Asian fish tapeworm, Khawia japonensis (Yamaguti, 1934), has expanded its European invasive range

Deciphering the impact of endoparasitic infection on immune response and gut microbial composition of Channa punctata

Intestinal parasitic infections caused by helminths are globally distributed and are a major cause of morbidity worldwide. Parasites may modulate the virulence, gut microbiota diversity and host responses during infection. Despite numerous works, little is known about the complex interaction between parasites and the gut microbiota. In the present study, the complex interplay between parasites and the gut microbiota was investigated. A total of 12 bacterial strains across four major families, including Enterobacteriaceae, Morganellaceae, Flavobacteriaceae, and Pseudomonadaceae, were isolated from Channa punctata, infected with the nematode species Aporcella sp., Axonchium sp., Tylencholaimus mirabilis, and Dioctophyme renale. The findings revealed that nematode infection shaped the fish gut bacterial microbiota and significantly affected their virulence levels. Nematode-infected fish bacterial isolates are more likely to be pathogenic, with elevated hemolytic activity and biofilm formation, causing high fish mortality. In contrast, isolates recovered further from non-parasitised C. punctata were observed to be non-pathogenic and had negligible hemolytic activity and biofilm formation. Antibiogram analysis of the bacterial isolates revealed a disproportionately high percentage of bacteria that were either marginally or multidrug resistant, suggesting that parasitic infection-induced stress modulates the gut microenvironment and enables colonization by antibiotic-resistant strains. This isolation-based study provides an avenue to unravel the influence of parasitic infection on gut bacterial characteristics, which is valuable for understanding the infection mechanism and designing further studies aimed at optimizing treatment strategies. In addition, the cultured isolates can supplement future gut microbiome studies by providing wet lab specimens to compare (meta)genomic information discovered within the gut microenvironment of fish.

The Asian fish tapeworm (Schyzocotyle acheilognathi) discovered in Western Australia may pose a threat to the health of endemic native fishes

The Asian fish tapeworm (Schyzocotyle acheilognathi) is an important fish parasite with a wide host range that infects over 300 species of fish worldwide. Schyzocotyle acheilognathi has been reported from eastern coastal areas of Australia, but has not been previously reported in Western Australia (WA). During a control program for invasive freshwater fishes in south-western WA, a region with a unique and highly endangered freshwater fish fauna, tapeworms identified as S. acheilognathi from their distinctive scolex morphology were found at a prevalence of 3.3% in goldfish (Carassius auratus), 37.0% in koi carp (Cyprinus carpio haematopterus) and 65.0% in eastern gambusia (Gambusia holbrooki) in a small suburban lake to the north of Perth. For molecular confirmation, the 18S ribosomal RNA gene was targeted at hypervariable V4 region. Koi carp isolates were 100% identical to S. acheilognathi isolated from varying hosts, including the red shiner (Cyprinella lutrensis) and a human sample. Sequences obtained from two eastern gambusia were identified as S. acheilognathi, but formed a discrete cluster and may represent a novel genotype. Isolates from two other eastern gambusia and two goldfish formed a distinct clade with only 91.9% similarity to previously sequenced isolates of S. acheilognathi. This emphasizes the importance of molecular identification methods in addition to morphological identification. The presence and potential for transmission of these parasites in south-western WA may threaten the health of native fishes, which are immunologically naïve to this introduced parasite. Immediate control or containment measures should be implemented to halt the spread of these parasites.

Effect of intestinal tapeworms on the gut microbiota of the common carp, Cyprinus carpio

BACKGROUND

Parasitic protozoans, helminths, alter the gut microbiota in mammals, yet little is known about the influence of intestinal cestodes on gut microbiota in fish. In the present study, the composition and diversity of the hindgut microbiota were determined in the intestine of common carp (Cyprinus carpio) infected with two tapeworm species, Khawia japonensis and Atractolytocestus tenuicollis.

RESULTS

The intestine contained a core microbiota composed of Proteobacteria, Fusobacteria and Tenericutes. Infection with the two cestode species had no significant effect on the microbial diversity and richness, but it altered the microbial composition at the genus level. PCoA analysis indicated that microbial communities in the infected and uninfected common carp could not be distinguished from each other. However, a Mantel test indicated that the abundance of K. japonensis was significantly correlated with the microbial composition (P = 0.015), while the abundance of A. tenuicollis was not (P = 0.954). According to Pearson's correlation analysis, the abundance of K. japonensis exhibited an extremely significant (P < 0.001) positive correlation with the following gut microbiota taxa: Epulopiscium, U114, Bacteroides, Clostridium and Peptostreptococcaceae (0.8< r < 0.9); and a significant (P < 0.05) correlation with Enterobacteriaceae, Micrococcaceae, Rummeliibacillus, Lysinibacillus boronitolerans, Veillonellaceae, Oxalobacteraceae, Aeromonadaceae (negative), Marinibacillus and Chitinilyticum (0.4< r < 0.7).

CONCLUSIONS

These results suggest that the composition of gut microbiota was somewhat affected by the K. japonensis infection. Additionally, increased ratios of pathogenic bacteria (Lawsonia and Plesiomonas) were also associated with the K. japonensis infection, which may therefore increase the likelihood of disease.

The occurrence of the common European fish cestode Caryophyllaeus laticeps (Pallas, 1781) in the River Irtysh, China: a morphological characterization and molecular data

The cestode Caryophyllaeus laticeps (Pallas, 1781) is a highly polymorphic species with several morphotypes, and belongs to the most widespread species of monozoic tapeworm (Cestoda: Caryophyllidea) found in the Palaearctic zoogeographic region with a wide range of cyprinid fish hosts. This paper provides the first reliable evidence about the occurrence of C. laticeps in northern China that is based on detailed morphological characteristics and mitochondrial cox1 sequences. C. laticeps was found in freshwater bream Abramis brama (L.), in the River Irtysh, with the prevalence of 40% and mean intensity of infection 8. The tapeworms were rather similar in their morphological characters to the morphotype 1 of C. laticeps which is typified by the possession of a slender body with a flabellate wide scolex, narrow neck, robust, long and clearly visible vas deferens, large, and almost spherical cirrus-sac containing well-developed internal seminal vesicle and the first vitelline follicles and first testes beginning far from anterior margin of the body. Subsequent molecular analysis confirmed the morphological identification of the species. Our results show that the studied specimens were firmly clustered into the C. laticeps clade and formed a monophyletic group with C. laticeps morphotype 1 and 2 from Europe and Russia. In China, C. laticeps is a non-indigenous fish parasite, which has the most probably been introduced into the Irtysh River basin with its typical host inhabiting Russia.