Separation of viable and non-viable Onchocerca microfilariae using an ion exchanger

A technique has been developed for separating viable and non-viable Onchocerca lienalis microfilariae (mff) by passing a suspension of the parasites through a column of DEAE cellulose. A proportion (between 42% and 87%) of normally motile parasites, whether unfrozen or cryopreserved, passed through the cellulose columns and retained their viability. Non-motile and sluggish mff were retained by the cellulose. The proportion of viable cryopreserved mff was greater after passage through the column as assessed by motility, migration in mice and development in the insect vector. Numbers of cryopreserved mff eluted through the columns peak quickly at a relatively high level after about 20 ml of eluate had been passed through, whereas normal unfrozen parasites rose and fell in numbers more slowly. By using sodium chloride gradients and buffers of differing conductivity it was concluded that the separation of the mff is probably due to net charge changes as well as motility. It is believed that this technique offers considerable promise as a tool to provide populations of mff of more uniform viability following freezing and thawing with existing cryopreservation techniques.