Publikationsdatenbank

Molecular diagnosis and characterization of ticks and tick-borne pathogens infecting cattle in Mymensingh district of Bangladesh (2018)

Art

Hochschulschrift

Autor

Roy, Babul Chandra (WE 13)

Quelle

Berlin, 2018 — VIII, 100 Seiten

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/23134

Kontakt

Institut für Parasitologie und Tropenveterinärmedizin

Robert-von-Ostertag-Str. 7-13
14163 Berlin
+49 30 838 62310
parasitologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

Tick-borne diseases (TBDs) affect the majority of world’s cattle population and are considered a major constraint to the health and productive performance of profitable livestock production throughout the world. Bovine anaplasmosis, babesiosis and theileriosis are the most economically important and widely distributed TBDs affecting cattle and are also endemic in Bangladesh. However, detailed information on the prevalence of bovine tick-borne pathogens (TBPs) determined using sensitive and specific molecular diagnostic tools is scarce for this country. The main objective of this cumulative thesis therefore was to investigate the prevalence of TBPs from blood samples collected from local cattle in Mymensingh district of Bangladesh using a Reverse Line Hybridization (RLB) assay. The first study aimed to estimate the prevalence of TBP´s in cattle of Mymensingh districct of Bangladesh. In total, 384 blood samples from apparently healthy cattle from 12 sub-districts (Upazilas) of Mymensingh district were spotted on FTA cards in the field and subsequently screened using a Reverse Line Blot (RLB) hybridization assay for the presence of Anaplasma, Ehrlichia, Rickettsia, Babesia and Theileria spp.. Rhipicephalus microplus and Haemaphysalis bispinosa were the main tick species infecting the examineed cattle. In the blood samples, Theileria orientalis infections were most frequently found (212/384, 55.2%) followed by infections with Anaplasma bovis (137/384, 35.67%), Anaplasma marginale (16/384, 4.17%), Babesia bigemina (4/384, 1.04%) and Babesia bovis (2/384, 0.52%). Two previously uncharacterized tick-borne pathogens (TBPs) were also found and further characterized. This included a novel Anaplasma sp. (Anaplasma sp. Mymensingh) and Babesia sp. (Babesia sp. Mymensingh) with estimated prevalences of (50/384, 13.0%) and (1/384, 0.3%). A phylogenetic analysis demonstrated that these newly described pathogens are genetically closely related to Anaplasma platys and Babesia bigemina, respectively. Several key risk factors e.g. access to grazing land, mud-made cattle house, tick infestation and presence of other TBDs were also identified on the prevalence of T. orientalis, A. marginale and Anaplasma sp. Mymensingh. A previously described inexpensive and in-house prepared ECL solution for Western blots was successfully adapted for use within the RLB assay and used in this study. These findings contribute to our knowledge on the occurrence of TBPs in Bangladesh and provide us with a better understanding of the epidemiology of ticks and TBPs, which will be helpful in the development of control strategies to limit the impact of TBPs. The second study aimed to elucidate the phylogenetic relationship between R. microplus ticks collected from Bangladesh, Myanmar and Pakistan with other Rhipicephalus spp. using Scanning Electron Microscopic (SEM) imaging and mitochondrial genome sequence analyses. Boophilid ticks are classified in the genus Rhipicephalus and are widely distributed in subtropical and tropical countries. Rhipicephalus microplus, also known as the common cattle tick, is the most important representative of the Rhipicephalus microplus complex. This complex is composed of several species that share many morphological similarities, complicating their identification. This one-host tick account for a significant economic losses to the livestock industry by causing irritation and blood loss, decreasing leather quality and acting as vectors for potentially fatal diseases such as bovine anaplasmosis and bovine babesiosis. However, little is known about the morphology and genetic background of R. microplus from Asia. Phylogenetic analyses of cytochrome oxidase 1 (cox1), internal transcribed spacer 2 (ITS-2) and 12S rRNA gene sequences confirmed that the R. microplus complex consists of at least five independent taxa. This includes R. annulatus, R. australis, R. microplus clade A sensu Burger et al. (2014), R. microplus clade B sensu Burger et al. (2014) and R. microplus clade C sensu Low et al. (2015). Rhipicephalus microplus ticks from Bangladesh, Myanmar and Pakistan were all assigned to R. microplus clade C. Furthermore, we confirmed that the cox1 gene was the preferred genetic marker for resolving the evolutionary relationships among closely related species within the R. microplus complex. SEM images of adult specimens from R. microplus clade C revealed a wide range of intraspecific morphological variations, including the features previously identified as critical for distinguishing R. microplus clade A from R. australis ticks, which is illustrative for the complications in identifying species within the R. microplus complex solely relied on the morphology. The results from this study highlight the need for more genetic sampling of the R. microplus complex from a wider geographical range and crossbreeding experiments between the different taxa or comparison of populations using nuclear genome data after deep sequencing to elucidate the species status of R. microplus clades.