Evaluation of natural transmission of bovine leukaemia virus within dairy herds of Argentina.

The purpose of this study was to describe patterns of seroconversion to bovine leukaemia virus and to estimate the main parameters needed for future model building. A longitudinal study was carried out between February 1999 and November 2001 in seven commercial dairy farms in Argentina using 1535 lactating cows. Time-interval parameters were analysed using a parametric survival model with shared frailty, time until infection was analysed using a Bayesian interval-censoring survival model and the infection transmission parameter (beta) was estimated by a generalized linear model. The reproduction ratio (R0) was calculated. In total, 1000 cows tested positive and 494 tested negative. The predicted median age at infection was 4.6 years for seroconverted cows. For infected herds, the proportion of positive calves was as high as for infected cows and showed a large proportion of infected breeding heifers. Peaks in the overall average incidence per season-year were observed during autumn and spring. Results reveal that the period around parturition is a high-risk period. Moreover, heavily infected herds seem to have an increased proportion of young stock infected. The overall beta was estimated as 2.9/year (95% CI 1.9-3.7) and combined with a relatively long infectious period it resulted in a high reproductive ratio (R0=8.9). Therefore, a high effectiveness of control measures needs to be achieved to eradicate the disease.

Growth and sexual maturation in children after kidney transplantation.

Linear growth and sexual maturation were assessed in 68 long-term pediatric renal allograft recipients (43 boys) receiving daily or alternate-day prednisone therapy. Growth was analyzed both during the prepubertal period and during puberty. Height at transplantation was greater than 2 SD below the mean in 34.2% of prepubertal children. After the first posttransplant year, 59.2% of the prepubertal children had a normal height increment (greater than 4.8 cm/yr). Onset of puberty was recorded at a chronologic age of 14.6 +/- 1.9 years in boys and 13.3 +/- 1.9 years in girls. Height at onset of puberty related to chronologic age was -2.4 +/- 1.3 SD. Height velocity during puberty was within normal limits in 62.5% of the children. No significant difference in pubertal growth was detected in patients who had received transplants before and after the onset of puberty. Duration of pubertal development was within normal limits. In girls, menarche was achieved at a mean chronologic age of 15.9 years and bone age 12.9 years. Adult height was attained at an average age of 20.3 years in boys and 18.7 years in girls. Overall, one third of the children attained an adult height greater than 2 SD below the mean. Our data indicate that although poor growth before kidney transplantation has a great influence on adult height, the loss of growth potential during pubertal development seems even more important.