Human Infection with R. felis, Kenya | CDC EID

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Volume 16, Number 7–July 2010
Research
Human Infection with Rickettsia felis, Kenya
Allen L. Richards, Ju Jiang, Sylvia Omulo, Ryan Dare, Khalif Abdirahman, Abdile Ali, Shanaaz K. Sharif, Daniel R. Feikin, Robert F. Breiman, and M. Kariuki Njenga
Author affiliations: Naval Medical Research Center, Silver Spring, Maryland, USA (A.L. Richards, J. Jiang); Uniformed Services University of the Health Sciences, Bethesda, Maryland, USA (A.L. Richards); US Centers for Disease Control and Prevention, Nairobi, Kenya (S. Omulo, R. Dare, D.R. Feikin, R.F. Breiman, M.K. Njenga); and Kenya Ministry of Health, Nairobi (K.A. Abdirahman, A. Ali, S.K. Sharif)

Suggested citation for this article

Abstract
To determine the cause of acute febrile illnesses other than malaria in the North Eastern Province, Kenya, we investigated rickettsial infection among patients from Garissa Provincial Hospital for 23 months during 2006–2008. Nucleic acid preparations of serum from 6 (3.7%) of 163 patients were positive for rickettsial DNA as determined by a genus-specific quantitative real-time PCR and were subsequently confirmed by molecular sequencing to be positive for Rickettsia felis. The 6 febrile patients' symptoms included headache; nausea; and muscle, back, and joint pain. None of the patients had a skin rash.
Rickettsial diseases are found worldwide and are caused by infection with obligate intracellular rickettsiae, which are transmitted to humans by arthropod vectors (e.g., lice, fleas, ticks, and mites). Rickettsiae are associated with arthropods for a least a part of their life cycle and are passed to other arthropods by transovarial transmission or horizontal transmission involving vertebrate hosts (1). Rickettsiae are small, gram-negative, fastidious bacteria of the α subdivision of Proteobacteria, which are frequently divided into 2 groups based on antigenicity, G+C content, culture conditions, and actin polymerization: 1) the typhus group including Rickettsia prowazekii and R. typhi, the causative agents of louse-borne epidemic and flea-borne murine typhus, and 2) the spotted fever group including >20 species that may cause tick-, flea-, and mite-borne rickettsioses (2). Infection of humans by rickettsiae often begins at the site of the bite of the arthropod vector and subsequently spreads through the draining lymph nodes throughout the body, resulting in infection of endothelial cells, which can lead to multiorgan pathologic changes associated with potentially life-threatening diseases (1).

Little is known about the full spectrum of rickettsial diseases that occur in Kenya. One frequently reported rickettsial disease has been described in many parts of Kenya as Kenya fever, Kenya typhus, Kenya tick fever, or Kenyan tick typhus (3,4). This disease was initially thought to be caused by a single pathogen, R. conorii, the causative agent of Mediterranean spotted fever (5). However, recently, a second agent has been suggested as a cause of at least a portion of these rickettsioses (6,7), R. africae, the causative agent of African tick-bite fever. In addition to the tick-borne spotted fever disease, flea-borne murine typhus is known to occur in Kenya, especially in urban areas where the house rat (Rattus rattus) is prevalent (4,8). However, louse-borne epidemic typhus does not appear to be endemic to Kenya (4).

The objective of the hospital-based surveillance we report here was to determine the etiologic agents of nonmalaria acute febrile illnesses in the North Eastern Province, Kenya, during a period when there is no Rift Valley fever (RVF) epidemic in the country. The North Eastern Province was severely affected by the 2 most recent RVF epidemics in the Eastern Africa region; >89,000 human RVF infections occurred during the 1997–98 epidemic and >300 acute cases occurred during the 2006–2007 epidemic (9,10). Therefore, the surveillance was established to investigate whether acute RVF cases occurred during interepidemic periods. As part of this investigation, we also investigated the occurrence of other causes of fever that are not routinely tested for at the local hospitals, including rickettsiosis, brucellosis, leptospirosis, and other viral infections. The study protocol was approved by the institutional review boards of the US Centers for Disease Control and Prevention, US Naval Medical Research Center, and Kenya Medical Research Institute in compliance with all applicable regulations governing the protection of human subjects.

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Suggested Citation for this Article
Richards AL, Jiang J, Omulu S, Dare R, Abdirahman K, Ali A, et al. Human infection with Rickettsia felis, Kenya. Emerg Infect Dis [serial on the Internet]. 2010 Jul [date cited]. http://www.cdc.gov/EID/content/16/7/1081.htm

DOI: 10.3201/eid1607.091885