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Horák P, Bulantová J, Mikeš L. Other Schistosomatoidea and Diplostomoidea. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2024; 1454:107-155. [PMID: 39008265 DOI: 10.1007/978-3-031-60121-7_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/16/2024]
Abstract
Trematodes of the order Diplostomida are well known as serious pathogens of man, and both farm and wild animals; members of the genus Schistosoma (Schistosomatidae) are responsible for human schistosomosis (schistosomiasis) affecting more than 200 million people in tropical and subtropical countries, and infections of mammals and birds by animal schistosomes are of great veterinary importance. The order Diplostomida is also rich in species parasitizing other major taxa of vertebrates. The "Aporocotylidae" sensu lato are pathogenic in fish, "Spirorchiidae" sensu lato in reptiles. All these flukes have two-host life cycles, with asexually reproducing larvae usually in mollusks and occasionally in annelids, and adults usually live in the blood vessels of their vertebrate hosts. Pathology is frequently associated with inflammatory reactions to eggs trapped in various tissues/organs. On the other hand, the representatives of Diplostomidae and Strigeidae have three- or four-host life cycles in which vertebrates often serve not only as definitive but also as intermediate or paratenic hosts. Pathology is usually associated with migration of metacercariae and mesocercariae within the host tissues. The impact of these trematode infections on both farm and wild animals may be significant.
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Affiliation(s)
- Petr Horák
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czech Republic.
| | - Jana Bulantová
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Libor Mikeš
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czech Republic
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Carabott MJ, Power C, Widdicombe M, Rough K, Nowak BF, Bott NJ. Dynamics of Cardicola spp. Infection in Ranched Southern Bluefin Tuna: First Observation of C. orientalis at Transfer. Pathogens 2023; 12:1443. [PMID: 38133326 PMCID: PMC10747332 DOI: 10.3390/pathogens12121443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Revised: 11/28/2023] [Accepted: 12/11/2023] [Indexed: 12/23/2023] Open
Abstract
Aporocotylid blood flukes Cardicola forsteri and C. orientalis are an ongoing health concern for the Southern Bluefin Tuna (Thunnus maccoyii, SBT) industry, where infections can lead to morbidity and mortality in ranched SBT populations. This study compared blood fluke infection in SBT from two companies during the 2021 ranching season. Both companies administered the same dosage of praziquantel approximately 5 weeks after transfer, feeding with frozen baitfish daily; the only difference in the company's practices was that the pontoons were located 2.5 km apart. Infection severity was measured as prevalence and intensity by quantifying adult C. forsteri in SBT heart and copy numbers of C. forsteri and C. orientalis ITS-2 DNA in SBT heart and gills. Data from the 2018 and 2019 harvests of SBT were used to make comparisons with 2021 harvest data. Cardicola orientalis was detected at transfer and no longer detected after treatment with praziquantel. Cardicola spp. were present in 83% of sampled SBT in 2021. Both companies demonstrated similar patterns of infection, and Company A had higher prevalence and intensity of Cardicola spp. infection. Based on C. forsteri ITS-2 DNA, infection intensity at harvest was significantly greater for both companies in 2021 when compared to 2018 and 2019. Continued monitoring of Cardicola spp. in SBT and improvements in diagnostics contribute to our understanding of Cardicola spp. epizootiology and the detection of changes in treatment efficacy.
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Affiliation(s)
- Melissa J. Carabott
- School of Science, RMIT University, Melbourne, VIC 3083, Australia; (M.J.C.); (C.P.); (M.W.); (B.F.N.)
| | - Cecilia Power
- School of Science, RMIT University, Melbourne, VIC 3083, Australia; (M.J.C.); (C.P.); (M.W.); (B.F.N.)
| | - Maree Widdicombe
- School of Science, RMIT University, Melbourne, VIC 3083, Australia; (M.J.C.); (C.P.); (M.W.); (B.F.N.)
| | - Kirsten Rough
- Australian Southern Bluefin Tuna Industry Association, South Quay Blvd, Port Lincoln, SA 5606, Australia;
| | - Barbara F. Nowak
- School of Science, RMIT University, Melbourne, VIC 3083, Australia; (M.J.C.); (C.P.); (M.W.); (B.F.N.)
| | - Nathan J. Bott
- School of Science, RMIT University, Melbourne, VIC 3083, Australia; (M.J.C.); (C.P.); (M.W.); (B.F.N.)
