Microsporidia/Microsporidiosis

Microsporidia are a group of obligate intracellular organisms that were recently reclassified as fungi Fungi Fungi belong to the eukaryote domain and, like plants, have cell walls and vacuoles, exhibit cytoplasmic streaming, and are immobile. Almost all fungi, however, have cell walls composed of chitin and not cellulose. Fungi do not carry out photosynthesis but obtain their substrates for metabolism as saprophytes (obtain their food from dead matter). Mycosis is an infection caused by fungi. Mycology: Overview. Microsporidia is made up of around 15 clinically relevant species, with the most common being Enterocytozoon bieneusi. There is much we do not understand about this group of organisms, and knowledge is evolving. Microsporidia species are ubiquitous, with a wide range of reservoirs. Immunocompromised individuals (particularly those with AIDS and a CD4 count < 100 cells/µL) most commonly develop symptomatic microsporidiosis. GI diseases range from acute, self-limited watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea to chronic diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea causing malabsorption Malabsorption Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion and wasting. Extraintestinal manifestations and dissemination can also occur, affecting the eyes, respiratory tract, brain, biliary tract Biliary tract Bile is secreted by hepatocytes into thin channels called canaliculi. These canaliculi lead into slightly larger interlobular bile ductules, which are part of the portal triads at the "corners" of hepatic lobules. The bile leaves the liver via the right and left hepatic ducts, which join together to form the common hepatic duct. Gallbladder and Biliary Tract, urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract, and/or muscles. Diagnosis occurs through identification of spores on examination of the stool. Antimicrobials, such as albendazole and fumagillin, can be used to treat infections with most microsporidia species.

Last update:

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

Share this concept:

Share on facebook
Share on twitter
Share on linkedin
Share on reddit
Share on email
Share on whatsapp

General Characteristics and Epidemiology

Basic features of microsporidia

  • Recently reclassified as a group of fungi Fungi Fungi belong to the eukaryote domain and, like plants, have cell walls and vacuoles, exhibit cytoplasmic streaming, and are immobile. Almost all fungi, however, have cell walls composed of chitin and not cellulose. Fungi do not carry out photosynthesis but obtain their substrates for metabolism as saprophytes (obtain their food from dead matter). Mycosis is an infection caused by fungi. Mycology: Overview (previously classified as protozoa) and includes approximately:
    • 200 genera
    • 1500 species
  • Vary in:
    • Spore size
    • Nucleus arrangement
    • Life cycle
  • Obligate intracellular 
  • Unicellular
  • Spore-forming 
    • Usually oval
    • Resistant to degradation (survive for long months in the environment)
    • Contain a unique organelle called a polar tubule → helps inject spore contents into a host cell
  • Lack many eukaryotic Eukaryotic Eukaryotes can be single-celled or multicellular organisms and include plants, animals, fungi, and protozoa. Eukaryotic cells contain a well-organized nucleus contained by a membrane, along with other membrane-bound organelles. Cell Types: Eukaryotic versus Prokaryotic organelles Organelles A cell is a complex unit that performs several complex functions. An organelle is a specialized subunit within a cell that fulfills a specific role or function. Organelles are enclosed within their own lipid bilayers or are unbound by membranes. The Cell: Organelles, including:
    • Conventional mitochondria (contain mitosomes instead)
    • Peroxisomes
    • Golgi apparatus

Clinically relevant species

Microsporidiosis is caused by approximately 15 species, including:

  • Enterocytozoon bieneusi is the most common species causing human infections.
  • Encephalitozoon intestinalis
  • Encephalitozoon hellem
  • Encephalitozoon cuniculi
  • Nosema connori
  • N. ocularum
  • Trachipleistophora hominis
  • T. anthropopthera
  • Pleistophora spp.
  • Vittaforma corneae
  • Microsporidium spp.

Epidemiology

  • Worldwide distribution
  • Most infections occur in individuals with HIV/AIDS.

