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Title- Treatment failure in patients with chronic Blastocystis infection
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Running title- Blastocystis treatment failure
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Tamalee Roberts1,2*, John Ellis2 , John Harkness1, Deborah Marriott1 and Damien Stark1
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N.S.W, Australia
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Ultimo, N.S.W, Australia
Department of Microbiology, SydPath, St. Vincent’s Hospital, Victoria st, Darlinghurst,
i3 Institute, School of Medical and Molecular Sciences, University of Technology, Sydney,
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Vincent’s Hospital, Darlinghurst, 2010, N.S.W, Australia. Phone 61 2 8382 9209. Fax: 61 2
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8382 2989. E-mail: troberts@stvincents.com.au
Corresponding author. Mailing address: Tamalee Roberts, Department of Microbiology, St.
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ABSTRACT
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This article reports long term infection and treatment failure in 18 symptomatic
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individuals infected with Blastocystis spp. Patients were initially treated with either
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metronidazole, iodoquinol or triple combination therapy consisting of nitazoxanide,
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furazolidone and secnidazole. Following treatment, resolution of clinical symptoms did not
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occur and follow up testing revealed ongoing infection with the same subtype. Patients then
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underwent secondary treatment with a variety of antimicrobial agents but remained
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symptomatic with Blastocystis spp. still present in faeces. Sequencing of the SSU rDNA was
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completed on all isolates and four subtypes were identified in this group- ST1, ST3, ST4 and
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ST5. This study highlights the lack of efficacy of several commonly used antimicrobial
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regiments in the treatment of Blastocystis and the chronic nature of some infections. It also
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demonstrates the need for further research into treatment options for Blastocystis infection.
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INTRODUCTION
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Blastocystis is the most common enteric parasite present in humans (Tan et al. 2002).
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There have been up to 14 subtypes described in humans and animals with subtype (ST) 3
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being the predominant subtype identified in most epidemiological studies (Parkar et al. 2010;
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Meloni et al. 2011; Forsell et al. 2012; Roberts et al. 2013). Transmission has been attributed
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to the faecal-oral route as well as consumption of contaminated food and water (Leelayoova
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et al. 2004). Although there is still some debate about the pathogenicity of Blastocystis,
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symptoms attributed to Blastocystis infection include diarrhoea, abdominal pain, bloating and
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vomiting (Boorom et al. 2008; Stensvold et al. 2009). Due to the lack of knowledge of
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Blastocystis pathogenicity, treatment may not be offered resulting in ongoing symptoms and
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possible transmission to family and household members. Metronidazole is the most
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commonly prescribed drug for the treatment of Blastocystis with a large variation in efficacy
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ranging from 0%- 100% (Nigro et al. 2003; Moghaddam et al. 2005; Stensvold et al. 2008).
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Other antimicrobial agents which have been used to treat Blastocystis infection include
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paromomycin, nitazoxanide, iodoquinol and trimethoprim- sulfamethoxazole with varying
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results (Cimerman et al. 2003; Pasqui et al. 2004; Rossignol et al. 2005; Andiran et al. 2006).
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In this study, 18 symptomatic patients infected with Blastocystis were followed to
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determine the efficacy of antimicrobial treatment. We report emergence of treatment failure
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with metronidazole involving four different Blastocystis subtypes.
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METHODS
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Stool samples were collected from 18 individuals complaining of intestinal symptoms
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including diarrhoea, abdominal cramps and bloating. All samples were submitted to
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microscopy of a permanent modified iron haematoxylin stain according to the manufacturer’s
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instructions (Fronine, Australia). DNA was extracted using the Bioline Isolate fecal DNA kit
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as per manufacturer’s instructions, and underwent PCR for the detection of Blastocystis sp.