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Power C, Carabott M, Widdicombe M, Coff L, Rough K, Nowak B, Bott NJ. Effects of company and season on blood fluke ( Cardicola spp.) infection in ranched Southern Bluefin Tuna: preliminary evidence infection has a negative effect on fish growth. PeerJ 2023; 11:e15763. [PMID: 37520261 PMCID: PMC10377432 DOI: 10.7717/peerj.15763] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Accepted: 06/27/2023] [Indexed: 08/01/2023] Open
Abstract
Aporocotylid blood flukes Cardicola forsteri and C. orientalis are an ongoing health concern for Southern Bluefin Tuna (SBT), Thunnus maccoyii, ranched in Australia. Therapeutic application of praziquantel (PZQ) has reduced SBT mortalities, however PZQ is not a residual treatment therefore reinfection can occur after the single treatment application. This study documents the epidemiology of Cardicola spp. infection in ranched SBT post treatment over three ranching seasons (2018, 2019 and 2021). Infection prevalence (percentage of SBT affected) and intensity (parasite load) was determined by adult fluke counts from heart, egg counts from gill filaments and the use of specific quantitative polymerase chain reaction (qPCR) for detection of C. forsteri and C. orientalis ITS-2 DNA in SBT hearts and gills. SBT Condition Index decreased as intensity of Cardicola spp. DNA in SBT gills increased, suggesting blood fluke infection had a negative effect on SBT growth (Spearman's r = -0.2426, d.f. = 138, p = 0.0041). Prevalence and intensity of infection indicated PZQ remained highly effective at controlling Cardicola spp. infection in ranched SBT, 10 years after PZQ administration began in this industry. Company A had the highest prevalence and intensity of Cardicola spp. infection in 2018, and Company G had the highest in 2019. No consistent pattern was seen in 2021. Overall, intensity of infection did not increase as ranching duration increased post treatment. Results from this study improve our knowledge of the biology of blood flukes and helps the SBT industry to modify or design new blood fluke management strategies to reduce health risks and improve performance of SBT.
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Affiliation(s)
- Cecilia Power
- School of Science, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia
| | - Melissa Carabott
- School of Science, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia
| | - Maree Widdicombe
- School of Science, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia
| | - Lachlan Coff
- School of Science, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia
| | - Kirsten Rough
- Australian Southern Bluefin Tuna Industry Association, Port Lincoln, South Australia, Australia
| | - Barbara Nowak
- School of Science, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia
| | - Nathan J. Bott
- School of Science, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia
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Bosi G, Maynard BJ, Pironi F, Sayyaf Dezfuli B. Parasites and the neuroendocrine control of fish intestinal function: an ancient struggle between pathogens and host. Parasitology 2022; 149:1842-1861. [PMID: 36076315 PMCID: PMC11010486 DOI: 10.1017/s0031182022001160] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Revised: 08/03/2022] [Accepted: 08/11/2022] [Indexed: 12/29/2022]
Abstract
Most individual fish in wild and farmed populations can be infected with parasites. Fish intestines can harbour protozoans, myxozoans and helminths, which include several species of digeneans, cestodes, nematodes and acanthocephalans. Enteric parasites often induce inflammation of the intestine; the pathogen provokes changes in the host physiology, which will be genetically selected for if they benefit the parasite. The host response to intestinal parasites involves neural, endocrine and immune systems and interaction among these systems is coordinated by hormones, chemokines, cytokines and neurotransmitters including peptides. Intestinal fish parasites have effects on the components of the enteric nervous and endocrine systems; mechanical/chemical changes impair the activity of these systems, including gut motility and digestion. Investigations on the role of the neuroendocrine system in response to fish intestinal parasites are very few. This paper provides immunohistochemical and ultrastructural data on effects of parasites on the enteric nervous system and the enteric endocrine system in several fish–parasite systems. Emphasis is on the occurrence of 21 molecules including cholecystokinin-8, neuropeptide Y, enkephalins, galanin, vasoactive intestinal peptide and serotonin in infected tissues.
