Easy. Malaria was a farming country, farming requires physical labor, too much physical labor can lead to a curvature of the spine especialy in children, also if the curvature is ignored for too long it can worsen and eventually develop into a hunch. Seeing how the Igors all look quite young (most likely 20s to 30s) and the clouds had been around about the same time, it possible that because of the economic crisis that their curvatures went untreated and became hunchs. The bad news with this theory is that it's most likely that all of the Igor's families sold them to the various scientists for money and (possibly) allowed the hunches to develop.
Also in account for the blind orphans (a bit of a longshot), Malaria has had no sunlight for years, most likely that some folk developed sub-terrain blindness (seen in many creature who live in low light areas) and seeing how along with failed crops, not to kindly politicians and scientists tinkering with death machines every year - alot of children can lose their eyes and their families simply for being in the wrong place at the wrong time.
Actually it is specifically for blind orphans, plus Rule of Funny.
Radiation, teratogenic chemicals, strange energies... mad science just keeps on giving and giving! And, of course, the Igors are more likely to have deformed children because they get higher rates of exposure.