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using a previously described method (Stensvold et al. 2007). DNA sequence analysis was
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performed on all PCR products generated. PCR products were purified using the QIAquick™
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PCR purification Kit (Qiagen) as per the manufacturer’s instructions and sent to the
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Australian Genome Research Facility (Westmead Millennium Institute, Sydney) for
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sequencing in both directions and reads were assembled in to a consensus. The SSU rDNA
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sequences were then compared to those available in the GenBank database using the
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BLASTN program run on the National Centre for Biotechnology Information server
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(http://www.ncbi.nlm.nih.gov/BLAST). Samples also underwent PCR for the detection of
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Dientamoeba fragilis using a previously published method (Stark et al. 2010). PCR was
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performed on all samples positive for Entamoeba histolytica complex by microscopy to
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speciate (Fotedar et al. 2007). All samples were also screened for bacterial pathogens
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including Salmonella sp, Shigella sp, Vibrio cholerae, Campylobacter sp, Clostridium
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difficile and Aeromonas sp. Household members and pets were also screened for the presence
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of Blastocystis.
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RESULTS
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Eighteen patients were identified as infected with Blastocystis spp. by microscopy and
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confirmed by PCR. All patients were symptomatic. A total of four different subtypes (ST)
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were identified by sequencing- ST1 (n=1), ST3 (n=14), ST4 (n=2) and ST5 (n=1). No
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bacterial pathogens were isolated. Due to the chronic nature of infection no viral testing was
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performed. The cohort consisted of eight females and 10 males with an average age of 37
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years (6-62 years). Results summarised in Table 1.
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Patients 1-3 were family members living at the same residence. Symptoms of
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diarrhoea were described after the ingestion of water from a contaminated water tank from a
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property in rural New South Wales, Australia. Blastocystis sp. and Dientamoeba fragilis were
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detected by microscopy in all three patients. The patients were prescribed a dose of
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metronidazole 400mg three times daily but remained symptomatic following treatment.
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Follow- up testing one month post- therapy revealed that all patients were still infected with
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Blastocystis and patient 2 was still positive for D. fragilis. Subtyping of the isolates
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demonstrated the same subtypes were present in both the pre and post treatment samples
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(ST5 in patient 1 and ST3 in patients 2 and 3). All three patients were then treated with
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paromomycin (25mg/kg three times daily). Follow-up clinical consultation and subsequent
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stool samples revealed clearance of Blastocystis (and Dientamoeba fragilis in patient 2) with
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resolution of symptoms.
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Patient 4 was positive for Blastocystis ST1. This patient also had E. histolytica
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complex by microscopy which was subsequently confirmed as the non-pathogenic E. dispar
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by PCR. The patient complained of diarrhoea, nausea and abdominal pain. Initial treatment
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with metronidazole 400mg three times daily for seven days resulted in the clearance of E.
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dispar; however Blastocystis was still present and symptoms persisted. The patient was then
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prescribed a single dose of tinidazole but remained symptomatic and failed to clear
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Blastocystis. Finally norfloxacin was administered for four weeks. The patient reported a
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slight reduction in gastrointestinal symptoms and follow-up samples six months later showed
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that while the patient was no longer symptomatic, Blastocystis was still present in the stool
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but in very low numbers. The patient’s household contacts were tested for Blastocystis and
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both the housemate and pet dog tested negative for Blastocystis by microscopy and PCR.
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Patient 5 first presented with intestinal symptoms of diarrhoea and abdominal cramps
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after travelling to Borneo. A laboratory diagnosis of Blastocystis infection was made but the
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physician did not prescribe anti-parasitic treatment. The patients’ gastrointestinal symptoms
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continued for 12 months. The patient was subsequently diagnosed with Blastocystis (ST4) in
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the absence of any other pathogens. Treatment was commenced immediately with
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metronidazole 400mg of three times daily for ten days. Three months following treatment the
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patient was still symptomatic and follow-up samples confirmed that Blastocystis (ST4) was
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still present. The patient was then treated with ciprofloxacin. However, one year later
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gastrointestinal symptoms remained and the faeces was confirmed positive for Blastocystis
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ST4 by microscopy and PCR.
