Zoonotic Rickettsia Species in Small Ruminant Ticks From Tunisia

Roaming Dogs, Intense Brown Dog Tick Infestation, and Emerging Rocky Mountain Spotted Fever in Tijuana, México

A two decades-long epidemic of Rocky Mountain spotted fever in northern México reached the U.S. border city of Tijuana in 2021. Cases were near the city periphery in marginalized areas, some lacking infrastructure such as streets or utilities. We worked in the three census areas where human cases were reported and in 12 additional control Áreas Geoestadisticas Básicas. There were dogs, the primary tick host and Rickettsia rickettsii reservoir, in 76% of homes, with 2.2 owned dogs per home on average, approximately equal numbers of roaming dogs were seen, and 46.2% of owned dogs were allowed to roam in the street. Sixty-eight percent of people had heard of Rocky Mountain spotted fever (RMSF), and 35% self-reported tick infestation, including 19% of homes without dogs. Ticks appeared to move among houses of adjacent neighbors. Of 191 examined dogs, 61.8% were tick-infested, with 6-fold increased odds if they were allowed to roam. Although no dogs were Rickettsia polymerase chain reaction-positive, we found one R. rickettsii- and 11 Rickettsia massiliae-infected ticks. The rickettsial IgG seroprevalence by immunofluorescence antibody assay was 76.4%, associated with unhealthy body condition, adults, dogs with >10 ticks, more dogs being seen in the area, and dogs being permitted in the street. Insufficient medical and canine management resources have contributed to a case fatality rate of RMSF that has exceeded 50% in areas. High canine seroprevalence suggests risks to people and dogs; unfortunately, herd immunity is impeded by high turnover in the canine population owing to the birth of puppies and high death rates. Binational One Health workers should monitor disease spread, enact canine population management and tick eradication, and provide prevention, diagnostic, and treatment support.

Distribution of different Rickettsia species in countries of the WHO Eastern Mediterranean (WHO-EMRO) region: An overview

SUBJECT

Rickettsia is a zoonotic bacterial pathogen transmitted by vectors and has extensive reservoirs in animal and human populations. Rickettsiosis is a public health problem all over the world. However, comprehensive information on the geographical distribution of different Rickettsia species, infection status of reservoirs, vectors, and human cases is lacking in most parts of the world. Therefore, this study aimed to investigate the geographical distribution of different Rickettsia species and their vectors in countries of the WHO-EMRO region.

METHODS

In this review study, a search was conducted for reports and published studies on Rickettsia species from WHO-EMRO region countries in various databases from 1995 to 2022. Finally, the reported status of human cases, reservoirs, and vectors associated with each species in different countries was documented.

RESULTS

Reports of infections related to the detection of Rickettsia species were only available for 15 out of 22 WHO-EMRO member countries. A total of twenty-four Rickettsia species, including R. sibrica, R. lusitaniae, R. africae, R. prowazekii, R. felis, R. typhi, R. rickettsii, R. aeschlimannii, R. conorii, R. massiliae, R. helvetica, R. monacensis, R. rhipicephali, R. bellii, R. asembonensis, R. hoogstraalii, R. andeanae, R. raoultii, R. asiatica, R. slovaca, R. australis, R. barbariae, Candidatus R. amblyommii, and Candidatus R. goldwasserii, were reported from WHO-EMRO member countries. Furthermore, human cases infected with six different Rickettsia species, including R. sibrica, R. prowazekii, R. felis, R. typhi, R. rickettsii, R. aeschlimannii, R. conorii, R. massiliae, and R. helvetica, were reported from these countries.

CONCLUSION

The vast diversity of Rickettsia vectors has contributed to the ongoing discovery of new Rickettsia species. Therefore, further research on the reservoir hosts of Rickettsia infections in the understudied WHO-EMRO region is crucial. This research sheds light on Rickettsia disease's epidemiology and transmission dynamics in this region.

Microbial diversity of ticks and a novel typhus group Rickettsia species (Rickettsiales bacterium Ac37b) in Inner Mongolia, China

Ticks can carry multiple pathogens, and Inner Mongolia's animal husbandry provides excellent environmental conditions for ticks. This study characterized the microbiome of ticks from different geographical locations in Inner Mongolia; 905 Dermacentor nuttalli and 36 Ixodes persulcatus were collected from sheep in three main pasture areas and from bushes within the forested area. Mixed DNA samples were prepared from three specimens from each region and tick species. Microbial diversity was analyzed by 16S rRNA sequencing, and α and β diversity were determined. The predominant bacterial genera were Rickettsia (54.60%), including Rickettsiales bacterium Ac37b (19.33%) and other Rickettsia (35.27%), Arsenophonus (11.21%), Candidatus Lariskella (10.84%), and Acinetobacter (7.17%). Rickettsia bellii was identified in I. persulcatus, while Rickettsiales bacterium Ac37b was found in D. nuttalli from Ordos and Chifeng. Potential Rickettsia and Anaplasma coinfections were observed in the Ordos region. Tick microbial diversity analysis in Inner Mongolia suggests that sheep at the sampling sites were exposed to multiple pathogens.

