Morphological and molecular characterization of a marine fish trypanosome from South Africa, including its development in a leech vector

Polly M Hayes,Wendy C Gibson,Nico J Smit,Angela J Davies,Scott P Lawton

doi:10.1186/1756-3305-7-50

Abstract

BackgroundTrypanosomes are ubiquitous blood parasites of marine and freshwater fishes, typically transmitted by aquatic leeches. Phylogenetic studies have been dominated by examples derived from freshwater fishes, with few marine representatives. Furthermore, life cycle studies on marine fish trypanosomes have focused on those of the northern hemisphere. In this investigation, we have examined the life cycle and molecular taxonomy of a marine fish trypanosome from South Africa.MethodsTo locate trypanosome stages, leeches were removed from fishes captured on the west and south coasts of South Africa, and fish blood films and leech squashes were Giemsa-stained and screened; leeches were also examined histologically. To determine whether trypanosome stages in fishes and leeches were of the same genotype, DNA was extracted from Giemsa-stained fish blood films and leech squashes, and from fish whole blood. Fragments of the 18S rRNA gene were amplified by PCR using trypanosome-specific primers and sequenced. Resulting sequence data were compared with each other and with published trypanosome 18S rDNA sequences, and used for phylogenetic analysis.ResultsTrypanosomes were detected in blood films from fishes of the families Clinidae, Blenniidae and Gobiidae. The flagellates ranged in size and staining properties within the films and across fish hosts. In squashes and histological sections of adult and juvenile leeches, identified as Zeylanicobdella arugamensis, trypanosome developmental stages were predominantly slender epimastigotes. Sequence data showed that trypanosomes derived from fishes were identical, irrespective of whether they were small or large forms; sequences derived largely from leech epimastigotes were also identical to those obtained from fish trypanosomes. Fish and leech trypanosome sequences fell into a marine fish aquatic clade, and aligned most closely with two trypanosome sequences from marine fishes off Norway.ConclusionsCombined morphological and molecular methods indicate that the trypanosomes examined here represent a single pleomorphic species, rather than the three species described originally. This species is identified as Trypanosoma nudigobii Fantham, 1919 with the leech Z. arugamensis as its vector, and T. capigobii Fantham, 1919 and T. blenniclini Fantham, 1930 are regarded as junior synonyms of the species. Phylogenetic analysis establishes its affinity with marine fish trypanosomes off Norway.

Highlights

Trypanosomes are ubiquitous blood parasites of marine and freshwater fishes, typically transmitted by aquatic leeches
In 2006, Yeld and Smit [14] described a trypanosome, Trypanosoma haploblephari Yeld and Smit, 2006, from marine elasmobranchs in South Africa, no developmental stages were detected in leeches taken from the captured fishes
Juvenile gnathiid isopods identified as Gnathia africana Barnard, 1914 [22], were found on the fishes at Tsitsikamma, but since no trypanosome stages had been found in these crustaceans previously [15], they played no further part in the current study and were used for other research purposes

Summary

Introduction

Trypanosomes are ubiquitous blood parasites of marine and freshwater fishes, typically transmitted by aquatic leeches. Life cycle studies on marine fish trypanosomes have focused on those of the northern hemisphere. In this investigation, we have examined the life cycle and molecular taxonomy of a marine fish trypanosome from South Africa. In 2006, Yeld and Smit [14] described a trypanosome, Trypanosoma haploblephari Yeld and Smit, 2006, from marine elasmobranchs in South Africa, no developmental stages were detected in leeches taken from the captured fishes. Hayes et al [15] reported briefly trypanosomes resembling those of Fantham [10,11], parasitizing several small marine teleosts in South Africa, with their possible development in an intertidal leech

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