Balantidium coli
Dongyou Liu in Handbook of Foodborne Diseases, 2018
Balantidium coli has two stages in its life cycle: trophozoites and cysts (Figure 50.1). Trophozoites are an active form of the protozoan.13 Being pleomorphic, they vary greatly in size and shape depending on the amount of food ingested, and may appear rounded and large or elongated and thin or small.4,14 Overall, trophozoites can range from 30 to 300 μm in length and from 30 to 100 μm in width.4 Trophozoites have an anterior region that is more tapered and a posterior region that is more rounded. At the anterior end the parasite has a funnel-shaped depression known as the peristome, which leads to the cytostome (also called the mouth) and the cytopharynx, that is, the interior oral cavity (Figure 50.2).13,15
Giardia lamblia
Peter D. Walzer, Robert M. Genta in Parasitic Infections in the Compromised Host, 2020
Infrequently, syndromes related to the biliary system may accompany giardiasis. These syndromes include nonopacification of the gall bladder on oral cholescystography (162) and cholecystitis (163). The presence of trophozoites in the gall bladder and biliary passages, which was reported over 50 years ago (164), may contribute to these conditions. Russian and Polish clinicians also have reported cholecystitis (165-167) as well as pancreatitis (168) in association with giardiasis. A case of granulomatous heptatitis has been attributed to infection with G. lamblia (169). The mechanism for the association of these biliary tract, pancreatic, and hepatic conditions with giardiasis may involve trophozoites ascending the common bile duct and then inducing an inflammatory reaction in the end organs. In contrast, the identification of G. lamblia trophozoites in the hepatic vessels of rodents (170) suggests that the parasite also could gain access to the liver via the portal venous system after penetrating the intestinal mucosa. However, this route of access to the liver seems exceedingly unlikely, since in humans trophozoites do not enter the vascular system.
Pathobiology of Amebiasis
Roberto R. Kretschmer in Amebiasis: Infection and Disease by Entamoeba histolytica, 2020
Despite the fact that Entamoeba histolytica has been known to be the cause of human amebiasis for more than 100 years, and that current estimates of the disease reveal a prevalence of 400 × 106 cases per year (approximately 10% of the world population1) there is still much that is not adequately understood in this peculiar host/parasite relation. The life cycle of the parasite lacks sexual stages and intermediate hosts, and oscillates between two different forms, the infective cyst and the vegetative trophozoite, but the conditions required for both encystation and excystation are not known. This has proven a formidable stumbling block for the experimental reproduction of the disease, which has yet to be satisfactorily accomplished. The trophozoite reproduces by binary fission, but the organization of its nuclear DNA during reproduction, and even the existence of chromasomes, are still undecided. The life cycle of E. histolytica does not require a tissue invasive and destructive stage, since the parasite can survive and reproduce in the lumen of the intestine, undergo encystment and pass with the stools to the outer world. But in some cases the trophozoites destroy the intestinal mucosa and invade the intestinal wall, causing what is known as invasive intestinal amebiasis. Again, virtually nothing is known about the conditions that permit or inhibit such aggressive behavior of the parasite. In fact, there is still controversy over the real existence of permanently nonpathogenic and pathogenic strains of E. histolytica.
Curcuma longa ethanol extract and Curcumin inhibit the growth of Acanthamoeba triangularis trophozoites and cysts isolated from water reservoirs at Walailak University, Thailand
Published in Pathogens and Global Health, 2020
Watcharapong Mitsuwan, Chooseel Bunsuwansakul, Theodore Ebenezer Leonard, Sawanya Laohaprapanon, Kruawan Hounkong, Kingkan Bunluepuech, Chalermpon Kaewjai, Tooba Mahboob, Chandramathi Sumudi Raju, Mahaveer Dhobi, Maria de Lourdes Pereira, Muhammad Nawaz, Christophe Wiart, Abolghasem Siyadatpanah, Roghayeh Norouzi, Veeranoot Nissapatorn
Free-living amebae belonging to the genus Acanthamoeba are protozoa ubiquitously in nature such as water and soil. The protozoa are causative agents of several diseases including granulomatous amebic encephalitis [1–3] and amebic keratitis [4]. The occurrence of Acanthamoeba keratitis in contact lens users can cause severe vision loss and complete blindness [5]. In addition, the infection caused by the organism is severe in immunocompromised patients. The parasite has two stages of growth including trophozoite and cyst. Trophozoite is a vegetative amoeba form moving by amoeboid locomotion. Cyst form is dormant stage that survives in harsh environment conditions such as lack of nutrients. Acanthamoeba cysts are classified into three groups including astronyxids, polyphagids, and culbertsonids [6]. The cysts contain two strong layers of cyst wall including ectocyst and endocyst walls. Acanthamoeba cysts have been reported to resist to antimicrobial substances [7,8]. Therefore, the treatment of Acanthamoeba infections is difficult due to its double-walled cyst layers.
Novel therapeutic opportunities for Toxoplasma gondii, Trichomonas vaginalis, and Giardia intestinalis infections
Published in Expert Opinion on Therapeutic Patents, 2023
Francesca Arrighi, Arianna Granese, Paola Chimenti, Paolo Guglielmi
Giardia intestinalis (syn., G. lamblia, G. duodenalis) is, similar to T. vaginalis, a flagellate protozoan involved in the insurgence of intestinal infection called giardiasis [32]. Its life cycle includes trophozoite and cystic forms. After ingestion of giardia cysts, typically via contaminated food or water or via the fecal-oral route, they direct to the stomach, where host proteases and acidic pH weaken cyst walls beginning the excystation, that is complete in the upper small intestine [33]. The released vegetative trophozoites divide by binary fission and attach to the small intestinal lumen epithelium via a ventral adhesive disk. The completion of life cycle is reached when trophozoites, after detachment, move along the GI tract where they are exposed to bile, and initiate encystation to create new cysts that are excreted into the environment [34]. Giardia intestinalis infection can occur without symptoms or exhibiting acute watery diarrhea, nausea, epigastric pain, and weight loss [32].
Brain-eating amoebae: is killing the parasite our only option to prevent death?
Published in Expert Review of Anti-infective Therapy, 2022
Naveed Ahmed Khan, Jibran Sualeh Muhammad, Ruqaiyyah Siddiqui
Depending on the environmental conditions, it exhibits three phenotypic stages: (i) under favorable conditions it transforms into a trophozoite/amoeboid form during which it feeds, propagates, and expands in numbers; (ii) in the absence of food, it transforms into a flagellate form that allows it to travel long distance in search of food; and (iii) under harsh conditions, and it transforms into a cyst form [2]. During the cyst stage, Naegleria becomes dormant with little metabolic activity, but it can remain viable for decades. Basically, the parasite builds a shell around itself and goes into hibernation until the return of favorable conditions. In this regard, cyst formation is an integral part of the life cycle of Naegleria. This process is known as ‘encystation’. Upon return of favorable conditions, the parasite leaves the shell and emerges as a viable trophozoite (a process known as excystation), multiplies, and establishes an infection, if contracted by a host upon accidental encounter with humans and animals.
Related Knowledge Centers
- Balantidium Coli
- Giardia
- Malaria
- Plasmodium Falciparum
- Microbial Cyst
- Balantidiasis
- Apicomplexan Life Cycle
- Giardia Duodenalis