Identification of proteins from the secretory/excretory products (SEPs) of the branchiuran ectoparasite Argulus foliaceus (Linnaeus, 1758) reveals unique secreted proteins amongst haematophagous ecdysozoa

Comprehensive review of Argulus infestations in aquaculture: Biological impacts and advanced management strategies

The aquaculture industry is hindered by various factors. One of the most noticeable factors is infection by parasites and pathogens. Argulus stands out as a prominent and economically significant ectoparasite in freshwater aquaculture. Argulus infestation causes severe immunomodulatory effects on its hosts by promoting argulosis, causing inflammation, extensive tissue damage, and death. Indian aquaculture sector faced a loss of 62.5 million USD due to Argulus infection. However, current control methods, such as pesticides, cause serious environmental damage. Herbal treatment methods are ineffective and have limitations. Hence, a more efficient and cost-effective control method is needed. In recent years, vaccine development has emerged as a promising avenue of research. Understanding the effect of the host-parasite relationship in the host immune system is essential to develop strategies for prevention, control, and management of argulosis. These interactions provide insights into the co-evolutionary dynamics between hosts and parasites. This review provides an overview of the current knowledge on the host-searching behaviour of Argulus, host-parasite interaction and control strategies. This review also highlights the need for further research and the development of sustainable control measures for Argulus infection.

Exploring the Efficacy of Pellitorine as an Antiparasitic Agent Against Argulus: Impacts on Antioxidant Levels and Immune Responses in Goldfish (Carassius auratus)

INTRODUCTION

Argulus spp. infestation is a significant challenge for aquaculture, currently, there are no approved medications available to efficiently manage this parasite. Consequently, mechanical removal of parasites using forceps and natural substances like herbs are being explored as alternative treatment methods. Pellitorine (PLE) is a naturally occurring compound found in several plant species. It is classified as an alkaloid and belongs to the class of compounds known as amides.

MATERIALS AND METHODS

This study aimed to evaluate the effectiveness of PLE in preventing Argulus spp. infestations in goldfish (Carassius auratus) and to determine the optimal dosage of PLE for the detachment of Argulus spp.

RESULTS

The findings of this study revealed that PLE enhanced the immune response of goldfish by promoting superoxide dismutase (SOD) and catalase (CAT) in Argulus-infected goldfish. Additionally, PLE induces reactive oxygen species (ROS) generation and cellular damage in the Argulus. PLE at a dosage of 5 mg/mL was able to detach 80% of the argulus from goldfish within 12 h. Therapeutic index was found to be 5.99, suggesting that PLE is the safest drug.

CONCLUSIONS

Therefore, our findings suggest that PLE can be a suitable and effective treatment option for preventing Argulus infestations in goldfish. The results of this study can guide the use of PLE at an optimal dosage to control Argulus infestation in goldfish.

Structural and evolutionary insights into astacin metallopeptidases

The astacins are a family of metallopeptidases (MPs) that has been extensively described from animals. They are multidomain extracellular proteins, which have a conserved core architecture encompassing a signal peptide for secretion, a prodomain or prosegment and a zinc-dependent catalytic domain (CD). This constellation is found in the archetypal name-giving digestive enzyme astacin from the European crayfish Astacus astacus. Astacin catalytic domains span ∼200 residues and consist of two subdomains that flank an extended active-site cleft. They share several structural elements including a long zinc-binding consensus sequence (HEXXHXXGXXH) immediately followed by an EXXRXDRD motif, which features a family-specific glutamate. In addition, a downstream SIMHY-motif encompasses a "Met-turn" methionine and a zinc-binding tyrosine. The overall architecture and some structural features of astacin catalytic domains match those of other more distantly related MPs, which together constitute the metzincin clan of metallopeptidases. We further analysed the structures of PRO-, MAM, TRAF, CUB and EGF-like domains, and described their essential molecular determinants. In addition, we investigated the distribution of astacins across kingdoms and their phylogenetic origin. Through extensive sequence searches we found astacin CDs in > 25,000 sequences down the tree of life from humans beyond Metazoa, including Choanoflagellata, Filasterea and Ichtyosporea. We also found < 400 sequences scattered across non-holozoan eukaryotes including some fungi and one virus, as well as in selected taxa of archaea and bacteria that are pathogens or colonizers of animal hosts, but not in plants. Overall, we propose that astacins originate in the root of Holozoa consistent with Darwinian descent and that the latter genes might be the result of horizontal gene transfer from holozoan donors.

Daily patterns in parasite processes: diel variation in fish louse transcriptomes

Parasites, similar to all other organisms, time themselves to environmental cues using a molecular clock to generate and maintain rhythms. Chronotherapeutic (timed treatment) techniques based on such rhythms offer great potential for improving control of chronic, problematic parasites. Fish lice are a key disease threat in aquaculture, with current control insufficient. Assessing the rhythmicity of fish lice transcriptomes offers not only insight into the viability of chronotherapy, but the opportunity to identify new drug targets. Here, for the first known time in any crustacean parasite, diel changes in gene transcription are examined, revealing that approximately half of the Argulus foliaceus annotated transcriptome displays significant daily rhythmicity. We identified rhythmically transcribed putative clock genes including core clock/cycle and period/timeless pairs, alongside rhythms in feeding-associated genes and processes involving immune response, as well as fish louse drug targets. A substantial number of gene pathways showed peak transcription in hours immediately preceding onset of light, potentially in anticipation of peak host anti-parasite responses or in preparation for increased feeding activity. Genes related to immune haemocyte activity and chitin development were more highly transcribed 4 h post light onset, although inflammatory gene transcription was highest during dark periods. Our study provides an important resource for application of chronotherapy in fish lice; timed application could increase efficacy and/or reduce dose requirement, improving the current landscape of drug resistance and fish health while reducing the economic cost of infection.

Genetic Diversity of Serine Protease Inhibitors in Myxozoan (Cnidaria, Myxozoa) Fish Parasites

We studied the genetic variability of serine protease inhibitors (serpins) of Myxozoa, microscopic endoparasites of fish. Myxozoans affect the health of both farmed and wild fish populations, causing diseases and mortalities. Despite their global impact, no effective protection exists against these parasites. Serpins were reported as important factors for host invasion and immune evasion, and as promising targets for the development of antiparasitic therapies. For the first time, we identified and aligned serpin sequences from high throughput sequencing datasets of ten myxozoan species, and analyzed 146 serpins from this parasite group together with those of other taxa phylogenetically, to explore their relationship and origins. High intra- and interspecific variability was detected among the examined serpins. The average sequence identity was 25–30% only. The conserved domains (i.e., motif and signature) showed taxon-level differences. Serpins clustered according to taxonomy rather than to serpin types, and myxozoan serpins seemed to be highly divergent from that of other taxa. None of them clustered with their closest relative free-living cnidarians. The genetic distinction of myxozoan serpins further strengthens the idea of an independent origin of Myxozoa, and may indicate novel protein functions potentially related to parasitism in this animal group.