Resistance to reinfection with Schistosoma japonicum in the mouse.

BALB/c and outbred mice infected with a Philippine isolate of Schistosoma japonicum for 50 to 60 days expressed strong resistance to reinfection. The extent of this reinfection resistance ranged from 72 to 93% in 5 experiments (mean = 80% resistance) as determined by numbers of immature worms recovered from already infected and age- and sex-matched challenge control mice exposed 20 days previously to cercariae. Determination of numbers of recoverable worms from (the initial) infection suggest that adult worms are lost progressively during the period in which impressive resistance to reinfection is demonstrable. An important unresolved question is whether loss of adult worms is related in any way to expression of resistance to reinfection. Some indirect evidence indicates that the major component of reinfection resistance is expressed prior to day 4 of challenge infection. This evidence derives from analysis of lung petechiae which, in a primary infection, have been shown to provide an indication of number of adult worms which can be detected subsequently (e.g. at 30-40 days of infection). Although anti-parasite immune response have not yet been shown to be responsible for this apparent concomitant immunity, the magnitude of resistance to reinfection in the S. japonicum/mouse system should facilitate identification of any immunological effector mechanisms involved.

Attempts to standardize the circumoval precipitin test (copt) for Schistosomiasis japonica.

The circumoval precipition test (COPT) is a simple and inexpensive immunodiagnostic test for schistosomiasis japonica which, in the Philippines, has high sensitivity and specificity. Lack of standardization does, however, increase the variability of the test. Parameters which influence the COPT have been examined using large numbers of sera from known S. japonicum infected individuals. In this series of experiments, optimal conditions were determined to be as follows using 2 drops of neat serum and incubation at 37 degrees C in a sealed slide chamber; - approximately 100 eggs from 55 or 60 days infected rabbits for a 24 to 48 hour incubation period. COP reactions (i.e. precipitates associated with eggs) were much less obvious when either immature eggs or eggs obtained from long-term infected rabbits were used. The results emphasize the prime importance of the source of Schistosoma japonicum eggs in the performance of a standardized COPT.

Schistosoma japonicum: use of a radioimmunoassay for anti egg antibodies in human sera.

A solid-phase radioimmunoassay (RIA) was developed for schistosomiasis japonica using extracted egg antigens and compared with circumoval precipitin test (COPT) results on 20 sera from known S. japonicum-infected individuals and on 10 control sera. The quantitative RIA very clearly differentiated between infected and uninfected individuals with highest titers being obtained in teenagers. However, in the series employed, information relevant to immunodiagnosis of S. japonicum infection was contained in the non-quantitative but simple COPT and little was apparently added to the quantitative but expensive RIA.