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Affiliation(s)
- Giampaolo Bosi
- Department of Veterinary Medicine and Animal Science, University of Milan, St. dell'Università 6, 26900 Lodi, Italy
| | - Barbara J. Maynard
- The Institute for Learning and Teaching, Colorado State University, Fort Collins, CO 80523, USA
| | - Flavio Pironi
- Department of Life Sciences and Biotechnology, University of Ferrara, St. Borsari 46, 44121 Ferrara, Italy
| | - Bahram Sayyaf Dezfuli
- Department of Life Sciences and Biotechnology, University of Ferrara, St. Borsari 46, 44121 Ferrara, Italy
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Draft genome of the bluefin tuna blood fluke, Cardicola forsteri. PLoS One 2022; 17:e0276287. [PMID: 36240154 PMCID: PMC9565688 DOI: 10.1371/journal.pone.0276287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Accepted: 10/03/2022] [Indexed: 11/12/2022] Open
Abstract
The blood fluke Cardicola forsteri (Trematoda: Aporocotylidae) is a pathogen of ranched bluefin tuna in Japan and Australia. Genomics of Cardicola spp. have thus far been limited to molecular phylogenetics of select gene sequences. In this study, sequencing of the C. forsteri genome was performed using Illumina short-read and Oxford Nanopore long-read technologies. The sequences were assembled de novo using a hybrid of short and long reads, which produced a high-quality contig-level assembly (N50 > 430 kb and L50 = 138). The assembly was also relatively complete and unfragmented, comprising 66% and 7.2% complete and fragmented metazoan Benchmarking Universal Single-Copy Orthologs (BUSCOs), respectively. A large portion (> 55%) of the genome was made up of intergenic repetitive elements, primarily long interspersed nuclear elements (LINEs), while protein-coding regions cover > 6%. Gene prediction identified 8,564 hypothetical polypeptides, > 77% of which are homologous to published sequences of other species. The identification of select putative proteins, including cathepsins, calpains, tetraspanins, and glycosyltransferases is discussed. This is the first genome assembly of any aporocotylid, a major step toward understanding of the biology of this family of fish blood flukes and their interactions within hosts.
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Norbury LJ, Shirakashi S, Power C, Nowak BF, Bott NJ. Praziquantel use in aquaculture - Current status and emerging issues. Int J Parasitol Drugs Drug Resist 2022; 18:87-102. [PMID: 35220160 PMCID: PMC8881684 DOI: 10.1016/j.ijpddr.2022.02.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Revised: 02/13/2022] [Accepted: 02/17/2022] [Indexed: 12/02/2022]
Abstract
Parasitic diseases are major constraints in fish mariculture. The anthelmintic praziquantel (PZQ) can effectively treat a range of flatworm parasites in a variety of fish species and has potential for broader application than its current use in the global aquaculture industry. In this review we report on PZQ's current use in the aquaculture industry and discuss its efficacy against various flatworm parasites of fish. Routes of PZQ administration are evaluated, along with issues related to palatability, pharmacokinetics and toxicity in fish, while PZQ's effects on non-target species, environmental impacts, and the development of drug-resistance are discussed.
