There are so many horrible diseases in the world, and it's difficult to name the most horrible one, as it differs from a place to another place, for example Heart diseases and cancer may be the most horrible diseases in developed countries, but not in developing or under-developed countries, where infectious disease still comes first.
It is difficult to answer vague, poorly worded questions.
So, with that in mind, here is--at least the beginning of--the list:
Physically most destructive: Hantavirus with cardio-pulmonary syndrome. A hemoragic disease, Hanta has an instance of mortality, believed to be, 100%
Disease causing the greatest number of deaths: The winner here goes to smallpox. An estimated 500 million people have died from smallpox worldwide. This toll is over twice that of malaria and three times that of Bubonic Plague.
Most deadly non-communicable disease: Ischaemic Heart disease, warns the WHO, is the single greatest cause of death by a non-communicable, preventable disease.
maybe poliosis or cancer
Disease
They mainly brought disease such as smallpox or measles, but they also brought muskets.
the most harmful disease in the world is cancer (it kills the most people).
Aids
Hurricane katrina and hurricane Ivan
Black death
The most devastating world war 1 weapons had to be machine guns, mustard gas, and artillery. Mustard gas was a really nasty chemical that created big blisters on the flesh and lungs if inhaled.
It was the largest and most devastating war in human history.
The second world war has been terribly devastating. The devastating hurricane caused serious damages in that city.
Well, this time, a magical sky dude flooded the Earth...
Tooth decay The most common noncontagious disease is periodontal disease, such as gingivitis or inflammation of the gums. Gum disease is the most common disease in the world, and poor oral health is generally recognised as an indicator of social deprivation.
Coronary artery disease.