Skip directly to site content Skip directly to page options Skip directly to A-Z link Skip directly to A-Z link Skip directly to A-Z link
Volume 21, Number 3—March 2015

Molecular Detection of Ehrlichia chaffeensis in Humans, Costa Rica

Cite This Article

To the Editor: Human monocytic ehrlichiosis (HME), a tickborne zoonosis caused by the rickettsial pathogen Ehrlichia chaffeensis (Rickettsiales: Anaplasmataceae), is considered an emerging pathogen in the United States and, increasingly, in many countries around the world (1). In Costa Rica, past reports of human cases of ehrlichiosis were diagnosed solely by clinical evaluation and cytomorphology (2,3); recent studies have detected E. canis in dogs and their ectoparasites (4,5). However, molecular detection of natural Ehrlichia infection detected in humans in Costa Rica has not been reported.

In a small rural area of Zarcero, province of Alajuela, north central region of Costa Rica, blood samples were drawn from 20 patients who had histories of tick bites and nonspecific symptoms of fatigue, arthralgia, and myalgia beginning >1 year before sampling. The samples were referred for Ehrlichia molecular analysis. In addition, blood samples were drawn from 2 patients of 2 health care clinics in the Alajuela province districts of San Carlos and Alajuela who had clinical signs compatible with recent ehrlichiosis; the samples were sent for confirmation by PCR. All anticoagulated samples were transported within 4 hours to the laboratory for processing. No serologic assays were performed; cytomorphologic estimation and laboratory data were provided from the local health facilities, mostly generated 1 year before this molecular analysis.

DNA was isolated the same day of sampling from whole blood (200 μL) by using the QIAamp Blood Kit (QIAGEN, Santa Clarita, CA, USA) according to the manufacturer’s instructions. Purified DNA from each blood sample was quantified by spectrophotometry, yielding 20–32 ng/μL of DNA. Nested PCR assays were performed as described (6,7). To avoid DNA contamination, first PCR, second PCR, and electrophoresis were performed in separate rooms, following strict rules of pipetting and cleaning, and repeated >3 times. In addition, endpoint PCR for the variable-length PCR target gene was performed on samples that were positive in the nested assay, according to Paddock et al. (8). For DNA sequencing, PCR reactions were performed, and products were separated by agarose gel electrophoresis. A nested PCR mixture containing water and 1 containing unrelated Brucella abortus DNA were used as negative controls in every assay. As an internal control, the 22 samples were assayed for the b-globin gene (TaKaRa Bio/Clontech, Mountain View, CA, USA). All samples were positive for the β-globin gene by PCR with primers PC04 and GH20. Fragments (bands) were excised from electrophoretic gels by using sterile scalpels. These fragments were then were placed in a PCR mixture and used as a template.  PCR mixtures were pooled and purified by using the QIAquick PCR Purification Kit (QIAGEN) according to the manufacturer’s instructions. DNA was sequenced at Macrogen Inc. (Seoul, South Korea). The sequences obtained were compared to those previously deposited in GenBank.

Three of the 20 human blood samples from Zarcero that were tested, and the 2 samples from patients of different locations, were positive for 16S rRNA gene fragment of 390 bp and showed 99%–100% identity to the E. chaffeensis strain Arkansas gene (GenBank accession no. NR074500.1). These fragments were sequenced and deposited in GenBank, under accession numbers CR1 San Carlos (KF888343), CR2 Alajuela (KF888344), CR3 Zarcero (KF888345), CR4 Zarcero (KF888346), and CR5 Zarcero (KF888347). Amplifed bands for 2 of the 5 samples positive by nested PCR (CR1 and CR4) were identical to those specific for the 5 repeats of variable-length PCR target gene (459 bp).

A summary of clinical manifestations and results of DNA analysis is shown in the Table. The major symptoms reported by most patients were rash, predominantly macular in extremities; general arthralgia and myalgia; and headache. Comparison of clinical and laboratory findings of patients with PCR-positive and -negative results showed no clear differences, possibly related to the length of time between the acute phase of illness and the sampling for molecular analysis, which was usually 1 year. Nevertheless, it is noteworthy that the patients’ samples harbored detectable Ehrlichia DNA 1 year after the acute phase, which was similar to findings in recent reports (9). Equally, related to the 2 patients evaluated in this study who had a recent history of infection (CR1 and CR2), no major physical or biochemical alterations were observed, suggesting that disease manifestation was mild or that samples were taken during the convalescent phase. The incongruent high detection of intracellular morulae and low PCR results point out the necessity of improving techniques for early diagnosis of this disease, particularly in primary health care clinics. Clinicians and public health authorities should be aware of the presence of this pathogen in the region and should include molecular tools in the diagnosis of this zoonosis.

