Rickettsia africae infection in man after travel to Ethiopia

Geographical distribution of ixodid ticks and tick-borne pathogens of domestic animals in Ethiopia: a systematic review

BACKGROUND

In Ethiopia, ixodid ticks and associated tick-borne pathogens (TBPs) are of great importance from both a veterinary and public health point of view. This review aimed at compiling available published data on the distribution of ixodid tick species and TBPs in the country.

METHODS

A standard review approach was employed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. Published peer-reviewed articles and theses/dissertations reporting on ixodid ticks and TBPs in Ethiopia were searched using different keywords in many electronic databases including PubMed, Scopus, Web of Science, Google Scholar, African Journals OnLine, and institutional repositories. Articles were screened based on inclusion and exclusion criteria using the PRISMA flowchart. Data were retrieved from eligible articles and recorded in a preformed data record sheet. Descriptive statistics were employed to present data using graphs. QGIS (Quantum GIS) software version 3.4.5 was used to show the distribution of ixodid tick species and TBPs.

RESULTS

Overall, 35 articles that met the inclusion criteria were included in this review. Of these, 24 articles report only on ixodid ticks of domestic animals, six articles report only on TBPs in livestock or ticks, and five articles report on both ticks and TBPs in either animals or ticks. Of these studies, 54% were in the Oromia region, while only 3% of studies were in the Benishangul-Gumuz region. The Gambela region lacked studies on ticks and TBPs. At least 19 ixodid tick species have been recorded from different domestic animals including cattle, small ruminants, donkeys, horses, camels, dogs, and cats. Morphological characterization appears to be the sole method of tick species identification in the country. The distribution and abundance of specific tick species depend on geographical locations and agroecological factors. Sixteen molecularly confirmed TBPs have been identified in animal and tick tissue using molecular methods from only four administrative regions, despite the wide distribution of ticks. Among TBPs, five Anaplasma, two Ehrlichia, two Rickettsia, five Theileria, two Babesia, and one Coxiella species are the major pathogens in both livestock and humans.

CONCLUSIONS

Many ixodid ticks circulate in a wide geographical zone of Ethiopia. However, the limited reports on TBPs at the country level in general, and the absence of either tick or TBP reports around the border region with neighboring countries in particular, highlights the need for further study.

Clinical, epidemiological, and laboratory features of Rickettsia africae infection, African tick-bite fever: A systematic review

African tick-bite fever (ATBF), caused by Rickettsia africae, is the main tick-borne rickettsiosis and the second most frequent cause of fever after malaria in travelers returning from sub-Saharan Africa. General descriptions on ATBF were made in the first two decades after recognized as a new infectious entity, and since then, many authors have contributed to the knowledge of the disease by reporting clinical cases in scientific literature. We developed a systematic review that evaluated all available evidence in the literature regarding clinical, epidemiological, and laboratory features of confirmed R. africae rickettsiosis cases. We followed the recommendations made by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guide. A total of 48 scientific publications (108 confirmed cases) were analyzed in order to extract data for developing this review. Overall, our results show that R. africae rickettsiosis is more frequent in males in the age group of 18-64 years, more than 80% of the cases occurred in European travelers, South Africa was the country where most infections were acquired, and almost 40% of cases occurred in clusters. Clinically, more than 80% of the cases had fever and eschar (55% developed multiple eschars), rash was present in less than the half of cases, and lymphangitis was not a common sign (11%). Headache, myalgia and regional lymphadenopathy were predominant nonspecific clinical manifestation (mean of 60%, 49% and 51%, respectively). Our results show that at least 70% of R. africae cases had altered laboratory parameters, most often showing an increase in transaminases and C-reactive protein. Tetracycline-class antibiotics, as monotherapy, were used in most (>90%) of the patients. Overall, only 4% of cases had complications, 12% required hospitalization, and there was a 100% rate of clinical recovery.

