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Yabsley MJ. Natural history of Ehrlichia chaffeensis: vertebrate hosts and tick vectors from the United States and evidence for endemic transmission in other countries. Vet Parasitol 2009; 167:136-48. [PMID: 19819631 DOI: 10.1016/j.vetpar.2009.09.015] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Ehrlichia chaffeensis, an intracellular gram-negative zoonotic bacterium, is the causative agent of human monocytotropic ehrlichiosis (HME). In humans, the disease can range from a mild, non-specific illness with few to no clinical signs to a moderately severe to fatal disease, especially those with compromised immune systems. E. chaffeensis is maintained in a complex cycle involving white-tailed deer (WTD; Odocoileus virginianus) as a primary reservoir and the lone star tick (LST; Amblyomma americanum) as a primary vector. Numerous other species are naturally exposed to E. chaffeensis and disease has been documented in some domestic animals and wildlife including domestic dogs and ring-tailed lemurs. The organism has been found throughout the natural range of the LST and as the tick continues to expand its range, the geographic range of risk for E. chaffeensis infections will likely continue to expand. Recent data have indicated that E. chaffeensis, or a closely related organism, has been found in many species of ticks and vertebrate hosts in numerous countries.
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Affiliation(s)
- Michael J Yabsley
- Department of Population Health, The University of Georgia, Athens, GA 30602, USA.
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Delos Santos JRC, Boughan K, Bremer WG, Rizzo B, Schaefer JJ, Rikihisa Y, Needham GR, Capitini LA, Anderson DE, Oglesbee M, Ewing SA, Stich RW. Experimental infection of dairy calves with Ehrlichia chaffeensis. J Med Microbiol 2008; 56:1660-1668. [PMID: 18033836 DOI: 10.1099/jmm.0.47427-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human monocytic ehrlichiosis (HME) is a zoonotic emerging tick-borne disease with clinical signs that range from mild symptoms to multiple organ failure and death. Ehrlichia chaffeensis, the aetiologic agent of HME, is reported to infect a divergent range of mammals. Although cattle are common hosts of the primary vector of this pathogen, the susceptibility of this host to E. chaffeensis has not been reported to date. This study was undertaken to determine if cattle could provide a useful infection model of E. chaffeensis. Dairy calves were injected with DH82 cells infected with the Arkansas, St Vincent or 91HE17 strain of E. chaffeensis, and monitored for signs of clinical ehrlichiosis and for infection of peripheral blood and ticks by PCR assay. Splenectomized and spleen-intact calves were injected with cryopreserved stabilates of E. chaffeensis-infected DH82 cells for the first experiment. Mild clinical signs were occasionally observed among these calves, and only two blood samples were PCR-positive, while several ticks fed on each calf tested PCR-positive. The second experiment involved injection of normal calves with active cultures of the same E. chaffeensis strains. Interestingly, three of six calves inoculated with active cultures became recumbent and died or had to be euthanized. All of the surviving calves in this experiment tested PCR-positive on multiple dates, but fewer ticks fed on these calves were PCR-positive. These results suggest that a bovine disease model could facilitate the understanding of factors that affect the severity of HME.
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Affiliation(s)
- Jose R C Delos Santos
- Department of Veterinary Preventive Medicine, Ohio State University, Columbus, OH, USA
| | - Kirsten Boughan
- Department of Veterinary Preventive Medicine, Ohio State University, Columbus, OH, USA
| | - William G Bremer
- Department of Veterinary Preventive Medicine, Ohio State University, Columbus, OH, USA
| | - Brian Rizzo
- Department of Veterinary Preventive Medicine, Ohio State University, Columbus, OH, USA
| | - John J Schaefer
- Department of Entomology, Ohio State University, Columbus, OH, USA
| | - Yasuko Rikihisa
- Department of Veterinary Biosciences, Ohio State University, Columbus, OH, USA
| | - Glen R Needham
- Department of Entomology, Ohio State University, Columbus, OH, USA
| | - L A Capitini
- University Laboratory Animal Resources, Ohio State University, Columbus, OH, USA
| | - David E Anderson
- Department of Veterinary Clinical Sciences, Ohio State University, Columbus, OH, USA
| | - Michael Oglesbee
- Department of Veterinary Biosciences, Ohio State University, Columbus, OH, USA
| | - S A Ewing
- Department of Veterinary Pathobiology, Oklahoma State University, Stillwater, OK, USA
| | - Roger W Stich
- Department of Veterinary Pathobiology, University of Missouri, Columbia, MO, USA
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Loftis AD, Nicholson WL, Levin ML. Evaluation of immunocompetent and immunocompromised mice (Mus musculus) for infection with Ehrlichia chaffeensis and transmission to Amblyomma americanum ticks. Vector Borne Zoonotic Dis 2005; 4:323-33. [PMID: 15671738 DOI: 10.1089/vbz.2004.4.323] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Experiments on the natural history of Ehrlichia chaffeensis, the agent of human monocytic ehrlichiosis (HME), would be facilitated by the availability of a laboratory animal model for transmission to vector ticks. Five strains of mice were evaluated for their susceptibility to infection with E. chaffeensis and transmission competence: C57BL/6 mice, inducible nitric oxide synthase (iNOS) deficient mice, MHC I deficient (beta2m /) mice, MHC II deficient mice (Abb /), and B and T cell deficient (Rag1 /) mice. Mice were inoculated with a low passage isolate of E. chaffeensis, and infection and morbidity were monitored for 57 days. Three xenodiagnostic infestations with A. americanum nymphs were performed 1, 8, and 15 days following inoculation. C57BL/6 mice cleared the organism in less than 17 days, with no indication of morbidity, and mounted a rapid, strong antibody response. Transmission to feeding A. americanum nymphs was seen in 1/30 nymphs fed on C57BL/6 mice immediately after inoculation. In MHC I and iNOS deficient mice, pathogen DNA was detected up to 17 or 24 days, respectively, after inoculation. Persistent infection for the duration of the experiment (57 days) was observed in MHC II deficient mice. However, E. chaffeensis was not detected in ticks fed on iNOS, MHC I, or MHC II deficient mice. Susceptibility to infection was greatest in Rag1 knockout mice, with significant morbidity and mortality within 24 days after inoculation. E. chaffeensis DNA was detected in up to 55% of replete nymphs that fed on Rag1 mice. However, E. chaffeensis was not detected in molted adult ticks from the same cohorts.
