Diagnosis

Development of a novel serologic test, the dye test, in 1948 by Albert Sabin and Harry Feldman was perhaps the greatest advancement in the field of toxoplasmosis (Sabin and Feldman, 1948). The dye test is highly sensitive and specific, with no evidence for false results in humans. Even titers as low as 1 2 are meaningful for the diagnosis of ocular disease. The ability to identify T. gondii infections based on a simple serological test opened the door for extensive epidemiological studies on...

Differential diagnosis

Congenital toxoplasmosis must be differentiated from other possible causes of the classic clinical acronym 'TORCH' for a series of etiologies that share similar signs and symptoms. The acronym includes Toxoplasma, rubella, cytomegalovirus, syphilis, and herpes simplex virus. However, emerging pathogens such as West Nile Virus must be considered as part of any differential in known congenital infection (Alpert et al., 2003). Recurrent toxoplasmosis with its unilateral active lesion associated...

Egress from the host cell

Changes in intracellular Ca2+ have also been involved in T. gondii egress from the host cells on the basis of the use of Ca2+ ionophores (Endo et al., 1982 Black et al., 2000 reviewed in Arrizabalaga and Boothroyd, 2004). Addition of the Ca2+ ionophore A23187 to infected macrophages stimulated the movement and egress of tachyzoites, resulting in host-cell lysis (Endo et al., 1982). Most of the parasite population exited from infected human foreskin fibroblasts after only a 2-minute exposure to...

Environmental factors

Though it is believed that T. gondii has no geographical and host boundaries (Howe and Sibley, 1995), it may well be that particular genotypes are associated with specific host groups or with different geographic locations. To date, isolates have been obtained from many different species (see Tables 3.2 and 3.3). Variation has been seen in the relative abundance of strains. At this stage it is difficult to read too much into these studies, in part because most of them rest on measuring...

Exocytosis of dense granules

The secretion of the dense granules has been difficult to capture fusion of the dense-granule membrane with the parasite plasma membrane (PPM) takes place sub-apically, at supposed gaps between the plates forming the inner membrane complex (Leriche and Dubremetz, 1990 Dubremetz et al., 1993). Dense-granule secretion appears to respond to signals associated with both constitutive and regulated pathways of secretion. In favor of constitutive secretion, dense-granule fusion with the target PPM is...

F

There are only two apicoplast-encoded genes that have predicted functions other than gene expression clpC and sufB (see section 9.2.9). Finally, a handful of unidentified open reading frames are modestly conserved between T. gondii and P falciparum html). They predict small basic proteins which may be additional ribosomal proteins, some of which are difficult to identify due to limited conservation. This possibility is particularly attractive given that the total number of plastid ribosomal...

Figure 210

(A) Small schizont with few nuclei (N) but showing the initiation of daughter formation (D). Bar 1 im. (B) Detail of a schizont showing the plate-like structures of the inner membrane complex representing the initiation of daughter formation (arrows). Ce, centriole N, nucleus NP nuclear pole G, Golgi body. Bar 0.5 im. (C) Low-power image of a large schizont with a number of nuclei showing the formation of a larger number of daughters. Bar 1 im. (D) Detail showing the posterior growth on the...

Figure 215

(A) Early stage of oocyst wall formation showing the outer veil (V) and partial formation of the outer layer of the oocyst wall (arrows). Note this is associated with the loss of the VFB and the WFB1 from the macrogamete cytoplasm, while the WFB2 (W2) remain. L, lipid droplet PG, polysaccharide granule N, nucleus. Bar 1 im. (B) Newly released oocyst showing the outer veil (V) and fully formed oocyst wall (OW) enclosing a cytoplasmic mass containing polysaccharide granules (PG) and lipid...

Figure 221

(A) Scanning electron micrograph of a sporocyst undergoing excystation, showing the separation of the plates of the sporocyst wall (arrows). Bar 1 im. (B) Transmission electron micrograph through an excysting sporocyst, showing separation and infolding of the plates of the sporocyst wall (arrows). The sporozoites (SP) contain a posteriorly located nucleus (N) and numerous micronemes (MN) and polysaccharide granules (PG). C, conoid. Bar 1 im. (C) Early stage in excystation showing inward curling...

Fluorescence Methods To Study Calcium Homeostasis In T Gondii

Because of its importance, numerous methods for analyzing the mechanisms of cellular and or subcellular Ca2+ activity have been established. Although each method has some advantages over Toxoplasma gondii. The Model Apicomplexan-Perspectives and Methods, edited by Weiss & Kim ISBN-13 978-0-12-369542-0 ISBN-10 0-12-369542-2 Copyright 2007 Elsevier Ltd. All rights of reproduction in any form reserved. the others, each also suffers drawbacks. Investigation of Ca2+ i was boosted dramatically...

G 35 51g

Each other in the number of apical organelles, the shape and electron-density of the rhoptries, the location of the nucleus, and the presence or absence of polysaccharide granules. The nucleus is more centrally located in the tachyzoite (Figure 2.1 A) and merozoite (Figure 2.11B) and more basally located in the bradyzoite (Figure 2.23B) and sporozoite (Figure 2.21B). An additional cytoplasmic structure not described above is the polysaccharide granule. The polysaccharide granules are ovoid...

