[Serodiagnosis of toxoplasmosis: a comparative multicenter study of a standard scale through various actual tests and expression of the results in international units. Groupe de travail toxoplasmose du Contrôle national de qualité en parasotologie. Syndicat des fabricants de réactifs de laboratoire. Groupe de travail standardisation des tests sérologiques du Réseau européen de lutte contre la toxoplasmose congénitale]. / Le sérodiagnostic de la toxoplasmose: etude comparative multicentrique d'une gamme étalon, par les différents tests actuels et avec expression des résultats en unités internationales. Groupe de travail toxoplasmose du Contrôle national de qualité en parasitologie, Syndicat des fabricants de réactifs de laboratoire, Groupe de travail standardisation des tests sérologiques du Réseau européen de lutte contre la toxoplasmose congénitale.

Reported are the results of a multicentre study involving 40 laboratories that was carried out in France to assess all the currently available methods used for the serodiagnosis of toxoplasmosis. For this purpose 10 batches of control sera were prepared with titres in the range 0-260 IU per ml. These sera were tested in nine laboratories using immunofluorescence methods; in three laboratories using dye tests; in forty laboratories using enzyme-linked immunosorbent assay; in four laboratories using direct agglutination and haemagglutination; in seven laboratories using the high-sensitivity IgG agglutination test; and in three laboratories using the latex agglutination test. In this way, 70 series of titrations were carried out using seven procedures and the results were compared with those obtained using the WHO reference serum in 15 cases, with the French national E6 serum in 16 other cases, and in 39 cases using 15 reference sera supplied by the reagent manufacturers. Rigorous comparison of the tests was not possible in all cases because one aim of the study was to ensure that the tests were carried out under the usual working conditions that prevailed in the participating laboratories. The results obtained indicate that the serological tests currently available for toxoplasmosis are acceptable for its serodiagnosis. Presentation of the titres in IU has advantages; however, caution is required since the definition of IU varies according to the test and reagents used. It is therefore essential that the conditions and limits for a positive reaction be carefully defined in each case, especially for commercially available kits.

Performance of European laboratories testing serum samples for Toxoplasma gondii.

One hundred twenty-nine European laboratories participated in a collaborative, multicentre study designed to evaluate the overall reliability of different serological techniques for diagnosis of Toxoplasma gondii infection. Five freeze-dried reference sera were distributed to each laboratory, each of which analysed the sera with its routine methods. The enzyme-linked immunosorbent assay was the technique used most frequently, followed by the immunofluorescent antibody technique. Only nine laboratories performed the Sabin-Feldman dye test. In general, there was good concordance between qualitative results, but for sera with low concentrations of Toxoplasma gondii-specific IgG antibodies, some false-negative results were found. For specific IgM and IgA antibodies, the immunosorbent agglutination assay proved the most sensitive. The present study demonstrates the need for regular assessment of laboratory serodiagnosis of Toxoplasma gondii infection.

[Prevention of AIDS transmission by syringes and needles in France and Africa]. / Prévention de la transmission par les seringues et aiguilles du V.I.H. en France et en Afrique.

A study made among drug addicts in the Northern suburbs of Paris enables establishing a stabilisation of positive H.I.V. serology prevalence among them, a fact related to the free sale of syringes and needles. In Africa, the nosocomial transmission of H.I.V. by non-sterilisable but reused needles and syringes is demonstrated, and two cases are described. Its importance is certain but must be precise. The prevention of this epidemiological modality must be done by systematic use of reusable and sterilisable injectable material.

PIP: Reuse of disposable needles and syringes plays an important role in the transmission of HIV in France as in Africa. From September 1985-March 1986, 51% of drug addicts systematically screened in the northern suburbs of Paris were found to be HIV positive. Studies in the same population through 1988 indicated that the rate of HIV infection had remained stable, as had the average age of addicts, duration of addiction, and sex ratio. Stabilization of seropositivity rates among drug addicts in the northern suburbs in believed to have been due to information programs alerting addicts to the risk of contamination through sharing of needles and to the legal sale of syringes and needles instituted in May 1987. HIV transmission through reuse of disposable needles and syringes has been demonstrated in Africa. It is attributable to the poverty of health services and of the general population. The significance of HIV transmission by reuse of disposable materials in the health services appears to be considerable but is difficult to quantify. Prevention of transmission by this means will require correct use of sterilizable needles and syringes.

[Opportunistic aspects of parasitosis]. / Aspects opportunistes des parasitoses.

Parasitosis opportunist are becoming clearer thanks to a better knowledge of immunological mechanisms, especially in AIDS. Child immunological immaturity and corticotherapy are the two other main immunodeficiencies among opportunist parasitosis. For the protozoosis, coccidiosis (especially toxoplasmosis), cryptosporidiosis, but isosporosis too and microsporidiosis represent a privileged group among opportunistic infections. Among adult, leishmaniasis caused by L. infantum is an opportunist parasistosis, favoured by corticotherapy or AIDS, but among children, it is the child's immunological immaturity which is involved in the immunodeficiency. Babesia occurs among splenectomized people. Giardiasis is more frequent and more severe among IgA immunodeficiencies especially secretories IgA. Among helminthiasis, generalised strongyloidiasis is very severe among patients under corticotherapy, but AIDS is not involved.

Probabilistic automata as a model for epigenesis of cellular networks.

Probabilistic automata are compared with deterministic ones in simulations of growing networks made of dividing interconnected cells. On examples of chains, wheels and tree-like structures made of large numbers of cells it is shown that the number of necessary states in the initial generating cell automaton is reduced drastically when the automaton is probabilistic rather than deterministic. Since the price being paid is a decrease in the accuracy of the generated network, conditions under which reasonable compromises can be achieved are studied. They depend on the degree of redundancy of the final network (defined from the complexity of a deterministic automaton capable of generating it with maximum accuracy), on the "entropy" of the generating probabilistic automaton, and on the effects of different inputs on its transition probabilities (as measured by its "'capacity" in the sense of Shannon's information theory). The results are used to discuss and make more precise the notion of biological specificity. It is suggested that the weak metaphor of a genetic program, classically used to account for the role of DNA in specific genetic determinations, is replaced by that of inputs to biochemical probabilistic automata.