Philasterides dicentrarchi

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Philasterides dicentrarchi
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Philasterides dicentrarchi
Figure 1: "Philasterides dicentrarchi, image provided by Jose Manuel Leiro, Jesus Lamas. University of Santiago de Compostela" Philasterides dicentrarchi.png
Figure 1: “Philasterides dicentrarchi, image provided by José Manuel Leiro, Jesús Lamas. University of Santiago de Compostela”

Philasterides dicentrarchi is a marine protozoan ciliate that was first identified in 1995 after being isolated from infected European sea bass (Dicentrarchus labrax) reared in France. [1] The species was also identified as the causative agent of outbreaks of scuticociliatosis that occurred between summer 1999 and spring 2000 in turbot (Scophthalmus maximus) cultivated in the Atlantic Ocean (Galicia, Northwest Spain). [2] Infections caused by P. dicentrarchi have since been observed in turbot reared in both open flow and recirculating production systems. [3] In addition, the ciliate has also been reported to cause infections in other flatfishes, such as the olive flounder (Paralichthys olivaceus) in Korea [4] and the fine flounder (Paralichthys adspersus) in Peru, [5] as well as in seadragons ( Phyllopteryx taeniolatus and Phycodurus eques ), [6] [7] seahorses (Hippocampuskuda and H. abdominalis ), [8] and several species of sharks [9] in other parts of the world.

Contents

Biology and pathology

P. dicentrarchi is included within the subclass Scuticociliatia, which includes about 20 species of ciliates that are typically microphagous bacteriovores and generally abundant in eutrophic habitats in lakes and in coastal marine habitats. Some of these ciliates, characterized by possessing a scutica (a transient kinetosomal structure that is present during stomatogenesis), can behave as endoparasites and are capable of producing serious infections in a wide variety of vertebrates, especially fish, and invertebrates such as crustaceans and echinoderms. [4] [10] [11] [12] [13] [14] P. dicentrarchi is a microaerophilic scuticociliate that lives at the sea bottom, at or below the oxycline or on the monimolimnion, where it feeds on bacteria. [15] However, when it encounters a host it can also behave as an opportunistic histiophagous parasite. [2] Survival of the species inside the host and adaptation to a parasitic lifestyle are attributed to the existence of physiological adaptations at the level of mitochondrial metabolism. Such adaptations include the presence of a second terminal oxidase (which enables the ciliates to obtain energy and survive low levels of oxygen [16] ), antioxidant enzymes, [17] inorganic pyrophosphatases (capable of producing energy by an ATP alternative pathway produced during oxidative metabolism) and the ability of the species to survive in hyposaline environments. [18] Although the route of entry to the host is unknown, the findings of experimental infection studies suggest that the ciliate probably gains access through lesions in the gills and/or the skin. [19] Infected fish show haemorrhagic ulcers on the skin (particularly around the operculum), abundant ascitic fluid in the abdominal cavity, uni- or bilateral exophthalmia, and systemic infection with the presence of ciliates in blood, gills, gastrointestinal tract, liver, spleen, kidneys and musculature. In the final phase of infection, ciliates reach the brain and cause softening and liquefaction of the tissue. [2]

Diagnosis

Diagnosis of P. dicentrarchi in the sea bass and the turbot was initially based primarily on morphological characteristics associated with the oral apparatus and the number of kineties. [1] [2] However, it has been suggested that the combined use of morphological, biological, molecular and serological techniques is necessary for correct identification of the species. [3] [6] P. dicentrarchi was previously considered a junior synonym of Miamiensis avidus . [20] However, recent physiological and molecular studies have shown that P. dicentrarchi and M. avidus strain Ma/2 -ATCC 50180™- are different species. [5]

