Microsporidiosis is an opportunistic intestinal infection that causes

diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...

and wasting in immunocompromised individuals ( HIV, for example). It results from different species of

microsporidia Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or pr ...

, a group of microbial (unicellular) fungi. In HIV infected individuals, microsporidiosis generally occurs when

CD4 In molecular biology, CD4 (cluster of differentiation 4) is a glycoprotein that serves as a co-receptor for the T-cell receptor (TCR). CD4 is found on the surface of immune cells such as T helper cells, monocytes, macrophages, and dendritic ce ...

T cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...

counts fall below 150. ''Microsporidia'' have emerged with significant mortality risk in immunocompromised individuals. These are small, single-celled, obligately

intracellular parasite Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host. Types of parasites There are two main types of intracellular parasites: Facultative and Obligate. Facultative intracellular pa ...

s linked to water sources as well as wild, and domestic animals. They were once considered

protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...

ns or

protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the e ...

s, but are now known to be

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

, or a sister group to fungi. The most common causes of microsporidiosis is ''Enterocytozoon bieneusi'' and ''Encephalitozoon intestinalis.''

Cause

At least 15 microsporidian species have been recognized as human

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a g ...

s, spread across nine genera: * '' Anncaliia'' ** '' A. algerae'', ''A. connori'', ''A. vesicularum'' * '' Encephalitozoon'' ** '' E. cuniculi'', ''E. hellem'', '' E. intestinalis'' * Enterocytozoon ** '' E. bieneusi'' * ''

Microsporidium Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or pro ...

'' ** ''M. ceylonensis'', ''M. africanum'' * '' Nosema'' ** ''N. ocularum'' * '' Pleistophora sp.'' * '' Trachipleistophora'' ** ''T. hominis'', ''T. anthropophthera'' * '' Vittaforma'' ** ''V. corneae.'' * ''Tubulinosema'' ** ''T. acridophagus'' The primary causes are '' Enterocytozoon bieneusi'' and ''

Encephalitozoon intestinalis ''Encephalitozoon intestinalis'' is a parasite. It can cause microsporidiosis. It is notable as having one of the smallest genome among known eukaryotic organisms, containing only 2.25 million base pairs. Its genome was completely sequenced in ...

''.

Life cycle

''(Coded to

image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensio ...

at right).'' # The infective form of microsporidia is the resistant

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, ...

and it can survive for an extended period of time in the environment. # The spore extrudes its polar tubule and infects the host cell. # The spore injects the infective sporoplasm into the

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

host cell through the polar tubule. # Inside the cell, the sporoplasm undergoes extensive multiplication either by merogony (binary fission) or

schizogony Fission, in biology, is the division of a single entity into two or more parts and the regeneration of those parts to separate entities resembling the original. The object experiencing fission is usually a cell, but the term may also refer to how ...

(multiple fission). # This development can occur either in direct contact with the host cell

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. ...

('' E. bieneusi'') or inside a

vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic m ...

called a parasitophorous vacuole ('' E. intestinalis''). Either free in the cytoplasm or inside a parasitophorous vacuole, microsporidia develop by

sporogony Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...

to mature spores. # During sporogony, a thick wall is formed around the spore, which provides resistance to adverse environmental conditions. When the spores increase in number and completely fill the host cell cytoplasm, the cell membrane is disrupted and releases the spores to the surroundings. # These free mature spores can infect new cells thus continuing the cycle.

Diagnosis

The best option for diagnosis is using PCR. Diagnosis with Microsporidia can be done through

gram The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...

- positive, acid-fast spores in stool and biopsy material with morphologic demonstration of the organism. Initial detection through light microscopic examination of tissue sections, stools, duodenal aspirates, nasal discharges,

bronchoalveolar lavage Bronchoalveolar lavage (BAL) (also known as bronchoalveolar washing) is a diagnostic method of the lower respiratory system in which a bronchoscope is passed through the mouth or nose into an appropriate airway in the lungs, with a measured amoun ...

fluids, and conjunctival smears.Weber R, Bryan RT, Schwartz DA, Owen RL. Human microsporidial infections. Clin Microbiol Rev. 1994 Oct;7(4):426-61. doi: 10.1128/cmr.7.4.426. PMID: 7834600; PMCID: PMC358336. Definitive diagnosis can also be achieved through fluorescein-tagged antibody

immunofluorescence Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on microbiological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to spe ...

or electron microscopy, and species identification can be done through PCR.

Classification

Although it is classified as a protozoal disease in

ICD-10 ICD-10 is the 10th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD), a medical classification list by the World Health Organization (WHO). It contains codes for diseases, signs and symptoms ...

, their phylogenetic placement has been resolved to be within the

Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

, and some sources classify microsporidiosis as a mycosis, however, they are highly divergent and rapidly evolving.

Treatment

Fumagillin Fumagillin is a complex biomolecule and used as an antimicrobial agent. It was isolated in 1949 from the microbial organism ''Aspergillus fumigatus''. Uses In animals It was originally used against microsporidian parasites '' Nosema apis'' infect ...

has been used in the treatment. Another agent used is albendazole. Because of its severe mortality risk in immunocompromised individuals, two main agents are used: Albendazole, which inhibits tubulin, and

, which inhibits methionine aminopeptidase type two.Han B, Weiss LM. Therapeutic targets for the treatment of microsporidiosis in humans. Expert Opin Ther Targets. 2018 Nov;22(11):903-915. doi: 10.1080/14728222.2018.1538360. Epub 2018 Nov 1. PMID: 30336698; PMCID: PMC6300147.

References

External links

* CDC'
microsporidiosis
info page. {{Mycoses Gastrointestinal tract disorders Animal fungal diseases