There is no transitive disease, no ill omen, no ghoul. Note: The majority of scholars interpret this to mean that these things in and of themselves do not transmit or cause harm through supernatural or hidden means but that Allah is ultimately in control and any fearful superstition around these is false.
قَالَ رَسُولُ اللَّهِ ﷺ لاَ عَدْوَى وَلاَ طِيَرَةَ وَلاَ غُولَ