Ehrlichia chaffeensis

Ehrlichia chaffeensis
Scientific classification Edit this classification
Domain: Bacteria
Kingdom: Pseudomonadati
Phylum: Pseudomonadota
Class: Alphaproteobacteria
Order: Rickettsiales
Family: Ehrlichiaceae
Genus: Ehrlichia
Species:
E. chaffeensis
Binomial name
Ehrlichia chaffeensis
Anderson et al. 1992

Ehrlichia chaffeensis is an obligately intracellular, Gram-negative species of Rickettsiales bacteria.[1][2] It is a zoonotic pathogen transmitted to humans by the lone star tick (Amblyomma americanum).[3]

It is the causative agent of human monocytic ehrlichiosis.[4]

Human monocytic ehrlichiosis caused by E. chaffeensis is known to spread through tick infection primarily in the Southern, South-central and Mid-Atlantic regions of the United States.[5] In recent years, the lone star tick has expanded its range along the East Coast to New England, putting more humans at risk for tick-borne infections.[6]

It is named for Fort Chaffee, where the bacterium was first discovered in the blood sample of an infected patient in 1986.[1][7]

Transmission cycle

E. chaffeensis is maintained in nature through a complex zoonotic relationship. The white-tailed deer (Odocoileus virginianus) is known to be the main competent reservoir for E. chaffeensis and the lone star tick (Amblyomma americanum) is the principal vector for human transmission.[2] [3] Some evidence shows that other organisms may serve as reservoirs for the bacteria such as domestic goats, domestic dogs, raccoons, and coyotes.[2] [5]

E. chaffeensis can be transmitted to uninfected tick larvae when feeding on the blood from an infected host.[8] The infection is then maintained and can be transmitted to a reservoir organism or humans at the nymphal stage. Adult ticks can maintain the infection or be infected from feeding on the blood of an infected reservoir organism and may also pass E. chaffeensis to humans or other uninfected reservoir organisms.[2] Transovarial transmission is not known to occur, so eggs and unfed larvae are not believed to be infected.[8]

Experimental studies in the related species Ehrlichia japonica have suggested that the conserved effector TRP120 promotes sustained bacteremia needed for efficient tick acquisition, providing a possible molecular explanation for maintenance of the tick–mammal transmission cycle in Ehrlichia.[9]

The seroprevalence of E. chaffeensis ranges from 0.4-12.5% in endemic regions, and approximately 75% of seroconversions are subclinical. [10]

Microbiology

All members of the genus Ehrlichia are obligate intracellular bacteria, being closely related to the genera Rickettsia and Orientia. Taxonomic classification largely relies on the sequencing of the 16S rRNA genes and the heat shock operon. [11][12]

The small dense core form (approximately 0.2-0.4 micrometers) of intracytoplasmic clusters of E. chaffeensis found inside of infected cells resemble elementary bodies of Chlamydia spp., the larger form (0.6-1.5 micrometers) resemble reticulate bodies. [13] A few days post infection, the elementary bodies form an inclusion called a morula, which can then be seen microscopically. Eventual cell lysis allows for the release of bacteria, which can then infect new cells. [14]

In contrast to the reductive evolution commonly seen in other intracellular bacteria, many pseudo genes are present in the Ehrlichia genus, including E. chaffeensis, demonstrating potential gene duplication events. The duplication of the tandemly repeated sequences is likely to result in new genes, antigenic variation, immune evasion, thus supporting enhanced survival. [15]

E. chaffeensis has been isolated from peripheral blood by direct inoculation of leukocyte fractions or whole blood into flasks containing adherent cells; the most commonly used cell in successful isolation is the canine histiocytic cell line DH82, however, a wide variety of cells have been used for primary isolation, including the human macrophage like THP-1 cells, the fibroblast-like HEL-22 cells, Vero cells, and HL-60 cells. [16] Growth is enhanced by incubation with rocking at 37°C in 5% CO2. Even so, culture may take up to one month, although growth has been achieved in just a few days.[17] Culture is slightly more sensitive than direct peripheral blood observation, thus E. chaffeensis could be isolated even when infected leukocytes are not initially observed. [18]