Morphological, molecular and MALDI-TOF mass spectrometry identification of ixodid tick species collected in Oromia, Ethiopia

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) technology has recently been reported as a promising method for arthropods identification. More recently, our laboratory reported the correct identification of tick species via the MALDI-TOF MS protein spectra profiling of legs from fresh specimens. The aim of the present study was to assess the use of MALDI-TOF MS for correct identification of ixodid tick species preserved in 70 % ethanol during field collection in Ethiopia. Following morphological identification of 12 tick species, the legs from 85 tick specimens were subjected to MALDI-TOF MS. Spectral analysis revealed an intra-species reproducibility and inter-species specificity that were consistent with the morphological classification. To support the results of the MALDI-TOF MS tick species identification, 41 tick specimens comprising 3 to 5 specimens per tick species were used to create a reference spectra database, which was evaluated using the spectra of the 44 remaining tick specimens. The blind tests revealed that 100 % of the tick specimens studied by MALDI-TOF MS were correctly identified. A relevant Log score value (LSV) of >1.8 was recorded for all of the tick species studied by MALDI-TOF MS, except for Rhipicephalus praetextatus. The morphological and MALDI-TOF MS identifications were confirmed by sequencing the 12S ribosomal RNA (rRNA) gene of 40 tick specimens belonging to 11 ixodid species. Taken together, the results of the present study indicate that MALDI-TOF MS is a reliable tool for tick species identification, even after preservation in ethanol, provided that a reference spectra database is built from specimens that represent the respective species stored under the same conditions.

Spotted fever group rickettsiae in ixodid ticks in Oromia, Ethiopia

In Ethiopia, information on the transmission of human zoonotic pathogens through ixodid ticks remains scarce. To address the occurrence and molecular identity of spotted fever group rickettsiae using molecular tools, a total of 767 ixodid ticks belonging to thirteen different species were collected from domestic animals from September 2011 to March 2014. Rickettsia africae DNA was detected in 30.2% (16/53) Amblyommma variegatum, 28.6% (12/42) Am. gemma, 0.8% (1/119) Am. cohaerens, 18.2% (4/22) Amblyomma larvae, 6.7% (2/60) Amblyomma nymphs, 0.7% (1/139) Rhipicephalus (Boophilus) decoloratus and 25% (1/4) nymphs of Rh. (Bo.) decoloratus. A markedly low prevalence of R. africae was recorded in both Am. cohaerens and Rh. (Bo.) decoloratus (p<0.0001) compared with that in Am. variegatum and Am. gemma. The prevalence of R. africae was markedly low in the western districts (Gachi and Abdela) (p<0.0001); however, the prevalence of R. africae was relatively high in the central (Ada'a, Wolmara and Arsi) and eastern (Arero, Moyale and Yabelo) districts, where Am. variegatum and Am. gemma were predominantly associated with R. africae, respectively. R. aeschlimannii DNA was detected in 45.4% (5/11) Hyalomma marginatum rufipes and 2.2% (1/46) Hy. truncatum. Moreover, the first report of R. massiliae DNA in 1.9% (1/52) Rhipicephalus praetextatus ticks in Ethiopia is presented herein. Altogether, these results suggest that the transmission of spotted fever group rickettsiae through ixodid ticks is a potential risk for human health in different parts of Ethiopia. Clinicians in this country should consider these pathogens as a potential cause of febrile illness in patients.

Rickettsioses and Q fever in travelers (2004-2013)

Rickettsioses (also called typhus) are associated with arthropods, including ticks, mites, fleas, and lice, although Q fever is more frequently acquired through the inhalation of contaminated aerosols or the consumption of milk. These zoonoses first emerged in the field of travel medicine 20 years ago. Here, we review rickettsioses and Q fever in travelers, highlighting cases reported in the past decade. African tick bite fever and Mediterranean spotted fever are the two most frequent spotted fevers. While the presentation of these fevers is typically benign, cardiac and neurological complications due to African tick bite fever have been reported, and Mediterranean spotted fever has been complicated by multi-organ failure and death in a few cases. Murine typhus and Q fever remain difficult to recognize and diagnose because these illnesses often present with only fever. New molecular tools, particularly when deployed with samples obtained from eschar swabs, might be easily implemented in laboratories with PCR facilities. Doxycycline must be introduced upon clinical suspicion of rickettsioses or Q fever and should be considered in cases of fever of unknown origin in travelers who are returning from at-risk geographic areas.

Case report of African tick-bite fever from Poland

A confirmed case of rickettsiosis acquired in South Africa and recognized in Poland was described. The patient fulfilled clinical criteria highly suggestive of African tick bite fever, such as eschars, regional lymphadenitis, cutaneous rash within 10 days after his return from sub-Saharan Africa. Infection with Rickettsia africae was confirmed by polymerase chain reaction and sequencing.

