Researchers have published conflicting reports concerning whether Blastocystis causes symptoms in humans, with one of the earliest reports in 1916. The incidence of reports associated with symptoms began to increase in 1984, with physicians from Saudi Arabia reporting symptoms in humans and US physicians reporting symptoms in individuals with travel to less developed countries. A lively debate ensued in the early 1990s, with some physicians objecting to publication of reports that Blastocystis caused disease. Some researchers believe the debate has been resolved by finding of multiple species of Blastocystis that can infect humans, with some causing symptoms and others being harmless (see Genetics and Symptoms). A few of most commonly reported symptoms are: * abdominal pain * itching, usually anal itching * constipation * diarrhea * watery or loose stools * weight loss * fatigue * flatulence Some less commonly reported symptoms include: * Skin rash * Arthritic symptoms and joint pain * Intestinal inflammation Variation in severity Researchers have sought to develop models to understand the variety of symptoms seen in humans. Some patients do not have symptoms, while others report severe diarrhea and fatigue. A number of researchers have investigated the possibility that some species of Blastocystis are more virulent than others. An Italian researcher reported differences in the protein profiles of isolates associated with chronic and acute infection. A research team from Malaysia reported that isolates from symptomatic patients produced large amoeboid forms that were not present in isolates from asymptomatic patients. The development of a classification system for Blastocystis in 2007 produced a series of studies investigating this possibility. The studies that followed generally found that no specific "pathogenic" or nonpathogenic species of Blastocystis exists. One study investigated the subtypes found in patients with irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and chronic diarrhea, and found the subtypes in these diseases were similar (subtypes 2 and 3), and have also been found in asymptomatic carriers. The researchers concluded that host factors, such as age and genetics, may play the dominant role in determining the symptoms seen in the disease. Associations Blastocystis colonisation is positively associated with IBS and is a possible risk factor for developing IBS. A study of IBS patients in the Middle East showed a "significantly increased" immune reaction in IBS patients to Blastocystis, even when the organism could not be identified in stool samples. The following reports have linked Blastocystis infection to inflammatory bowel disease: * A study using riboprinting identified specific types of Blastocystis as associated with inflammation. * A case report described IBD in conjunction with Blastocystis infection. * Three research groups have reported experimental infection of mice with Blastocystis produces intestinal inflammation.
Blastocystosis
Hematidrosis
Nemosis
Toxocariasis
Bertielliasis
Porocephaliasis
Helminthiasis
Acariasis