Agent Of African Tick-bite Fever Research Articles

Evidence of Rickettsia and Orientia Infections Among Abattoir Workers in Djibouti.

Of 49 workers at a Djiboutian abattoir, eight (16%, 95% confidence interval [CI]: 9-29) were seropositive against spotted fever group rickettsiae (SFGR), two (4%, 95% CI: 1-14) against typhus group rickettsiae, and three (6%, 95% CI: 2-17) against orientiae. One worker (9%, 95% CI: 2-38) seroconverted against orientiae during the study period. This is the first evidence of orientiae exposure in the Horn of Africa. SFGR were also identified by polymerase chain reaction in 32 of 189 (11%, 95% CI: 8-15) tick pools from 26 of 72 (36%) cattle. Twenty-five (8%, 95% CI: 6-12) tick pools were positive for Rickettsia africae, the causative agent of African tick-bite fever. Health-care providers in Djibouti should be aware of the possibility of rickettsiae infections among patients, although further research is needed to determine the impact of these infections in the country.

Emergence ofRickettsia africae, Oceania

We detected Rickettsia africae, the agent of African tick-bite fever (ATBF), by amplification of fragments of gltA, ompA, and ompB genes from 3 specimens of Amblyomma loculosum ticks collected from humans and birds in New Caledonia. Clinicians who treat persons in this region should be on alert for ATBF.

Rickettsia africae in Amblyomma variegatum and Domestic Ruminants on Eight Caribbean Islands

We used PCRs with omp A primers to determine if spotted fever group rickettsiae occurred in Amblyomma variegatum from 6 Caribbean islands. Positive amplicons were obtained from ticks from the U.S. Virgin Islands (9/18; 50%), Dominica (39/171; 30%), Montserrat (2/5; 40%), Nevis (17/34; 50%), St. Kitts (46/227; 20%), and St. Lucia (1/14; 7%). Sequences for a convenience sample of reaction products obtained from A. variegatum on St. Kitts (7), American Virgin Islands (4), Montserrat (2), and St. Lucia (1) were 100% homologous with that of Rickettsia africae , the agent of African tick-bite fever. To determine if transmission of R. africae occurred, we used Rickettsia rickettsii antigen in IFA tests and found positive titers (≥ 1/80) with sera from cattle, goats, and sheep from Dominica (24/95 [25%], 2/136 [2%], 0/58 [0%]), Nevis (12/45 [27%], 5/157 [3%], 0/90 [0%]), St. Kitts (2/43 [5%], 1/25 [4%), 1/35 [3%]), and St. Lucia (6/184 [3%] cattle), respectively. No seropositive animals were found in Grenada (0/4, 0/98/, 0/86), Montserrat (0/12, 0/26, 0/52), or Puerto Rico (0/80 cattle). Our study indicates that R. africae and African tick-bite fever are widespread in the Caribbean.

Rickettsia africae, Western Africa

<i>Rickettsia africae</i>, Western Africa

Analysis of the Rickettsia africae genome reveals that virulence acquisition in Rickettsia species may be explained by genome reduction

BackgroundThe Rickettsia genus includes 25 validated species, 17 of which are proven human pathogens. Among these, the pathogenicity varies greatly, from the highly virulent R. prowazekii, which causes epidemic typhus and kills its arthropod host, to the mild pathogen R. africae, the agent of African tick-bite fever, which does not affect the fitness of its tick vector.ResultsWe evaluated the clonality of R. africae in 70 patients and 155 ticks, and determined its genome sequence, which comprises a circular chromosome of 1,278,540 bp including a tra operon and an unstable 12,377-bp plasmid. To study the genetic characteristics associated with virulence, we compared this species to R. prowazekii, R. rickettsii and R. conorii. R. africae and R. prowazekii have, respectively, the less and most decayed genomes. Eighteen genes are present only in R. africae including one with a putative protease domain upregulated at 37°C.ConclusionBased on these data, we speculate that a loss of regulatory genes causes an increase of virulence of rickettsial species in ticks and mammals. We also speculate that in Rickettsia species virulence is mostly associated with gene loss.The genome sequence was deposited in GenBank under accession number [GenBank: NZ_AAUY01000001].

Detection of Rickettsia africae in Rhipicephalus (Boophilus) decoloratus Ticks from the Republic of Botswana, South Africa

A total of 53 engorged adult ticks belonging to the species Rhipicephalus (Boophilus) decoloratus (N = 9), Rhipicephalus evertsi evertsi (N = 27), Rhipicephalus appendiculatus (N = 9), Amblyomma hebraeum (N = 5), and Hyalomma marginatum turanicum (N = 3), were removed from oryx in Botswana (South Africa). They were tested for the presence of spotted fever group (SFG) Rickettsia and Anaplasma phagocytophilum using polymerase chain reaction (PCR). Seventy-seven percent of R. decoloratus as well as twenty percent of A. hebraeum were positive for ompA, gltA and 16S rRNA SFG Rickettsia PCR assays. All nucleotide sequences were homologous to Rickettsia africae, the agent of African tick-bite fever (ATBF). None of the tested ticks was positive for 16S rRNA A. phagocytophilum PCR assays. These results suggest for the first time that R. decoloratus ticks may be reservoirs of R. africae, and support the ATBF risk in this area.