Update on tick-borne rickettsioses around the world: a geographic approach

Tick-borne rickettsioses are caused by obligate intracellular bacteria belonging to the spotted fever group of the genus Rickettsia. These zoonoses are among the oldest known vector-borne diseases. However, in the past 25 years, the scope and importance of the recognized tick-associated rickettsial pathogens have increased dramatically, making this complex of diseases an ideal paradigm for the understanding of emerging and reemerging infections. Several species of tick-borne rickettsiae that were considered nonpathogenic for decades are now associated with human infections, and novel Rickettsia species of undetermined pathogenicity continue to be detected in or isolated from ticks around the world. This remarkable expansion of information has been driven largely by the use of molecular techniques that have facilitated the identification of novel and previously recognized rickettsiae in ticks. New approaches, such as swabbing of eschars to obtain material to be tested by PCR, have emerged in recent years and have played a role in describing emerging tick-borne rickettsioses. Here, we present the current knowledge on tick-borne rickettsiae and rickettsioses using a geographic approach toward the epidemiology of these diseases.

Detection of a new Borrelia species in ticks taken from cattle in Southwest Ethiopia

We collected 284 ticks in Ethiopia (109 Amblyomma cohaerens, 173 Rhipicephalus decoloratus, and 2 Rhipicephalus praetextatus). We found no rickettsiae and bartonellae. In 7.3% of the A. cohaerens, we found a Borrelia sp. that may represent a new species distant from both relapsing fever group and Lyme borreliae.

Tick-borne relapsing fever with cutaneous eschar and radiculopathy, Ethiopia

We report the first confirmed case of tick-borne borreliosis by molecular tools in a French traveler returning from Ethiopia with unusual presentation: the presence of cutaneous eschar after a hard tick-bite suggesting firstly to clinicians a diagnosis of tick-borne rickettsiosis.

Preliminary investigation on rodent-ectoparasite associations in the highlands of Tigray, Northern Ethiopia: implications for potential zoonoses

We studied associations between rodents and their arthropod ectoparasites in crop fields and household compounds in the highlands of Tigray, Northern Ethiopia. Ectoparasite infestation indices, such as percent infestation, mean abundance, prevalence and host preferences, were calculated for each taxon. In total, 172 rodents from crop fields and 97 from household compounds were trapped. Rodent species and numbers trapped from the crop fields and household compounds were Mastomys awashensis (Lavrenchenko, Likhnova & Baskevich, 1998) (88 and 44), Arvicanthis dembeensis (Ruppel, 1842) (63 and 37) and Acomys sp. (21 and 16), respectively. A total of 558 insects and acarids (belonging to 11 taxa) were recovered from the rodents trapped in the crop fields, and 296 insects and acarid (belonging to 6 taxa) from the rodents trapped in the household compounds. Approximately 66% of the rodents trapped from the crop fields and 47% of those trapped from the household compounds were infested with ectoparasites. Laelaps sp. (64.9%) and Xenopsylla sp. (20.6%) comprised the highest proportion of the ectoparasites recovered in the crop fields, and the same ectoparasites, but in reverse order, comprised the highest proportions in the household compounds (Xenopsylla [50.3%] and Laelaps sp. [29%]). Our study revealed that crop fields and household compounds in the highlands share similar rodents and several ectoparasites. Furthermore, at least 1 of the rodent species and some of the ectoparasites identified in this study were reported to have posed medical and veterinary threats in other parts of Ethiopia and neighboring countries.

Molecular diagnostics of Rickettsia africae infection in travelers returning from South Africa to The Netherlands

BACKGROUND

African tick-bite fever (ATBF) is frequently diagnosed in The Netherlands in travelers returning from South Africa. It is caused by Rickettsia africae and diagnosis is based on travel history and clinical presentation and usually confirmed by detecting serum antibodies against rickettsiae of the spotted fever group. However, these typically occur late in the course of the disease, and a mild clinical course or early antibiotic treatment can diminish antibody production.

METHODS AND RESULTS

Four travelers presented with (sub)febrile temperatures and eschar(s), several days after returning from South Africa. R. africae DNA was amplified and sequenced from skin biopsies of the eschars of all patients. Initial immunofluorescence assays yielded no immunoglobulin M (IgM)/IgG antibodies directed against spotted fever group rickettsiae; however, serology in the convalescent phase-several weeks after the patients had fully recovered-was positive.

CONCLUSIONS

ATBF should be considered in travelers returning from South Africa to The Netherlands with febrile illness and (multiple) skin lesions. The diagnosis can be confirmed by (paired) serology; however, polymerase chain reaction and sequencing on skin biopsies could be a (faster and more accurate) confirmatory test. Advantages of molecular methods over serology are species identification and high sensitivity early in the course of the disease.