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The effects of the extrinsic incubation temperature on the vector competence of Culex univittatus Theobald for West Nile (WN) virus were studied. A mean titer of 7.0 log10 CPD50/ml of mosquito suspension was reached in orally infected mosquitoes after 11, 15, and 16 d of incubation at 26 and 30 degrees C and at fluctuating temperatures in an outside cage (mean temperature, 23.5 degrees C), respectively. In contrast, 22 and 58 d were required to reach the same titers at 18 and 14 degrees C, respectively. Transmission rates of 100% were reached after 58 d (14 degrees C), 22 d (18 degrees C), and 15 and 16 d (30 degrees C and outside). Except at 30 degrees C, transmission rates fluctuated; e.g., at 18 degrees C from day 19, the transmission rate was 80-100%, whereas at 14 degrees C on day 36, the transmission rate was 60% and thereafter 20-100%. The maximum transmission rate occurred concurrently with maximum titers of virus secreted into capillary tubes during in vitro transmission attempts. Mosquito longevity increased as incubation temperature decreased and was maximum at 114 d at 14 degrees C. Mosquitoes that were transferred from 14 to 26 degrees C after 49 d subsequently oviposited, engorged on a pigeon, and transmitted virus, which indicated the possibility for overwintering of WN virus in adult Cx. univittatus. Vector competence at outside cycling temperatures was intermediate between that at 26 and 30 degrees C, indicating that incubation at 26 degrees C would give a fair reflection of the vector competence of Cx. univittatus during the summer near Johannesburg. Two human epidemics of WN virus are reevaluated in the light of these results; it is concluded that, in addition to abnormal rainfall, higher than normal temperatures were important factors for their occurrence.

Cytomegalovirus (CMV) is probably the most common agent of prenatal infection of the newborn, and one of 20 congenitally infected newborns shows serious symptoms. It was therefore considered important to be able to differentiate primary CMV from reactivation in pregnant females. A urea denaturation test was used to distinguish primary from secondary rubella infection in which the urea is included in the wash step of the standard IgG ELISA. This resulted in the removal of low-avidity antibodies, which are the antibodies produced early in infection. A group of CMV IgM-negative and -positive sera were tested, and all but one showed moderate to high avidity, with an avidity index reading of more than 30%. Among a group of babies 3-12 months of age, who were CMV IgM positive, 55% (16 of 29) showed low-avidity CMV antibodies. A small group of renal transplant patients and patients with clinically and laboratory-confirmed CMV gave more or less predicted avidity index results. It appears that, with the method used at this laboratory, the urea denaturation test can be applied to CMV to determine primary infection or reactivation in the majority of cases.

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Longitudinal muscle growth was studied in normal and spastic mice. Muscle growth takes place at the musculotendinous junction-the 'muscle growth-plate'. In spastic mice muscle growth is reduced by 45 per cent, resulting in contractures. RESUMECroissance musculaire chez les souris normales et spastiques La croissance longitudinale du muscle a it6 etudite chez la souris normale er spastique. La croissance musculaire est sit& i la jonction musculo-tendineuse, plaque de croissance du muscle. Chez les souris spastiques, la croissance est rtduite de 45 pour cent provoquant des rktractions. ZUSAMMENFASSUNG Muskelentwicklung bei normalen und spastischen MausenBei normalen und spastischen Mausen wurde das Langenwachstum der Muskeln untersucht. Das Muskelwachstum erfolgt in der Ubergangszone zwischen Sehne und Muskel-der 'Muskelwachstumsplatte'. Bei spastischen Mausen ist das Muskelwachstum um 45 Prozent reduziert, was zu Kontrakturen fuhrt. RESUMENCrecimiento muscular en ratones normales y espasticos Se estudi6 el crecimiento muscular longitudinal en ratones normales y espasticos. El crecimiento muscular tiene lugar en la conexi6n misculotendinosa-la "placa de crecimiento muscular". En 10s ratones espasticos el crecimiento muscular esti reducido en un 45 por ciento, dando lugar a contracturas. m Q\ .J m W-N d