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Increased genetic diversity and prevalence of co-infection with Trypanosoma spp. in koalas (Phascolarctos cinereus) and their ticks identified using next-generation sequencing (NGS)

Barbosa, AD, Gofton, AW, Paparini, A, Codello, A, Greay, T, Gillett, A, Warren, K, Irwin, P & Ryan, U 2017, PLoS ONE, vol. 12, no. 7, e0181279.

Protozoan infections by Trypanosoma species can affect koala health. In this study koalas were found to harbor many different species of trypanosomes, and mixed infections by multiple species were more common than single infections. T. irwini was found to be the dominant species. Ticks collected from koalas may play a role in trypanosome transmission.

Trypanosoma spp. are genetically diverse protozoans that are commonly found in koalas and their potential vectors – ticks. Blood samples of 168 koalas and 91 ticks, collected from koalas, were sequenced for trypanosome DNA using next generation sequencing (NGS), a novel and efficient way to sequence DNA. A total of 54 koalas were found to be infected with T. irwini (32.1%), T. gilletti (25%), T. copemani (27.4%), T. vagrandis (10.1%), T. noyesi (0.6%, documented here for the first time in koalas) and one novel Trypanosoma species (4.8%). Twenty-three ticks were infected with the same mix of Trypanosoma species except for T. noyesi. Infections with multiple Trypanosoma spp., rather than a single species, were more common, especially with the combination T. irwini, T. gilleti and T. copemani (12.5%). T. irwini was the most commonly identified parasite in single infections of koalas. Slightly different trypanosome populations were found in the koala when compared to the tick collected from it; however, data are incomplete as there was a relatively small number of ticks collected from koalas.

NGS was used for the first time in this study to analyse the diversity of trypanosomes in wild koalas and ticks. The study established NGS to be an efficient and accurate method in comparison to an older method of Sanger sequencing. It is unclear how Trypanosoma spp. affect koala health at either the individual or population level. Some species such as T. gilletti have been associated with disease and decreased survival, and others such as T. compermani are genetically close to pathogenic T. cruzi.

This study is important because it for the first time establishes polyparasitism of trypanosomes in the koala and tick populations. The study has identified T. tasmani as a new potential vector for infecting koalas with trypanosomes. Additional research is needed, however, to understand the role of ticks in transmitting trypanosomes to koalas.


 Summarised by Alexandra Selivanova


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