Pathogenesis

Ehrlichia chaffeensis

E. chaffeensis causes human monocytic ehrlichiosis and is known to infect monocytes.[2] It has also been known to infect other cell types such as lymphocytes, atypical lymphocytes, myelocytes, and neutrophils, but monocytes appear to best harbor the infection.[2]

E. chaffeensis has also been shown to infect canines both naturally and artificially.[6] [19] Symptoms in canine infections are hard to differentiate between E. chaffeensis infection and E. canis, which is the species of Ehrlichia that most commonly affects canines.[19]

Signs and symptoms

The median incubation time for E. chaffeensis infection is 9 days, the median patient age is 44 years, and approximately 66% of patients are male. [20] [21]

Early symptoms include fever, headache, malaise, low-back pain, or gastrointestinal symptoms.[3][22] Some patients may also have myalgias or arthralgias, and an estimated 10–40% of patients may develop coughing, pharyngitis, diarrhea, vomiting, abdominal pain, and changes in mental status.[2] Fulminant infections are more common in patients immunocompromised by HIV, high dose costeroids, and/or medications related to organ transplant.

Petechial, macular, and maculopapular rashes may occur with varied distribution and onset, and are most common in children, occurring in 67% of pediatric cases.[4][21]

Atypical laboratory results occur in approximately 86% of patients, and may include thrombocytopenia, leukopenia with lymphopenia and/or neutropenia, and increased serumaspartate transaminases. [23][24][25]

Overall case fatality is 2-3%, but male sex, advanced age, and an immunocompromised status have been associated with a higher mortality. [20]

Diagnosis and detection

There are three primary methods in diagnosing E. chaffeensis infection: PCR amplification of nucleic acids, detection of morulae in the cytoplasm of infected leukocytes by nonspecific Romanowsky stains (such as Giemsa or Wright) or immunocytologic/immunohistologic stains using antibodies against E. chaffeensis, or by culture of blood or cerebrospinal fluid.[21] [26] The ideal specimen is EDTA-anticoagulated blood, as it can be used for most tests, and should be obtained during the active phase of illness. [10]

In culture, the presence of infected cells is demonstrated by sampling some of the cell containing medium, or by scraping a part of the monolayer, then centrifuging the sample. Staining with Romanowsky or immunofluorescent stains will demonstrate the presence of intra-cytoplasmic morulae or E. chaffeensis antigen, depending on the stain used. [14][26]

Treatment

E. chaffeensis is susceptible to tetracyclines.[21] Doxycycline is the treatment of choice for suspected human monocytotropic ehrlichiosis in adults and children of all ages, and treatment should be started as soon as the disease is suspected rather than delayed pending laboratory confirmation.[27] Patients are typically treated for at least 5 to 7 days and until 72 hours after fever has resolved with evidence of clinical improvement.[28]