Histopathology

Several reports characterizing the destructive retinochoroiditis exist (Hogan, 1951 Wilder, 1952 Zimmerman, 1961 Rao and Font, 1977). Organisms in immunocompetent individuals are identified in the retina and optic nerve, but not in the choroid. Toxoplasma cysts have also been demonstrated in the retinal pigmented epithelium (Nicholson and Wolchok, 1976). Tachyzoites stain well by both Wright and Giemsa stains, and brady-zoites stain well with periodic acid-Schiff stain. Granulomatous choroidal...

Ecq

Laboratory animal species genetic background of the strain (inbred, outbred, genetically altered strains, etc.) FIGURE 7.1 Factors influencing the outcome of Toxoplasma infection in animals. the conditions of the infection in the human host. In addition, the outcome of the infection should be clearly assessable. In practice, the fulfillment of these requirements seems to be dependent on several conditions the nature of the animal placenta, as the organ the duration of parasitemia the size of...

Ovp

*For definition of animal or Toxoplasma strains, please see respective articles. **Due to numerous publications on this topic, only few were exemplarily chosen for this table. orally infected with 10 tissue cysts of the Me49 strain, by immunosuppression with DXM alone and, more efficiently, by combined hydrocortisone-21-acetate (CA) treatment (Djurkovic-Djakovic and Milenkovic, 2001 Djurkovic-Djakovic et al., 2002). In addition to the above-mentioned models, reactivation may be induced in...

Immunocompromised patients

Because reactivation of latent Toxoplasma infection is the most common cause of toxoplasmosis in immunocompromised patients, detection of T. gondii IgG antibodies is indicated. Patients with a positive result are at risk of reactivation of the infection patients with a negative result should be instructed on how they can prevent becoming infected. The most important factor in the management of the seropositive immunosuppressed patient is to consider T. gondii as a potential causative agent in...

Improvement of EIA tests for Toxoplasmaspecific IgG and IgM antibodies

The problems with IgM-based diagnostic tests in T. gondii infections have resulted in attempts to improve them. The accepted reference test is the ISAGA, but most analyses are performed with an EIA capture test. The assays use whole-cell, lysed T. gondii as antigen, and attempts have been made to improve the test by using recombinant antigens (Ferrandiz et al., 2004). The ISAGA IgM and EIA IgM, and IgM immunofluorescence, were evaluated in a prospective European cohort study, EMSCOT, of women...

Info

Cover photograph Tachyzoites of ME49 (Type II strain) T. gondii in the primary murine astrocytes in vitro. Electron microscopy performed at the Albert Einstein College of Medicine, Bronx, New York, USA in 1995. Photomicrograph courtesy of Dr Sandra Halonen, Montana State University Working together to grow libraries in developing countries www.elsevier.com www.bookaid.org www.sabre.org

Intravitreal therapy

Intravitreal therapy has the risk of irreversible blindness with each administration of any medicine, as well as other potential complications. However, recently, intravitreal therapy has been the mode of administration of medicines for a variety of eye diseases. The benefit of intravitreal therapy is that it has excellent bioavailability and almost no risk of systemic side effects. Intravitreal clindamycin dexamethasone, clindamycin triamcinolone ace-tonide with systemic anti-Toxoplasma...

Introduction

Even though ocular toxoplasmosis is the most common etiology of posterior uveitis in the United States and the world, it remains a poorly understood disease. For instance, there is limited understanding as to why macular lesions are common in congenitally infected individuals, limited understanding regarding the details of ocular recurrences, and there is no agreement on best treatment. There is no regimen that can eliminate the bradyzoite stage of infection therefore, once an individual is...

Invasion A Rapid And Active Process Depending On Gliding Motility

Host-cell invasion by T. gondii is fundamentally different from phagocytosis or endocytosis induced by intracellular pathogens such as viruses, bacteria, or Trypanosoma cruzi (Finlay and Cossart, 1997 Antoine et al., 1998, Sibley and Andrews, 2000). Invasion is essentially completed in less than 20 seconds, and occurs with apparent passivity of the host cell (i.e. without inducing host-cell membrane ruffling, actin microfilament reorganization, or tyrosine phosphorylation of the host cell)...

Lipids

T. gondii rhoptries also contain lipids, including large amounts of cholesterol and phospholipids (Foussard et al., 1991). Phosphatidylcholine is the major rhoptry phospholipids, and significant amounts of phosphatidic acid and lysophospho-lipids were also found, but not phosphatidylserine, phosphatidylinositol, or sphingomyelin. The lipid to protein ratio is estimated to be 0.26, and the cholesterol to lipid molar ratio is 1.5 to 1 (Foussard et al., 1991). This ratio indicates that lipids...