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Patient 6 had a history of abdominal cramps, vomiting, diarrhoea and bloating for
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three years. This patient saw several gastroenterologists and was diagnosed with irritable
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bowel syndrome without having any stool samples collected to exclude infective pathogens.
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After another year a stool sample was finally obtained and Blastocystis ST4 was identified.
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The patient was prescribed metronidazole 400mg three times daily. Symptoms partially
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subsided after treatment but two years later the patient had ongoing gastrointestinal
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symptoms and Blastocystis ST4 was still present. The patient had several animals which were
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all tested for Blastocystis. One chicken was positive for Blastocystis ST2 and two guinea fowl
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were positive for ST7.
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Patients 7-18 were all diagnosed with Blastocystis ST3 infection after seeing a
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gastroenterologist complaining of diarrhoea and abdominal pain. Five patients were initially
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treated with metronidazole (400mg three times daily) for 10 days, two with iodoquinol
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(630mg three times daily) and doxycycline (50mg twice daily) for 20 days, and five with a
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triple therapy of nitazoxanide, furazolidone and secnidazole. After treatment all patients
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continued to describe ongoing gastrointestinal symptoms. None of these patients owned pets
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or had other household members complaining of gastrointestinal symptoms.
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DISCUSSION
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There is increasing debate over the pathogenicity of Blastocystis with some studies
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stating that it is not pathogenic while others argue the validity of Blastocystis being
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considered a pathogen (Stark et al. 2007; Tan 2008; Roberts, Stark et al. 2013). One
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viewpoint is that some subtypes of Blastocystis may be pathogenic. This study’s results are
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consistent with that viewpoint, as we demonstrated by the presence of chronic symptoms in
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the absence of any other infectious agents (Hussein et al. 2008; Ozyurt et al. 2008; Roberts,
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Stark et al. 2013). This study reports treatment failure for 18 individuals identified with
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chronic Blastocystis infection. All patients complained of intestinal symptoms including
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diarrhoea, abdominal cramps and nausea. All patients were infected with Blastocystis and
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four different subtypes were identified from this group- one ST1, 14 ST3, two ST4, and one
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ST5.
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ST3 is the most common subtype found in most epidemiological studies and there has
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been a low association between subtype and symptoms. There have been several previous
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studies that have shown approximately 40- 60% of patients with ST3 have some sort of
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gastrointestinal symptom (Jones et al. 2009; Jantermtor et al. 2013; Roberts, Stark et al.
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2013). ST3 was the most common subtype isolated in this group and all patients had
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symptoms suggesting that this subtype is pathogenic. Although four patients had other
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parasites present on initial testing, after the first treatment these parasites were cleared while
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intestinal symptoms still persisted. No other pathogens were identified which suggests that
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Blastocystis was the probable cause of these symptoms.
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The three family members that presented with Blastocystis stated that symptoms
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started after the consumption of water from a water tank whilst on holiday in rural Australia.
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There were four members of the family that were infected with Blastocystis but after the
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initial treatment, one patient had resolution of symptoms and diagnostic methods confirmed
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that infection had been cleared. There is the possibility that re-infection rather than treatment
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failure occurred with the other three members of the family, but as two different subtypes
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were isolated within this group and that the fourth member did not have any further
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symptoms, this appears unlikely. It has been previously suggested that treatment failure could
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be mistaken for re-infection. This should be considered in all cases where symptoms persist
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(Stensvold et al. 2010).