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Affiliation(s)
- Luke J Norbury
- School of Science, STEM College, RMIT University, Bundoora, 3083, Victoria, Australia
| | - Sho Shirakashi
- Aquaculture Research Institute, Kindai University, Wakayama, 649-2211, Japan
| | - Cecilia Power
- School of Science, STEM College, RMIT University, Bundoora, 3083, Victoria, Australia
| | - Barbara F Nowak
- School of Science, STEM College, RMIT University, Bundoora, 3083, Victoria, Australia; Institute for Marine and Antarctic Studies, University of Tasmania, Launceston, 7250, Tasmania, Australia
| | - Nathan J Bott
- School of Science, STEM College, RMIT University, Bundoora, 3083, Victoria, Australia.
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Power C, Evenden S, Rough K, Webber C, Widdicombe M, Nowak BF, Bott NJ. Prevalence and Intensity of Cardicola spp. Infection in Ranched Southern Bluefin Tuna and a Comparison of Diagnostic Methods. Pathogens 2021; 10:pathogens10101248. [PMID: 34684197 PMCID: PMC8541539 DOI: 10.3390/pathogens10101248] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Revised: 09/24/2021] [Accepted: 09/24/2021] [Indexed: 11/21/2022] Open
Abstract
The parasitic blood flukes Cardicola forsteri and C. orientalis are an ongoing health concern for Southern Bluefin Tuna Thunnus maccoyii (SBT) ranched in Australia. In this study we compared the effect of treatment, company, and ranching year on blood fluke infections in ranched SBT. SBT were sampled during the 2018 and 2019 ranching seasons from praziquantel (PZQ) treated pontoons and untreated pontoons managed by two companies. Severity of infection was diagnosed by several criteria including adult fluke counts from hearts, egg counts from gill filaments and the use of specific quantitative polymerase chain reaction (qPCR) for detection of C. forsteri and C. orientalis ITS-2 DNA in SBT hearts and gills. PZQ treatment remains highly effective against C. forsteri infection. Prevalence and intensity of Cardicola spp. infection was lower in 2019 than 2018 for Company A in treated pontoons at week 12 and week 17 of ranching, and lower for Company A than Company B in untreated pontoons at month 5 of ranching. Results indicate re-infection may be less likely in the environment near Company A pontoons, and consistent years of treatment may have lowered the parasite load in the environment. qPCR demonstrated higher sensitivity when comparing diagnostic methods for C. forsteri in heart, and higher specificity when comparing diagnostic methods for Cardicola spp. in gills. Continuing to monitor blood fluke infections in ranched SBT can help to detect changes in drug efficacy over time and help industry to develop a best practice for treatment.
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Affiliation(s)
- Cecilia Power
- School of Science, RMIT University, Bundoora, VIC 3083, Australia; (C.P.); (M.W.); (B.F.N.)
| | - Shannon Evenden
- Australian Southern Bluefin Tuna Industry Association, South Quay Blvd, Port Lincoln, SA 5606, Australia; (S.E.); (K.R.); (C.W.)
| | - Kirsten Rough
- Australian Southern Bluefin Tuna Industry Association, South Quay Blvd, Port Lincoln, SA 5606, Australia; (S.E.); (K.R.); (C.W.)
| | - Claire Webber
- Australian Southern Bluefin Tuna Industry Association, South Quay Blvd, Port Lincoln, SA 5606, Australia; (S.E.); (K.R.); (C.W.)
| | - Maree Widdicombe
- School of Science, RMIT University, Bundoora, VIC 3083, Australia; (C.P.); (M.W.); (B.F.N.)
| | - Barbara F. Nowak
- School of Science, RMIT University, Bundoora, VIC 3083, Australia; (C.P.); (M.W.); (B.F.N.)
| | - Nathan J. Bott
- School of Science, RMIT University, Bundoora, VIC 3083, Australia; (C.P.); (M.W.); (B.F.N.)