Localized brain infection models

The direct inoculation of tachyzoites into the frontal lobe of mice may deliver the most reproducible results, with lesions histologically resembling those that could be observed in immunocompromised man (Hofflin et al., 1987). The model has been successfully used, for example, to demonstrate the efficacy of clindamycin, roxithromycine, and gamma interferon on Toxoplasma encephalitis (Hofflin and Remington, 1987a, 1987b). However, later, in another model also with localized brain infection with...

M2ap

Non-essential protein KO mutant is less invasive and less virulent in mice Essential protein C-terminal truncation mutant is non-viable substitution with Eimeria MIC1 is viable but less invasive Non-essential protein KO mutant has reduced virulence in mice Adhesion, folding, assembly of the MIC1 4 6 complex Fourmaux et al., 1996 Cerede et al., 2005 Saouros et al., 2005 Jewett and Sibley, 2004 Wan et al., 1997 Garcia-Reguet et al., 2000 Cerede et al., 2002, 2005

Manipulation of [Ca2

Calcium buffers and ionophores are frequently used to lower or raise intracellular or extracellular calcium. The purpose of these protocols is to study Ca2+-dependent cellular processes (Kao, 1994). EGTA is highly selective for binding Ca2+ over Mg2+, and because of this it is the most commonly used Ca2+ buffer. However, the Ca2+-binding activity by EGTA is very pH-dependent when used at physiological pH. This is because at these pH values EGTA exists primarily as protonated species (H2EGTA2-)...

Markers For Genetic Studies

Numerous markers have been described for typing of Toxoplasma isolates (Table 3.1). Initially, prior to sequencing of the Toxoplasma genome, methods such as isoenzyme analysis and restriction fragment length polymorphism (RFLP) were used. However, as sequence information became available specific polymorphic markers were identified, and the discovery of these has been greatly facilitated by the development of the Toxoplasma genome project (Ajioka et al., 1998 Manger et al., 1998 http toxodb.org...

Markers for individual characterization of stocks and isolates

Several strategies have been proposed for fingerprinting of isolates, to allow epidemiological tracking, or identification of laboratory lines. These use either multiple-copy genes or an association of several rapidly evolving markers in order to give sufficient resolution to identify isolates beyond the lineage level. Several techniques have used multiple-copy loci to detect a high polymorphism among Toxoplasma isolates. For example, probing a total genomic DNA digest with a 32P-labelled BS...

Maturation of the parasitophorous vacuole a prominent role of dense granules

Toxoplasma and Plasmodium have evolved two distinct types of parasitophorous vacuole (PV), linked to differential strategies of intracellular parasitism. While initial formation of both types of vacuole is driven by the same active invasion process, maturation of the nascent PV is different in terms of both architecture and metabolism, and leads to two distinct modes of parasite replication -endodyogeny versus schizogony. The fate of the Toxoplasma-containing vacuole strictly correlates with...

Microneme secretion attachment and invasion of the host cell

The invasion process of T. gondii is marked by the sequential secretion of parasite organelles. Micronemes, rhoptries, and dense-granule contents are released by invading parasites, and participate in attachment, vacuole formation, and intracellu-lar survival (Carruthers and Sibley, 1997). Micronemes are the first secretory organelles to be discharged. Host-cell contact triggers a burst of microneme release. Microneme proteins participate in attachment to host-cell surfaces (Fourmaux et al.,...

Microneme secretion

Microneme secretion is a regulated process (also known as stimulus-coupled secretion). The external stimulus that triggers MICs secretion is unknown, but fluorescence imaging studies have revealed that parasites in association with host cells show elevated levels of cytoplasmic calcium (Vieira and Moreno, 2000). Chelation of extracellular calcium with EGTA or BAPTA or addition of excess calcium has little effect on microneme secretion, parasite motility, or cell invasion (Lovett and Sibley,...

Molecular and other diagnostic techniques

The diagnosis of acute toxoplasmosis may be established by the detection of anti- T. gondii antibodies by serological tests, or of tachyzoites or T. gondii-specific DNA in body fluids or tissue samples. In most cases of toxoplasmosis in immunocompetent individuals, diagnosis is established by serological tests however, molecular (i.e. PCR) diagnostic tests have proven useful in the diagnosis of infection in utero as well as in immunocompromised hosts. The detection of T. gondii tachyzoite DNA...

Molecular Epidemiological Studies

To determine the patterns of transmission of Toxoplasma requires intensive studies which employ polymorphic markers to track strains in contiguous space and time. Such studies are rare, but perhaps the best examples are the careful studies of marine mammals, in which close typing of isolates shows infection by both type II strains and by isolates clustered into a new strain, type X (Miller et al., 2004). The risk of infection in sea otters was related to the level of freshwater runoff (Miller...

New World monkeys

Toxoplasmosis can be a problem in exhibited New World monkeys (Table 6.1). Many reports of acute disease have come from squirrel monkeys (Saimiri sciureus) (Anderson and McClure, 1982 Dickson et al., 1983 Cunningham et al., 1992 Dietz et al., 1997 Inoue, 1997 Epiphanio et al., 2003) and golden lion tamarins (Leontopithecus rosalia) (Dietz et al., 1997 Pertz et al., 1997 Juan-Salles et al., 1998 Epiphanio et al., 2003). Squirrel monkeys and Panamanian night monkeys (Aotus lemurinus) are highly...