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Although there have been several publications that have reported the eradication of
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Blastocystis with metronidazole, there have been few studies that have examined treatment
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failure in relation to subtype. Metronidazole is considered first-line treatment but reported
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success rates vary between 0%-100% (Stensvold, Smith et al. 2010). Metronidazole treatment
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failure has been reported in one patient with ST2 related urticaria and gastrointestinal disease
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(Vogelberg et al. 2010), a patient with severe intestinal symptoms associated with ST8
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(Stensvold, Arendrup et al. 2008), and six ST3 and one ST1 infections in patients whom
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presented with both urticarial and gastrointestinal symptoms (Jones, Whipps et al. 2009). A
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study of 11 symptomatic patients (five with ST1, four ST3, four ST4 and one ST6 with three
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mixed infections) treated with either metronidazole or trimethoprim/ sulfamethoxazole
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reported that no infection was cleared by treatment (Nagel et al. 2012). The 11 patients in our
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study who were initially treated with metronidazole were shown to have treatment failure
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along with the other seven patients treated with combination therapy. It has previously been
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suggested that some subtypes might be more resistant or are more likely to fail treatment than
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others. However our study, where four different subtypes were identified, suggests that any
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subtype could result in treatment failure. These results also highlight the fact that Blastocystis
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should be considered a pathogen as all patients noted severe symptoms in the absence of any
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other pathogen.
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This study also highlights the need for other treatment options for Blastocystis
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infection. One study has demonstrated the efficacy of Saccharomyces boulardii (250mg twice
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a day, Reflor) (Dinleyici et al. 2010) while others have reported treatment with
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trimethoprim/sulfamethoxazole with varying results; 22% eradication (Moghaddam,
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Ghadirian et al. 2005), 95% clearance (Ok et al. 1999) and 100% efficacy (Stensvold,
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Arendrup et al. 2008). Other studies suggest paromomycin is the most effective agent for
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clearing Blastocystis with up to 100% efficacy and in our study paromomycin also appeared
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to be effective (Armentia et al. 1993; Kick et al. 2002; Pasqui, Savini et al. 2004; Valsecchi
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et al. 2004; van Hellemond et al. 2012). A number of other studies have highlighted the
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variable efficacy of a number of antimicrobial agents including nitazoxanide, iodoquinol,
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tinidazole, emetine, pentamidine, iodochlorohydroxyquine and furazolidone (Markell &
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Udkow 1986; Romero Cabello et al. 1997; Moghaddam, Ghadirian et al. 2005; Rossignol,
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Kabil et al. 2005; Mirza et al. 2011).
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Both the Centre for Disease Control (CDC) and the Australian Therapeutic Guidelines
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refer to the clinical significance of Blastocystis as controversial. The CDC recommends
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treatment with metronidazole, trimethoprim/sulfamethoxazole or nitazoxanide, while the
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Therapeutic Guidelines recommend Blastocystis is treated with tinidazole, metronidazole or
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nitazoxanide. There is a minor comment that says that pregnant woman should be treated
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with paromomycin. Unfortunately paromomycin is not readily available in Australia and is
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accessed on a case by case basis via the Special Access Scheme. From this and other studies
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it would appear that the recommended treatments should be revised and that further studies
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are required to determine the most effective treatment options for Blastocystis infection.
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Blastocystis should be considered a potential pathogen when in the presence of symptoms
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and the absence of any other infectious agents. Metronidazole should no longer be considered
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the first line treatment prescribed.
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Host factors such as age and ethnicity may play a role in the severity and length of
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Blastocystis infection. The average age for patients in this group was 37 with only one child
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in the group. A previous study showed that clearance rates for Blastocystis infection increase
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as age increases and this could be a factor in this group with almost all of the patients above
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the age of 27 (Pipatsatitpong et al. 2012). It has previously been shown that IL-8 and IL-10
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single nucleotide polymorphisms (SNPs) play a role in Blastocystis infection (Olivo-Diaz et
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al. 2012). SNPs at IL-10 have shown to vary between populations and this may play a role in
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this Australian Caucasian study group in terms of disease and clearance (Meenagh et al.
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2002).
