog are very similar in exhibiting clinical symptoms and pathogen persistence (13).…”