Pathogenesis

Reservoirs

Microsporidia have an extensive range of reservoirs, including (but not limited to):

  • Humans
  • Swine
  • Primates
  • Cattle
  • Cats
  • Dogs
  • Rodents
  • Fish
  • Birds
  • Mosquitos
  • Honeybees

Host risk factors

Though mild or subclinical disease may occur in immunocompetent individuals, most symptomatic infection occurs in those who are immunocompromised:

  • HIV/AIDS (particularly if CD4 < 100 cells/µL)
  • Individuals with solid organ transplants
  • Bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow graft recipients

Transmission

Transmission of microsporidia is not fully understood, but possibilities include:

  • Waterborne
  • Foodborne
  • Contact with infected animals 
  • Vectorborne
  • Airborne

Life cycle and pathophysiology

The pathophysiology is not completely understood.

  • Spore (infective form) can persist in the environment for months
  • Spore enters host (e.g., inhalation, ingestion) → lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs or GI tract
  • Germination occurs, and polar tubule injects sporoplasm into a host cell
  • Proliferation occurs via either:
    • Binary fission
    • Schizogony (multiple fission)
  • Multinucleate plasmodial forms produced → sporogony (maturation process) → mature spores formed
  • Cell ruptures, and spores are released to either:
    • Infect other cells
    • Pass into the environment (shed in feces)
  • Some species can, via macrophages, disseminate to other organs:
    • Kidneys
    • Eyes
    • Brain
    • Biliary tract
    • Muscle
Life cycle of the microsporidia

This diagram demonstrates the life cycle of the microsporidia:
After spores enter the body, the polar tubule connects with a host cell and injects sporoplasm. Replication occurs, followed by maturation of spores. When the host cell is filled, the cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane bursts and releases the spores, and the cycle continues.

Image: “Life cycle of the different species of microsporidia” by CDC. License: Public Domain

Clinical Presentation

The clinical presentation of microsporidiosis depends on:

  • The species causing infection
  • The immune status of the host:
    • Immunocompetent individuals more often experience:
      • Asymptomatic infection or
      • Mild and self-limited disease
    • Immunocompromised individuals are more likely to have:
      • Symptomatic infection
      • Disseminated disease

GI infection

  • Acute disease (more common in immunocompetent individuals):
    • Fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever 
    • Diarrhea:
      • Watery
      • Nonbloody
    • Nausea 
    • Abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
  • Chronic diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea (more common in individuals with AIDS):
    • Malabsorption
    • Weight loss (can cause severe wasting)

Extraintestinal infection

  • Ocular infection (keratoconjunctivitis)
  • Myositis
  • Biliary tract:
    • Acalculous cholecystitis Cholecystitis Cholecystitis is the inflammation of the gallbladder (GB) usually caused by the obstruction of the cystic duct (acute cholecystitis). Mechanical irritation by gallstones can also produce chronic GB inflammation. Cholecystitis is one of the most common complications of cholelithiasis but inflammation without gallstones can occur in a minority of patients. Cholecystitis
    • Cholangitis
  • Respiratory:
    • Sinusitis Sinusitis Sinusitis refers to inflammation of the mucosal lining of the paranasal sinuses. The condition usually occurs concurrently with inflammation of the nasal mucosa (rhinitis), a condition known as rhinosinusitis. Acute sinusitis is due to an upper respiratory infection caused by a viral, bacterial, or fungal agent. Sinusitis
    • Pneumonitis
    • Bronchiolitis
  • Urinary:
    • Impaired renal function
    • Urinary tract infection
  • CNS infection

Diagnosis and Management

Diagnosis

  • The diagnosis is made with detection of spores.
    • Samples can be obtained of:
      • Stool
      • Tissue
      • Body fluids
    • Requires a modified trichrome stain: spores are stained pink
  • Other options:
    • Indirect immunofluorescence 
    • PCR to detect organism DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure

Management

  • The following antimicrobials are effective against most species of microsporidia:
    • Albendazole
    • Fumagillin
  • Antiretroviral therapy Antiretroviral therapy Antiretroviral therapy (ART) targets the replication cycle of the human immunodeficiency virus (HIV) and is classified based on the viral enzyme or mechanism that is inhibited. The goal of therapy is to suppress viral replication to reach the outcome of undetected viral load. Anti-HIV Drugs for individuals with AIDS
  • IV fluid and electrolyte replacement for severe diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
  • Nutritional support for those with malabsorption Malabsorption Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion and weight loss

