title: High prevalence of Rickettsia africae variants in Amblyomma variegatum ticks from domestic mammals in rural western Kenya: implications for human health.
abstract: Tick-borne spotted fever group (SFG) rickettsioses are emerging human diseases caused by obligate intracellular Gram-negative bacteria of the genus Rickettsia. Despite being important causes of systemic febrile illnesses in travelers returning from sub-Saharan Africa, little is known about the reservoir hosts of these pathogens. We conducted surveys for rickettsiae in domestic animals and ticks in a rural setting in western Kenya. Of the 100 serum specimens tested from each species of domestic ruminant 43% of goats, 23% of sheep, and 1% of cattle had immunoglobulin G (IgG) antibodies to the SFG rickettsiae. None of these sera were positive for IgG against typhus group rickettsiae. We detected Rickettsia africae-genotype DNA in 92.6% of adult Amblyomma variegatum ticks collected from domestic ruminants, but found no evidence of the pathogen in blood specimens from cattle, goats, or sheep. Sequencing of a subset of 21 rickettsia-positive ticks revealed R. africae variants in 95.2% (20/21) of ticks tested. Our findings show a high prevalence of R. africae variants in A. variegatum ticks in western Kenya, which may represent a low disease risk for humans. This may provide a possible explanation for the lack of African tick-bite fever cases among febrile patients in Kenya.
authors.affiliation: 1 Jomo Kenyatta University of Agriculture and Technology , Nairobi, Kenya .
authors.forename: Alice N
authors.initials: AN
authors.lastname: Maina
authors.forename: Ju
authors.initials: J
authors.lastname: Jiang
authors.forename: Sylvia A
authors.initials: SA
authors.lastname: Omulo
authors.forename: Sally J
authors.initials: SJ
authors.lastname: Cutler
authors.forename: Fredrick
authors.initials: F
authors.lastname: Ade
authors.forename: Eric
authors.initials: E
authors.lastname: Ogola
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Feikin
authors.forename: M Kariuki
authors.initials: MK
authors.lastname: Njenga
authors.forename: Sarah
authors.initials: S
authors.lastname: Cleaveland
authors.forename: Solomon
authors.initials: S
authors.lastname: Mpoke
authors.forename: Zipporah
authors.initials: Z
authors.lastname: Ng'ang'a
authors.forename: Robert F
authors.initials: RF
authors.lastname: Breiman
authors.forename: Darryn L
authors.initials: DL
authors.lastname: Knobel
authors.forename: Allen L
authors.initials: AL
authors.lastname: Richards
mesh_terms: D000818:Animals; D000829:Animals, Domestic; D000907:Antibodies, Bacterial / Q000097:blood*; D001096:Arachnid Vectors / Q000382:microbiology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D001483:Base Sequence; D002417:Cattle; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004285:Dogs; D005260:Female; D006041:Goats; D006801:Humans; D026863:Ixodidae / Q000382:microbiology*; D007630:Kenya / Q000453:epidemiology; D008297:Male; D008969:Molecular Sequence Data; D012281:Rickettsia / Q000235:genetics / Q000276:immunology* / Q000302:isolation & purification; D012282:Rickettsia Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D012423:Rural Health; D017422:Sequence Analysis, DNA / Q000662:veterinary; D016036:Seroepidemiologic Studies; D012756:Sheep; D017282:Tick-Borne Diseases / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D015047:Zoonoses
chemical_list: D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins; D017931:DNA Primers; D004269:DNA, Bacterial
keywords: African tick-bite fever.; Ambylomma variegatum; Rickettsia africae; Tick-borne spotted fever group