Morphological and molecular characterization of an African freshwater fish trypanosome, including its development in a leech vector

• Published in: International journal for parasitology Vol. 50; no. 10-11; pp. 921 - 929
• Main Authors: Smit, Nico J., Joubert, Adri, Lawton, Scott P, Hayes, Polly M., Cook, Courtney A.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.09.2020
• Subjects: 18S rRNA sequences; Fish parasites; Leeches; Trypanosomes; Trypanosomes; 18S rRNA sequences; Fish parasites; Leeches
• ISSN: 0020-7519; 1879-0135
• DOI: 10.1016/j.ijpara.2020.06.004

[Display omitted] •This is the first known record of freshwater fish trypanosomes from the Phongolo River, South Africa.•A morphological description of the development of a fish trypanosome in a leech vector is provided.•This is the first known molecular characterisation of an African fish trypanosome from its leech vector.•The molecular phylogeny of freshwater fish trypanosomes is discussed in detail.•New insights into resolving the taxonomy of African freshwater fish trypanosomes are provided. Trypanosomes are ubiquitous blood parasites of fishes and at least 16 species were originally described infecting African freshwater fishes. This number was later reduced to six and in the late 1990s it was proposed that most records of freshwater fish trypanosomes across Africa are Trypanosoma mukasai Hoare, 1932. Recently, results from a molecular analysis of fish trypanosomes from the Okavango Delta, Botswana, reported the presence of at least two genotypic groups and concluded that the identification of T. mukasai remains problematic. The aims of the present study were thus to elucidate the life cycle of a freshwater fish trypanosome from southern Africa and to do a morphological and molecular characterization of this parasite from both the fish host and leech vector. To locate trypanosome stages, leeches were removed from fishes captured in the Phongolo River, South Africa, and fish blood films and leech squashes were Giemsa-stained and screened. To determine whether trypanosome stages in fishes and leeches were of the same genotype, DNA was extracted and fragments of the 18S rDNA gene were amplified and sequenced. Trypanosomes were detected in the fish families Cichlidae, Clariidae, Mochokidae and Schilbeidae. Sequence data showed that the trypanosome from one of the leeches, identified as Batracobdelloides tricarinata (Blanchard, 1897), was highly similar to those obtained from the plain squeaker, Synodontis zambezensis, with 0.7% difference recorded between them. From morphological and molecular data presented here, it is clear that the trypanosomes from Phongolo are closely related to those of the Okavango and should be considered as a single diverse species with genetic differentiation between 0.4–2.9%, under the 3–5% differences expected to be seen between true distinct species within the rRNA. Developmental stages of the trypanosome found in the leech B. tricarinata supports its status as the vector and the molecular evidence shows the relationship between the trypanosome in the fish and leech, but also illustrates the exceptional genetic and morphological diversity of a single species of trypanosome between host species. The work presented here provides us with clear information to take further steps in resolving the taxonomy and systematics of African freshwater fish trypanosomes.