Most of the people thinking about missions probably mean a white missionary among African children who receive apart from spiritual formation also material help.
But missions is about more than Africa, is about more than hungry children, orphanages, school buildings and wells. For missions God sends specific people who as everyone from us are limited e.g. by condition. We need to take care of their health so that they will be able to serve in evangelization work as long as possible.
The best opportunity to cure themselves is usually missionary's holiday in Poland. But then there is no time to wait in the queues to the specialist. In that situation there is no other way like paying for visiting the doctor.