Rickettsioses in Sub‐Saharan Africa

Although rickettsioses are among the oldest known vector-borne zoonoses, several species or subspecies of rickettsias have been identified in recent years as emerging pathogens throughout the world including in sub-Saharan Africa. To date, six tick-borne spotted fever group pathogenic rickettsias are known to occur in sub-Saharan Africa, including Rickettsia conorii conorii, the agent of Mediterranean spotted fever; R. conorii caspia, the agent of Astrakhan fever; R. africae, the agent of African tick-bite fever; R. aeschlimannii; R. sibirica mongolitimonae; and R. massiliae. On the other hand, fleas have long been known as vectors of the ubiquitous murine typhus, a typhus group rickettsiosis induced by R. typhi. However, a new spotted fever rickettsia, R. felis, has also been found to be associated with fleas, to be a human pathogen, and to be present in sub-Saharan Africa. Finally, R. prowazekii the agent of louse-borne epidemic typhus continues to strikes tens to hundreds of thousands of persons who live in Sub-Saharan with civil war, famine and poor conditions. We present an overview of these rickettsioses occurring in sub-Saharan Africa, focusing on the epidemiological aspects of emerging diseases.

Rickettsia africaein the West Indies

Rickettsia africae is the agent of African tick-bite fever, a mild but common disease of local persons and tourists in Africa. The major vector of this spotted fever group rickettsia is most likely Amblyomma variegatum, the tropical bont tick, which has become widely distributed through the West Indies in the last 30 years. This report reviews all available information on R. africae in the West Indies.

Cardiac involvement in a patient with clinical and serological evidence of African tick-bite fever

BackgroundMyocarditis and pericarditis are rare complications of rickettsiosis, usually associated with Rickettsia rickettsii and R. conorii. African tick-bite fever (ATBF) is generally considered as a benign disease and no cases of myocardial involvement due to Rickettsia africae, the agent of ATBF, have yet been described.Case presentationThe patient, that travelled in an endemic area, presented typical inoculation eschars, and a seroconversion against R. africae, was admitted for chest pains and increased cardiac enzymes in the context of an acute myocarditis.ConclusionOur findings suggest that ATBF, that usually presents a benign course, may be complicated by an acute myocarditis.

A SURVEY FOR SPOTTED FEVER GROUP RICKETTSIAE AND EHRLICHIAE IN AMBLYOMMA VARIEGATUM FROM ST. KITTS AND NEVIS

Eighty-nine Amblyomma variegatum ticks were collected from the islands of St. Kitts and Nevis in the Caribbean and preserved in 70% ethanol or local rum. After being washed in sterile water, their DNA was extracted and analyzed by a polymerase chain reaction (PCR) for DNA of spotted fever group rickettsiae and ehrlichiae. None of the tested ticks was positive in a PCR assay using the primers 16S EHRD and 16S EHRR for the 16S rRNA gene of Ehrlichia spp.. Forty-one percent of the A. variegatum (36 of 89 of which 34 [47%] of 72 were adult males, 2 (13%) of 16 were adult females, and 0 (0%) of 1 were nymphs) were positive in a PCR assay using the primer pair 190-70 and 190-701 for the outer membrane protein A (ompA) gene of spotted fever group rickettsiae. All PCR amplification products obtained had 100% sequence homology with Rickettsia africae, the agent of African tick-bite fever.

Tick-borne rickettiosis in Guadeloupe, the French West Indies: isolation of Rickettsia africae from Amblyomma variegatum ticks and serosurvey in humans, cattle, and goats.

Twenty-seven rickettsiae were isolated and/or detected from 100 Amblyomma variegatum ticks collected on Guadeloupe in the French West Indies. In this study, the polymerase chain reaction procedure appeared to be more sensitive in detecting rickettsiae in ticks than the shell-vial technique. Sequencing a portion of the outer membrane protein A-encoding gene showed that these rickettsiae appeared to be identical to Rickettsia africae, a member of the spotted fever group rickettsiae recently described as an agent of African tick-bite fever occurring in sub-Sahelian Africa. A high seroprevalence of antibodies to R. africae was demonstrated among mammals, particularly humans, cattle, and goats. These results and a recently reported case of an infection due to R. africae on Guadeloupe demonstrate that R. africae is present on this island. Although this disease has been underdiagnosed there, it may be frequent and may exist on other Caribbean islands where A. variegatum has propagated dramatically over recent years.

Prevalence of Rickettsia-Like Organisms and Spotted Fever Group Rickettsiae in Ticks (Acari: Ixodidae) from Zimbabwe

The prevalence of rickettsia-like organisms in ticks from Zimbabwe was determined using the hemolymph test. Amblyomma hebraeum had the highest prevalence of rickettsia-like organisms. Other species with rickettsia-like organisms included Amblyomma sparsum, Amblyomma variegatum, Hyalomma marginatum rufipes, Ripicephalus simus, Haemaphysalis leachi, Amblyomma rhinocerotis, and Hyalomma truncatum. Ticks with no demonstrable rickettsia-like organisms infection were Boophilus decoloratus, Haemaphysalis spinulosa, Rhipicephalus appendiculatus, Rhipicephalus evertsi evertsi, and Rhipicephalus sanguineus. Polymerase chain reaction followed by restriction fragment-length polymorphism analysis on samples of hemolymph-positive ticks showed the agent of African tick-bite fever to be present in A. hebraeum, Rickettsia conorii to be present in Rhipicephalus simus and Haemaphysalis leachi, and a spotted fever group rickettsia similar to that in Hyalomma marginatum marginatum ticks from Morocco and Portugal to be present in Hyalomma marginatum rufipes.