Detection of Rickettsia spp. and Anaplasma ovis in Melophagus ovinus from southern Xinjiang, China

Melophagus ovinus is a hematophagous insect that is distributed worldwide and plays a crucial role in transmitting disease-causing pathogens. From June 2021 to March 2022, a total of 370 M. ovinus were collected from 11 sampling points in southern Xinjiang, China. The specimens were identified using morphological and molecular analyses. Rickettsia spp. and Anaplasma ovis were detected from all the samples using seven Rickettsia-specific genetic markers and the msp-4 gene of A. ovis. Approximately 11% of the M. ovinus specimens were positive for Rickettsia spp., and Candidatus Rickettsia barbariae was the most predominant species (35/41; 85.4%), while R. massiliae was least prevalent (6/41; 14.6%). Approximately 10.5% (39/370) of the M. ovinus specimens were positive for A. ovis of genotype III, which was co-detected with Candidatus R. barbariae in M. ovinus (3/370; 0.8%). To the best of our knowledge, this is the first report of the detection of R. massiliae and Candidatus R. barbariae in M. ovinus globally. The detection and control of insect-borne diseases originating from M. ovinus should be strengthened in southern Xinjiang, an area important to animal husbandry and production.

Molecular Survey of Rickettsia raoultii in Ticks Infesting Livestock from Pakistan with Notes on Pathogen Distribution in Palearctic and Oriental Regions

Ticks are hematophagous ectoparasites that transmit different pathogens such as Rickettsia spp. to domestic and wild animals as well as humans. Genetic characterizations of Rickettsia spp. from different regions of Pakistan are mostly based on one or two genetic markers and are confined to small sampling areas and limited host ranges. Therefore, this study aimed to molecularly screen and genetically characterize Rickettsia spp. in various tick species infesting camels, sheep, and goats. All the collected tick specimens were morphologically identified, and randomly selected tick species (148) were screened molecularly for the detection of Rickettsia spp. by amplifying three rickettsial DNA fragments, namely, the citrate-synthase gene (gltA), outer-membrane protein A (ompA), and outer-membrane protein B (ompB). After examining 261 hosts, 161 (61.7%) hosts were found infested by 564 ticks, including 287 (50.9%) nymphs, 171 (30.3%) females, and 106 (18.8%) males in five districts (Kohat, Dera Ismail Khan, Lower Dir, Bajaur, and Mansehra). The highest occurrence was noted for Hyalomma dromedarii (number = 72, 12.8%), followed by Haemaphysalis sulcata (n = 70, 12.4%), Rhipicephalus turanicus (n = 64, 11.3%), Rhipicephalus microplus (n = 55, 9.7%), Haemaphysalis cornupunctata (n = 49, 8.7%), Hyalomma turanicum (n = 48, 8.5%), Hyalomma isaaci (n = 45, 8.0%), Haemaphysalis montgomeryi (n = 44, 7.8%), Hyalomma anatolicum (n = 42, 7.5%), Haemaphysalis bispinosa (n = 38, 6.7%), and Rhipicephalus haemaphysaloides (n = 37, 6.6%). A subset of 148 ticks were tested, in which eight (5.4%) ticks, including four Hy. turanicum, two Ha. cornupunctata, one Ha. montgomeryi, and one Ha. bispinosa, were found positive for Rickettsia sp. The gltA, ompA, and ompB sequences revealed 100% identity and were phylogenetically clustered with Rickettsia raoultii reported in China, Russia, USA, Turkey, Denmark, Austria, Italy, and France. Additionally, various reports on R. raoultii from Palearctic and Oriental regions were summarized in this study. To the best of our knowledge, this is the first report regarding genetic characterization and phylogenetic analysis of R. raoultii from Pakistan. Further studies to investigate the association between Rickettsia spp. and ticks should be encouraged to apprise effective management of zoonotic consequences.

