Schistosoma japonicum: Day to day variation in excretion and hatchability of parasite eggs in the domestic pig, Suis suis

The aim of the present study was to describe the course of an Schistosoma j aponicum infection in individual pigs over time, with special regards to fe cal egg counts and egg hatchablilty, emphasizing the extent of variation du ring and between days. Five specific pathogen free Danish Landrace/Yorkshir e/Duroc crossbred male pigs were each given 3500 cercariae intramuscularly. From day 36 to 62 post infection, fecal samples were collected from each p ig, morning and evening. Pigs were perfused 62 days post infection. Actual fecal egg counts, miracidial counts, and worm burdens were determined. The trend of fecal egg excretion was adequately described with a third order po lynomial and logarithmic link function. Miracidial counts were related dire ctly to morning fecal egg counts through a simple linear function. The stud y revealed a fairly similar overall pattern of egg excretion for all pigs, showing an increase in egg excretion until week 8, followed by a marked red uction to almost zero. In general, large fluctuations around this trend wer e seen for all pigs, as revealed in variations in egg counts within the sam e day as well as between days. However, as revealed by the estimated model lines, these fluctuations are due to random variation in egg density in sto ols rather than being caused by biologically determined cycles. An exact ti me for both first occurrence of eggs in feces (days 35-38 post infection) a nd for peak egg counts (days 44-48 post infection) was predicted for each i ndividual pig. Furthermore, the model revealed that miracidial counts can b e related directly to the expected fecal egg counts of the same day through a parameter, which represents hatchability. This hatchability parameter wa s found to be independent of time post infection for each pig, but large in dividual differences were seen in hatchability between the pigs. (C) 2000 A cademic Press.