Morphological and molecular characterization of an African freshwater fish trypanosome, including its development in a leech vector
Research article published in Int J Parasitol (2020)
Abstract
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.
Abstract sourced from PubMed (NCBI) for the cited record. See the original publication for the authoritative version.
Summary
Trypanosoma mukasai morphological and molecular characterization in Phongolo River fishes and Batracobdelloides tricarinata leech vector; 0.7% difference between fish and leech genotypes.
Why This Matters for Hirudotherapy
This study characterized an African freshwater fish trypanosome morphologically and molecularly from both fish hosts and leech vectors collected from the Phongolo River, South Africa, identifying the leech Batracobdelloides tricarinata as a developmental vector. The work used 18S rDNA sequencing and Giemsa-stained blood films and leech squashes to establish the parasite's life cycle and genetic relationship between trypanosomes in fish and leeches. This study involves leeches but is tangential to ASH's domain, as it concerns leeches as vectors of fish parasites rather than hirudotherapy, anticoagulants, or the therapeutic leech secretome. The caveat is that this is a parasitology and taxonomy study with no connection to medicinal leech use, anticoagulant properties, or clinical applications; the leech species studied is not one used in hirudotherapy.
Citation
Morphological and molecular characterization of an African freshwater fish trypanosome, including its development in a leech vector.
Smit NJ et al. · Int J Parasitol, 2020
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