Association of SFG Rickettsia massiliae and Candidatus Rickettsia shennongii with Different Hard Ticks Infesting Livestock Hosts

Ixodid ticks are responsible for the transmission of various intracellular bacteria, such as the Rickettsia species. Little Information is available about the genetic characterization and epidemiology of Rickettsia spp. The current study was designed to assess the tick species infesting various livestock hosts and the associated Rickettsia spp. in Pakistan. Ticks were collected from different livestock hosts (equids, cattle, buffaloes, sheep, goats, and camels); morphologically identified; and screened for the genetic characterization of Rickettsia spp. by the amplification of partial fragments of the gltA, ompA and ompB genes. Altogether, 707 ticks were collected from 373 infested hosts out of 575 observed hosts. The infested hosts comprised 105 cattle, 71 buffaloes, 70 sheep, 60 goats, 34 camels, and 33 equids. The overall occurrence of Rickettsia spp. was 7.6% (25/330) in the tested ticks. Rickettsia DNA was detected in Rhipicephalus haemaphysaloides (9/50, 18.0%), followed by Rhipicephalus turanicus (13/99, 13.1%), Haemaphysalis cornupunctata (1/18, 5.5%), and Rhipicephalus microplus (2/49, 4.1%); however, no rickettsial DNA was detected in Hyalomma anatolicum (71), Hyalomma dromedarii (35), and Haemaphysalis sulcata (8). Two Rickettsia agents were identified based on partial gltA, ompA, and ompB DNA sequences. The Rickettsia species detected in Rh. haemaphysaloides, Rh. turanicus, and Rh. microplus showed 99-100% identity with Rickettsia sp. and Candidatus Rickettsia shennongii, and in the phylogenetic trees clustered with the corresponding Rickettsia spp. The Rickettsia species detected in Rh. haemaphysaloides, Rh. turanicus, Rh. microplus, and Ha. cornupunctata showed 100% identity with R. massiliae, and in the phylogenetic trees it was clustered with the same species. Candidatus R. shennongii was characterized for the first time in Rh. haemaphysaloides, Rh. turanicus, and Rh. microplus. The presence of SFG Rickettsia spp., including the human pathogen R. massiliae, indicates a zoonotic risk in the study region, thus stressing the need for regular surveillance.

Human-biting ticks and zoonotic tick-borne pathogens in North Africa: diversity, distribution, and trans-Mediterranean public health challenges

North Africa is home to more than 200 million people living across five developing economies (Egypt, Libya, Tunisia, Algeria, and Morocco) and two Spanish exclaves (Ceuta and Melilla), many of whom are impacted by ticks and tick-borne zoonoses. Populations in Europe are also increasingly vulnerable to North African ticks and tick-borne zoonoses due to a combination of climate change and the movement of ticks across the Mediterranean on migratory birds, human travellers, and trafficked wildlife. The human-biting ticks and tick-borne zoonoses in North Africa are reviewed along with their distribution in the region. We also assess present and future challenges associated with ticks and tick-borne zoonoses in North African and highlight opportunities for collaboration and coordination between governments in Europe and North Africa to address public health challenges posed by North African ticks and tick-borne zoonoses.

Diversity and Phylogeny of Cattle Ixodid Ticks and Associated Spotted Fever Group Rickettsia spp. in Tunisia

Tick-borne rickettsioses are mainly caused by obligate intracellular bacteria belonging to the spotted fever group (SFG) of the Rickettsia genus. So far, the causative agents of SFG rickettsioses have not been detected in cattle ticks from Tunisia. Therefore, the aim of this study was to investigate the diversity and phylogeny of ticks associated with cattle from northern Tunisia and their associated Rickettsia species. Adult ticks (n = 338) were collected from cattle in northern Tunisia. The obtained ticks were identified as Hyalomma excavatum (n = 129), Rhipicephalus sanguineus sensu lato (n = 111), Hyalomma marginatum (n = 84), Hyalomma scupense (n = 12) and Hyalomma rufipes (n = 2). After DNA extraction from the ticks, 83 PCR products based on the mitochondrial 16S rRNA gene were sequenced and a total of four genotypes for Rh. sanguineus s.l., two for Hy. marginatum and Hy. excavatum and only one for Hy. scupense and Hy. rufipes were recorded, with the occurrence of one, two and three novel genotypes, respectively, for Hy. marginatum, Hy. excavatum and Rh. sanguineus s.l. mitochondrial 16S rRNA partial sequences. The tick DNA was tested for the presence of Rickettsia spp. by using PCR measurements and sequencing targeting three different genes (ompB, ompA and gltA). Of the 338 analyzed ticks, 90 (26.6%), including 38 (34.2%) Rh. sanguineus s.l., 26 (20.1%) Hy. excavatum, 25 (29.8%) Hy. marginatum and one (50%) Hy. rufipes tick, were positive for Rickettsia spp. Based on 104 partial sequences of the three analyzed genes, the BLAST analysis and phylogenetic study showed the infection of Hy. excavatum, Hy. marginatum and Rh. sanguineus s.l. tick specimens with R. massiliae, R. aeschlimannii and R. sibirica subsp. mongolitimonae and one Hy. rufipes tick specimen with R. aeschlimannii. In addition, coinfection with R. massiliae and R. aeschlimannii was reported in one Hy. marginatum and one Rh. sanguineus s.l. tick specimen, while a coinfection with R. massiliae and R. sibirica subsp. mongolitimonae was recorded in one Rh. sanguineus s.l. tick specimen. In conclusion, our study reports, for the first time in Tunisia, the infection of cattle ticks belonging to Hyalomma and Rhipicephalus genera with zoonotic Rickettsia species belonging to the SFG group.

