PATHOPHYSIOLOGICAL ASPECTS OF MECISTOCIRRUS-DIGITATUS (NEMATODA, TRICHOSTRONGYLIDAE) INFECTION IN CALVES

Three groups of four calves were experimentally infected with infectio us larvae of Mecistocirrus digitatus. One group received a trickle inf ection of 5000 L-3 per day for 8 days, the other two groups received a single infection of 5000 and 40000 L-3, respectively. All animals wer e necropsied 120 days after infection. Prepatent periods varied betwee n 61 and 79 days, and maximal faecal egg output was reached between 80 and 100 days after infection. Repeated infections were not additive a nd worm counts at 120 days after infection varied between 100 and 440 in the first two groups and between 120 and 1700 in the last group. Th ere was no significant difference in worm counts between the different infection regimes. However, there was a significant positive relation ship between worm burden and faecal egg counts. Ln addition, there wer e significant negative relationships between worm burden and packed ce ll volume, and weight gain. The relative decreases in packed cell volu me and weight gain emerged 70-80 days after infection. Serum pepsinoge n levels were significantly elevated by the end of the trial, but the observed positive relationship between worm burden and pepsinogen was not significant. An enzyme immunoassay based on crude adult antigen wa s able to detect M. digitatus infection at 90 and 100 days after infec tion, but again there was no significant association between worm burd en and antibody levels. Therefore, anaemia and a reduction in weight g ain caused by the haematophagous activity of adult stages seem to be t he most important pathogenic effects of M. digitatus infection in calv es. (C) 1997 Elsevier Science B.V.