NTPase isoforms and their molecular properties

The type I strains of T. gondii, which are acutely virulent in mice (Sibley and Boothroyd, 1992), contain two isoforms of NTPase (Bermudes et al., FIGURE 8.7 Behavior of NTPase in the tachyzoite-infected cell. NTPase is secreted from the dense granule of tachyzoite into the parasitophorous vacuolar space and associates to the intravacuolar network. Then, NTPase activity may be regulated by oxido-reduction change in its molecule affected by dithiol compound or unknown dithiol-disulfide...

Nucleotide Biosynthesis

The most extensively studied metabolic pathways in T. gondii are those of pyrimidine and purine nucleotide biosynthesis. These pathways provide the substrates for DNA RNA biosynthesis, and are commonly targeted for chemotherapy. They are logical areas to study in the rapidly multiplying tachyzoite form. Due to limited material, nearly all studies have been performed exclusively in tachy-zoites. Illustrations of the present overall knowledge of nucleotide biosynthesis in the tachyzoite form of...

Ocular biopsies

There is a risk of irreversible blindness with any type of intraocular procedure, owing to possible complications that include bacterial endoph-thalmitis and retinal detachment. Since most cases of ocular toxoplasmosis can be diagnosed on clinical grounds, the need for an intraocular procedure to make the diagnosis is highly unusual. Although the risks are severe, the actual likelihood of risk of blindness is low (< 1 100). There are two intraocular compartments that can be sampled. The...

Ocular Toxoplasmosis

Ocular toxoplasmosis may be acquired by infection after birth, but in a substantial percentage of cases the etiology of human ocular toxoplasmosis seems to be connected with in utero infection of the fetus via a mother whose primary infection was acquired during gestation (for review, see Holland, 2003). Consequently, ocular toxoplasmo-sis may be considered to be on the one hand a postnatally acquired disease, and on the other a late manifestation of congenital toxoplasmosis. However, it seems...

Other densegranule proteins

Despite their homology with well-characterized proteins, the function of the other dense-granule proteins is not clearly established. The abundant NTPases are essential, and display apyrase activity (Asai et al., 1995 Nakaar et al., 1999). Hence, in a primary model, as Toxoplasma is an auxotroph for purines, it was postulated that the presence of vacuolar NTPases, as well as of a 5' nucleotidase, would allow stepwise degradation of ATP into ADP, AMP, and adenosine, with the latter being...

Other wild ruminants

Elk (Cervus canadensis) are resistant to clinical disease following oral infection with oocysts but T. gondii can be isolated from many of their tissues, indicating that elk are a potential source of infection for humans (Dubey et al., 1980). Toxoplasma gondii has been isolated from naturally infected pronghorn antelope (Dubey, 1981). Acute toxoplasmosis and death can occur in pronghorn antelopes experimentally inoculated with T. gondii oocysts (Dubey et al., 1982). Toxoplasmic encephalitis has...

Parasite glycolytic enzymes involved in other biological functions

In eukaryotic cells, many kinds of multifunctional regulatory proteins have been identified that perform distinct biochemical functions in the nucleus, the cytoplasm, or both. Recent studies establish that metabolic enzymes display biological roles distinct from their cognate functions. Perhaps the best-studied examples are enzymes that double as eye-lens proteins essential for normal vision lactate dehydrogenase (crystalline in ducks and crocodiles), a-enolase (crystalline in lamprey and...

Parasite Factors In Ocular Infection

Three clonal types of T. gondii predominate in nature (Howe and Sibley, 1995). Virulent strains of T. gondii appear to have their origin in a single, genetically homogeneous lineage. This is despite the parasite's pervasive nature and ability to reproduce sexually (Sibley and Boothroyd, 1992). Recently, a composite genome map of the 14 chromosomes of T. gondii was reported (Khan et al., 2005). There is at most a 1 percent difference between the three strains, and reports examining only one...

Parasite Morphology And Life Cycle

The life cycle of Toxoplasma gondii is illustrated in Figure 1.1. The tachyzoite (Frenkel, 1973) is lunate (Figure 1.2A), and is the stage that Nicolle and Manceaux (1909) found in the gundi. This stage has also been called trophozoite, the proliferative form, the feeding form, and endozoite. It can infect virtually any cell in the body. It divides by a specialized process called endodyogeny, first described by Goldman et al. (1958). Gustafson et al. (1954) first studied the ultrastructure of...

Parasite surface exposition and posterior capping of MICs

As the parasite penetrates the host cell, most MICs are excluded from entering the vacuole and are progressively capped behind the MJ, remaining confined to the portion of the parasite that still protrudes from the host cell (Carruthers and Sibley, 1997 Carruthers et al., 1999b Garcia-Reguet et al., 2000). As a consequence of MIC protein capping, binding to a fixed substrate would lead to forward locomotion, and binding to cell-surface receptors would lead to penetration of the cell. The...

