سنن ابن ماجه

It was narrated that Ibn 'Umar said: "The Messenger of Allah (ﷺ) said: 'There is no 'Adwa (contagion), no Tiyarah (evil omen) and no Hamah.' A Bedouin man stood up and said: 'O Messenger of Allah, what do you think about a camel that suffers from mange and then all other camels get mange?' He said: 'That is because of the Divine Decree. How else did the first one get mange?'"

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.