Unraveling the epidemiological relationship between ticks and rickettsial infection in Africa

Tick-borne rickettsioses are emerging and re-emerging diseases of public health concern caused by over 30 species of Rickettsia. Ticks are obligate hematophagous arthropods with over 700 species of Ixodid ticks known worldwide. The escalating geographical dispersal of tick vectors and concomitant increase in the incidences of tick-borne diseases have fueled interest in the ecology of tick-borne pathogens. This review focuses on aspects of the Rickettsia pathogen, including biology, taxonomy, phylogeny, genetic diversity, epidemiology of the disease, and the role of vertebrate host in the perpetuation of rickettsioses in Africa. Our review also highlights some of the species of Rickettsia that are responsible for disease, the role of tick vectors (both hard and soft ticks) and the species of Rickettsia associated with diverse tick species across the continent. Additionally, this article emphasizes the evolutionary perspective of rickettsiae perpetuation and the possible role of amplifying vertebrate host and other small mammals, domestic animals and wildlife in the epidemiology of Rickettsia species. We also specifically, discussed the role of avian population in the epidemiology of SFG rickettsiae. Furthermore, we highlighted tick-borne rickettsioses among travelers due to African tick-bite fever (ATBF) and the challenges to surveillance of rickettsial infection, and research on rickettsiology in Africa. Our review canvasses the need for more rickettsiologists of African origin based within the continent to further research towards understanding the biology, characterization, and species distribution, including the competent tick vectors involved in their transmission of rickettsiae across the continent in collaboration with established researchers in western countries. We further highlighted the need for proper funding to encourage research despite competing demands for resources across the various sectors. We finalize by discussing the similarities between rickettsial diseases around the world and which steps need to be taken to help foster our understanding on the eco-epidemiology of rickettsioses by bridging the gap between the growing epidemiological data and the molecular characterization of Rickettsia species.

Rickettsia massiliae circulation in sheep and attached Rhipicephalus sanguineus in Central Portugal

Rickettsiosis is considered an emerging/re-emerging vector-borne disease that causes significant public health threats. Ticks are reservoirs and vectors of Rickettsia having a significant role in the transmission of rickettsiae. In Portugal, little is known about tick-borne Rickettsia species in sheep. Therefore, this study aimed to investigate rickettsiae infection in ticks and their sheep host from 27 farms in four districts of central Portugal, to clarify the role of the sheep host in the circulation of this zoonotic agent. Between March and May 2021, EDTA blood samples (n = 100) of healthy grazing sheep and their ticks (n = 100, one tick per animal) were collected during a herd health program in central Portugal. Obtained ticks were identified as Rhipicephalus sanguineus sensu lato by PCR targeting a partial sequence of 16S rRNA gene followed by sequence analysis. Rhipicephalus sanguineus s.l. and host sheep blood were tested for the presence of Rickettsia spp. by PCR targeting a partial sequence of ompB and ompA genes. From a total of 100 paired R. sanguineus s.l. and host sheep, Rickettsia massiliae was detected in 62 ticks and 35 grazing sheep blood samples, collected in central Portugal, 2021. All 35 positive sheep had attached positive R. sanguineus s.l., with matching nucleotidic sequences. These findings suggest that sheep may develop rickettsiemia and are likely capable of transmitting and amplifying the infection to uninfected ticks maintaining rickettsiae in circulation in the domestic cycle.