Laboratory of Parasite Immunology, Department of Biology, University of Puerto Rico, Center for Field and Applied Research, Ministry of Health, Department of Tropical Medicine, Tulane University, School of Public Health and Tropical Medicine, Río Piedras, Puerto Rico 00931, Arab Republic of Egypt
The circumoval precipitin (COP) test was used to detect serum antibodies to Schistosoma mansoni, S. haematobium, or both species by using eggs of either species of schistosome. Eggs of either species were adequate as antigens but, in general, the sera of S. mansoni-infected individuals caused more circumoval precipitates for form around S. mansoni eggs (higher reactivity) than did the sera of S. haematobium-infected individuals. However, sera from individuals with either or double infections reacted equally with S. haematobium eggs. In addition, more circumoval precipitates were formed around S. haematobium eggs obtained from human urine than around S. mansoni eggs obtained from mouse livers. We demonstrate that human infection with either species of schistosome can be diagnosed by the COP test, but that identification of the schistosome species involved in the infection is not possible with this test. In addition, by eliminating the need for maintaining a schistosome life cycle in the laboratory the demonstration of the high reactivity of S. haematobium eggs from urine greatly simplifes the performance of the COP test in areas where S. haematobium-infected individuals can be found and will cooperate by providing urine. We also obtained serum specimens by venipuncture, and capillary blood dried on filter paper, from Egyptians infected with S. mansoni, S. haematobium, or with both species of schistosome. Serum eluted from the filter paper was then compared with serum from venipunctures with respect to their reactivity in the COP test done with fresh S. haematobium eggs as antigen. Serum eluates from freshly dried blood were significantly less reactive than serum obtained by venipuncture in terms of positive reactions and characteristics of the COP precipitate. Storage of the filter paper blood at 4°C for 6–12 months resulted in an even greater reduction of reactivity. Thus, for the COP test serum obtained by venipuncture is preferable to serum eluates obtained from blood on filter paper for the serodiagnosis of infection with S. mansoni and S. haematobium.