Infectivity, growth, distribution and acetabular attachment of a one-hundred metacercarial cyst inoculum of Echinostoma trivolvis in ICR mice.

Female ICR mice, 6-8 weeks old, were exposed to 100 metacercarial cysts/host of Echinostoma trivolvis to determine the effects of this cyst dosage on worm infectivity, distribution, growth and acetabular attachment in the host small intestine. Of 42 exposed mice, 22 were infected 4 to 17 days postinfection (PI) with a mean worm recovery of 11 to 41%. Mean body area of worms increased from about 0.4 mm2 on day 4 PI to about 2.0 mm2 by day 9 PI. No consistent pattern of worm growth was seen beyond day 9. Distribution data showed that worms were found mainly in the anterior part of the small intestines on day 4 PI and then more posteriorly up to day 8 PI. Worm distribution patterns were quite variable beyond day 11 PI. Scanning electron microscopy showed that the acetabulum left a distinct 'fingerprint' or acetabular plug on the intestinal mucosa of the host. The 'fingerprint' was temporary and disappeared within 1 min after worms were removed from the intestines.