Animal diseases may be transmitted by wild birds which have eaten from infected carcasses, and which provide a complicating factor in the control of the disease, as in the case of anthrax. Anthrax is transmitted from birds having eaten from infected carcasses to trees and other plant life which provide fodder for susceptible animals. Parasitic and fungal animal diseases can be transmitted by birds to domestic poultry or other animals. Most birds support sizeable groups of parasites, and while wild birds may develop a certain immunity to the diseases caused by them, domestic poultry reared in artificial conditions are more susceptible to epidemics. Wild birds also usually support parasitic fungi, but to a lesser extent than they do parasitic insects. Parasitic insects include ticks, mites, lice, flies, intestinal worms, roundworms (filaria) and protozoa, which may be present in vast quantities.