Pathologic features of mycobacteriosis in naturally infected Syngnathidae and novel transcriptome assembly in association with disease

Abstract

Syngnathidae (seahorses, seadragons and pipefish) suffer significant losses from non-tuberculous mycobacteria. However, they produce markedly different lesions in response to the disease compared to other teleost species, notably infrequent granuloma formation. This study evaluated 270 syngnathid fish, from which 92 were diagnosed with mycobacteriosis by histopathology, culture or both. Microscopic lesions variably consisted of random foci of coagulative necrosis in multiple organs, containing high numbers of free bacteria and large aggregates or sheets of macrophages with cytoplasm laden with acid-fast bacilli. Mycobacterial associated granulomas were identified in only six seahorses. Five fish had positive cultures with no observed microscopic changes. RNA-seq of the head kidney was performed to investigate the transcriptome of two infected and six non-infected lined seahorses Hippocampus erectus. Assembled and annotated putative transcripts serve to enrich the database for this species, as well as provide baseline data for understanding the pathogenesis of mycobacteriosis in seahorses. Putative components of the innate immune system (IL-1β, IL-6, TNF, NOS, Toll-like receptor 1, MHC Class I, NF-κβ, transforming growth factor beta, MyD88) were identified in the RNA-seq data set. However, a homolog for a key component in the TH1 adaptive immune response, interferon-gamma, was not identified and may underlie the unique pathologic presentation.

Histopathology of laboratory‐reared Nothobranchius fishes: Mycobacterial infections versus neoplastic lesions

“…The comparison of GRZ infections with data accumulated on spontaneous mycobacterial infections in other bony fishes shows considerable similarity with those of captive syngnathids (Fogelson et al., 2017). Host reactions in syngnathid fishes were dominated by macrophages and “atypical” inflammatory reactions sensu Gauthier et al.…”

“…(2003) or “defective” inflammatory reactions sensu Fogelson et al. (2017). Special terms were used to emphasize that inflammatory reactions differ from typical chronic granulomas described in other teleosts including zebrafish (Kent et al., 2004) in the absence of concentrically arranged connective tissue/spindle‐cell capsule demarcating the necrotic core of the lesion from surrounding tissue.…”

Gas gland adenoma in a lined seahorse, Hippocampus erectus, Perry 1810

“…Syngnathid fishes have significant economic and educational importance as display animals in public aquaria, in the ornamental fish trade, and as research models for infectious diseases (Fogelson, Fast, Leary, & Camus, ). Loss of habitat, changing climate and human harvesting threaten wild populations of many syngnathid species (Vincent, Foster, & Koldewey, ).…”

Dual RNA-Seq Unveils Pseudomonas plecoglossicida htpG Gene Functions During Host-Pathogen Interactions With Epinephelus coioides

“…To date, more than 30 ILs have been identified in fish (50). IL-6 as a key member of cytokines plays key roles in immune process, including acute phase response, hematopoiesis, energy sensor, and immune cell differentiation through modulating immune-signaling pathways (51, 52). Simultaneously, as a pro-inflammatory factor, up-regulation of IL-6 transcripts was detected in many fish defending against various pathogenic infections (53–55).…”