Polymerase chain reaction PCR

Since PCR testing requires a small sample volume, it is well suited for the samples available from most invasive ocular biopsies (Burg et al., 1989 Brezin et al., 1990). Unfortunately the vitreous, being 99 percent water by weight, does not have the dense cellular substrate ideally suited for the presence of T. gondii (Brezin et al., 1991). Large, atypical lesions which would be more likely to necessitate biopsy to help substantiate diagnosis also appear to be more likely to have positive...

Postsecretory trafficking of GRAs within the parasitophorous vacuole

The involvement of GRAs in the maturation of the PV has only been examined in detail during tachy-zoite development. Shortly alter invasion, the burst of dense-granule secretion into the PV coincides with specific structural changes of the PV that are characteristic of tachyzoite development. At this stage, only GRA1, TgPIs, and NTPases remain primarily in the lumen of the vacuole (Sibley et al., 1994, 1995 Pszenny et al., 2002 Morris and Carruthers, 2003). By immuno-electron microscopy, most...

Possible physiological function for NTPase

Protozoan parasites are purine auxotrophs (Berens et al., 1995). It has been speculated that the NTPases of T. gondii are involved in the salvage of purine nucleosides from the host cell (Bermudes et al., 1994). The T. gondii NTPase is secreted from the tachyzoite into the parasitophorous vacuole therefore it contains a higher potency of hydrolyz-ing ATP to ADP and AMP (Figure 8.7). As mentioned earlier, purines are salvaged through adenosine kinase or HXGPRTase. However, the tachyzoite lacks...

Protein trafficking to the mitochondrion

As described above, proteins destined for secondary plastids traffic first to the secretory system and then enter the plastid. In contrast, entry into primary endosymbionts - both mitochondria and plastids - typically does not involve the secretory system. Rather, proteins are translated on free cytosolic ribosomes, or on ribosomes studding the organelle's outer membrane, and enter the organelle directly by virtue of translocation machinery. This is a largely understudied topic for...

PVMassociated ROPs

Rhoptry-derived vesicles are secreted in host-cell cytoplasm. These vesicles contain lipid components, derived presumably from the rhoptry lipids and some rhoptry proteins, such as ROP1, and proteins of the ROP2 family (at least ROP2, ROP4, ROP5, and ROP7) (Saffer et al., 1992 Beckers et al., 1994 Carey et al., 2004b El Hajj et al., 2005, 2006c). They are likely to contain other rhoptry components as well. These vesicles fuse with the nascent PVM (Hakansson et al., 2001), and ROPs proteins...

Rabbit models of ocular toxoplasmosis

Hogan was the first to create a published animal model of ocular toxoplasmosis by injecting tachy-zoites into the carotid arteries (Hogan, 1951 Garweg et al., 1998) however, the RH strain used in this model frequently resulted in meningoencephalitis and rapid mortality. Beverley and others injected the inoculum into the anterior chamber of rabbits (Beverley et al., 1954). The BK strain in PBS inoculated intravitreally near the retinal wing of the posterior pole (the entry site was through the...

Rabbit

Surprisingly, rabbit congenital toxoplasmosis has not been extensively studied, although rabbits are widely used laboratory animals and transmission from the mother to the fetus has been demonstrated (Uhlikova and Hubner, 1973). In addition, fetuses from chronically infected mothers have been protected, thus a rabbit model would share common features with the infection in man (Werner et al., 1977). A rabbit model may be of particular interest when the small size of other common laboratory...

References

Ajioka, J.W, Boothroyd, J.C., Brunk, B.P et al. (1998). Gene discovery by EST sequencing in Toxoplasma gondii reveals sequences restricted to the Apicomplexa. Genome Res. 8, 18-28. Ajzenberg, D., Banuls, A.L., Tibayrenc, M. and Dard , M.L. (2002a). Microsatellite analysis of Toxoplasma gondii shows considerable polymorphism structured into two main clonal groups. IntlJ. Parasitol. 32, 27-38. Ajzenberg, D., Cogn , N., Paris, L. et al. (2002b). Genotype of 86 Toxoplasma gondii isolates associated...

Rh

1 x 103 tachyzoites injected intracerebrally 100 of animals died within 5 days after infection due to necrotizing Toxoplasma meningoencephalitis Pharmaceutical study evaluation of highly active drugs possible TABLE 7.6 Relapsing TE models of toxoplasmosis cont'd Models based on chronic progressive brain infection instead of reactivation (Cystogenic models) TABLE 7.6 Relapsing TE models of toxoplasmosis cont'd Models based on chronic progressive brain infection instead of reactivation...

ROPs and RONs

Identification of the major components of the rhoptries in T. gondii has been obtained by subcellular fractionation and generation of monoclonal antibodies (Leriche and Subremetz, 1991 see also Table 11.2). More recently, purified rhop-try proteomics has allowed the characterization of 38 previously unidentified proteins (Bradley et al., 2005), of which some have been confirmed to be localized in the organelles. All of the ROPs contain a signal peptide and many have at least one predicted...

