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Identification of Rickettsial Infections (Rickettsia sp. TH2014) in Ctenocephalides orientis Fleas (Siphonaptera: Pulicidae)

Kho KL, Tay ST

J Med Entomol, 2019 02 25;56(2):526-532.
PMID: 30312440 DOI: 10.1093/jme/tjy169

Rickettsia felis (Rickettsiales: Rickettsiaceae) is an emergent human pathogen that causes febrile illnesses in various parts of the world. This study describes the identification and growth characteristics of a R. felis-like organism (designated as Rickettsia sp. TH2014) cultured from Ctenocephalides orientis fleas in rural Malaysia. In this study, culturing of rickettsiae from filtered triturated flea lysates was performed in Aedes albopictus C6/36 cells. Cytopathic effects were observed from one of the samples 4 d post-inoculation. Electron microscopy revealed actively replicating intracytosolic coccobacillary organisms in the rickettsia-infected cells. Sequence analysis of amplified citrate synthase (gltA) gene fragment shows complete match of the rickettsia with Rickettsia sp. Rf31 in Southeast Asia, and 'Candidatus Rickettsia senegalensis' strain PU01-02 in Africa. The whole-genome sequence of Rickettsia sp. TH2014 was determined and assembled. The estimated genome size and guanine + cytosine content of the rickettsia are 1.37 Mb and 32.9%, respectively. The high values of average nucleotide identity and tetra-nucleotide signature correlation index obtained from pairwise genome comparison study suggest the identification of the rickettsia as R. felis. The whole-genome single-nucleotide polymorphism analysis demonstrates close genetic relatedness of the rickettsia with R. felis and Rickettsia asemboensis. However, based on sequence analyses of rickettsial genes (16S rDNA, gltA, ompB, and sca4), Rickettsia sp. TH2014 is found to be distinct from R. felis and R. asemboensis. The sequence analyses reveal that Rickettsia sp. TH2014 is highly similar to 'Ca. Rickettsia senegalensis' detected in fleas from Africa, Asia, and North America. Further investigation to provide insights on pathogenic potential and transmission dynamics of the rickettsia is warranted.

Matched MeSH terms: Rickettsia/genetics
An overview of rickettsiae in Southeast Asia: Vector-animal-human interface

Low VL, Tan TK, Khoo JJ, Lim FS, AbuBakar S

Acta Trop, 2020 Feb;202:105282.
PMID: 31778642 DOI: 10.1016/j.actatropica.2019.105282

Rickettsioses are emerging, and re-emerging diseases caused by obligate intracellular arthropod-borne bacteria that infect humans and animals worldwide. Various rickettsiae such as Orientia, Rickettsia, Anaplasma and Ehrlichia have been circulated in companion, domesticated and wild animals through bites of infected ticks, fleas, lice or mites. This review summarizes the infections of rickettsiae, including the newly discovered regional species Rickettsia thailandii, Candidatus Rickettsia sepangensis, Candidatus Rickettsia johorensis, Candidatus Rickettsia laoensis, Candidatus Rickettsia mahosotii, Candidatus Rickettsia khammouanensis, Candidatus Anaplasma pangolinii, and other novel genotypes in vectors, humans and animals in Southeast Asia. Issues on some unidentified rickettsiae that elicit immune responses and production of antibodies that are cross-reactive with the antigens used are discussed. Knowledge gaps which required attention are also identified in this review.

Matched MeSH terms: Rickettsia/genetics
Fulltext Rickettsial infections in monkeys, Malaysia

Tay ST, Koh FX, Kho KL, Sitam FT

Emerg Infect Dis, 2015 Mar;21(3):545-7.
PMID: 25695615 DOI: 10.3201/eid2103.141457
Matched MeSH terms: Rickettsia/genetics*
Fulltext Molecular evidence of potential novel spotted fever group rickettsiae, Anaplasma and Ehrlichia species in Amblyomma ticks parasitizing wild snakes

Kho KL, Koh FX, Tay ST

Parasit Vectors, 2015;8:112.
PMID: 25889376 DOI: 10.1186/s13071-015-0719-3

Amblyomma ticks parasitize a wide range of animals in tropical regions. This study describes the identification of Amblyomma ticks from wild snakes in Malaysia and the detection of potential human pathogens such as Rickettsia, Anaplasma, Ehrlichia and bartonellae in the ticks.

