Giardiaintestinalis and B. hominis infections are common worldwide. Rates of infection in the current study are relatively higher than those reported in developed countries (Harhay et al. 2010) but concur with a previous study in Egypt indicating a constant unchanging pattern of infection (Omaran et al. 2013). Neither age nor gender-related differences were detected suggesting equal exposure and/or susceptibility to infection. Generally, dissemination of intestinal protozoa reflects the sanitary, hygienic, and socio-economic standards of the population as they are transmitted primarily through the faeco-oral route ( Fletcher et al. 2012).
The parasitological and clinical cure rates of nitazoxanide observed in the present study agree with previous reports which reported that nitazoxanide rapidly and efficiently reduced the duration of illness in G. intestinalis infected patients even before the parasitological cure was achieved (Rossignol et al. 2005; Escobedo and Cimerman 2007; Ordóñez-Mena et al. 2018). Treatment failure that was observed in four children may be attributed to high infection intensity and/or variable drug sensitivity among genetically different isolates. An in vitro study illustrated that nitazoxanide had highest efficacy against Blastocystis subtype 1 isolate at 0.1 mg/ml. However, at an increased concentration, subtype 5 was more sensitive to the treatment with an efficacy of 95.1 % (Rossignol et al. 2012; Girish et al. 2015).
Despite significant improvement of symptoms in nitazoxanide-treated children, abdominal pain persisted after clearance of G. intestinalis infection in one child. A similar observation was previously reported after treatment of G. intestinalis infection acquired in a waterborne outbreak. Possible explanations include bacterial overgrowth, prolonged lactose intolerance, or post-infectious functional disorder (Hanevik et al. 2007).
High calprotectin level in feces is an indicator of neutrophil migration towards the intestinal tract and it correlates with the degree of intestinal mucosal inflammation (D'Angelo et al. 2017). Data of the present study indicate that G. intestinalis and B. hominis infection had no significant impact on calprotectin levels in children. The present result is consistent with a recent study in rural Bangladesh demonstrating a non-significant association between the presence of G. intestinalis in stool and high FC among 203 children (George et al. 2018). Among Guatemalan children, neither the presence nor the intensity of G. intestinalis infection had an association with FC ( Soto-Méndez et al. 2016). Fecal myeloperoxidase, another marker of neutrophil inflammation, was found to be unexpectedly lower in children with giardiasis (McCormick et al. 2017). Other authors suggested that G. intestinalis infection is classically characterized by little or no inflammatory intestinal response ( Roxström-Lindquist et al. 2006).
Regarding B. hominis, a recent study in Italy found no association between B. hominis colonization and FC level in both symptomatic and asymptomatic patients (Sulekova et al. 2018). Nieves-Ramírez et al. (2018) detected even a significantly lower calprotectin concentration among B. hominis colonized compared to non – colonized persons. In contrast to these studies, Tibble et al. (2002) examined eight children with infectious diarrhea, with seven having confirmed giardiasis and observed excess FC level.
The extent of gut inflammation may be related to the clinical presentation of the studied patients. All children included in the present study were complaining of abdominal pain and none had diarrhea. Sulekova et al. (2018) found that FC level in B. hominis infection was significantly higher in patients with diarrhea than in the asymptomatic group or those with other gastrointestinal symptoms. They suggested the use of calprotectin as a marker for B. hominis pathogenicity. Furthermore, the present study was carried out in an endemic area with possibly high rates of reinfection. Reduction in inflammatory response and protection against disease severity probably occur with recurrent G. intestinalis infection (Kohli et al. 2008).
Abnormally elevated FC levels were observed in the present study in few children (two infected with G. intestinalis and three with B. hominis. Similarly, A study in Iraq reported FC positive test results in 10 out of 47 G. intestinalis cases and in one out of 31 B. hominis positive samples (Salman et al. 2017). In an Australian study, mild inflammation of the duodenal mucosa was observed in only 3.7% of 567 G. intestinalis patients ( Oberhuber et al. 1997).
The parasite genotype may determine the degree of intestinal inflammation. G. intestinalis assemblage B has been linked to extensive mucosal damage and infiltration by inflammatory cells while G. intestinalis assemblage A does not induce overt intestinal pro-inflammatory responses and may attenuate intestinal neutrophil recruitment (Campbell et al. 2004; Cotton et al. 2014). Differential induction of the anti-inflammatory cytokine, IL-10 by Blastocystis subtypes was also reported (Yakoob et al. 2014).
Post-treatment FC level was higher in G. intestinalis infected than in B. hominis infected children. Moreover, a slightly elevated FC level was observed in a G. intestinalis infected child despite clearance of infection. Slow recovery of mucosal inflammation was previously reported following treatment of G. intestinalis infection acquired in an outbreak (Asseman et al. 1999). A histopathological study using murine models demonstrated increased neutrophils infiltration and myeloperoxidase activity throughout the gut, 35 days after Giardia elimination ( Campbell et al. 2004). On the other hand, the normal post-treatment FC level in B. hominis infected children denotes recovery of all affected children.
A limitation in the study was the difficulty in recruiting children with single Giardia infection; associated Blastocystis infection was detected in 9 out of 21 Giardia infected children (42.9 %) using the direct microscopic method and culture in Jones's medium. Due to the small number of children with a single infection who were initially examined for FC level, the pre and post-treatment comparison was performed to confirm the study findings.
In conclusion, both G. intestinalis and B. hominis infections appear to cause no remarkable intestinal inflammation. However, they may elicit abnormally elevated levels in a subset of children who may be erroneously diagnosed as having inflammatory bowel disease.