The longevity of Hymeonlepis microstoma in mice, and its immunological cross-reaction with Hymenolepis diminuta

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Abstract
Hymenolepis microstoma was found to live for at least 728 days in a mouse, but an initial infection of 10 worms per mosue decreased exponentially for approximately the first 110 days to a level of 3–5 worms, after which little further loss occurred.A primary infection of six H. microstoma, expelled with anthelmintic on day 21, strongly protected against a single worm H. diminuta challenge; worms in 80 ‘immunized’ mice weighed less than 5% of the weight of worms from 80 control mice. However, a primary (5-worm) H. diminuta infection led only to a small, though statistically significant, decrease in weight of the 3-worm H. microstoma challenge.The results are interpreted as indicating that H. microstoma evokes a strong immunological response which cross-reacts with H. diminuta. The failure of H. diminutato protect strongly against a 3-worm challenge by H. microstoma suggests, as does the long survival of a primary infection when it is reduced to approximately 4 worms, that H. microstoma survives in low infection because it is able to avoid the immune response. This could be due to antigen camounflage, ability to repair immune damage or to the low permeability of the bile duct wall to components of the immune response. The worm loss which occurs from heavy infection until only 3–5 worms remain may be physiologically rather than immunologiacally mediated.