Differential Diagnosis

  • Cystoisosporiasis Cystoisosporiasis Cystoisospora is a genus within the Coccidia subclass of protozoans. They are single-celled, obligate intracellular parasites that cause intestinal infections in humans. Humans are the only host for these species, and they are both transmitted through the fecal-oral route. The symptoms of cystoisosporiasis are watery diarrhea, abdominal pain, and fever. Cystoisospora/Cystoisosporiasis and Cyclospora/Cyclosporiasis: infection caused by Cystoisospora Cystoisospora Cystoisospora is a genus within the Coccidia subclass of protozoans. They are single-celled, obligate intracellular parasites that cause intestinal infections in humans. Humans are the only host for these species, and they are both transmitted through the fecal-oral route. The symptoms of cystoisosporiasis are watery diarrhea, abdominal pain, and fever. Cystoisospora/Cystoisosporiasis and Cyclospora/Cyclosporiasis belli, an obligate intracellular protozoan that causes GI disease. Immunocompetent individuals may have mild, self-limited watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea. Immunocompromised individuals tend to have chronic or severe diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, resulting in malabsorption Malabsorption Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion, weight loss, and dehydration. Diagnosis is made by identifying oocysts in stool samples. Treatment includes supportive care and antimicrobial therapy, such as trimethoprim Trimethoprim The sulfonamides are a class of antimicrobial drugs inhibiting folic acid synthesize in pathogens. The prototypical drug in the class is sulfamethoxazole. Although not technically sulfonamides, trimethoprim, dapsone, and pyrimethamine are also important antimicrobial agents inhibiting folic acid synthesis. The agents are often combined with sulfonamides, resulting in a synergistic effect. Sulfonamides and Trimethoprim–sulfamethoxazole. 
  • Cyclosporiasis Cyclosporiasis Cyclospora is a genus within the Coccidia subclass of protozoans. They are single-celled, obligate intracellular parasites that cause intestinal infections in humans. Humans are the only host for these species, and they are both transmitted through the fecal-oral route. The symptoms of cyclosporiasis are watery diarrhea, abdominal pain, and fever. Cystoisospora/Cystoisosporiasis and Cyclospora/Cyclosporiasis: infection caused by Cyclospora Cyclospora Cyclospora is a genus within the Coccidia subclass of protozoans. They are single-celled, obligate intracellular parasites that cause intestinal infections in humans. Humans are the only host for these species, and they are both transmitted through the fecal-oral route. The symptoms of cyclosporiasis are watery diarrhea, abdominal pain, and fever. Cystoisospora/Cystoisosporiasis and Cyclospora/Cyclosporiasis cayetanensis, an obligate intracellular protozoan that causes GI disease. The disease causes watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, which can last weeks to months if untreated. Diagnosis is made by identifying oocysts in stool samples. Treatment includes antimicrobial therapy, such as with trimethoprim Trimethoprim The sulfonamides are a class of antimicrobial drugs inhibiting folic acid synthesize in pathogens. The prototypical drug in the class is sulfamethoxazole. Although not technically sulfonamides, trimethoprim, dapsone, and pyrimethamine are also important antimicrobial agents inhibiting folic acid synthesis. The agents are often combined with sulfonamides, resulting in a synergistic effect. Sulfonamides and Trimethoprim–sulfamethoxazole. 
  • Gastroenteritis Gastroenteritis Gastroenteritis is inflammation of the stomach and intestines, commonly caused by infections from bacteria, viruses, or parasites. Transmission may be foodborne, fecal-oral, or through animal contact. Common clinical features include abdominal pain, diarrhea, vomiting, fever, and dehydration. Gastroenteritis: inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach and intestines, commonly caused by infections from bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview, viruses, or parasites. Common clinical features include abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, vomiting, fever, and dehydration. Diagnostic testing with stool analysis or culture is not always required but can help determine the etiology in certain circumstances. Most cases are self-limited; therefore, the only required treatment is supportive therapy (fluids). 
  • Cryptosporidiosis: infection with Cryptosporidium. Individuals will have watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, abdominal cramping, nausea, and fever that lasts 2–3 weeks, but the infection can be more persistent and severe in immunocompromised individuals. Diagnosis is with identification of the organism in a stool specimen. Cryptosporidiosis is generally self-limited, but it may require nitazoxanide in persistent or severe cases.  
  • Giardiasis Giardiasis Giardiasis is caused by Giardia lamblia (G. lamblia), a flagellated protozoan that can infect the intestinal tract. The hallmark symptom of giardiasis is foul-smelling steatorrhea. Patients who develop chronic infections may experience weight loss, failure to thrive, and vitamin deficiencies as a result of malabsorption. Giardia/Giardiasis: caused by Giardia lamblia Giardia lamblia Giardiasis is caused by Giardia lamblia (G. lamblia), a flagellated protozoan that can infect the intestinal tract. Giardia transmission occurs most commonly through consumption of cysts in contaminated water or through the fecal-oral route. Excystation occurs in the gastrointestinal (GI) tract, and trophozoites attach to the intestinal wall villi and cause malabsorption. Giardia/Giardiasis, a flagellated protozoan that can infect the intestinal tract. The hallmark symptom of giardiasis is foul-smelling steatorrhea. Individuals who develop chronic infections may experience weight loss, failure to thrive Failure to Thrive Failure to thrive (FTT), or faltering growth, describes suboptimal weight gain and growth in children. The majority of cases are due to inadequate caloric intake; however, genetic, infectious, and oncological etiologies are also common. Failure to Thrive, and vitamin deficiencies as a result of malabsorption Malabsorption Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion. The diagnosis is made through detection of Giardia organisms, antigens, or DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure in the stool. Management includes supportive treatment and antimicrobial therapy with metronidazole, tinidazole, or nitazoxanide. 
  • Traveler’s diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea: gastroenteritis that is usually caused by bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview or viruses in the local water, such as enterotoxigenic E. coli (ETEC) or norovirus Norovirus Norovirus is a nonenveloped, single-stranded, positive-sense RNA virus belonging to the Caliciviridae family. Norovirus infections are transmitted via the fecal-oral route or by aerosols from vomiting. The virus is one of the most common causes of nonbacterial gastroenteritis epidemic worldwide. Symptoms include watery and nonbloody diarrhea, nausea, vomiting, and low-grade fever. Norovirus. Symptoms occur after consumption of contaminated water or food and include watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, malaise, and abdominal cramping. The diagnosis is clinical, and the illness is self-limited.