Serology

There is currently clinically a limited role for serologic testing in recurrent ocular toxoplasmosis. The author always obtains a confirmatory IgG ELISA in suspected recurrent disease however, there is no test available that can confirm that ocular inflammation is in fact due to ocular toxoplasmosis. High-avidity (> 40 percent) antibodies are associated with infections that are over 6 months old (Paul, 1999 Liesenfeld et al., 2001). Documented seroconversion is a scenario where serologic...

Sheep

Toxoplasma gondii is a common cause of abortion in ewes, and an important production problem. Multiple abortions can occur in a flock, indicating a common oocyst source for ewes. Ewes develop solid immunity after aborting T. gondii-infected fetuses. A vaccine to prevent abortion in ewes is available in several countries (Buxton and Innes, 1995). Diagnosis of T. gondii abortion in ewes is best done by examining fetal fluids for antibodies using the modified agglutination test. Undercooked lamb...

Stage conversion tachyzoite to bradyzoite

There appears to be very marked tissue tropism in relation to the organs where the majority of tissue cysts are formed. The two tissues where the FIGURE 2.20 A diagrammatic representation of the changes observed during development of the sporo-cysts and formation of the sporozoites. C, conoid ER, rough endoplasmic reticulum G, Golgi body L, lipid droplet MI, mitochondrion MN, microneme MP, micropore N, nucleus NP nuclear pole P plaque representing the inner membrane complex of the developing...

Stagespecific expression of genes involved in glucose catabolism

It is noteworthy that some genes coding for enzymes involved in the biosynthesis of amylopectin and others in the glycolytic pathway are developmen-tally regulated during tachyzoite to bradyzoite stage conversion (see Chapter 13 for a discussion of bradyzoite differentiation). 8.2.4.1 Stage-specific expression of genes involved in amylopectin degradation The expression pattern of the genes involved in amylopectin biosynthesis in tachyzoites and bradyzoites isolated from mouse brain cysts has...

Structure of the tissue cyst and bradyzoite

The structure of the mature tissue cyst observed from 3 to 24 months following infection (approximately the lifespan of the mouse) remained relatively unchanged (Figure 2.23D). The first important observation is that throughout this period the tissue cysts are retained within a viable host cell (Figures 2.23D, 2.23E). It had originally been thought that the mature cysts are extracellular however, on ultrastructural examination a thin rim of host-cell cytoplasm could be observed enclosing the...

Tgr

Sibley and Boothroyd, 1992 Rinder et al., 1995 Lehmann et al., 2000 Grigg et al., 2001a Tinti et al., 2003 Sibley and Boothroyd, 1992 Parmley et al., 1994 Meisel et al., 1996 Fazaeli et al., 2000a Grigg et al., 2001a Lehmann et al., 2000 Aspinall et al., 2002 Sibley and Boothroyd, 1992 Grigg and Boothroyd, 2001 Costa et al., 1997 Ajzenberg et al., 2004 Ajzenberg et al., 2002a Blackston et al., 2001 Sibley and Boothroyd, 1992 Cristina et al., 1991 H0gdall et al., 2000 Terry et al., 2001 strains...

The historical development of diagnostic assays

The complement fixation assay, CFA, was the first diagnostic test for Toxoplasma-specific antibodies (Warren and Sabin, 1942 Steen and Kass, 1951). The dye test described by Sabin and Feldman (1948) is based on antibody-mediated killing of live T. gondii parasites in the presence of complement. If antibodies are present in the sample, the parasites are made penetrable for methylene blue and are colored in the presence of complement if antibodies are not present, the parasites remain unstained...

The Model Apicomplexan Perspectives and Methods

Weiss and Kami Kim Amsterdam Boston Heidelberg London New York Oxford Paris San Diego San Francisco Singapore Sydney Tokyo ELLSEVIER Academic Press is an imprint of Elsevier Academic Press is an imprint of Elsevier 84 Theobald's Road, London WC1X 8RR, UK 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA 525 B Street, Suite 1900, San Diego, CA 92101-4495, USA Copyright 2007, Elsevier Ltd. All rights reserved No part of this publication may be reproduced, stored in a...

Tm Mic Tm

FIGURE 11.1 Toxoplasma ultrastructure and molecular components of the moving junction during invasion. (A) Transmission electron micrograph of a Toxoplasma tachyzoite actively invading a Caco2 cell. Relevant structures of the parasite and host cell are labeled, including the parasitophorous vacuole (PV), which is created by invaginating the host plasma membrane (HPM) to form the parasitophorous vacuolar membrane (PVM). Parasite internal structures including the nucleus (N), mitochondrion (M),...

Toxoplasma Animal Models And Therapeutics

Strains (Johnson, 1984), suggesting at least partly independent modes of defense involved in each infection route. In this context it is important to be aware that, in general, two infection modes are used (1) injection of tachyzoites grown in culture or in mice i.p., s.c., or i.v., and (2) oral administration of tissue cysts of T. gondii obtained mostly from brains of chronically infected mice (McLeod et al., 1984) (oocysts are rarely used for infection). Whereas the latter model is inherently...

