CIRCULATING ANTIGEN LEVELS IN SERUM OF CATTLE NATURALLY INFECTED WITHSCHISTOSOMA-MATTHEEI

Levels of 2 Schistosoma circulating antigens, the circulating anodic a ntigen (CAA) and the circulating cathodic antigen (CCA), were determin ed in serum samples collected, on a monthly basis over a period of 1.5 years, from 32 farm animals of different ages and from 12 tracer calv es exposed to Schistosoma mattheei infection on a Zambian farm. Faecal egg counts were monitored in all animals and worm burdens in tracers determined after perfusion. Antigen determination tests in serum, with sensitivities between 95 and 100% in heifers and adult cows, proved t o be excellent tools for the diagnosis of cattle schistosomiasis. Also in young calves, some infections could be demonstrated earlier by CCA determination than by faecal egg examination. A poor correlation was seen between the data for faecal egg counts and for CAA and CCA levels . It therefore appears that circulating antigen measurements in serum are of limited Value as indicators of the pathogenesis of infection in cattle. Although all tracer calves were found infected at perfusion, large variations were recorded in antigen levels. An unexpected findin g was the observation in farm animals of a clear seasonal pattern in C AA levels, with significant increase between August and October during the second half of the dry season, when animals are subjected to heav y physical and nutritional stress. It therefore appears that, although circulating antigen determination may provide an indication of the wo rm burden in ageing infections, possible Variations of antigen clearan ce rate with the physiological condition of the host may complicate th e interpretation of the results.