- Correspondence:
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Coff L, Abrahams JL, Collett S, Power C, Nowak BF, Kolarich D, Bott NJ, Ramsland PA. Profiling the glycome of Cardicola forsteri, a blood fluke parasitic to bluefin tuna. Int J Parasitol 2021; 52:1-12. [PMID: 34391752 DOI: 10.1016/j.ijpara.2021.06.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Revised: 06/16/2021] [Accepted: 06/17/2021] [Indexed: 11/05/2022]
Abstract
Infections by blood flukes (Cardicola spp.) are considered the most significant health issue for ranched bluefin tuna, a major aquaculture industry in Japan and Australia. The host-parasite interfaces of trematodes, namely their teguments, are particularly rich in carbohydrates, which function both in evasion and modulation of the host immune system, while some are primary antigenic targets. In this study, histochemistry and mass spectrometry techniques were used to profile the glycans of Cardicola forsteri. Fluorescent lectin staining of adult flukes indicates the presence of oligomannose (Concanavalin A-reactive) and fucosylated (Pisum sativum agglutinin-reactive) N-glycans. Additionally, reactivity of succinylated wheat germ agglutinin (s-WGA) was localised to several internal organs of the digestive and monoecious reproductive systems. Glycan structures were further investigated with tandem mass spectrometry, which revealed structures indicated by lectin reactivity. While O-glycans from these adult specimens were not detectable by mass spectrometry, several oligomannose, paucimannosidic, and complex-type N-glycans were identified, including some carrying hexuronic acid and many carrying core xylose. This is, to our knowledge, the first glycomic characterisation of a marine platyhelminth, with broader implications for research into other trematodes.
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Affiliation(s)
- Lachlan Coff
- School of Science, STEM College, RMIT University, Bundoora, VIC 3083, Australia
| | - Jodie L Abrahams
- Institute for Glycomics, Griffith University, Southport, QLD 4215, Australia
| | - Simon Collett
- School of Science, STEM College, RMIT University, Bundoora, VIC 3083, Australia
| | - Cecilia Power
- School of Science, STEM College, RMIT University, Bundoora, VIC 3083, Australia
| | - Barbara F Nowak
- School of Science, STEM College, RMIT University, Bundoora, VIC 3083, Australia; Institute for Marine and Antarctic Studies, University of Tasmania, Locked Bag 1370, Launceston, TAS 7250, Australia
| | - Daniel Kolarich
- Institute for Glycomics, Griffith University, Southport, QLD 4215, Australia; ARC Centre of Excellence for Nanoscale BioPhotonics, Griffith University, Southport, QLD 4215, Australia
| | - Nathan J Bott
- School of Science, STEM College, RMIT University, Bundoora, VIC 3083, Australia.
| | - Paul A Ramsland
- School of Science, STEM College, RMIT University, Bundoora, VIC 3083, Australia; Department of Immunology, Monash University, Melbourne, VIC 3004, Australia; Department of Surgery, Austin Health, University of Melbourne, Heidelberg, VIC 3084, Australia.
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First Report of Blood Fluke Pathogens with Potential Risk for Emerging Yellowtail Kingfish ( Seriola lalandi) Aquaculture on the Chilean Coast, with Descriptions of Two New Species of Paradeontacylix (Aporocotylidae). Pathogens 2021; 10:pathogens10070849. [PMID: 34357999 PMCID: PMC8308527 DOI: 10.3390/pathogens10070849] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 05/11/2021] [Accepted: 05/11/2021] [Indexed: 11/17/2022] Open
Abstract
Blood flukes are digeneans that infect wild and farmed fish that can cause a severe and potentially lethal disease in farmed fish. These parasites are undetectable in the larval stage based on macroscopic observations in the definitive host with the infection becoming evident when eggs accumulate in the branchial vessels. There are nine known species of the genus Paradeontacylix and seven exclusively parasitize Seriola spp. from several geographical areas. Seriola lalandi aquaculture farms are emerging at various localities in northern Chile. Here, we report, for the first time, two blood fluke species parasitizing S. lalandi in the Southeastern Pacific (Chile). In the laboratory, the gills and heart of fish were removed. The retained blood flukes were separated according to the infection site, fixed in 70% or 95% ethanol for taxonomic and molecular analysis, respectively. Morphometrical differences among the fluke species were evaluated with a principal component analysis (PCA) using proportional body measurements. Phylogenetic trees were constructed based on 28S rDNA, cox1 mDNA using Bayesian inference (BI), and maximum likelihood (ML). Based on morphology, morphometry, and molecular analyses, two new species are proposed: P. humboldti n. sp. from the gills and P. olivai n. sp. from the heart of S. lalandi. Both were clearly distinguished from other species of Paradeontacylix by a combination of morphologic features (posterior tegumental spines, testes arrangement, body size). The genetic distance (based on cox1) among species was >10%. P. humboldti n. sp. and P. olivai n. sp. are sister species (with a common ancestor) independent of P. godfreyi from S. lalandi in Australia. The newly identified parasites may pose a risk to farmed S. lalandi as aporocotylids have been the cause of diseases in farmed fish from other geographical areas. In addition, some cages of S. lalandi are currently maintained in an open circulating system, which could favor the transmission of these parasites (if involved hosts are present in the environment).
