The significance of 'Blastocystis' in different hosts

Abstract

Blastocystis is an obligate anaerobic, protistan parasite found in the intestinal tract of human and various other hosts. Blastocystis is placed within the stramenopiles. This diverse group also includes slime nets, water moulds and brown algae. The transmission of Blastocystis is believed to take place through the faecal-oral route. Waterborne transmission of Blastocystis through the use of untreated water or poor sanitary conditions has also been reported. Numerous epidemiological surveys have shown prevalence up to 10% of the population in developed countries and as much as 50-60% in developing countries. Differences in virulence among Blastocystis subtypes have been reported in a recent animal infection study. Blastocystis shows extensive genetic diversity and is divided into numerous genetic subtypes The parasite is commonly associated with gastrointestinal symptoms such as watery and mucous diarrhea, vomiting, and abdominal cramps and bloating. Epidemiological studies suggest an association between Blastocystis infection and irritable bowel syndrome. Irritable bowel syndrome (IBS) is identified as a functional bowel disorder in which abdominal pain or discomfort is associated with a defect or alteration in the consistency or frequency of stools. Diagnosis of IBS by physicians is carried out using symptom -based criteria known as the Rome criteria. To see whether there is any link between Blastocystis infection and irritable bowel syndrome (IBS), I have compared the frequency of subtypes of Blastocystis in IBS patients with those in the general population. In human population both UK and Libya showed similar distribution of Blastocystis subtypes 2 ST I, 2 and 3 are common in the two populations and ST3 has the highest frequency in UK while STI was the most common in Libya. Epidemiology studies on Blastocystis infection in animals have revealed high frequency of occurrence in cattle, pigs, primates and birds and it has often been suggested that Blastocystis infection is a zoonosis. In Libya, Blastocystis subtypes were detected from humans, birds and numerous mammals' hosts (camel, cow, sheep, goat, gazelle, Barbary sheep and gundi). Ten subtypes were detected (1, 2, 3, 5, 7,10,14, IS, 16, 17) and four new subtypes were found in cow, camel and gundi. Subtype I, 3, and 7 were in common between animal and human but subtypes 5, 10 and the four new subtypes were found only in animals. ST 2 was found in human only. Also I discovered four new hosts for Blastocystis from mouse deer, gundi, gazelle and barbary sheep. Both human and animal showed diversity in Blastocystis sUbtypes. Both human and animals become infected with same Blastocystis subtype and for this reason we need to find refined tool to differentiate between them, so I have developed MLST for Blastocystis subtype I based on mitochondrial DNA. Application ofMLST to 39 isolates from different host and different geographic place showed variation in the sequence of related isolates. Over all MLST proved to be a highly discriminatory and stable method for unambiguous characterization of Blastocystis.