Molecular detection of Borrelia, Bartonella and Orientia in small mammals from oil palm plantations in Malaysia / Siti Nurul Izzah Mohd Azami

Siti Nurul Izzah , Mohd Azami (2023) Molecular detection of Borrelia, Bartonella and Orientia in small mammals from oil palm plantations in Malaysia / Siti Nurul Izzah Mohd Azami. Masters thesis, Universiti Malaya.

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Abstract

Many human clinical cases due to vector-borne infections are underreported in Malaysia, especially in rural localities where healthcare infrastructures are lacking. Land clearing activities and encroachment into the forest, bring the human-animal interface closer to each other. Rodents and other small mammals in the wild also carry diseases, which are relatively different from those carried by urban rodents, increasing the risk of transmission to humans when forests are cleared. In this study, the aim was to detect the presence of vector-borne pathogens such as Orientia spp., Borrelia spp., Bartonella spp. and Rickettsia spp. in the spleen of small mammals trapped on site. 217 small mammals were selected for this study, of which 100 samples were from UM Plantation Sdn. Bhd., Johor (oil palm plantation) and 117 samples from Kampung Tumbuh Hangat, Perak (oil palm plantation in the vicinity of an Orang Asli village). From the morphological identification and DNA barcoding assay performed using the mitochondrial gene, cytochrome c oxidase (COI), the individuals were identified as Rattus rattus diardii, Rattus tiomanicus, Rattus argentiventer, Rattus exulans, Rattus tanezumi and Tupaia glis. 203 spleens were collected and screened via conventional Polymerase Chain Reaction (PCR) assay. The molecular examination was performed for the detection of Orientia spp., Borrelia spp., Bartonella spp. and Rickettsia spp. from the harvested spleens. From the PCR assays, there was a prevalence of each pathogen such as 12.3% (25/203) for Orientia sp., 5.9% (12/203) for Borrelia spp., 4.9% (10/203) for Bartonella sp. and none for Rickettsia spp. Almost all of the animals were found to be infested with chiggers and several were infested with ticks. Fleas were not found on the individuals. There were also lice and mites infesting the rodents. The infestation of a substantial number of chiggers could explain the exposure of Orientia tsutsugamushi in the rodents and tree shrews. This speculation must be investigated further in order to confirm the vector for this pathogen. As for the Borrelia sp., all the infected individuals were not infested by any tick which is known to be the vector for Lyme disease. Similarly, Bartonella phoceensis was detected in individuals with no infestation of the tick vector. No flea was found on the trapped animals which explained the negative detection for Rickettsia spp. Based on the phylogenetic analysis, some of the detected Borrelia sp. were clustered together with the Lyme disease group and some were grouped together with the relapsing fever group. Interestingly, one positive Borrelia sp. sample was neither close nor similar to any of the Lyme disease and relapsing fever groups Borreliae in GenBank. From the result, there was a sign of current infection of Borrelia spp., O. tsutsugamushi and B. phoceensis in Rattus r. diardii, R. exulans, R. argentiventer, R. tiomanicus and T. glis. To the best of the current literature, this is the first report of the infection of Borrelia sp. and O. tsutsugamushi in T. glis in Malaysia. Further investigations are warranted to elucidate the relationships between the ectoparasites, the host and the respective pathogens.

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