There is not one "most harmful disease". In fact, there are lists of "harmful" diseases that can kill anyone at any time (example: kidney disease, Heart disease), or can take years to kill.
the most harmful disease in the world is cancer (it kills the most people).
Ignorance
they carry disease that can be harmful
A contagion is either a disease spread by contact, the spread of such a disease, or the spread of anything harmful, as if it were a disease.
It kills you...
There has been no harmful disease noted about this.
Both.
Starvation, disease, death.
it can cause harmful sun rays which causes cancer disease
Assuming your partner is disease free, then no.
No, not unless your partner has a disease
harmful mutation