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Abstract
BackgroundFlea-borne spotted fever is a zoonosis caused by Rickettsia felis, a Gram-negative obligate intracellular bacterium. The disease has a worldwide distribution including western and eastern sub-Saharan Africa where it is associated with febrile illness in humans. However, epidemiology and the public health risks it poses remain neglected especially in developing countries including Zambia. While Ctenocephalides felis (cat fleas) has been suggested to be the main vector, other arthropods including mosquitoes have been implicated in transmission and maintenance of the pathogen; however, their role in the epidemiological cycle remains to be elucidated. Thus, the aim of this study was to detect and characterize R. felis from animal hosts and blood-sucking arthropod vectors in Zambia.MethodsDog blood and rodent tissue samples as well as cat fleas and mosquitoes were collected from various areas in Zambia. DNA was extracted and screened by polymerase chain reaction (PCR) targeting genus Rickettsia and amplicons subjected to sequence analysis. Positive samples were further subjected to R. felis-specific real-time quantitative polymerase chain reactions.ResultsRickettsia felis was detected in 4.7% (7/150) of dog blood samples and in 11.3% (12/106) of rodent tissue samples tested by PCR; this species was also detected in 3.7% (2/53) of cat fleas infesting dogs, co-infected with Rickettsia asembonensis. Furthermore, 37.7% (20/53) of cat flea samples tested positive for R. asembonensis, a member of spotted fever group rickettsiae of unknown pathogenicity. All the mosquitoes tested (n = 190 pools) were negative for Rickettsia spp.ConclusionsThese observations suggest that R. felis is circulating among domestic dogs and cat fleas as well as rodents in Zambia, posing a potential public health risk to humans. This is because R. felis, a known human pathogen is present in hosts and vectors sharing habitat with humans.
Highlights
Flea-borne spotted fever is a zoonosis caused by Rickettsia felis, a Gram-negative obligate intracellular bacterium
Sequence homology based on outer membrane protein A (OmpA) and outer membrane protein B (OmpB) genes was used to further confirm other Rickettsia species including Rickettsia felis-like organisms (RFLOs) to the species level
Rickettsia felis was detected in 4.7% (7/150) of the dogs from Lusaka and Mazabuka, and 3.7% (2/53) of the cat fleas collected from Mazabuka
Summary
Flea-borne spotted fever is a zoonosis caused by Rickettsia felis, a Gram-negative obligate intracellular bacterium. Rickettsia felis is an obligate intracellular gram-negative alpha-proteobacterium that causes zoonotic cat flea typhus known as flea-borne spotted fever in humans. The bacterium was first described by Adams et al in 1990 in the cytoplasm of midgut cells of the cat flea Ctenocephalides felis [1]. It was later characterized as R. felis. The first human case of R. felis infection was reported in 1994 in Texas, USA [3] Since it remained neglected until its emergence as a cause of febrile illness in sub-Saharan Africa [5]. It has since been reported in eastern and western sub-Saharan Africa [6, 7]
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