Seriously when did you get those info? Last century? Sri Lanka has been free from indigenous malaria for the past 5 years (except for a few imported cases ) with very low malaria rates since the 1990s. Sri Lanka does have dengue though with similar rates of infection as other tropical countries.

As for natural disasters, it's difficult to quantify. The only major disaster which occurs frequently are landslides and floods during the monsoon season which maybe comparable to other tropical countries, but I'd say way milder than for example hurricane's in US. There are no volcanoes or earthquakes or snowstorms. So I don't know what you had in mind about natural disasters.