The arthropod vector or vectors, and vertebrate reservoir or reservoirs of E. chaffeensis in Costa Rica are unknown, and further ecologic studies are required to determine these aspects of human monocytic ehrlichiosis in Central America. Epidemiologic and ecologic surveys are needed to trace and control the dissemination of this public health threat.

Dr. Rojas is a professor of Bacteriology at the School of Microbiology, University of Costa Rica. His research interests include molecular biology, diagnostics, and epidemiology of human and zoonotic bacteria, especially Brucella, methicillin-resistant Staphylococcus aureus, and tickborne pathogens.



We thank Ricardo Gutiérrez for his assistance in the sequence analysis.

This work was supported by a Fondos del Sistema grant from the Consejo Nacional de Rectores.


Norman RojasComments to Author , Daniela Castillo, and Priscilla Marin
Author affiliations: Universidad de Costa Rica, San Jose, Costa Rica



  1. Ismail  N, Bloch  KC, McBride  JW. Human ehrlichiosis and anaplasmosis. Clin Lab Med. 2010;30:26192 . DOIPubMedGoogle Scholar
  2. Hernández-de Mezerville  V, Padilla-Cuadra  JI. Choque séptico por ehrliquiosis. Acta Med Costarric. 2007;49:118–20 [cited 2013 Nov 25].
  3. Rojas-Solano  JR, Villalobos-Vindas  J. Ehrliquiosis granulocitotrópica humana. Acta Med Costarric. 2007;49:121–3 [cited 2013 Nov 25].
  4. Rojas  A, Rojas  D, Montenegro  V, Gutiérrez  R, Yasur-Landau  D, Baneth  G. Vector-borne pathogens in dogs from Costa Rica: first molecular description of Babesia vogeli and Hepatozoon canis infections with a high prevalence of monocytic ehrlichiosis and the manifestations of co-infection. Vet Parasitol. 2014;199:1218. DOIPubMedGoogle Scholar
  5. Romero  LE, Meneses  AI, Salazar  L, Jiménez  M, Romero  JJ, Aguiar  DM, First isolation and molecular characterization of Ehrlichia canis in Costa Rica, Central America. Res Vet Sci. 2011;91:957. DOIPubMedGoogle Scholar
  6. Dawson  JE, Stallknecht  DE, Howerth  EW, Warner  C, Biggie  K, Davidson  WR, Susceptibility of white-tailed deer (Odocoileus virginianus) to infection with Ehrlichia chaffeensis, the etiologic agent of human ehrlichiosis. J Clin Microbiol. 1994;32:27258 .PubMedGoogle Scholar
  7. Kocan  AA, Levesque  GC, Whitworth  LC, Murphy  GL, Ewing  SA, Barker  RW. Naturally occurring Ehrlichia chaffeensis infection in coyotes from Oklahoma. Emerg Infect Dis. 2000;6:47780. DOIPubMedGoogle Scholar
  8. Paddock  CD. Sumner JW, Shore GM, Bartley DC, Elie RC, McQuade JG, et al. Isolation and characterization of Ehrlichia chaffeensis strains from patients with fatal ehrlichiosis. J Clin Microbiol. 1997;35:2496–502.
  9. Breitschwerdt  EB, Hegarty  BC, Qurollo  BA, Saito  TB, Maggi  RG, Blanton  LS, Intravascular persistence of Anaplasma platys, Ehrlichia chaffeensis, and Ehrlichia ewingii DNA in the blood of a dog and two family members. Parasit Vectors. 2014;7:298–305.




Cite This Article

DOI: 10.3201/eid2103.131759

Related Links


Table of Contents – Volume 21, Number 3—March 2015

EID Search Options
presentation_01 Advanced Article Search – Search articles by author and/or keyword.
presentation_01 Articles by Country Search – Search articles by the topic country.
presentation_01 Article Type Search – Search articles by article type and issue.



Please use the form below to submit correspondence to the authors or contact them at the following address:

Norman Rojas, Centro de Investigación en EnfermedadesTropicales, Facultad de Microbiología, Universidad de Costa Rica, 2060 San Jose, Costa Rica

Send To

10000 character(s) remaining.


Page created: February 18, 2015
Page updated: February 18, 2015
Page reviewed: February 18, 2015
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.