How to estimate a population prevalence from several primary studies

I have received point estimates from several studies for the prevalence of a rare disease, and I would like to estimate the over-all prevalence in the population of interest, together with some indication of the precision of the estimation (preferrably a confidence interval). The trouble is that I have got only the point estimates from the primary studies, but no confidence intervals, variance measures, and in some cases not even the sample size (only the number of individuals in the finite populations from which the samples were taken is always known).

Is there anything that I can do to obtain a confidence interval for the over-all prevalence estimate?