Based on the no. of invertebrate & vertebrate hosts involved- subtype I- 1 invert, 1 vert. (japanese encephalitis- Culex tritaeniorhynchus, yellow fever- Aedes aegypti) subtype II- 2 invert, 1 vert. (paragoniomosis- snail, crab) subtype III- 1 invert, 2 vert (Clonorchiosis/ chinese liver fluke- snail, fish, humans) subtype IV- trans ovarian transmission in invert, 1 vert (KFD- deer tick, humans)