Pathogenesis Of Toxoplasmosis Research Articles

Chronic Infection with Toxoplasma gondii Does Not Prevent Acute Disease or Colonization of the Brain with Tissue Cysts Following Reinfection with Different Strains of the Parasite

Two strains of Toxoplasma gondii with different capacities to induce disease and brain lesions in mice were used to study the effects of reinfection with the parasite on a previously infected host. In spite of marked antibody and cell-mediated immune responses, chronically infected mice developed disease and died of acute toxoplasmosis when reinfected with a strain different from the one causing the primary infection. Moreover, the marked antibody and cell-mediated immune responses of the chronically infected mice did not prevent invasion of their brains and formation of tissue cysts by the reinfecting strain. Tissue cysts of the reinfecting strain were demonstrated in the brains of the chronically infected and subsequently reinfected mice. These results highlight the importance of strain differences in the pathogenesis of toxoplasmosis.

Developmental differentiation between tachyzoites and bradyzoites of Toxoplasma gondii

An important event in the pathogenesis of toxoplasmosis is the interconversion between the bradyzoite and the tachyzoite stage of Toxoplasma gondii within the intermediate host. The factors that influence either cyst formation (bradyzoites) or reactivation (tachyzoites) are unknown. Uwe Gross, Wolfgang Bohne, Martine Soête and Jean François Dubremetz here describe current knowledge about the mechanisms that might lead to the induction of stage differentiation of this protozoan parasite.

Role of secretory dense granule organelles in the pathogenesis of toxoplasmosis.

Multiplication of Toxoplasma gondii only occurs intracellularly inside a specialized compartment called the parasitophorous vacuole (PV). Regulated secretory processes are key to the success of the intracellular parasitism of Toxoplasma as the parasite extensively modifies the newly formed vacuole using secreted proteins (Beckers et al. 1994; Charif et al. 1990; Sibley and Krahenbuhl 1988). The main structural modification of the PV consists of elaboration of a network of tubular membranes that are continuous with the vacuolar membrane (Sibley and Krahenbuhl 1988; Sibley et al. 1986, 1995).

Cloning and characterization of a bradyzoite‐specifically expressed gene (hsp30/bag1) of Toxoplasma gondii, related to genes encoding small heat‐shock proteins of plants

Stage conversion between the tachyzoite and bradyzoite forms of the protozoan parasite Toxoplasma gondii is an important aspect in the pathogenesis of toxoplasmosis. In an initial investigation of molecular regulation of stage conversion in T. gondii, we describe the cloning and characterization of a bradyzoite-specifically expressed gene (hsp30/bag1). Bradyzoite formation was induced in cell culture by alkaline pH, and this was followed by purification of this parasitic stage using magnetic cell sorting. A bradyzoite cDNA library was constructed by random amplification using the polymerase chain reaction. Screening with a bradyzoite-specific monoclonal antibody identified a reactive clone. The amino acid sequence derived from the 687 bp open reading frame showed similarity to the conserved C-terminal region of small heat-shock proteins from plants. Stage-specific expression of the naturally occurring 30 kDa antigen in bradyzoites was confirmed by polyclonal antisera generated against the recombinant antigen. Immunoelectron microscopy indicated a cytosolic location of this antigen in bradyzoites. The expression of HSP30/BAG1 seems to be regulated at the mRNA level, since reverse polymerase chain reaction using bradyzoite-specific primers amplified transcripts in bradyzoites only, not in tachyzoites.

Immune response against toxoplasma and sarcoscystis infections in ruminants : diagnosis and prospects for vaccination

Toxoplasma gondii and a variety of Sarcocystis species are common cyst-forming coccidian parasites of domestic ruminants worldwide. T. gondii infection is a major cause of ovine and caprine abortion and perinatal mortality, but does not appear commonly to cause significant disease in other ruminants. Sarcocystis infections are probably most important in growing ruminants in which they can cause subclinical anaemia and reduced weight gain. The life cycles, pathogenesis and current knowledge of immunity to these protozoa, in ruminants, are reviewed. Although clinical signs may suggest a diagnosis, confirmation requires the use of specific immunological methods such as serology and immunohistochemistry. These are discussed and the necessity for using characterised antigens and antisera is emphasised. Whereas live Toxoplasma "vaccines" may be effective in sheep and goats, the eventual preparation of a killed vaccine capable of inducing long-term protection is of the utmost importance. To achieve this goal it will be necessary to identify the specific antigens capable of stimulating protective immunity and to conduct further research on both the pathogenesis of toxoplasmosis and fundamental aspects of the immune response of pregnant ruminants to T. gondii.

Enzootic toxoplasmosis in caged squirrel monkeys Saimiri sciureus.

An enzootic of toxoplasmosis occurred in caged squirrel monkeys ( Saimiri sciureus, a New World primate) which resulted in 9 deaths during an interval of 22 months. Diagnosis was based on morphology of the organism, character and distribution of the lesions, and laboratory history of the monkeys. The character of the lesions was essentially necrotic. The chronological incidence of the disease and distribution of lesions and organisms are tabulated. Trypanosoma cruzi which causes Chaga's disease is differentiated morphologically from toxoplasma. Incidence and lesions of the enzootic suggest 5 factors to be considered in the pathogenesis of toxoplasmosis in squirrel monkeys. They are: (1) lack of protective immunity, (2) local concentration of toxin and/or catabolites of reproduction of the organism, (3) individual tissue susceptibility to the organism, (4) capillary thrombosis, and (5) ability of the individual to adapt to its environment.

PATHOGENESIS OF TOXOPLASMOSIS AND OF INFECTIONS WITH ORGANISMS RESEMBLING TOXOPLASMA

PATHOGENESIS OF TOXOPLASMOSIS AND OF INFECTIONS WITH ORGANISMS RESEMBLING TOXOPLASMA

Treatment of toxoplasmosis with pyrimethamine (daraprim) and triple sulfonamide.

Excerpt In the short space of 16 years since toxoplasmosis was first recognized as a disease in human beings, great strides have been made in delineating the various clinical syndromes, pathology a...