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Blastocystis hominis, Molecular Detection and Subtyping

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Blastocystis hominis molecular detection is used for laboratory confirmation of the presence of the parasites in the gastrointestinal tract as well as to determine the subtype of the microorganism.

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Blastocystis parasites are commonly found in the digestive tract in species of several animal groups. It is the most prevalent protozoon found in human fecal samples and has widespread geographic distribution.

The role of Blastocystis as a human pathogen remains unclear, but studies have associated Blastocystis with acute or chronic digestive disorders. Knowledge about its life cycle is equally limited, and various morphological forms, including the cyst and vacuolar forms that are commonly found in feces, have previously been described. The cyst represents the smallest (2 to 5 μm in diameter) form of the organism and is responsible for the environmental dissemination of the parasite. The results of in vivo experiments previously performed with mice have suggested that cysts represent the infectious stage, but the most common form detected during parasitological examination of feces is the vacuolar form (2 to 200μm in diameter). The vacuolar form also represents the major parasitic stage observed in in vitro cultures of Blastocystis parasites.

Recent molecular studies revealed high genetic diversity among Blastocystis strains, identifying 10 different subtypes (ST-1 to ST-10) that are defined by the sequence of a 600 bp region of the gene encoding the 18S rRNA of the small ribosomal subunit (SSU rRNA). Subtype distribution differs among hosts such as mammals and birds, but recent observations indicate that numerous subtypes previously considered “zoonotic” are also found in humans. Studies of zookeepers suggest direct transmission of Blastocystis from animals to humans, while cyst detection in sewage evidence waterborne transmission. Subtypes ST-1 to ST-9 have been recovered from human fecal samples, with ST-3 as the predominant ST followed by ST-1, ST-2, and ST-4. Subtypes ST-5 to ST-9 are rarely found in human feces. Some subtypes have a particular distribution, such as avian subtypes ST-6 and ST-7, which are more frequently found in Asia and the Middle East. Prevalence levels also differ between areas and are higher in developing countries, reaching 60% in Indonesian children. Blastocystis species are also widely observed in developed countries, including the United States (23%), France (3%), the United Kingdom (3.9%), and Greece (1.8%).

Blastocystosis is generally associated with nonspecific symptoms such as diarrhea and/or abdominal pain. There are reports of acute gastroenteritis and cutaneous disorders in some cases, while other studies have indicated that blastocystosis may be correlated to chronic symptoms. There is evidence that Blastocystis species are associated with irritable bowel syndrome. Numerous studies have tackled the pathogenic ambivalence of Blastocystis. Most of these data focused on parasite factors in an attempt to correlate parasite density and/or subtype with pathogenic power, with few studies addressing host factors. A high prevalence of Blastocystis in HIV patients was previously found to be associated with clinical relevance in severely immunocompromised subjects.

Risk factors for Blastocystis hominis infection

Consuming water or ice that is contaminated with the parasite. The most common sources of contaminated water include:

  • Streams and rivers
  • Lakes
  • Poorly-maintained wells
  • Consuming food washed or cooked with contaminated water
  • Traveling to countries with poor sanitation standards 
  • Having close contact with infected individuals
  • Swimming in potentially contaminated water
Signs and symptoms of Blastocystis hominis infection

Many individuals with Blastocystis hominis Infection may never show any signs and symptoms of infection. The parasite can be present in normal, healthy individuals asymptomatically.

In case of symptoms, those that may be associated with Blastocystis hominis infection include: 

  • Nausea and fatigue
  • Loss of appetite
  • Bloating, excessive gas (flatulence)
  • Abdominal cramps
  • Hives or other skin rashes
  • Joint pain
  • Constipation or greasy stools that float
  • Diarrhea

The symptoms can begin and last for any period of time following infection.

Recent epidemiological data demonstrate the association of Blastocystis with disorders, such as:

  • Irritable bowel syndrome (IBS)
  • Urticaria
How is Blastocystis hominis infection treated?

Individuals with Blastocystis hominis Infection without symptoms do not need to undergo any treatment. However, in individuals presenting symptoms, the treatment measures may include the following:

  • Antibiotics
  • Antiprotozoal medications 
  • A combination of medications may be necessary, in some cases

If medications are ineffective, further diagnostic procedures may be necessary to check for other causes of symptoms

Furthermore, some strains develop resistance against currently recommended drugs, such as metronidazole; therefore, the use of natural remedies or special diets has many positive aspects that may address this problem.

The literature has revealed that garlic, ginger, some medicinal plants, and many spices contain the most effective organic compounds for parasite eradication.

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