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CONCLUSION
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This study reports the failure of treatment to clear Blastocystis infections in 18
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patients treated with a number of different antimicrobial agents, in particular the
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recommended treatment agent, metronidazole. This study identified four different subtypes-
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ST1, ST3, ST4 and ST5 and demonstrated that there is not one particular subtype that has a
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higher rate of treatment failure. This study also highlights the pathogenic role of Blastocystis
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and reasserts that it should be considered a pathogen when found in conjunction with
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symptoms and no other infectious agents. Treatment failures highlight the need for further
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antimicrobial testing to be performed to expand therapeutic options for the management of
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Blastocystis when treatment failure does occur.
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Vogelberg, C., C. R. Stensvold, S. Monecke, A. Ditzen, K. Stopsack, U. Heinrich-Grafe & C.
Pohlmann (2010). "Blastocystis sp. subtype 2 detection during recurrence of gastrointestinal
and urticarial symptoms." Parasitol Int 59(3), 469-471.
345
346
347
348
349
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350
Table 1. Blastocystis subtype results, treatment and household contacts for patients
Patient
Age
Subtype Symptoms
(years)
Initial
Clearance
2nd
Treatment
of
treatment
line Clearance
symptoms
Time elapsed Household
of
between
symptoms
initial
Contacts
Travel
and
and subtype
latest positive
sample
1
6
5
Diarrhoea
Metronidazole
No
Paromomycin
Yes
7mths
2 ST3
Rural N.S.W
2
44
3
Diarrhoea
Metronidazole
No
Paromomycin
Yes
7mths
1 ST5, 1 ST3
Rural N.S.W
3
16
3
Diarrhoea
Metronidazole
No
Paromomycin
Yes
7mths
1 ST5, 1 ST3
Rural N.S.W
4
31
1
Diarrhoea,
Metronidazole
No
Tinidazole,
No
4 yrs
Housemate and South East Asia
nausea
and
norfloxacin
dog both PCR
abdominal
negative
pains
5
30
4
Diarrhoea and Metronidazole
No
Ciprofloxacin
No
3yrs
No
No
-
-
4yrs
Chicken
Borneo
abdominal
pains
6
27
4
Diarrhoea,
Metronidazole
ST2, 14
nausea,
bloating
Guinea
and
fowl
ST7
abdominal
pains
7
34
3
Diarrhoea and Metronidazole
No
-
-
1yr
No
-
No
-
-
1yr
No
-
No
-
-
1yr
No
-
No
-
-
1yr
No
-
No
-
-
1yr
No
-
abdominal
pains
8
44
3
Diarrhoea and Metronidazole
abdominal
pains
9
54
3
Diarrhoea and Iodoquinol,
abdominal
doxycycline
pains
10
48
3
Diarrhoea and Iodoquinol,
abdominal
doxycycline
pains
11
49
3
Diarrhoea and Metronidazole
15
abdominal
pains
12
26
3
Diarrhoea and Metronidazole
No
-
-
1yr
No
-
No
-
-
1yr
No
-
Diarrhoea and Triple therapy- No
-
-
1yr
No
-
-
-
1yr
No
-
-
-
1yr
No
-
abdominal
pains
13
38
3
Diarrhoea and Metronidazole
abdominal
pains
14
54
3
abdominal
nitazoxanide,
pains
furazolidone,
secnidazole
15
29
3
Diarrhoea and Triple therapy- No
abdominal
nitazoxanide,
pains
furazolidone,
secnidazole
16
39
3
Diarrhoea and Triple therapy- No
16
abdominal
nitazoxanide,
pains
furazolidone,
secnidazole
17
51
3
Diarrhoea and Triple therapy- No
abdominal
nitazoxanide,
pains
furazolidone,
-
-
1yr
No
-
-
-
1yr
No
-
secnidazole
18
62
3
Diarrhoea and Triple therapy- No
abdominal
nitazoxanide,
pains
furazolidone,
secnidazole
351
17