Assessing the effects of multiple infections and long latency in the dynamics of tuberculosis

In order to achieve a better understanding of multiple infections and long latency in the dynamics of Mycobacterium tuberculosis infection, we analyze a simple model. Since backward bifurcation is well documented in the literature with respect to the model we are considering, our aim is to illustrate this behavior in terms of the range of variations of the model's parameters. We show that backward bifurcation disappears (and forward bifurcation occurs) if: (a) the latent period is shortened below a critical value; and (b) the rates of super-infection and re-infection are decreased. This result shows that among immunosuppressed individuals, super-infection and/or changes in the latent period could act to facilitate the onset of tuberculosis. When we decrease the incubation period below the critical value, we obtain the curve of the incidence of tuberculosis following forward bifurcation; however, this curve envelops that obtained from the backward bifurcation diagram.

Luteal function and follicular growth following follicular aspiration during the peri-luteolysis period in bos indicus and crossbred cattle

Follicular estradiol triggers luteolysis in cattle. Therefore, the control of follicle growth and steroidogenesis is expected to modulate luteal function and might be used as an anti-luteolytic strategy to improve embryo survival. Objectives were to evaluate follicular dynamics, plasma concentrations of estradiol and luteal lifespan in Bos indicus and crossbred cows subjected to sequential follicular aspirations. From D13 to D25 of a synchronized cycle (ovulation = D1), Nelore or crossbred, non-pregnant and non-lactating cows were submitted to daily ultrasound-guided aspiration of follicles >6 mm (n = 10) or to sham aspirations (n = 8). Diameter of the largest follicle on the day of luteolysis (7.4 +/- 1.0 vs 9.7 +/- 1.0 mm; mean +/- SEM), number of days in which follicles >6 mm were present (2.3 +/- 0.4 vs 4.6 +/- 0.5 days) and daily mean diameter of the largest follicle between D15 and D19 (6.4 +/- 0.2 vs 8.5 +/- 0.3 mm) were smaller (p <0.01) in the aspirated group compared with the control group, respectively. Aspiration tended to reduce (p< 0.10) plasma estradiol concentrations between D18 and D20 (2.95 +/- 0.54 vs 4.30 +/- 0.55 pg/ml). The luteal lifespan was similar (p > 0.10) between the groups (19.6 +/- 0.4 days), whereas the oestrous cycle was longer (p <0.01) in the aspirated group (31.4 +/- 1.2 vs 21.2 +/- 1.3 days). Hyperechogenic structures were present at the sites of aspiration and were associated with increase in concentration of progesterone between luteolysis and oestrus. It is concluded that follicular aspiration extended the oestrous cycle and decreased the average follicular diameter on the peri-luteolysis period but failed to delay luteolysis.