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Neuroinfectious Diseases
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Jeremy D. Young, Jesica A. Herrick, Scott Borgetti
Human ingestion of oocysts is followed by invasion of the intestinal epithelium and parasitemia and dissemination to the brain, spinal cord, skeletal muscle, eyes, and many other organs. Tachyzoites invade target cells where they convert into the bradyzoite form. These replicating bradyzoites form tissue cysts, which persist in tissues for the life of the host. In the vast majority of immunocompetent patients, these cysts have no clinical sequelae.
Toxoplasma gondii
Published in Peter D. Walzer, Robert M. Genta, Parasitic Infections in the Compromised Host, 2020
The tissue cyst is associated with transmission because it persists in tissues of chronically infected animals, which may be ingested by carnivores, including humans. Undercooked meat has been implicated as the source of several common-source outbreaks of toxoplasmosis (21-23). In various surveys, as much as 25% of the mutton and pork in butcher shops contains Toxoplasma (24). However, it is rare for beef to contain Toxoplasma except for those occasions on which it is contaminated with pork (22,23). After ingestion, the cyst wall is disrupted by peptic or tryptic digestion, which liberates viable T. gondii bradyzoites. The bradyzoites resist peptic and tryptic digestion and survive several hours after exposure to these digestive enzymes and are capable of invading the host through the digestive tract. The cyst may also be important in the transmission of infection in organ transplantation (28-30). It has been demonstrated that heart transplant patients who are seronegative for Toxoplasma antibody and receive a heart from a seropositive donor have a high incidence of developing disseminated toxoplasmosis. This mode of transmission has also been demonstrated in other organ transplant recipients (75).
Toxoplasma
Published in Dongyou Liu, Handbook of Foodborne Diseases, 2018
Fernanda Silva de Souza, Renato Augusto DaMatta
Tachyzoites have an arched shape, present a size of about 2 by 7 μm, the anterior portion is slightly pointed, the posterior end is rounded, and they can be easily observed in infected cells in culture (Figure 59.2a); impression smears of different organs of acute infected animals also reveal tachyzoites, especially the lung.14 Parasites that multiply in host cells in culture form rosettes (Figure 59.2b). In imunocompetent hosts, tachyzoites will convert to bradyzoites forming tissue cysts, in different tissues of the hosts, especially at the central nervous system and striated muscles. These cysts have a round shape with a typical cyst wall and vary in size with many bradyzoites.14
Cerebral toxoplasmosis in HIV-infected patients: a review
Published in Pathogens and Global Health, 2023
Sofiati Dian, Ahmad Rizal Ganiem, Savira Ekawardhani
A non-sporulated oocyst excreted in cat feces transforms into a highly infectious sporulated form in fresh air [17,18]. The sexual reproductive phase of T. gondii occurs only in cats, its definitive host, facilitated by the intrinsic abundance of linoleic acid and the absence of the enzyme delta-6-desaturase. The intermediate host, including humans, mammals, and birds are infected after consuming water or food contaminated by infectious oocyst or after ingesting prey containing tissue cysts [18]. The cyst wall is later digested in the host’s stomach and intestine, releasing bradyzoites, which penetrate further into the epithelium of the intestine. Inside the cysts, several hundred bradyzoites remain covered from the host immune system. Host immune responses and anti-toxoplasmosis can limit their growth and force the tachyzoite to transform into slowly replicating bradyzoites. Bradyzoites become active when the immune system becomes compromised, leading to clinical manifestation [18].
Inhibition of Toxoplasma gondii by 1,2,4-triazole-based compounds: marked improvement in selectivity relative to the standard therapy pyrimethamine and sulfadiazine
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2022
Lidia Węglińska, Adrian Bekier, Nazar Trotsko, Barbara Kaproń, Tomasz Plech, Katarzyna Dzitko, Agata Paneth
Following primary infection, the tachyzoite disseminates widely in the organism via the bloodstream and lymphatic system. After passage of the BBB, they differentiate into cyst stages (bradyzoites), located predominantly in the neuronal cells of cerebral cortex, hippocampus, basal ganglia, and amygdala. This results in chronic, lifelong infection56,57. Chronic infection is usually asymptomatic and low rate of spontaneous reactivation is observed whereby bradyzoites differentiate back to tachyzoites. However, in patients with immune deficiency or those with prolonged treatments with immunosuppressants, reactivation of the infection can lead to lethal Toxoplasma encephalitis23,58. Additionally, chronic infection has been associated with development of neuropsychiatric disorders, including depression and schizophrenia59–65.
Immunogenicity and protection efficacy of enhanced fitness recombinant Salmonella Typhi monovalent and bivalent vaccine strains against acute toxoplasmosis
Published in Pathogens and Global Health, 2021
Fei-Kean Loh, Sheila Nathan, Sek-Chuen Chow, Chee-Mun Fang
T. gondii present as tachyzoites or bradyzoites in human host. Tachyzoites can repetitively invade, replicate, and egress to spread throughout the host tissues [15]. Subsequently, tachyzoites could differentiate into dormant bradyzoites which multiply very slowly in a quiescent metabolic stage and develop into cysts within host cells [16]. Hence, an effective T. gondii vaccine against acute toxoplasmosis serves as the first line of defense against actively replicating tachyzoites, which also prevents conversion of tachyzoites into bradyzoites. In this study, T. gondii surface antigen glycoprotein 1 (SAG1) and dense granule protein 2 (GRA2) were selected for the bivalent vaccine combination. SAG1 is the best characterized and immunodominant antigen to generate immune response against tachyzoite [17]. Moreover, GRA2 has been proven to elicit both T-cell and antibody immune responses [18].