Protozoa
Loretta A. Cormier, Pauline E. Jolly in The Primate Zoonoses, 2017
Toxoplasma gondii is a parasite found worldwide. In the United States, it is estimated that approximately 22.5% of the population over age 12 have been infected, with rates up to 95% in hot, humid climates in other parts of the world (CDC 2015c). T. gondii is spread through ingestion of contaminated food or water, accidental ingestion of fecal material, or vertical transmission from mother to child in utero (Montoya et al. 2015). The only known definitive hosts are felids, including both domesticated cats and wild felids, such as lions, tigers, jaguars, and bobcats (Fayer et al. 2004). A wide range of mammals and birds are susceptible to infection in the wild due to its presence in the environment in soil and water (Montoya et al. 2015). Infection in humans is typically asymptomatic, but congenital infection may cause severe symptoms in infants including neurological disease, ocular disease leading to blindness, and cardiac and cerebral abnormities (Paquet et al. 2013). Congenital transmission often occurs when pregnant women are infected when cleaning the litter boxes of pet cats (CDC 2015c). In immunocompromised individuals (such as those with HIV/AIDS), symptoms present typically as a reactivation of a latent infection, rather than one that has been newly acquired (Montoya et al. 2015).
Infectious Optic Neuropathies
Vivek Lal in A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Toxoplasma gondii is an intracellular parasite that affects immunocompromised hosts. Ocular toxoplasmosis typically presents with unifocal retino-choriditis.2 Other ocular manifestations include multifocal retino-choriditis, scleritis, retinitis and uveitis.61 Optic nerve involvement manifests with reactive optic disc hyperemia, neuroretinitis, papillitis and isolated anterior optic neuritis.2,62 Prompt clinical suspicion is needed for an early diagnosis of toxoplasmosis. A positive anti-toxoplasma IgG antibody assay does not confirm the diagnosis; however, a negative serology rules out the possibility of toxoplasmosis. Western blot techniques can be used for antibody detection in aqueous or vitreous humor. A PCR test is used for demonstration of Toxoplasma DNA in ocular fluid.2 A combination of anti-parasitic treatment along with corticosteroids is used for the treatment. The standard anti-parasitic treatment includes pyrimethamine plus sulfadiazine along with folinic acid.61 Overall visual prognosis, after treatment, is generally good.62
Toxoplasma: Animal and In Vitro Models on Toxoplasmosis
Dongyou Liu in Laboratory Models for Foodborne Infections, 2017
Most often, toxoplasmosis is asymptomatic in immunocompetent individuals.2–4,11 However, depending on the Toxoplasma gondii strain,2 the genetic constitution of the host, parasite load, and the mode of transmission,12,13 infection can cause severe clinical manifestations including ocular toxoplasmosis,14 cerebral toxoplasmosis,15 and congenital toxoplasmosis.1 When acquired by healthy individuals, toxoplasmosis most often causes lymphadenopathy, usually of the head and neck, but pneumonia, retinochoroiditis, myocarditis, neurological disorders, and severe ocular infection have also been reported in severe cases especially in French Guiana16 and in Brazil.17 Congenital toxoplasmosis can cause mental retardation, encephalitis, neonatal mortality, and abortion of the fetuses.2,17,18 In immunocompromised patients, the reactivation of the parasite into fast replicating forms in the central nervous system (CNS) causes cerebral toxoplasmosis.5 In addition, T. gondii infection has been implicated in schizophrenia and other neurological disorders.15,19 Domestic animals also develop toxoplasmosis upon infection, causing relevant economic losses, and wild animals are also infected by T. gondii.1,20 Due to its severe manifestations, worldwide distribution, and diverse host infection, toxoplasmosis is a relevant public health problem.21,22
Immunological, histopathological, and ultrastructural evidence of steroid-induced reactivation of chronic murine toxoplasmosis
Published in Ultrastructural Pathology, 2021
Aida A. Abdel-Magied, Doaa S. Ghorab, Abeer A. Elhenawy, Nora I. Aboulfotouh
Toxoplasma gondii (T. gondii) is an intra-cellular protozoan parasite that infects many animals as well as humans with global prevalence of 10–80%.1 The disease is characterized by tachyzoite proliferation in the acute stage, followed by a chronic stage of latent cysts within the central nervous system.2The clinical manifestations are affected by the strain of the parasite and immunity of the host. The estimated prevalence of latent toxoplasmosis among immunocompromised individuals is 35.9%.3 In immunocompetent individuals, the disease is usually asymptomatic in 60% of cases. However, it can have serious complications on the fetus, neonates, and in immunocompromised individuals.,4,5 The cysts remain dormant in the brain of infected humans and can reactivate in immunocompromised patients resulting in acute toxoplasmic encephalitis which may be fatal.6,7Toxoplasma Type II strains (e.g. Me49) are characterized by moderate virulence for laboratory mice. However, they are associated with human infections and chronic persistent tissue cysts while type III strains are avirulent.8,9
Synthesis and biological evaluation of ursolic acid derivatives bearing triazole moieties as potential anti-Toxoplasma gondii agents
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Tian Luan, Chunmei Jin, Chun-Mei Jin, Guo-Hua Gong, Zhe-Shan Quan
Toxoplasma gondii is an opportunistic pathogen that causes infection in human beings and various animals, thereby severely impairing their health. Congenital toxoplasmosis, caused by T. gondii, is especially harmful to pregnant women as the infection may result in abortion, stillbirth, and abnormality of foetus thinking barrier. The infection could also be fatal for immuno-compromised patients1. Owing to the complexity of T. gondii life cycle, its multifarious pathogenesis and different biological characteristics, no preventive and medicine-specific treatment exists currently. Traditional anti-T. gondii drugs have various disadvantages, such as the inability to completely kill the protozoa and oocysts, high toxicity, frequent recurrence, and failure in immuno-compromised individuals2,3. Considering the increasing percentage of natural product-based drugs in the market in the past years, researchers have now focussed their attention to plant-based compounds with anti-T. gondii activity. Moreover, several studies have shown natural products and their derivatives to exert strong anti-T. gondii effects, making these an attractive source of anti-T. gondii drugs4,5. In this regard, structural modifications of natural products to generate effective and less-toxic derivatives are considered to be very promising for the development of anti-T. gondii drugs.
Role of environmental factors in multiple sclerosis
Published in Expert Review of Neurotherapeutics, 2021
Amin Zarghami, Ying Li, Suzi B. Claflin, Ingrid van der Mei, Bruce V. Taylor
Toxoplasmosis is a parasitic disease caused by infection with Toxoplasma gondii, an intracellular protozoan and a neurotropic parasite that has been linked to several neuropsychiatric disorders [154]. However, its effect on MS onset remains unclear. A 2018 meta-analysis of five studies (n = 669 PwMS vs. 770 controls) reported a lower seroprevalence of T. gondii among PwMS (32.4%) compared to controls (39.1%). However, T. gondii infection (past or current) was not associated with a lower likelihood of living with MS (OR: 0.72; 95%CI:0.49–1.06) [155]. We identified two case-control studies on the role of T. gondii in MS onset risk. One (2020, n = 129 MS, 287 control) found a significant protective effect of T. gondii seropositivity [156], while the other (2020, n = 45 MS, 225 control) did not support an association [157].
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