''Enterospora nucleophila'' is a
microsporidian infecting the
gilt-head bream
The gilt-head (sea) bream (''Sparus aurata''), known as Orata in antiquity and still today in Italy and Tunisia (known as "Dorada" in Spain, "Dourada" in Portugal and "Dorade Royale" in France), is a fish of the bream family Sparidae found in th ...
(''Sparus aurata''). It develops primarily within the
nuclei of
rodlet cells and
enterocyte
Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells which line the inner surface of the small and large intestines. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase its s ...
s, at the
intestinal epithelium
The intestinal epithelium is the single cell layer that form the luminal surface (lining) of both the small and large intestine (colon) of the gastrointestinal tract. Composed of simple columnar epithelial cells, it serves two main functio ...
. It can also be found in
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...
ic position within other cell types, including
phagocyte
Phagocytes are cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. Their name comes from the Greek ', "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell", from the Greek ...
s, at
subepithelial layers. It is the causative agent of emaciative microsporidiosis of gilthead sea bream, a chronic condition manifested as a severe
growth arrestment, normally accompanied by
trickling mortality.
Taxonomy
''E. nucleophila'' is a microsporidian, a group of intracellular parasites related to
fungi
A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...
. This species is rooted within the family
Enterocytozoonidae. According to
SSUrDNA-based
phylogenetic inference
Computational phylogenetics is the application of computational algorithms, methods, and programs to phylogenetic "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary hist ...
, it clusters with ''Enterocytozoon hepatopenaei'', ''Enterospora canceri'' and ''Enterocytozoon bieneusi'' in a well-supported
clade.
[Palenzuela, O., Redondo, M. J., Cali, A., Takvorian, P. M., Alonso-Naveiro, M., Alvarez-Pellitero, P., & Sitja-Bobadilla, A. (2014). A new intranuclear microsporidium, ''Enterospora nucleophila'' n. sp., causing an emaciative syndrome in a piscine host (''Sparus aurata''), prompts the redescription of the family Enterocytozoonidae. Int. J. Parasitol. 44:189-203.http://doi.org/10.1016/j.ijpara.2013.10.005]
The Enterocytozoonidae branches within the class
Terresporidia in molecular-based classification of microsporidians but taxonomical classification above the family level is currently not entirely settled in this phylum.
Life cycle
Only the development within gilthead sea bream is currently known.
Since some of the closest relatives of ''E. nucleophila'' infect
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
s (e.g., ''Enterospora canceri'' or ''E. hepatopenaei''), and some of them have
heteroxenous
Heteroxeny, or heteroxenous development, characterizes a parasite whose development involves several host species. Heteroxeny has been used as the basis for splitting genera.
When there are two or three hosts, the development cycle is named d ...
cycles alternating between crustacean and fish hosts (e.g., ''
Desmozoon lepeophtheri''
, a similar alternating cycle could occur for ''E. nucleophila''.
Pathology and clinical signs
Infections by ''E. nucleophila'' are associated with stunted growth of gilthead sea bream
stocks
Stocks are feet restraining devices that were used as a form of corporal punishment and public humiliation. The use of stocks is seen as early as Ancient Greece, where they are described as being in use in Solon's law code. The law describing ...
, which can be accompanied by low-level but sustained trickling mortality (0.1-0.3% daily, up to 1% at peaks per
sea cage).
Affected fish normally appear
lethargic
Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwor ...
and
cachectic, with other nonspecific signs like discolouration and occasional
scale
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number ...
loss.
Upon
necropsy
An autopsy (post-mortem examination, obduction, necropsy, or autopsia cadaverum) is a surgical procedure that consists of a thorough Physical examination, examination of a Cadaver, corpse by dissection to determine the cause, mode, and manner o ...
, gross pathological alterations include thinned and transparent wall in the intestines, which frequently accumulate clear or greenish fluid and white faeces in the terminal portion. The condition seems to appear in gilthead sea bream during their first winter in sea cages. As a result of the arrested growth of infected animals, these can average half the weight of the unaffected stock.
Impact
The disease was first noticed in the early 2000s. However, the difficulties in the diagnosis of the parasite probably delayed acknowledgement of its presence and impact. Indeed, the parasite and its association with gilthead sea bream emaciative microsporidiosis were not described until recently, but retrospective studies identified it in samples taken in 1993.
The main clinical signs are only noticed in severe infections and can be largely masked by other infectious diseases of gilthead sea bream. Therefore, the approaches to understand the true impact of the disease can only be formed after the development of appropriate diagnostic methods to conduct specific epidemiological and risk-assessment studies. Besides the mortality, the main economic impact of the parasite is related to the segregation of sizes caused by the infection within affected sea cages, as it results in inefficient feeding, serious biomass and quality losses at the harvest.
Diagnosis
Presumptive diagnosis can be made based on clinical signs and
histopathological
Histopathology (compound of three Greek words: ''histos'' "tissue", πάθος ''pathos'' "suffering", and -λογία ''-logia'' "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Spec ...
examination of the intestinal epithelium. The most common observation in heavy infections is the presence of numerous
hypertrophied
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J. ...
cell nuclei and a remarkable
hypercellularity.
When present, tiny microsporidian
spore
In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
s (1.67 x 1.05 µm) can be identified. Like in other microsporidioses, the detection of spores can be facilitated with
calcofluor-white M2R or
luna stains
Luna commonly refers to:
* Earth's Moon, named "Luna" in Latin
* Luna (goddess), the ancient Roman personification of the Moon
Luna may also refer to:
Places Philippines
* Luna, Apayao
* Luna, Isabela
* Luna, La Union
* Luna, San Jose
Romania ...
. More reliable confirmatory diagnosis of ''E. nucleophila'' is possible with molecular-based methods,
''in situ'' hybridization and
RT-PCR
Reverse transcription polymerase chain reaction (RT-PCR) is a laboratory technique combining reverse transcription of RNA into DNA (in this context called complementary DNA or cDNA) and amplification of specific DNA targets using polymerase chai ...
tests.
Treatments
There are currently no approved therapies for ''E. nucleophila''. Microsporidian infections relevant for human and animal medicine are normally treated with
Albendazole
Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infectio ...
,
Metronidazole
Metronidazole, sold under the brand name Flagyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vaginosis. It is e ...
or
Fumagillin, but the use of these drugs in aquaculture settings is not regulated and their effectivity for treating gilthead sea bream microsporidiosis is unknown.
Research
As an emerging disease of gilthead sea bream, understanding ''E. nucleophila'' infection and exploring ways to mitigate its impact in
aquaculture
Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lotus ...
facilities has just started. The
EU funded
Horizon 2020
The Framework Programmes for Research and Technological Development, also called Framework Programmes or abbreviated FP1 to FP9, are funding programmes created by the European Union/European Commission to support and foster research in the Europea ...
Project
has tackled several objectives related to this infection, like the development and validation of diagnostic methods and their use in epidemiological studies to evaluate the impact and risks factors associated to the disease. Ongoing research framed within the project has also focused on developing means for the transmission and maintenance of the infection in the laboratory, as well as its ''in vitro'' cultivation. More ambitious goals, such as the
genome sequencing
Whole genome sequencing (WGS), also known as full genome sequencing, complete genome sequencing, or entire genome sequencing, is the process of determining the entirety, or nearly the entirety, of the DNA sequence of an organism's genome at a ...
and the identification of therapeutic and diagnostic targets have also been attempted but are currently struggling with difficulties in reproducing the disease in the laboratory and generating appropriate material.
References
{{Taxonbar, from=Q97358948
Microsporidia