Toxoplasma infection in immunocompromised hosts

The treatment for encephalitis due to T. gondii is pyrimethamine 200 mg (loading dose) followed by 50-75 mg d, with sulfadiazine 1-1.5 g every 6 hours and folinic acid 10-25 mg d (Liesenfeld et al., 1999). In patients intolerant of sulfadiazine, clin-damycin 600-1200 mg every 6 hours can be used with pyrimethamine (Remington et al., 1991). Alternative combinations with reported efficacy in case reports include pyrimethamine with one of the following clarithromycin 1 g every 12 hours atovaquone...

Treatment Of Toxoplasmosis

With regard to therapy, it is useful to separate toxoplasmosis into several categories (Table 4.2). The decision to treat is based on the location of the infection, the immune status of the patient, and whether or not a woman with acute toxoplasmosis is pregnant. There are virtually no large, well-controlled clinical trials to establish the ideal therapeutic strategy however, there have been several studies of prophylaxis and treatment for toxoplas-mosis in the setting of AIDS or congenital...

W

(Kilejian, 1975) and Plasmodium berghei (Dore et al., 1983). These molecules matched the size range and conformation expected for mitochondrial genomes of unicellular eukaryotes, and so were immediately labeled as such. It was, of course, the logical conclusion. It was also wrong. Who would have suspected these were remnant chloroplast genomes The only clue was the cruciform structure, typical of chloroplast but not mitochondrial genomes. Certainly no one connected the circular genomes with the...

Whitetailed and mule deer

Toxoplasma gondii is prevalent in deer from North America. Consumption of venison has been linked with clinical toxoplasmosis in humans (Sacks et al., 1982 Ross et al., 2001). Clinical toxoplasmosis has not been described from naturally infected deer in North America. Toxoplasma gondii has been isolated from the tissues of white-tailed deer (Odocoileus virginianus) (Lindsay et al., 1991b, 1997a Dubey et al., 2004a) and mule deer (Odocoileus hemionus) (Dubey, 1982). The fetuses from T....

Protein trafficking to the apicoplast

With the identification of the apicoplast genome, it became apparent that the transcription and translation of its resident genes (including many ribosomal proteins), as well as any apicoplast-specific functions, would require the collaboration of additional proteins. These proteins are encoded in the nucleus, and hence are called nucleus-encoded apicoplast-targeted (NEAT) proteins. A search of the T. gondii EST databases for proteins homologous to those found in chloroplasts led to the...

Wild birds

Dubey (2002) reviewed the literature on T. gondii in wild birds. Table 6.2 lists the wild avian hosts TABLE 6.2 Host records for Toxoplasma gondii isolation from wild birds Red-shouldered hawk (Buteo lineatus) Blackheaded gull (Larus ridibundus) Common tern (Sterna hirundo) Columbiformes Collared dove (Streptopelia decaocto) Laughing dove (Streptopelia senegalensis) Woodpigeon (Columba palumbus) Source Dubey, 2002. from which viable T. gondii has been isolated, and Table 6.3 lists the avian...

The clinical features of congenital ocular toxoplasmosis

Congenital infection is more common later in gestation, but disease manifestations are worse if acquired earlier in gestation (Dunn et al., 1999). Classically, congenital disease is associated with bilateral macular scarring, but acquired infection can also result in macular disease and, rarely, bilateral scarring as well (Glasner et al., 1992). Other manifestations include optic neuritis, iritis, neuroretinitis, retinal vasculitis, acute retinal necrosis, recurrent iridocyclitis, and...

Role of GPIs in cell signaling and host immune response

Except for their role in membrane insertion of surface proteins in T. gondii, the biological junctions of GPIs are presently unknown. In other eukaryotic systems, GPIs can display functions involved in signal transduction. One possible function of the GPI anchor might be to allow a closer association of the proteins with themselves and other surface proteins in the membrane (Tomavo, 1996). Consistent with this idea, genetically engineered transmembrane-anchored SAG1 does not show the usual...

Models based on systemic infection

As can be seen in some 20 publications, meanwhile, the most frequently used animal for systemic infection models is the mouse. Basically, two different methods have been employed to establish the disease 1. Infection of pregnant mice to induce the development of ocular lesions in the pups (Hay et al., 1981, 1984 Hutchison et al., 1982 Lee et al., 1983 Dutton et al., 1986) 2. Systemic infection of mice which then predominantly develop ocular manifestations (Gazzinelli et al., 1994 Olle et al.,...

The mitochondrial genome

Despite considerable variation in size and gene content among species, all mitochondrial genomes known to date encode apocytochrome b (cob) and cytochrome c oxidase I (coxl). Cytochrome c oxidase III (cox3) is nearly invariant, missing from the mitochondrial genome only in some green algae. Mitochondrial genomes also invariably encode eubacterial-like large and small subunit rRNAs (reviewed in Gillham, 1994 Lang et al., 1999 Gray et al., 2004). The T. gondii mitochondr-ial genome has proven...

