• The prevalence of Blastocystis hominis infection varies widely across different populations, with rates ranging from 5% to 100%. Blastocystis hominis is considered one of the most common intestinal parasites worldwide, with an estimated global burden of over 1 billion cases. 
• Blastocystis hominis infection can affect all age groups, but it is more common in children than adults. Studies have reported prevalence rates of up to 50% in children under 10. 
• Geographical distribution: B. hominis infection is found worldwide, but prevalence rates are higher in developing countries with poor sanitation and hygiene. 
• Risk factors include poor hygiene, unsafe water and food, close contact with animals, and travel to endemic areas. 
• Asymptomatic carriers of B. hominis are common, and some studies have reported prevalence rates of up to 50%. Blastocystis hominis infection has been linked to irritable bowel syndrome and other inflammatory bowel diseases. 

• Kingdom: Protista 
• Phylum: Metamonada 
• Class: Blastocystea 
• Order: Blastocystida 
• Family: Blastocystidae 
• Genus: Blastocystis 
• Species: Blastocystis hominis 

Structure: 

• Blastocystis hominis is a unicellular protist with a relatively simple cell structure. It is a spherical or oval-shaped organism that can range from 5 to 25 microns in diameter, depending on the stage of its life cycle. 
• The structure of B. hominis is composed of a cell membrane comprising a lipid bilayer, which encloses the cytoplasm. The cytoplasm is a gel-like substance that contains various organelles, including a single nucleus that contains the organism’s genetic material. The cytoplasm also contains mitochondria responsible for energy production through cellular respiration. 
• B. hominis also has a Golgi apparatus responsible for processing and packaging proteins. The endoplasmic reticulum is another organelle in the cytoplasm involved in protein synthesis, folding, and transport. 
• Blastocystis hominis does not have a cell wall but may possess one or more vacuoles for storage or excretion purposes. The organism can exist in different forms, including vacuolar, granular, and amoeboid forms, with the vacuolar form being the most common. 

• Blastocystis hominis is known to exhibit a high degree of genetic diversity. As a result, it is classified into several subtypes or “STs” based on the genetic analysis of the organism. There are 17 identified B. hominis subtypes labeled ST1 to ST17. Differences in their genetic sequences define these subtypes and vary in their distribution, prevalence, and potential pathogenicity. 
• Some studies suggest that specific subtypes may be more commonly associated with clinical symptoms, while others may be more probable to be found in asymptomatic carriers. 
• For example, ST3, ST4, and ST7 have been linked to symptomatic infection, while ST1, ST2, and ST6 are more commonly associated with asymptomatic carriage. 

• Adherence to the intestinal lining: Blastocystis hominis can adhere to the intestinal epithelium, which may disrupt the intestinal barrier and lead to inflammation and tissue damage. 
• Production of toxins: Some B. hominis have been shown to produce toxins, which may contribute to symptoms like diarrhea and abdominal pain. 
• Disruption of the gut microbiota: B. hominis may alter the composition and function of the gut microbiota, which can have a wide range of effects on host health and disease. 
• Immune response: B. hominis can trigger an immune response in the host, which may contribute to inflammation and tissue damage. 

• Immune response: The host immune system controls Blastocystis hominis infection. When the parasite invades the gut, the immune system mounts a response to eliminate it. The immune response involves the activation of various immune cells and the assembly of cytokines and antibodies. 
• Intestinal mucus: The mucus layer covering the intestinal epithelium is a physical barrier against B. hominis invasion. The mucus contains antimicrobial peptides and antibodies that can neutralize the parasite. 
• Gut microbiota: The gut microbiota plays a vital role in protecting against B. hominis infection. Studies have shown that the gut microbiota can modulate the immune response to the parasite and prevent colonization. 
• Host genetic factors: Some studies suggest that certain host genetic factors may play a role in susceptibility to B. hominis infection. For example, individuals with specific genetic variants of the HLA gene may be more susceptible to infection. 

The clinical manifestations of Blastocystis hominis infection are variable, and not all infected individuals develop symptoms. Whenever symptoms occur, they can range from mild to severe and can include: 

• Gastrointestinal symptoms: The most common symptoms are gastrointestinal and include diarrhea, abdominal pain, bloating, and flatulence. Some individuals also face nausea, vomiting, and loss of appetite. 
• Skin and allergy symptoms: B. hominis infection has been associated with various skin conditions, including urticaria (hives), eczema, and pruritus (itching). Some individuals may also experience allergic symptoms, such as rhinitis (runny nose), cough, and asthma. 
• Fatigue and malaise: Some individuals may experience fatigue, malaise, and other non-specific symptoms. 

• Microscopic examination: A stool sample is examined under a microscope to identify the presence of the parasite. This method involves staining the sample with a specific dye and observing the characteristic morphology of B. hominis. 
• Stool culture: A stool sample is cultured in the laboratory to identify the growth of B. hominis. This method involves incubating the stool sample on specific media that promotes the parasite’s growth. 
• Polymerase chain reaction (PCR): A stool sample is analyzed using PCR technology to detect the DNA of Blastocystis hominis. This method involves amplifying the DNA of the parasite in the stool sample and detecting it using specific probes. 
• Antigen detection: Stool samples can be tested for the presence of B. hominis antigens using specific antibodies. This method is usually rapid and can provide results within a few hours. 
• Serological tests: Blood tests may be performed to detect antibodies against B. hominis. These tests are not widely used due to their low sensitivity and specificity. 

• Practice good personal hygiene: Frequent hand washing with soap and water, mainly before preparing food and eating, can help prevent the spread of Blastocystis hominis infection. 
• Avoid consuming contaminated water: Drinking clean and safe water, especially when traveling to areas where water quality is questionable, can help reduce the risk of B. hominis infection. 
• Cook food thoroughly: Proper cooking of food, especially meat, can help kill any potential parasites, including Blastocystis hominis. 
• Practice safe sex: Using condoms during sexual intercourse can help prevent the transmission of B. hominis and other sexually transmitted infections. 
• Maintain good sanitation: Ensuring proper sanitation practices in both domestic and community settings can help prevent the spread of Blastocystis hominis infection. 

• https://pubmed.ncbi.nlm.nih.gov/7777913 
• https://en.wikipedia.org/wiki/Blastocystis