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The Schistosoma mattheei egg output was monitored in 31 cattle over a 18-month period
on a dairy farm near Lusaka (Zambia). The animals were kept on pasture with free access
to two streams which were suitable for the intermediate host, Bulinus globosus. Individual
faecal egg excretion reached an average peak of 130 eggs per gram, around 9 months
after birth and decreased markedly before the age of 18 months. Average counts declined
significantly with age, down to less than five eggs per gram in adult cows. A seasonal
increase in B. globosus snails and S. mattheei transmission during the rainy season
had no effect on the egg output of animals older than 18 months. Two calves and two
adult cows were necropsied to compare fluke and tissue egg counts in young and old
infections. There was a marked decline in tissue egg accumulation in older cows, in
spite of an increase in the numbers of adult female flukes, as compared with young
animals. A shift of egg accumulation from the large intestine towards the liver was
also observed as infection progressed. It is concluded from the results of faecal
egg counts that cattle reared under conditions of continuous challenge develop acquired
resistance to S. mattheei infection within the first year following primary infection.
Comparison of fluke and tissue egg counts in farm animals of different ages suggests
the acquisition of an anti-fecundity effect as infection progresses.