Densegranule protein function more hypotheses than functions

As mentioned above, to date the function of most dense-granule proteins remains unknown. At the tachyzoite stage, their burst of secretion into the PV following host-cell invasion and their selective targeting within the PV compartment suggest that they might contribute significantly to the structural organization of this new compartment and or have important functions in PV metabolism (Dubremetz et al., 1993 Cesbron-Delauw et al., 1994 Carruthers and Sibley, 1997). BLAST searches performed on...

Toxoplasmosis In Humans

Three pathologists - Wolf, Cowen, and Paige, from New York, USA - first conclusively identified T. gondii in an infant girl who was delivered full term by Caesarean section on 23 May 1938 at Babies' Hospital, New York (Wolf et al., 1939a, 1939b). The girl developed convulsive seizures at 3 days of age, and lesions were noted in the maculae of both eyes through an ophthalmoscope. She died when a month old, and an autopsy was performed. At post mortem, brain, spinal cord, and right eye were...

Toxoplasmosis In Other Animals

Mello (1910), in Turin, Italy, first reported fatal toxoplasmosis in a domestic animal (a 4-month-old dog) that died of acute visceral toxoplasmosis. Over the next 30 years, canine toxoplasmosis was reported in Cuba, France, Germany, India, Iraq, Tunisia, the USSR, and the USA (Dubey and Beattie, 1988). Campbell et al. (1955) found that most cases of clinical toxoplasmosis were in dogs infected with canine distemper virus (CDV). Even vaccination with live attenuated CDV vaccine can trigger...

Energy metabolism

The mitochondrion is commonly described in introductory biology classes as the powerhouse of the cell. It is the site of the tricarboxylic acid cycle and the electron transport chain, which act in concert to efficiently convert the products of glucose catabolism to ATP. The other functions of the organelle often get little mention. However, while mitochondrial respiration is key for aerobi-cally respiring cells, many parasite cells are found in environments with low oxygen tension and rely at...

Why does T gondii exhibit this patchwork of MICs

The vast MIC repertoire of T. gondii may be correlated with the broad host-cell specificity in vitro and the spreading of infection in all organs in toxoplas-mosis, contrasting with the high cell and organ specificity found in Plasmodium. Apicomplexa show variable cell specificity, particularly at different stages of infection specificity may be related to the MIC repertoire, quite different from one genus to the other, and dependent upon the stage in the life cycle. MIC gene deletion in T....

Toxoplasmosis In Pets 651 Cats

Most cats are asymptomatic during a primary T. gondii infection. Fever 40.0-41.7 C is present in many cats with clinical toxoplasmosis. Clinical signs of dyspnea, polypnea, and icterus, and signs of abdominal discomfort were the most frequent findings in 100 cats with histologically confirmed toxoplasmosis Dubey and Carpenter, 1993 . Uveitis and retinochoroiditis are also common clinical signs in cats with toxoplasmosis. Gross and microscopic lesions are found in many organs, but are most...

The apicoplast genome

The number of plastid genomes per cell is contested. Based on nucleic acid hybridization, K hler et al. 1997 reported 5-6 copies per cell for the T. gondii plastid genome and a single plastid genome per cell for P. falciparum. This is consistent with a prior estimate of 1-2 copies for P. falciparum Wilson et al., 1993 . More recently, Matsuzaki et al. 2001 have re-examined genome copy number by measurement of apicoplast-localized fluorescence following DAPI staining. Their analysis suggests 25...

Toxoplasmosis In Zoos

Toxoplasmosis is a zoo management problem because wild felids can excrete T. gondii oocysts in their feces Jewell et al., 1972 Miller et al., 1972 Lukesov and Liter k, 1998 and because of the occurrence of feral cats in zoos Gorman et al., 1986 . Oocysts excreted by these felids can make their way into highly susceptible species. Mammalian species that frequently develop toxoplasmosis in zoos include Australian marsupials Dobos-Kovacs, 1974 Boorman et al., 1977 Dubey et al., 1988a Hartley et...

Murine models of ocular toxoplasmosis

One example of a murine model of ocular toxoplasmosis is the injection of tachyzoites into the anterior chamber of the mouse Hu et al., 1999 . The technique is to remove some aqueous humor by paracentesis. The eye is a closed environment, and removing fluid reduces the risk of raised intraocular pressure. This is followed by an injection of 5 pL of parasite suspension in Dulbecco's modified Eagle medium. It should be noted, however, that the most significant route of transmission of ocular...

T gondii displays a uniquely simple pathway for amylopectin synthesis

Using bioinformatic searches, several gene candidates encoding enzymes that are probably involved in amylopectin biosynthesis were identified Coppin et al., 2005 . These putative enzymes can be grouped in two classes 1. Enzymes that are involved in amylopectin synthesis, such as amylopectin synthase, branching enzymes, UDP-glucose pyrophosphorylase, isoamylase, indirect debranching enzyme, a-1, 4-glucanotransferase, and glycogenin 2. Enzymes for amylopectin degradation, like a-amylase, dikinase...