Treatments

No effective chemotherapeutic measures have been developed for controlling scuticociliatosis in the acute phase of the disease to date. However, the addition of disinfectants such as formalin, hydrogen peroxide and Jenoclean (a mixture of Atacama extract 97%-Zeolites- and citric acid 3%) to seawater has been demonstrated to kill the ciliates. [12] [21] [22] Bath treatments consisting of a combination of benzalkonium chloride and bronopol have also proved to be effective in reducing fish mortality. [23] Several compounds of well-known antiprotozoal activity, including niclosamide, oxyclozanide, bithionol sulfoxide, toltrazuril, N-(2 '-hydroxy-5 '-chloro-benzoyl) 2-chloro-4-nitroaniline, BP68, doxycycline hyclate, albendazole, carnidazole, pyrimethamine, hydrochloride quinacrine and quinine sulphate, are also active against P. dicentrarchi. [21] Antimalarial drugs such as chloroquine and artemisinin also inhibit the in vitro growth of P. dicentrarchi. [24] Other studies investigating the in vitro effects of several new synthetic compounds, including 2 naphthyridines, 2 pyridothienodiazines and 13 pyridothienotriazines, have demonstrated that all display parasiticide activity, and that pyridothienotriazine (12k) was the most active. [25] In addition, several compounds of natural origin have also shown in vitro antiparasitic activity: the polyphenols mangiferin and (–)-epigallocatechin-3-gallate (EGCG), [26] curcumin, [27] resveratrol [28] and the synthetic polyphenol propyl gallate. [29]

Prevention

Vaccines containing trophozoites inactivated with formalin and prepared in oil adjuvants have been developed and have shown good protection against the homologous serotype. [30] [31] Several P. dicentrarchi serotypes have been described. However, the protection induced against heterologous isolates appears to be very low or non-existent. [32]

Research

Research on Philasterides dicentrarchi, which includes aspects of cell biology, diagnostics, interactions with the host immune system, search for new treatments, development of vaccines or risk analysis, is being carried out under the EU funded Horizon2020 Project ParaFishControl. [33]

Related Research Articles

<i>Ichthyophthirius multifiliis</i> Parasitic species of protozoan

Ichthyophthirius multifiliis, often termed "Ich", is a parasitic ciliate described by the French parasitologist Fouquet in 1876. Only one species is found in the genus which also gave name to the family. The name literally translates as "the fish louse with many children". The parasite can infect most freshwater fish species and, in contrast to many other parasites, shows low host specificity. It penetrates gill epithelia, skin and fins of the fish host and resides as a feeding stage inside the epidermis. It is visible as a white spot on the surface of the fish but, due to its internal microhabitat, it is a true endoparasite and not an ectoparasite.

<span class="mw-page-title-main">Parasitic disease</span> Medical condition

A parasitic disease, also known as parasitosis, is an infectious disease caused by parasites. Parasites are organisms which derive sustenance from its host while causing it harm. The study of parasites and parasitic diseases is known as parasitology. Medical parasitology is concerned with three major groups of parasites: parasitic protozoa, helminths, and parasitic arthropods. Parasitic diseases are thus considered those diseases that are caused by pathogens belonging taxonomically to either the animal kingdom, or the protozoan kingdom.

<i>Balantidium</i> Genus of single-celled organisms

Balantidium is a genus of ciliates. It contains the parasitic species Balantidium coli, the only known cause of balantidiasis.

<i>Echinostoma</i> Genus of flukes

Echinostoma is a genus of trematodes (flukes), which can infect both humans and other animals. These intestinal flukes have a three-host life cycle with snails or other aquatic organisms as intermediate hosts, and a variety of animals, including humans, as their definitive hosts.

<span class="mw-page-title-main">Sea louse</span> Family of copepods

Sea lice are copepods of the family Caligidae within the order Siphonostomatoida. They are marine ectoparasites that feed on the mucus, epidermal tissue, and blood of host fish. The roughly 559 species in 37 genera include around 162 Lepeophtheirus and 268 Caligus species.

<span class="mw-page-title-main">Xenoma</span> Growth caused by various species of protists and fungi

A xenoma is a growth caused by various protists and fungi, most notably microsporidia. It can occur on numerous organisms; however is predominantly found on fish.

<i>Cryptocaryon</i> Genus of single-celled organisms

Cryptocaryon irritans is a species of ciliates that parasitizes marine fish, causing marine white spot disease or marine ich. It is one of the most common causes of disease in marine aquaria.

<span class="mw-page-title-main">Olive flounder</span> Species of fish

The olive flounder, bastard halibut or Korean halibut, is a temperate marine species of large-tooth flounder native to the North-western Pacific Ocean.