See also

References

  1. 1 2 Ehrlichia+chaffeensis at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
  2. 1 2 3 4 5 6 7 Ganguly, S (2008). "Tick-borne ehrlichiosis infection in human beings" (PDF). Journal of Vector Borne Diseases. 45 (4): 273–280. PMID 19248653.
  3. 1 2 3 Allan, B. F. (2012). "Blood meal analysis to identify reservoir hosts for amblyomma americanum ticks". Emerging Infectious Diseases. 16 (3): 433–440. doi:10.3201/eid1603.090911. PMC 3322017. PMID 20202418.
  4. 1 2 Schutze GE, Buckingham SC, Marshall GS, et al. (June 2007). "Human monocytic ehrlichiosis in children". Pediatr. Infect. Dis. J. 26 (6): 475–9. doi:10.1097/INF.0b013e318042b66c. PMID 17529862.
  5. 1 2 Barker, R. W. (2000). "Naturally occurring ehrlichia chaffeensis infection in coyotes from oklahoma". Emerging Infectious Diseases. 6 (5): 477–80. doi:10.3201/eid0605.000505. PMC 2627953. PMID 10998377.
  6. 1 2 Little, S. E. (2007, January). New developments in managing vector-borne diseases. Retrieved from http://www.iknowledgenow.com/tocnavc2007smallanimal.cfm
  7. ↑ "Species: Ehrlichia chaffeensis". lpsn.dsmz.de. Retrieved 2026-07-25.
  8. 1 2 Long, S. W. (2003). "Evaluation of transovarial transmission and transmissibility of Ehrlichia chaffeensis (Rickettsiales: Anaplasmataceae) in Amblyomma americanum (Acari: Ixodidae)". Journal of Medical Entomology. 40 (6): 1000–1004. doi:10.1603/0022-2585-40.6.1000. PMID 14765684.
  9. ↑ Zhang, Tsian; Chien, Rory C.; Budachetri, Khemraj; Lin, Mingqun; Boyaka, Prosper; Huang, Weiyan; Rikihisa, Yasuko (2024). "Ehrlichia effector TRP120 manipulates bacteremia to facilitate tick acquisition". mBio. 15 (4): e00476-24. doi:10.1128/mbio.00476-24. PMC 11005420. PMID 38501870.
  10. 1 2 Versalovic, James (2011). Manual of clinical microbiology (10th ed.). Washington (D.C.): ASM press. ISBN 978-1-55581-463-2.
  11. ↑ Dumler, J S; Barbet, A F; Bekker, C P; Dasch, G A; Palmer, G H; Ray, S C; Rikihisa, Y; Rurangirwa, F R (2001-11-01). "Reorganization of genera in the families Rickettsiaceae and Anaplasmataceae in the order Rickettsiales: unification of some species of Ehrlichia with Anaplasma, Cowdria with Ehrlichia and Ehrlichia with Neorickettsia, descriptions of six new species combinations and designation of Ehrlichia equi and 'HGE agent' as subjective synonyms of Ehrlichia phagocytophila". International Journal of Systematic and Evolutionary Microbiology. 51 (6): 2145–2165. doi:10.1099/00207713-51-6-2145. ISSN 1466-5026. PMID 11760958.
  12. ↑ Inokuma, Hisashi; Fujii, Kaori; Okuda, Masaru; Onishi, Takafumi; Beaufils, Jean-Pierre; Raoult, Didier; Brouqui, Philippe (2002). "Determination of the Nucleotide Sequences of Heat Shock Operon groESL and the Citrate Synthase Gene ( gltA ) of Anaplasma ( Ehrlichia ) platys for Phylogenetic and Diagnostic Studies". Clinical and Vaccine Immunology. 9 (5): 1132–1136. doi:10.1128/CDLI.9.5.1132-1136.2002. ISSN 1556-6811. PMC 120055. PMID 12204973.
  13. ↑ Popov, V. L.; Chen, S.-M.; Feng, H.-M.; Walker, O. H. (1995-12-01). "Ultrastructural variation of cultured Ehrlichia chaffeensis". Journal of Medical Microbiology. 43 (6): 411–421. doi:10.1099/00222615-43-6-411. ISSN 0022-2615. PMID 7473674.
  14. 1 2 Brouqui, P; Birg, M L; Raoult, D (1994). "Cytopathic effect, plaque formation, and lysis of Ehrlichia chaffeensis grown on continuous cell lines". Infection and Immunity. 62 (2): 405–411. doi:10.1128/iai.62.2.405-411.1994. ISSN 0019-9567. PMC 186122. PMID 8300201.
  15. ↑ Dunning Hotopp, Julie C.; Lin, Mingqun; Madupu, Ramana; Crabtree, Jonathan; Angiuoli, Samuel V; Eisen, Jonathan; Seshadri, Rekha; Ren, Qinghu; Wu, Martin; Utterback, Teresa R; Smith, Shannon; Lewis, Matthew; Khouri, Hoda; Zhang, Chunbin; Niu, Hua (2006-02-17). Richardson, Paul M. (ed.). "Comparative Genomics of Emerging Human Ehrlichiosis Agents". PLOS Genetics. 2 (2) e21. doi:10.1371/journal.pgen.0020021. ISSN 1553-7404. PMC 1366493. PMID 16482227.