Matched MeSH terms: Rickettsia/genetics
Fulltext Evidence for a specific host-endosymbiont relationship between 'Rickettsia sp. genotype RF2125' and Ctenocephalides felis orientis infesting dogs in India

Hii SF, Lawrence AL, Cuttell L, Tynas R, Abd Rani PA, Šlapeta J, et al.

Parasit Vectors, 2015;8:169.
PMID: 25884425 DOI: 10.1186/s13071-015-0781-x

Fleas of the genus Ctenocephalides serve as vectors for a number of rickettsial zoonoses, including Rickettsia felis. There are currently no published reports of the presence and distribution of R. felis in India, however, the ubiquitous distribution of its vector Ctenocephalides felis, makes it possible that the pathogen is endemic to the region. This study investigates the occurrence of Rickettsia spp. infection in various subspecies of C. felis infesting dogs from urban areas of Mumbai, Delhi and Rajasthan in India.

Matched MeSH terms: Rickettsia/genetics
Spotted Fever Group Rickettsioses and Murine Typhus in a Malaysian Teaching Hospital

Kho KL, Koh FX, Singh HK, Zan HA, Kukreja A, Ponnampalavanar S, et al.

Am J Trop Med Hyg, 2016 10 05;95(4):765-768.
PMID: 27402519

Limited information is available on the etiological agents of rickettsioses in southeast Asia. Herein, we report the molecular investigation of rickettsioses in four patients attending a teaching hospital in Malaysia. DNA of Rickettsia sp. RF2125, Rickettsia typhi, and a rickettsia closely related to Rickettsia raoultii was detected in the blood samples of the patients. Spotted fever group rickettsioses and murine typhus should be considered in the diagnosis of patients with nonspecific febrile illness in this region.

Matched MeSH terms: Rickettsia/genetics
Identification of rickettsiae from wild rats and cat fleas in Malaysia

Tay ST, Mokhtar AS, Low KC, Mohd Zain SN, Jeffery J, Abdul Aziz N, et al.

Med Vet Entomol, 2014 Aug;28 Suppl 1:104-8.
PMID: 25171613 DOI: 10.1111/mve.12075

Rickettsioses are emerging zoonotic diseases reported worldwide. In spite of the serological evidence of spotted fever group rickettsioses in febrile patients in Malaysia, limited studies have been conducted to identify the animal reservoirs and vectors of rickettsioses. This study investigated the presence of rickettsiae in the tissue homogenates of 95 wild rats and 589 animal ectoparasites. Using PCR assays targeting the citrate synthase gene (gltA), rickettsial DNA was detected in the tissue homogenates of 13 (13.7%) wild rats. Sequence analysis of the gltA amplicons showed 98.6-100% similarity with those of Rickettsia honei/R. conorii/R. raoultii (Rickettsiales: Rickettsiaceae). Sequence analysis of outer membrane protein A gene (ompA) identified Rickettsia sp. TCM1 strain from two rats. No rickettsia was detected from Laelaps mites, Rhipicephalus sanguineus and Haemaphysalis bispinosa ticks, and Felicola subrostratus lice in this study. R. felis was identified from 32.2% of 177 Ctenocephalides felis fleas. Sequence analysis of the gltA amplicons revealed two genotypes of R. felis (Rf31 and RF2125) in the fleas. As wild rats and cat fleas play an important role in the enzoonotic maintenance of rickettsiae, control of rodent and flea populations may be able to reduce transmission of rickettsioses in the local setting.

Matched MeSH terms: Rickettsia/genetics*
Fulltext Bacterial community in Haemaphysalis ticks of domesticated animals from the Orang Asli communities in Malaysia

Khoo JJ, Chen F, Kho KL, Ahmad Shanizza AI, Lim FS, Tan KK, et al.

Ticks Tick Borne Dis, 2016 07;7(5):929-937.
PMID: 27132518 DOI: 10.1016/j.ttbdis.2016.04.013

