Abstract
BackgroundSeveral Trypanosoma species transmitted by leeches infect marine and freshwater fish worldwide. To date, all South American fish trypanosome species identified have been based on unreliable morphological parameters. We recently isolated and cultured trypanosomes from the Brazilian armoured catfishes Hypostomus luetkeni and H. affinis. Here, we report the first phylogenetic analyses of South American (Brazilian) trypanosomes isolated from fish, and from leeches removed from these fish. We also analysed morphologically and morphometrically the different forms of fish, leech and cultured trypanosomes.MethodsV7V8 SSU rRNA and gGAPDH sequences were used for phylogenetic analysis of Brazilian fish and leech trypanosomes. Trypanosomes from cultures, fish blood and leech samples were also characterized morphologically and morphometrically by light and electron microscopy.ResultsIn blood smears from fish high trypanosome prevalence (90–100 %) and parasitemia (0.9-1.0x102) were observed. Phylogenetic relationships using SSU rRNA and gGAPDH showed that, despite relevant sequence divergence, all Brazilian fish (and derived cultures) and leech trypanosomes clustered together into a single clade. The Brazilian clade clustered with European, North American and African fish trypanosomes. Based on sequence analysis, we uncovered a new species of Brazilian fish trypanosome, Trypanosoma abeli n. sp. Trypanosoma abeli cultures contained pleomorphic epimastigotes, small trypomastigotes and rare sphaeromastigotes. Ultrastructural features of T. abeli included a cytostome-cytopharynx complex in epi- and trypomastigotes, a compact rod-like kinetoplast, lysosome-related organelles (LROs) and multivesicular bodies. Trypanosomes found in fish blood smears and leech samples were highly pleomorphic, in agreement with sequence data suggesting that catfishes and leeches often have mixed trypanosome infections.ConclusionsTrypanosoma abeli n. sp. is the first trypanosome from South American fishes isolated in culture, positioned in phylogenetic trees and characterized at the ultrastructural level. Trypanosoma abeli n. sp. is highly prevalent in H. luetkeni and H. affinis armoured catfish from the Atlantic Forest biome, and in other catfish species from the Amazon and the Pantanal. Sequencing data suggested that Brazilian catfish often have mixed trypanosome infections, highlighting the importance of molecular characterization to identify trypanosome species in fishes and leeches.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-1193-7) contains supplementary material, which is available to authorized users.
Highlights
Several Trypanosoma species transmitted by leeches infect marine and freshwater fish worldwide
Sequencing data suggested that Brazilian catfish often have mixed trypanosome infections, highlighting the importance of molecular characterization to identify trypanosome species in fishes and leeches
Prevalence of trypanosomes in armoured catfishes and in leeches removed from these fishes In this study, Giemsa-stained blood smears from 40 specimens of H. affinis were all positive for trypanosomes by microscopy, yielding 100 % prevalence, with an average of 0.9 × 102 parasites/ml
Summary
Several Trypanosoma species transmitted by leeches infect marine and freshwater fish worldwide. We report the first phylogenetic analyses of South American (Brazilian) trypanosomes isolated from fish, and from leeches removed from these fish. Most infected fish are asymptomatic, fish trypanosomiasis can be severe at high parasitemias, and symptoms include anaemia, leukocytosis, hypoglycemia and splenomegaly [4, 5]. Aquatic leeches are both hosts and vectors of fish trypanosomes [6, 7]. The genus Hypostomus is native to South America and comprises of large armoured catfish species used extensively as ornamental fish and food [15,16,17]
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