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Affiliation(s)
- Amanda D Loftis
- Viral and Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
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Abstract
Ehrlichia chaffeensis is an obligately intracellular, tick-transmitted bacterium that is maintained in nature in a cycle involving at least one and perhaps several vertebrate reservoir hosts. The moderate to severe disease caused by E. chaffeensis in humans, first identified in 1986 and reported for more than 1,000 patients through 2000, represents a prototypical "emerging infection." Knowledge of the biology and natural history of E. chaffeensis, and of the epidemiology, clinical features, and laboratory diagnosis of the zoonotic disease it causes (commonly referred to as human monocytic ehrlichiosis [HME]) has expanded considerably in the period since its discovery. In this review, we summarize briefly the current understanding of the microbiology, pathogenesis, and clinical manifestations associated with this pathogen but focus primarily on discussing various ecological factors responsible for the recent recognition of this important and potentially life-threatening tick-borne disease. Perhaps the most pivotal element in the emergence of HME has been the staggering increases in white-tailed deer populations in the eastern United States during the 20th century. This animal serves as a keystone host for all life stages of the principal tick vector (Amblyomma americanum) and is perhaps the most important vertebrate reservoir host for E. chaffeensis. The contributions of other components, including expansion of susceptible human populations, growth and broadening geographical distributions of other potential reservoir species and A. americanum, and improvements in confirmatory diagnostic methods, are also explored.
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Affiliation(s)
- Christopher D Paddock
- Viral and Rickettsial Zoonoses Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
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Sotomayor EA, Popov VL, Feng HM, Walker DH, Olano JP. Animal model of fatal human monocytotropic ehrlichiosis. THE AMERICAN JOURNAL OF PATHOLOGY 2001; 158:757-69. [PMID: 11159213 PMCID: PMC1850300 DOI: 10.1016/s0002-9440(10)64018-7] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 11/10/2000] [Indexed: 10/18/2022]
Abstract
Human monocytotropic ehrlichiosis caused by Ehrlichia chaffeensis is a life-threatening, tick-borne, emerging infectious disease for which no satisfactory animal model has been developed. Strain HF565, an ehrlichial organism closely related to E. chaffeensis isolated from Ixodes ovatus ticks in Japan, causes fatal infection of mice. C57BL/6 mice became ill on day 7 after inoculation and died on day 9. The liver revealed confluent necrosis, ballooning cell injury, apoptosis, poorly formed granulomas, Kupffer cell hyperplasia, erythrophagocytosis, and microvesicular fatty metamorphosis. The other significant histological findings consisted of marked expansion of the marginal zone and infiltration of the red pulp of the spleen by macrophages, interstitial pneumonitis, and increased numbers of immature myeloid cells and areas of necrosis in the bone marrow. Ehrlichiae were detected by immunohistology and electron microscopy in the liver, lungs, and spleen. The main target cells were macrophages, including Kupffer cells, hepatocytes, and endothelial cells. Apoptosis was detected in Kupffer cells, hepatocytes, and macrophages in the lungs and spleen. This tropism for macrophages and the pathological lesions closely resemble those of human monocytotropic ehrlichiosis for which it is a promising model for investigation of immunity and pathogenesis.
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Affiliation(s)
- E A Sotomayor
- Department of Pathology, University of Texas Medical Branch, Galveston, Texas, USA
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Dugan VG, Little SE, Stallknecht DE, Beall AD. Natural infection of domestic goats with Ehrlichia chaffeensis. J Clin Microbiol 2000; 38:448-9. [PMID: 10618139 PMCID: PMC88747 DOI: 10.1128/jcm.38.1.448-449.2000] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Thirty-eight domestic goats from an area of Ehrlichia chaffeensis endemicity were tested for antibodies reactive to E. chaffeensis and for E. chaffeensis-specific 16S rRNA gene fragments by an indirect fluorescent antibody test and a nested PCR assay, respectively. Twenty-eight of 38 (73.7%) goats had antibodies reactive to E. chaffeensis (>/=1:128), and 6 of 38 (15.8%) goats were positive by diagnostic PCR; E. chaffeensis was isolated in cell culture from one goat. Our data indicate that goats in areas of endemicity are naturally exposed to and infected with E. chaffeensis.
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Affiliation(s)
- V G Dugan
- Department of Medical Microbiology, College of Veterinary Medicine, The University of Georgia, Athens, Georgia 30602, USA
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