Ticks are vectors in the transmission of many important infectious diseases in human and animals. Ticks can be readily found in the semi-forested areas such as the settlements of the indigenous people in Malaysia, the Orang Asli. There is still minimal information available on the bacterial agents associated with ticks found in Malaysia. We performed a survey of the bacterial communities associated with ticks collected from domestic animals found in two Orang Asli villages in Malaysia. We collected 62 ticks, microscopically and molecularly identified as related to Haemaphysalis wellingtoni, Haemaphysalis hystricis and Haemaphysalis bispinosa. Bacterial 16s rRNA hypervariable region (V6) amplicon libraries prepared from the tick samples were sequenced on the Ion Torrent PGM platform. We detected a total of 392 possible bacterial genera after pooling and sequencing 20 samples, indicating a diverse bacterial community profile. Dominant taxa include the potential tick endosymbiont, Coxiella. Other dominant taxa include the tick-associated pathogen, Rickettsia, and environmental bacteria such as Bacillus, Mycobacterium, Sphingomonas and Pseudomonas. Other known tick-associated bacteria were also detected, including Anaplasma, Ehrlichia, Rickettsiella and Wolbachia, albeit at very low abundance. Specific PCR was performed on selected samples to identify Rickettsia and Coxiella. Sequence of Rickettsia felis, which causes spotted fever in human and cats, was identified in one sample. Coxiella endosymbionts were detected in three samples. This study provides the baseline knowledge of the microbiome of ticks in Malaysia, focusing on tick-associated bacteria affecting the Orang Asli communities. The role of the herein found Coxiella and Rickettsia in tick physiology or disease transmission merits further investigation.

Matched MeSH terms: Rickettsia/genetics
Fulltext Molecular detection of pathogens in ticks and fleas collected from companion dogs and cats in East and Southeast Asia

Nguyen VL, Colella V, Greco G, Fang F, Nurcahyo W, Hadi UK, et al.

Parasit Vectors, 2020 Aug 15;13(1):420.
PMID: 32799914 DOI: 10.1186/s13071-020-04288-8

BACKGROUND: Ticks and fleas are considered amongst the most important arthropod vectors of medical and veterinary concern due to their ability to transmit pathogens to a range of animal species including dogs, cats and humans. By sharing a common environment with humans, companion animal-associated parasitic arthropods may potentially transmit zoonotic vector-borne pathogens (VBPs). This study aimed to molecularly detect pathogens from ticks and fleas from companion dogs and cats in East and Southeast Asia.
METHODS: A total of 392 ticks and 248 fleas were collected from 401 infested animals (i.e. 271 dogs and 130 cats) from China, Taiwan, Indonesia, Malaysia, Singapore, Thailand, the Philippines and Vietnam, and molecularly screened for the presence of pathogens. Ticks were tested for Rickettsia spp., Anaplasma spp., Ehrlichia spp., Babesia spp. and Hepatozoon spp. while fleas were screened for the presence of Rickettsia spp. and Bartonella spp.
RESULT: Of the 392 ticks tested, 37 (9.4%) scored positive for at least one pathogen with Hepatozoon canis being the most prevalent (5.4%), followed by Ehrlichia canis (1.8%), Babesia vogeli (1%), Anaplasma platys (0.8%) and Rickettsia spp. (1%) [including Rickettsia sp. (0.5%), Rickettsia asembonensis (0.3%) and Rickettsia felis (0.3%)]. Out of 248 fleas tested, 106 (42.7%) were harboring at least one pathogen with R. felis being the most common (19.4%), followed by Bartonella spp. (16.5%), Rickettsia asembonensis (10.9%) and "Candidatus Rickettsia senegalensis" (0.4%). Furthermore, 35 Rhipicephalus sanguineus ticks were subjected to phylogenetic analysis, of which 34 ticks belonged to the tropical and only one belonged to the temperate lineage (Rh. sanguineus (sensu stricto)).
CONCLUSION: Our data reveals the circulation of different VBPs in ticks and fleas of dogs and cats from Asia, including zoonotic agents, which may represent a potential risk to animal and human health.

Matched MeSH terms: Rickettsia/genetics
Isolation and PCR detection of rickettsiae from clinical and rodent samples in Malaysia

Tay ST, Rohani MY, Ho TM, Devi S

Southeast Asian J Trop Med Public Health, 2002 Dec;33(4):772-9.
PMID: 12757225

Isolation of rickettsiae from patients' blood samples and organ samples of wild rodents from areas with high seroprevalence of rickettsial infections was attempted using cell culture assay and animal passages. L929 mouse fibroblast cells grown in 24 well tissue culture plate were inoculated with buffy coat of febrile patients and examined for the growth of rickettsiae by Giemsa, Gimenez staining and direct immunofluorescence assay. No rickettsiae were isolated from 48 patients' blood samples. No symptomatic infections were noted in mice or guinea pigs infected with 50 organ samples of wild rodents. There was no rickettsial DNA amplified from these samples using various PCR detection systems for Orientia tsutsugamushi, typhus and spotted fever group rickettsiae.

Matched MeSH terms: Rickettsia/genetics