Fleas and Ticks. Feral cats may carry ticks infected with Lyme disease, which could transfer to humans and other animals. Check your whole body carefully after spending time in a feral cat area, especially if tall grass is present. If you find a tick, send it to a testing center to determine if it's a carrier. You may want to spray the area for fleas and other pests.
Ringworm is actually a fungus and can be transferred to both humans and other animals.
It makes cat fur fall out in a circular area, and the skin underneath will look red. Wearing gloves will protect you. Many internal parasites live in cat feces. Toxoplasma dondii is a particularly nasty one that can be passed on to humans. In pregnant women it can lead to abortion or fetal abnormalities.