# Food and Drinking Water as Sources of Pathogenic Protozoans: An Update
## 8 Blastocystis hominis  
Blastocystis hominis is an anaerobic intestinal protozoan of the Sar Stramenophiles clade, phylum Bigyra, family Blastocytidae [2]. It has a broad host range and is one of the most prevalent microeukaryotes worldwide [22; 24; 33; 211]. It is highly polymorphic and has four development stages--i.e., cyst, granular, vacuolar, and amoeboid forms--witha complex life cycle not yet described [211; 212]. All the forms were observed in stool or cultures, and the cyst is the dominant form in the environment responsible for transmission to the host. The division processes include binary fission with rosette formation, plasmodium, schizogony, endodyogeny, and budding. Culture in different media can be used for _B. hominis_ detection in stool after incubation at 37 \({}^{\circ}\)C for 2/3 days, but it is time-consuming. Moreover, it does not allow the growth of all genotypes in the sample. Other detection methods are light and scanning or transmission electron microscopy [213; 214]. Sequence analysis of the small subunit ribosomal RNA (SSU-rRNA) allowed the distinction of more than 30 subtypes (STs) of _B. hominis_ of which STs ST1 to ST8 were found both in humans and animals, ST9 was exclusively identified in humans, and ST10 to ST17 were identified only in animals [215]. A study regarding Southeast Asian populations was the first to report ST8, ST10, and ST14 in humans [216]. The most frequently isolated STs in humans were ST1 to ST4, with ST3 being the most common worldwide and the most pathogenic [22; 23; 212; 216; 217; 218; 219; 220; 221]. This invades the intestine by releasing a cysteine protease, which induces an increase of interleukin-8 (IL-8) in human intestinal epithelial cells. It was associated with 53.3% of the abnormal findings from colonoscopies--including colitis, CRC, inflammatory ulcer, and iletis--and with 57.7% of histopathological abnormal findings. ST1 was associated with 4.4% of abnormal observations from colonoscopies and 2.7% of abnormal observations from histopathology [34]. Subtype ST3 was significantly associated with chronic spontaneous urtic, and a statistically significant association was found between total IgE value and subtypes ST2 and ST3 [32]. Subtypes ST2 and ST1 showed higher intra-subtype variability than other subtypes [220; 222]. ST1 was widespread in various water resources in Asiatic countries, so it is probably transmitted through water contaminated by feces from different hosts [216]. A large number of individuals were colonized with ST7 genotypes in Asian countries, and the majority of them did not report contact with animals so they were likely infected after contact with bird droppings in water or on vegetables. A similar hypothesis could explain the high frequency of bovine ST10 and ST14 genotypes in the Vietnamese population [216]. It is estimated that about 1 billion people worldwide are infected with _B. hominis_ and that 50% of them remain asymptomatic carriers for months or years. _B. hominis_ is the most commonly detected eukaryote in human fecal samples, especially in hot climates, with reported prevalence values of 58% in Alexandria, Egypt; 67% in Morocco [34; 218; 220; 223]; and 100% in 25 children below five years of age examined in Medellin, Colombia [224]. The infection occurs via the ingestion of cysts present in water or food or by direct contact with animal reservoirs and symptoms manifest as lack of appetite, nausea, loose stools, abdominal pain, flatulence, bloating, constipation, and--less frequently--skin lesions or pruritus [225] and are self-limiting [24]. The pathogenicity of _B. hominis_ could derive from oxidative damage and invasive activity, as demonstrated in a rat model [34]. In a large case-control study carried out in Zaragoza, Spain, _B. hominis_ was detected in 9.18% of patients and anorexia, aerophagia, halitosis, urtic, anal itching, and dysppesia were significantly more common in those patients than in controls. Significant associations of _B.