  16. ↑ Heimer, R; Tisdale, D; Dawson, J E (1998). "A single tissue culture system for the propagation of the agents of the human ehrlichioses". The American Journal of Tropical Medicine and Hygiene. 58 (6): 812–815. doi:10.4269/ajtmh.1998.58.812. ISSN 0002-9637. PMID 9660470.
  17. ↑ Dumler, J S; Chen, S M; Asanovich, K; Trigiani, E; Popov, V L; Walker, D H (1995). "Isolation and characterization of a new strain of Ehrlichia chaffeensis from a patient with nearly fatal monocytic ehrlichiosis". Journal of Clinical Microbiology. 33 (7): 1704–1711. doi:10.1128/jcm.33.7.1704-1711.1995. ISSN 0095-1137. PMC 228253. PMID 7665632.
  18. ↑ Standaert, Steven M.; Yu, Tina; Scott, Margie A.; Childs, James E.; Paddock, Christopher D.; Nicholson, William L.; Singleton, Joseph; Blaser, Martin J. (2000). "Primary Isolation of Ehrlichia chaffeensis from Patients with Febrile Illnesses: Clinical and Molecular Characteristics". The Journal of Infectious Diseases. 181 (3): 1082–1088. doi:10.1086/315346. ISSN 0022-1899. PMID 10720534.
  19. 1 2 Baneth, G. (2010). Ehrlichia and anaplasma infections. Paper presented at World small animal veterinary congress. Retrieved from http://www.ivis.org/proceedings/wsava/2010/d12.pdf
  20. 1 2 Demma, Linda J.; Holman, Robert C.; Mcquiston, Jennifer H.; Krebs, John W.; Swerdlow, David L. (2005). "EPIDEMIOLOGY OF HUMAN EHRLICHIOSIS AND ANAPLASMOSIS IN THE UNITED STATES, 2001–2002". The American Journal of Tropical Medicine and Hygiene. 73 (2): 400–409. doi:10.4269/ajtmh.2005.73.400. ISSN 0002-9637. PMID 16103612.
  21. 1 2 3 4 Paddock, Christopher D.; Childs, James E. (2003). "Ehrlichia chaffeensis: a prototypical emerging pathogen". Clinical Microbiology Reviews. 16 (1): 37–64. doi:10.1128/CMR.16.1.37-64.2003. PMC 145302. PMID 12525424.
  22. ↑ Baddour, L.M. (3 August 2011). "Newly discovered ehrlichia species implicated in human infection". NEJM Journal Watch. New England Journal of Medicine Group, Massachusetts Medical Society. Retrieved 18 April 2024.
  23. ↑ Paddock, Christopher D.; Folk, Scott M.; Shore, G. Merrill; Machado, Linda J. (2001). "Infections with Ehrlichia chaffeensis and Ehrlichia ewingii in Persons Coinfected with Human Immunodeficiency Virus". Clinical Infectious Diseases. 33 (9): 1586–1594. doi:10.1086/323981. ISSN 1058-4838. PMID 11568857.
  24. ↑ Safdar, Nasia; Love, Robert B.; Maki, Dennis G. (2002). "Severe Ehrlichia chaffeensis infection in a lung transplant recipient: a review of ehrlichiosis in the immunocompromised patient". Emerging Infectious Diseases. 8 (3): 320–323. doi:10.3201/eid0803.010249. ISSN 1080-6040. PMC 2732464. PMID 11927032.
  25. ↑ "Human monocytic ehrlichiosis". reference.medscape.com. Retrieved 2026-07-25.
  26. 1 2 Goodman, Jesse L.; Nelson, Curtis; Vitale, Blaise; Madigan, John E.; Dumler, J. Stephen; Kurtti, Timothy J.; Munderloh, Ulrike G. (1996-01-25). "Direct Cultivation of the Causative Agent of Human Granulocytic Ehrlichiosis". New England Journal of Medicine. 334 (4): 209–215. doi:10.1056/NEJM199601253340401. ISSN 0028-4793. PMID 8531996.
  27. ↑ Biggs, Holly M.; Behravesh, Casey Barton; Bradley, Kristy K.; Dahlgren, F. Scott; Drexler, Nausheen A.; Dumler, J. Stephen; Folk, Sarah M.; Kato, Carol Y.; Lasry, Anita; Levin, Michael L.; Lindsey, Nicholas P.; McQuiston, Jennifer H.; Paddock, Christopher D.; Traeger, Michelle S. (2016). "Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis — United States". MMWR Recommendations and Reports. 65 (2): 1–44. doi:10.15585/mmwr.rr6502a1. PMC 5075571. PMID 27172113.
  28. ↑ "Clinical Care of Ehrlichiosis". Centers for Disease Control and Prevention. 15 May 2024. Retrieved 22 March 2026.
This page is issued from Wikipedia. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.