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.

Arathy D S Nair,Deborah C Jaworski,Lloyd H Willard,Chuanmin Cheng,Roman R Ganta,Michael W Sanderson,Xue-Jie Yu

doi:10.1371/journal.pone.0109056

Arathy D S Nair, Deborah C Jaworski + Show 5 more

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https://doi.org/10.1371/journal.pone.0109056

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Journal: PloS one	Publication Date: Oct 10, 2014
Citations: 76	License type: CC BY 4.0

Affiliation: Kansas State University, Oklahoma State University

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.

Highlights

Ehrlichia chaffeensis is, an obligate, intracellular, Gram negative bacterium belonging to the family Anaplasmataceae
The animals were assessed for the 1) clinical signs and hematology, 2) presence of the organism in blood assessed by polymerase chain reaction (PCR) and culture recovery methods, 3) infection acquisition by ticks, and 4) IgG antibody responses
E. chaffeensis persisted in deer infected with ISE6 cell-derived inoculum; the blood samples which tested positive for the pathogen in this group of animals, were considerably less and detected only about 28% of the time (10 of the 36 samples tested positive) (Table 3)

Summary

Introduction

An obligate, intracellular, Gram negative bacterium belonging to the family Anaplasmataceae. It is transmitted by the bite of an infected tick, Amblyomma americanum (lone star tick) [1,2], and is responsible for an emerging disease, human monocytic ehrlichiosis (HME) [3,4,5]. E. chaffeensis infects several other vertebrate hosts, such as dogs, goats, coyotes and white-tailed deer [2,9,10,11,12,13]. White-tailed deer is identified as the reservoir host of E. chaffeensis [2], while humans, dogs and other vertebrate animals are considered incidental hosts [14]. Research on E. chaffeensis, focused on understanding the host response, has been carried out mostly in mice or in vitro using infection inoculum originating from canine or human macrophage/monocyte cell lines [15,16,17,18,19,20,21,22,23]

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