A total of 28 components were detected in the free amino acid (FAA) pool of hydatid fluid from primary and secondary equine cysts, secondary ovine cysts and host plasma. Examination of data from equine cysts revealed that the majority of FAAs were present in significantly greater concentrations in secondary cysts, glycine being over 30 times more concentrated. Values for total carbohydrates and glucose did not, however, differ significantly and total protein content was greater in primary cysts. Comparison of the (FAA) pool of secondary equine and ovine cysts revealed strain variation. It was demonstrated that most FAAs were more concentrated in hydatid fluid than in the corresponding host plasma, many concentration ratios exceeding 10. The possible contribution that mediated amino acid transport across the cyst wall and parasite amino acid metabolism makes to the composition of the FAA pool was discussed. No significant plasma aminoacidaemia was associated with infection.