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Survival of metazoan parasites in fish: Putting into context the protective immune responses of teleost fish. ADVANCES IN PARASITOLOGY 2021; 112:77-132. [PMID: 34024360 DOI: 10.1016/bs.apar.2021.03.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Defence mechanisms of fish can be divided into specific and non-specific that act in concert and are often interdependent. Most fish in both wild and cultured populations are vulnerable to metazoan parasites. Endoparasitic helminths include several species of digeneans, cestodes, nematodes, and acanthocephalans. Although they may occur in large numbers, helminth infections rarely result in fish mortality. Conversely, some ectoparasites cause mass mortality in farmed fish. Given the importance of fish innate immunity, this review addresses non-specific defence mechanisms of fish against metazoan parasites, with emphasis on granulocyte responses involving mast cells, neutrophils, macrophages, rodlet cells, and mucous cells. Metazoan parasites are important disease agents that affect wild and farmed fish and can induce high economic loss and, as pathogen organisms, deserve considerable attention. The paper will provide our light and transmission electron microscopy data on metazoan parasites-fish innate immune and neuroendocrine systems. Insights about the structure and functions of the cell types listed above and a brief account of the effects and harms of each metazoan taxon to specific fish apparati/organs will be presented.
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Changes in the Splenic Melanomacrophage Centre Surface Area in Southern Bluefin Tuna ( Thunnus maccoyii) Are Associated with Blood Fluke Infections. Pathogens 2021; 10:pathogens10010079. [PMID: 33477690 PMCID: PMC7835979 DOI: 10.3390/pathogens10010079] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 01/11/2021] [Accepted: 01/15/2021] [Indexed: 11/16/2022] Open
Abstract
Melanomacrophage centres (MMCs) are aggregates of macrophages accumulating various pigments. They have been proposed as an indicator of fish immune response. Blood flukes are common parasites in farmed fish. Two cohorts of wild Southern Bluefin Tuna (Thunnus maccoyi) were examined at transfer, before treatment against blood flukes (pre-treatment) and at harvest. MMCs were assessed in histological sections using image analysis, while Cardicola forsteri and Cardicola orientalis infection severity was determined using qPCR, count of adult flukes in heart flushes and count of eggs in gill filaments. Fish from both cohorts showed the same pattern in the changes in the surface area of MMCs. The surface area of splenic MMCs increased over the ranching duration and was positively correlated to the PCR determined copy numbers of Cardicola forsteri ITS2 rDNA in the gills of those fish. However, the infection with blood fluke was more variable, both between cohorts and individuals within the same cohort. Eggs of blood fluke were detected in renal MMCs using histology. Cardicola forsteri had a higher prevalence than Cardicola orientalis. This study contributes to our understanding of blood fluke infections in Southern Bluefin Tuna and their interactions with MMCs.
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