Detection of pathogenic bacteria in ticks from Isiolo and Kwale counties of Kenya using metagenomics

Abstract

Ticks are arachnid ectoparasites which rank second only to mosquitoes in the transmission of human diseases including bacteria responsible for anaplasmosis, ehrlichiosis, spotted fevers, and Lyme disease among other febrile illnesses. Due to paucity of data on bacteria transmitted by ticks in Kenya, this study undertook a bacterial metagenomic-based characterization of ticks collected from Isiolo, a semi-arid pastoralist County in Eastern Kenya, and Kwale, a coastal County with monsoon climate on the southern Kenyan border with Tanzania. A total of 2,918 ticks belonging to 3 genera and 10 species were pooled and screened in this study. Tick identification was confirmed through the sequencing of Cytochrome C Oxidase Subunit 1 (COI) gene. Bacterial 16S rRNA gene PCR amplicons obtained from the above samples were sequenced using the MinION (Oxford Nanopore Technologies) platform. The resulting reads were demultiplexed in Porechop, followed by trimming and filtering in Trimmomatic before clustering using Qiime2-VSearch. A SILVA database pretrained naïve Bayes classifier was used to taxonomically classify the Operational Taxonomic Units (OTUs). The bacteria of clinical interest detected in pooled tick assays were as follows:Rickettsia spp.59.43% of pools,Coxiella burnetii37.88%,Proteus mirabilis5.08%,Cutibacterium acnes6.08% andCorynebacterium ulcerans2.43%. These bacteria are responsible for spotted fevers, query fever (Q-fever), urinary tract infections, skin and soft tissue infections, eye infections and diphtheria-like infections in humans, respectively.P. mirabilis, C. acnesandC. ulceranswere detected only in Isiolo. Additionally, COI sequences allowed for the identification ofRickettsiaandCoxiellaspecies to strain level in some of the pools. Diversity analysis revealed that the tick genera had high levels of Alpha diversity but the differences between the microbiomes of the three tick genera studied were not significant. The detection ofCutibacterium acnes, commonly associated with human skin flora suggests that the ticks may have contact with humans potentially exposing them to bacterial infections. The findings in this study highlight the need for further investigation into the viability of these bacteria and the competency of ticks to transmit them. Clinicians in these high-risk areas also need to be appraised for them to include Rickettsial diseases and Q-fever as part of their differential diagnosis.