Reactivation of chronic toxoplasmosis resulting in Toxoplasma encephalitis (TE) is a common event in acquired immune deficiency syndrome (AIDS) patients. Conversion from Toxoplasma gondii bradyzoites to tachyzoites is a prerequisite for reactivation. Until recently, the study of stage conversion in human tissue was not possible due to the lack of antibodies that recognize stage-specific epitopes after long-term formaldehyde fixation. Using the combination of a polyclonal anti-T. gondii antibody, the cyst-stage-specific monoclonal antibody CC2, and a tachyzoite-specific polyclonal antibody (anti-SAG1, recombinant), we tried to demonstrate parasite differentiation in the brain tissue of 10 AIDS patients with clinically suspected TE. Double labeling of the stage-specific antibodies enabled us to demonstrate interconversion between tachyzoites and bradyzoites for the first time in human tissue. The study confirmed that the transformation process is nonsynchronous and that the manifestation of TE depends on the degree and site of tissue destruction caused by invading tachyzoites. The original source of tachyzoites could never be located, but a few samples suggested that tachyzoites may invade by dissemination across the blood–brain barrier. Cyst rupture as the first event in the process of reactivation was not seen. We conclude that the initial site(s) of reactivation will be destroyed by tissue-destructive tachyzoites long before clinical symptoms occur.

BACKGROUND:Alveolar echinococcosis (AE) primarily affects the liver and extrahepatic disease is considered the consequence of a secondary infection via metastatic spread from the hepatic focus.PATIENTS:Two patients with extrahepatic AE without liver involvement are presented. The first case is a patient with AE of the spleen and a small pulmonary calcification. In the second case exclusive affection of the spine was observed.DISCUSSION:Various pathogenetic explanations for hepatic omission appear plausible: a passage of oncospheres through hepatic sinuses without causing disease, a passage via lymphatic vessels or via portocaval anastomoses and the vascular passage in a retrograde fashion. Extrahepatic manifestation of AE without apparent liver involvement is rare. However, AE should be taken into account among other differential diagnoses even in cases of extrahepatic lesions without liver involvement.

The dye test for the detection of Toxoplasma-specific antibodies was first described by Sabin and Feldman 50 years ago. The test is highly specific and sensitive and considerable information is available on the development and persistence of dye test antibodies after primary Toxoplasma infection. However, the test uses live Toxoplasma gondii and is now only employed in a few laboratories. It is still the reference method for the serodiagnosis of toxoplasmosis, and a multicentre study comparing dye test results between different laboratories was much needed.We report in this article the results of a multicentre evaluation of the test involving nineteen laboratories in eight countries. The study revealed overall satisfactory standardization between the laboratories, but there were differences in the test protocols, the use of reference/standard preparations and the interpretation of results. There is still no agreement on the level of dye test values which reflect infection with the parasite, and conversion from titres to international units (IUs) did not improve standardization. However, the results indicated that a value of > 4 IU or a titre of 1:16 met the definition of positivity of most participants.We recommend that the dye test be retained as a reference method and that interlaboratory standardization be improved by the use of a common protocol and the expression of results in titres.

There is much hope that HIV-infected patients and AIDS patients can reckon with a prolonged survival in future. The increased survival of AIDS patients with positiveToxoplasma serology is not necessarily associated with an increased risk of developingToxoplasma encephalitis. For HIV-infected patients with negativeToxoplasma serology, the probability of acquiring a primaryToxoplasma infection in highly endemic areas such as Germany had not been studied to date. One hundred eighty-three HIV-infected patients were followed up between 1987 and 1995 in a retrospective study. Within the cohort, 95% of the patients were male and 83% haemophiliacs. The initial (1987) and final (1995) prevalence rate ofToxoplasma antibodies was 33.3% and 36.6%, respectively. The annual rise of the primary infection rate was calculated as 0.41%. The dye test was used for the detection ofToxoplasma-specific antibodies. This assay proved to be reliable and stable during long-term observation. The rate of primary toxoplasmosis found in this long-term study was not higher than that of pregnant women in Germany. Chemoprophylactic measurements for seronegative HIV-infected patients are therefore not recommended, but regular serological screening to detect seroconverters is.

A murine model of pulmonary toxoplasmosis was examined morphologically and immunochemically using 3 strains of Toxoplasma gondii. BALB/c and NMRI mice were infected with tachyzoites of a virulent strain (RH) or with brain cysts of an avirulent (GAIL), or moderately virulent, strain (NED). Depending on the strain of T. gondii, the degree of infection, number of parasites, and replicative potential of T. gondii in lungs varied. In lungs of mice infected with the RH strain, the number of parasites increased in mice during the survival period. Only tachyzoites were found, as confirmed by stage-specific monoclonal antibodies. In lungs of mice infected with the GAIL strain or the NED strain, different stages of parasites were detected. Up to day 14 after infection, only tachyzoites were present, followed by bradyzoites between days 14 and 20 after infection. The number of cysts decreased and finally could not be detected in this organ. In general, the number of cysts that developed in the lungs was smaller than the number that developed in the brain.

The sera of 849 Tanzanian pregnant women were tested at delivery for Toxoplasma gondii antibodies with the Sabin-Feldman dye test (DT) and an immunosorbent agglutination assay. A total of 296 (35%) of these women had DT titers greater than 1:4. The percentage of women with dye test titers greater than 1:4 was 34-37% regardless of the individual ages. The rate of positivity for human immunodeficiency virus 1/2 (HIV-1/2) using Western blotting was 11.5%. There was no relationship between prevalence of a positive DT result and HIV infection nor between the intensity of the DT result and HIV infection. Sixty-four parturients had a DT titer of 1:1,000 or more. From 57 newborns of these mothers, cord sera were available and were screened by the DT and the immunosorbent agglutination assay. Seven of these were found to be positive for IgM and/or IgA antibodies. It was concluded that the rate of serologic evidence for prenatal Toxoplasma infection in cord blood samples in the present study of Tanzanian pregnant women was approximately 0.8%.