Glugea is a genus of microsporidian parasites, predominantly infecting fish. Infections of Glugea cause xenoma formation.

<span class="mw-page-title-main">Mobilida</span> Order of protists belonging to the ciliates phylum

Mobilida is a group of parasitic or symbiotic peritrich ciliates, comprising more than 280 species. Mobilids live on or within a wide variety of aquatic organisms, including fish, amphibians, molluscs, cnidarians, flatworms and other ciliates, attaching to their host organism by means of an aboral adhesive disk. Some mobilid species are pathogens of wild or farmed fish, causing severe and economically damaging diseases such as trichodinosis.

<i>Trichomonas tenax</i> Species of single-celled organism

Trichomonas tenax, or oral trichomonas, is a species of Trichomonas commonly found in the oral cavity of humans. Routine hygiene is generally not sufficient to eliminate the parasite, hence its Latin name, meaning "tenacious". The parasite is frequently encountered in periodontal infections, affecting more than 50% of the population in some areas, but it is usually considered insignificant. T. tenax is generally not found on the gums of healthy patients. It is known to play a pathogenic role in necrotizing ulcerative gingivitis and necrotizing ulcerative periodontitis, worsening preexisting periodontal disease. This parasite is also implicated in some chronic lung diseases; in such cases, removal of the parasite is sufficient to allow recovery.

Tenacibaculum is a Gram-negative and motile bacterial genus from the family of Flavobacteriaceae.

Scuticociliatia is a subclass of ciliates in the class Oligohymenophorea. Its members are called scuticociliates. These unicellular eukaryotes are microorganisms that are usually free-living and can be found in freshwater, marine, and soil habitats. Around 20 members of the group have been identified as causative agents of the disease scuticociliatosis, in which the ciliates are parasites of other marine organisms. Species known to be susceptible include a broad range of teleosts, seahorses, sharks, and some crustaceans.

<span class="mw-page-title-main">Philasterida</span> Order of single-celled organisms

Philasterida is an order of ciliates in the subclass Scuticociliatia.

Miamiensis avidus is a species of unicellular marine eukaryote that is a parasite of many different types of fish. It is one of several organisms known to cause the fish disease scuticociliatosis and is considered an economically significant pathogen of farmed fish. M. avidus is believed to be the cause of a 2017 die-off of fish and sharks in the San Francisco Bay.

Scuticociliatosis is a severe and often fatal parasitic infection of several groups of marine organisms. Species known to be susceptible include a broad range of teleosts, seahorses, sharks, and some crustaceans. The disease can be caused by any one of about 20 distinct species of unicellular eukaryotes known as scuticociliates, which are free-living marine microorganisms that are opportunistic or facultative parasites. Scuticociliatosis has been described in the wild, in captive animals in aquariums, and in aquaculture. It is best studied in fish species that are commonly farmed, in which typical effects of infection include skin ulceration, hemorrhage, and necrosis, with post-mortem examination identifying ciliates in the skin, gills, blood, and internal organs including the brain.

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<i>Enteromyxum leei</i> Species of marine parasite

Enteromyxum leei is a species of myxozoan, histozoic parasite that infects the intestinal tract and sometimes associated organs, like gall bladder and liver, of several teleostean fish species. Myxozoans are microscopic metazoans, with an obligate parasitic life-style. The parasite stages of this species live in the paracelullar space between fish enterocytes. It is the causative agent of enteromyxosis, or emaciative disease, also known as "razor blade syndrome" in sparid fish. E. leei has a wide host and geographical range within marine fish, and even freshwater fish have been infected experimentally. E. leei initially emerged in the Mediterranean in the late 1980s and it is believed to have been unintentionally introduced into the Red Sea. Its pathogenicity and economic impact depend on the host species. In the gilt-head seabream, it is manifested as a chronic disease that provokes anorexia, delayed growth with weight loss, cachexia, reduced marketability and increased mortality. In other species, it has no clinical signs. In sharpsnout seabream, infection results in very high mortality rates, which have pushed fish farmers to abandon the culture of this fish species.

Philasteridae is a family of ciliates in the order Philasterida.

Philasterides is a genus of ciliates in the order Philasteridae.

References

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