Humans can get histoplasmosis from bird droppings, which affects the
lungs.  I don't know if it can affect ferrets, but given that it affects
lungs, I wouldn't want to take the chance.
 
(cut and pasted) Several thousand cases of food poisoning (Salmonella)
occur every year.  Food poisoning is caused by the Salmonella bacterium
getting into left out food.  A main source of the Salmonella bacteria is
dried fecal dust from air vents covered in bird droppings.  [can also
come from fecal dust, etc.  brought in on shoes]
 
Diseases Associated with Pest Birds
Bacterial - Paratyphoid, Vibriosis, Salmonella, Listeriosis &
Pasteurellosis
 
Viral - Encephalitis, Meningitis, Newcastle Disease & St. Louis
Encephalitis
 
Fungal - Histoplasmosis, Candidiasis, Sarcosporidiosias & Blastomycosis
 
Protozoal - Toxoplasmosis, Trichomoniasis & American Trypansomiasis
[Posted in FML issue 4807]