References

  1. Leder, K., Weller, P.F. (2020). Microsporidiosis. UpToDate. Retrieved August 30, 2021, from https://www.uptodate.com/contents/microsporidiosis
  2. Centers for Disease Control and Prevention. (2019). DPDx—Microsporidiosis. Retrieved August 30, 2021, from https://www.cdc.gov/dpdx/microsporidiosis/index.html
  3. Pearson, R.D. (2020). Microsporidiosis. MSD Manual Professional Version. Retrieved August 30, 2021, from https://www.msdmanuals.com/professional/infectious-diseases/intestinal-protozoa-and-microsporidia/microsporidiosis
  4. Mazumder, S.A. (2019). Microsporidiosis. In Chandrasekar, P.H. (Ed.), Medscape. Retrieved August 30, 2021, from https://emedicine.medscape.com/article/221631-overview
  5. Han, B., Takvorian, P.M., Weiss, L.M. (2020). Invasion of host cells by microsporidia. Frontiers in Microbiology. https://www.frontiersin.org/articles/10.3389/fmicb.2020.00172/full

Study on the Go

Lecturio Medical complements your studies with evidence-based learning strategies, video lectures, quiz questions, and more – all combined in one easy-to-use resource.

Learn even more with Lecturio:

Complement your med school studies with Lecturio’s all-in-one study companion, delivered with evidence-based learning strategies.

User Reviews

0.0

()

¡Hola!

Esta página está disponible en Español.

🍪 Lecturio is using cookies to improve your user experience. By continuing use of our service you agree upon our Data Privacy Statement.

Details