# Food and Drinking Water as Sources of Pathogenic Protozoans: An Update
## 7 Entamoeba spp  
The protozoan species _Entamoeba histolytica_, _E. dispar_, _E. moshkovskii_, and _E. hangladeshi_ are referred to as the _Entamoeba_ complex, are morphologically identical, and can all cause disease, with _E. histolytica_ showing the highest pathogenic potential [179]. _E. gingivalis_ is the only _Entamoeba_ species known to colonize the human oral cavity, and evidence suggests its involvement in periodontitis [180]. _Entamoeba coli_ and _E. hartmanii_ are considered non-pathogenic species, also transmitted through the fecal-oral route [181]. These protozoans belong to the Entamoebidae family of the Eukaryota clade Amoebozoa, phylum Evosea [2]. _E. histolytica_ can cause invasive intestinal and extrainetesinal infections and has a simple life cycle involving a quadrinucleated cyst, which is shed with feces by infected hosts, and, when ingested with contaminated water or food, undergoes excystation in the large intestine, releasing trophozoites that reproduce via binary fission. These penetrate the intestinal mucosa, where they form typical flask-shaped ulcers. From the intestine trophozoites can have access to the portal circulation reaching the liver where they can cause an inflammatory reaction that leads to hepatocyte necrosis and abscess formation (amoebic liver abscess, ALA). The progression of the disease depends on factors such as intestinal microbiome composition, dysbiosis, and reduced cell-mediated immunity. The intestinal infection is more frequent, and most infected individuals are asymptomatic [7].  
The first step of intestinal invasion by _E. histolytica_ is breaching the mucus layer by modulating the transcription of the MUCIN2 gene in host epithelial cells. Once in contact with epithelial cells, the amoeba induces apoptosis, causing epithelial damage, tissue invasion, and strong upregulation of the inflammatory cytokine interleukin 8 (IL-8), with neutrophil infiltration. The amoeba also actively increases the production of host matrix metalloproteinases (MMPs) that break down the extracellular matrix favoring the translocation of intestinal bacteria into the tissue and their dissemination in organs with risk of systemic disease [182]. Cysteine proteases, prostaglandin E2, and amoebaepores play important roles in trophozoite colonization and intestinal mucosa invasion by _E. histolytica_. Gal-lectin and a 21 KDa surface protein are involved in extrainetesinal dissemination [183]. _E. histolytica_ genotypes are distinguished on the basis of polymorphic repetitive markers, such as tRNA-linked short tandem repeat (STR), serine-rich _E. histolytica_ protein (SREHP) gene and the chitin (CHI) gene. These markers can discriminate between strains of different geographical origins with high resolution [184]. Multilocus sequence typing (MLST) of non-repetitive markers--such as _kep1_ and _kep2_, encoding plasma membrane proteins involved in the interaction of the parasite with the brush border of enterocytes, and amoebapore C (_apc_)--can be adopted to distinguish between genotypes associated with different clinical outcomes, namely asymptomatic infection, diarrhea, and ALA [184]. The tRNA-linked STR at different loci were also recently exploited to differentiate _E. histolytica_ haplotypes associated to different clinical manifestations [185]. Moreover, single nucleotide polymorphisms (SNPs) in KERP1 and amoebapore C can distinguish among _E. moshkovskii_ genotypes able to cause diarrhea [186].