[Kinetics of the population of worms in various developmental stages, Haemonchus contortus in sheep after a single experimental infection] experimental infection].

This work was performed to study, in 147 month-old male lambs experimentally infected with 14000 Haemonchus contortus infective larvae and slaughtered at 6, 12, 18 and 24h and at 2, 6, 8, 11, 15 and 39 days post-infection (pi): 1, the importance, localisation and nature (with or without sheath) of the worms during the first 24 h pi; 2, the kinetics of the total worm population and of each evolutionary stages from the first to the 39th day pi: 3, the period of emergence of the fourth-stage larvae from the mucosae; 4, the topographic distribution of the different evolutionary stages of the parasite in the abomasum. During the first 24 h pi, the total worm population and that of the intramucosal larvae increase in lineary function to time (r = 0.98). After a maximum value, reached between 24 and 48 h pi, the total worm population decreases in lineary function to time (r = -0.94). Only 52% approximately of the larvae administered develop. One of the reasons is the fact that a proportion of 3rd stage larvae cannot leave their sheath during the rumino-omasal transit. Other limiting factors are discussed. The fourth-stage larvae appear in the mucosae 24 h pi. Their emergence from the mucosae starts between day 1 and 2 pi and increases in intensity from days 2 to 6 pi. The immature adults and the adults are encountered from days 6 and 14 pi respectively, and the prepatent period is on average 16 days.(ABSTRACT TRUNCATED AT 250 WORDS)