SCHISTOSOMA MATTHEEI INFECTIONS IN CATTLE - CHANGES ASSOCIATED WITH SEASON AND AGE

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 f or the intermediate host, Bulinus globosus. Individual faecal egg excr etion reached an average peak of 130 eggs per gram, around 9 months af ter birth and decreased markedly before the age of 18 months. Average counts declined significantly with age, down to less than five eggs pe r gram in adult cows. A seasonal increase in B. globosus snails and S. mattheei transmission during the rainy season had no effect on the eg g output of animals older than 18 months. Two calves and two adult cow s 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 fr om the large intestine towards the liver was also observed as infectio n progressed. It is concluded from the results of faecal egg counts th at cattle reared under conditions of continuous challenge develop acqu ired resistance to S. mattheei infection within the first year followi ng primary infection. Comparison of fluke and tissue egg counts in far m animals of different ages suggests the acquisition of an anti-fecund ity effect as infection progresses.