Toxoplasma gondii: Presentations at the IX International Workshop onOpportunistic Protists and the International Society of

Protistologists 57th Annual Meetings

SHEILA MITCHELLa and ANTHONY SINAIb

aDepartment of Biomedical Sciences and Veterinary Medical Sciences, Center for Molecular Medicine and Infectious Diseases,

Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, Virginia, andbDepartment of Microbiology Immunology and Molecular Genetics, University of Kentucky College of Medicine, Lexington, Kentucky 40536

Anumber of reports on the basic biology, epidemiology, andtreatment of Toxoplasma gondii were presented at the joint

meetings of the IX International Workshop on Opportunistic Pro-tists (IWOP-9) and the International Society of Protistology.Highlights of these presentations are provided below.

Toxoplasma gondii, long recognized as an opportunistic patho-gen in terrestrial mammals appears to be increasingly found in themarine mammal population. A collaborative study by workers onthe west coast of North America was reported by W. A. Millerwho presented convincing evidence for the spread of Toxoplasmaoocysts from terrestrial runoff into the marine ecosystems wherethey appear to be concentrated in resident shellfish. These shell-fish, a major dietary input of the California sea otter serve as amechanism of transmission. Otters are remarkably susceptible toinfection that manifest as encephalitis and contributes to signifi-cant morbidity and mortality. In addition, evidence for infectionwith the parasite Sarcocystis neurona was also observed.

James et al. from the same research team on the West Coastexamined the genotype of the Toxoplasma isolates derived frommarine mammals. Remarkably, based on genotypic analysis andRFLP analysis this group reports the existence of a distinct typedesignated Type X that is distinct from the classical Type I, II andIII clonotypes. Molecular analyses aimed at identifying the basisfor these changes and results toward that end were presented.

In addition to these platform presentations two posters exam-ined the epidemiological distribution of Toxoplasma infection inhumans in the Czech Republic (Kodym et al.) and farm animals inPortugal (Sousa et al.). Their results are consistent with prior ep-idemiological studies in Europe and the United States suggesting astable population structure. In addition the Czech study using ser-ology showed that the incidence of toxoplasmosis within the HIV-positive population. When seroconversion was detected, it oc-curred in middle-aged patients (age 35–65 years). Not surprisinglythe incidence of Toxoplasmic encephalitis (TE) was significantlyhigher in patients with active AIDS disease (18.5%) as comparedwith those whose HIV status had not progressed to AIDS (4.7%).

A platform presentation by J. Menotti and colleagues in Paris,France examined current diagnostic regimens for the detection ofToxoplasma DNA in tissue samples. The specific target was ahighly repetitive AF146527 gene. Real-time PCR was used toamplify a fragment of this gene and they compared these resultswith those that targeted the B1 gene in previous studies. Of 347samples tested 15 that had tested negative using the marker B1were found to be positive using AF146527. These 15 were frompatients shown to have toxoplasmosis therefore, targeting thishighly repetitive gene combined with real-time PCR offers greater

sensitivity for detecting T. gondii. DNA-based techniques for de-tection are critically important in the context of immune suppres-sion where the serological response is unreliable.

Although multiple treatments for T. gondii infections exist,pyrimethamine alone or in combination with sulfadiazine is stillthe universal treatment. S. M. Mitchell in D. Lindsay’s researchgroup at Virginia Tech, examined the efficacy of ponazuril(a major metabolite of toltrazuril) against TE using an inter-feron-g knockout mouse model. Immunohistochemistry for tissuecysts and tachyzoites was performed on brain sections from micethat died or were euthanized. Mice that were treated with ponaz-uril or sulfadiazine were found to have fewer brain cysts than theuntreated group. These investigators concluded that ponazurilprevents TE when given at a dose of 20 mg/kg body weight, oncea day for 10 days.

Aspects of the molecular and cell biology of Toxoplasma werepresented in several talks. The efficient applications of interferingRNA approaches to control gene expression in Toxoplasma havebeen limited by technical problems. Work presented by S. Anan-voranich from the University of Windsor, Canada reported onsome significant advances including demonstration of the molec-ular machinery for RNA silencing. Also, introduction of the deltavirus ribozyme system affords a greater level of sensitivity andcontrol. Development of this system still in its early stages prom-ises to be a significant asset to the field.

With regard to the cell biology of Toxoplasma J. Murray fromthe University of Pennsylvania presented elegant studies thatexamined the temporal progression of endodyogeny using cyto-skeletal components tagged with fluorescent proteins. Further-more, the dynamics of nuclear division were monitored in real-time using histone YFP-expressing parasites. These tools providea rare insight into the dynamics of parasite replication.

Toxoplasma invasion is a highly regulated event governed inpart by proteolytic processing at the parasite surface. The role ofintermembrane cleavage by the rhomboid proteases was discussedby Dowse et al. who presented work on five rhomboid proteins(TgROM106) found in T. gondii. Five of the six are expressed intachyzoites while the expression of ROM3 is restricted to oocysts.That TgROM1, TgROM2 and TgROM5 are in fact active prote-ases was confirmed using the Drosophila target Spitz as a surro-gate substrate.

As a part of the ISOP symposium on ‘‘Intracellular and Host-Pathogen Membrane Traffic,’’ A. Sinai, University of Kentucky,reported on their latest findings on the biology of the parasito-phorous vacuole membrane (PVM) surrounding intracellulartachyzoites. The data indicate that the PVM is a dynamic organ-elle involved in the structural interactions, nutrient acquisition andsignaling. In addition, progress in the proteomic identification ofPVM-localized proteins was reported.

In summary, the scientific presentations at this conferencehighlight advances in the basic biology and epidemiology of T.gondii. Interactions with other protistologists and investigatorsworking on opportunistic pathogens revealed both common anddistinct aspects in their basics biology.

Corresponding Author: A. Sinai, Department of Microbiology Im-munology and Molecular Genetics, University of Kentucky Collegeof Medicine, 800 Rose St., Lexington, KY 40536, USA—Telephonenumber: 11-859-323-6680; FAX number: 11-859-257-8994; e-mail:sinai@uky.edu

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J. Eukaryot. Microbiol., 53(S1), 2006 pp. S159r 2006 The Author(s)Journal compilation r 2006 by the International Society of ProtistologistsDOI: 10.1111/j.1550-7408.2006.00214.x