Oh my aching gut: irritable bowel syndrome, Blastocystis, and asymptomatic infection - PubMed (original) (raw)

Oh my aching gut: irritable bowel syndrome, Blastocystis, and asymptomatic infection

Kenneth F Boorom et al. Parasit Vectors. 2008.

Abstract

Blastocystis is a prevalent enteric protozoan that infects a variety of vertebrates. Infection with Blastocystis in humans has been associated with abdominal pain, diarrhea, constipation, fatigue, skin rash, and other symptoms. Researchers using different methods and examining different patient groups have reported asymptomatic infection, acute symptomatic infection, and chronic symptomatic infection. The variation in accounts has lead to disagreements concerning the role of Blastocystis in human disease, and the importance of treating it. A better understanding of the number of species of Blastocystis that can infect humans, along with realization of the limitations of the existing clinical laboratory diagnostic techniques may account for much of the disagreement. The possibility that disagreement was caused by the emergence of particular pathogenic variants of Blastocystis is discussed, along with the potential role of Blastocystis infection in irritable bowel syndrome (IBS). Findings are discussed concerning the role of protease-activated receptor-2 in enteric disease which may account for the presence of abdominal pain and diffuse symptoms in Blastocystis infection, even in the absence of fever and endoscopic findings. The availability of better diagnostic techniques and treatments for Blastocystis infection may be of value in understanding chronic gastrointestinal illness of unknown etiology.

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Figures

Figure 1

Figure 1

Patients adapt to chronic gastrointestinal illness, which is found at an increasingly high rate in the United Kingdom[117]. The "Mobilet" was developed by an IBS patient and consists of a toilet in an enclosed structure which can be towed behind a vehicle to facilitate travel by persons with severe chronic diarrhea. The UK journal Gut Reaction reported that the device sells for £1349 [19].

Figure 2

Figure 2

Although IBS is ostensibly a functional disorder, IBS patients have been found to be infected with Blastocystis at statistically significant levels in Italy[37], Pakistan[25], the United Kingdom[24,26]but not Thailand [27]. A study from Pakistan identified an elevated serum antibody response to Blastocystis in patients from whom Blastocystis could not be cultured [36]. The figure for the UK includes IBS and chronic GI illness. Numbers shown represent the total number of participants in the study (symptomatic and asymptomatic).

Figure 3

Figure 3

Comparison of the frequency of symptoms seen in blastocystosis[1]to those seen in IBS[28]. Host genetics may influence expression of symptoms in IBS [29].

Figure 4

Figure 4

Comparison of the prevalence of IBS and chronic abdominal pain to the frequency of detection of Blastocystis in Japan[22,30], Canada[31,32], United States[14,33], Mexico[21,34], and Brazil[22,35].

Figure 5

Figure 5

Distribution of subtypes in Blastocystisfound in the general Chinese population[43], patients at a clinical lab in Denmark[44], samples from a hospital in Greece[46], patients in Egyptian lab [48]. These subtypes are associated with various non-human hosts [12,74].

Figure 6

Figure 6

Rash from 39-year old US male diagnosed with chronic blastocystosis acquired domestically[60]. Skin rash in Blastocystis infection has been described as recurrent [65] and intensely pruritic [67]. Diagnosis of blastocystosis was by exclusion: eleven ova and parasite exams (trichrome staining) performed at clinical laboratories from 2003–2006 were negative except for findings of Blastocystis. Colonoscopy, endoscopy, and gluten challenge test were negative. The infection was unresponsive to metronidazole, nitazoxanide, and TMP/SMX. The isolate was genotyped as Blastocystis sp. subtype 3 in a 2007 study [49].

Figure 7

Figure 7

(LEFT) Blastocystisin simple smear. Researchers have cited the non-descript appearance of Blastocystis as one reason for the low sensitivity of clinical diagnostic methods, along with the possibility that not all stages have been documented [52]. (RIGHT) The classic diagnostic form of Blastocystis found in the stool of patients varies in size from 6 to 40 μm. The parasite is characterized by a central body (blue) that morphologically resembles a vacuole. The central body pushes the nuclei to the periphery of the cell. The central body is a reservoir for proteases [83] and may serve other functions as well. Photos courtesy of Dr. Hanaa Moussa, Cairo University.

Figure 8

Figure 8

The characteristics of common enteric protozoa reported in study of 5792 specimens from US patients collected in 2000[14]. Studies from the 1980's reported Blastocystis was usually found as a co-infection with Giardia or Entamoeba histolytica in symptomatic patients [139,140], which was not the case in 2000 [14]. In 2000, the number of symptomatic patients who were found to be singly infected with Blastocystis (400) exceeded the number of samples found positive for Cryptosporidium, Giardia, and Entamoeba histolytica combined. Patients singly infected with Blastocystis were as likely to be symptomatic as patients singly infected with Cryptosporidium (69% vs. 70%) [14].

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